Science, Faculty of
Zoology, Department of
DSpace
UBCV
Radvanyi, Andrew
Doctor of Philosophy - PhD
University of British Columbia
For more than three and one-half years a study was made of the amount of locomotor activity of the northern flying squirrel, Glaucomys sabrinus (Shaw). These nocturnal animals were studied in captivity under both natural climatic (outdoor) and controlled artificial (indoor) environmental conditions. Over a sixteen month period, 1285 observations were made under all kinds of weather upon the time at which flying squirrels became active. The average "awakening" time was 35.4 minutes after sunset. Spontaneous locomotor activity, of both individual and groups of flying squirrels, were recorded under natural climatic conditions by means of activity wheels, a treadle-board activity recorder, and an electronic vibration amplifier. Under these outside conditions an inverse relationship exists between the level of activity and the intensity of the nocturnal illumination. Locomotor activity was at a high level between the last and first quarter phases of the moon and declined markedly at full moon, or just afterwards. The relationship appeared to be unaltered by temperature, vapor pressure, the season, or the sex of the animal. The internal physiological "clock" governing this activity cycle persisted even after nine months under constant environmental conditions in which only the light was manipulated to produce 2-3 month periods of continuous light, continuous darkness, or light-dark periods in normal or reversed sequences. In later experiments manipulation of artificial moonlight was used to produce in the animals cycles of activity corresponding to lunar cycles of normal duration and lengthened cycles of 40-days duration or shortened cycles as brief as 7-days in duration. Under 8-hours light and 8-hours darkness (a 16-hour day instead of a 24-hour day), responsiveness differed markedly from the previous experiments i. e. the animals became almost as active under illumination as under darkness. Only after two months under these conditions did daylight activity begin to decline. Whether or not the animals could eventually adapt to a 16-hour day was not determined. This study reveals a series of inherent physiological controls within the animal which govern the level of the spontaneous activity under varying natural climatic conditions and under controlled artificial experimental conditions. The flying squirrel is sensitive to slight changes in light intensity during the dark periods. By observing the responses to varying environmental photoperiods, an attempt was made to understand the inherent rhythms of activity of this species--whether these should be neural, endocrinological, or both. Most nocturnal animals respond mainly to olfactory stimuli. The activity of the flying squirrel is shown by this study to be intimately determined by illumination.
%\\t ptmui>rstij| of ^ t o t a l i Qlolumbta Faculty oi Graduate Studies PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE D E G R E E OF DOCTOR OF PHILOSOPHY °t ANDRAS (ANDREW) RADVANYI B. A., McMaster University, 1951 M. Sc., McMaster University, 1955 IN ROOM 187A, BIOLOGICAL SCIENCES BUILDING FRIDAY, APRIL 24, 1959 at 3:30 P. M. COMMITTEE IN CHARGE DEAN W. H. GAGE: Chairman J. R. ADAMS W. D. KITTS H. ADASKIN G. G. E . SCUDDER J. F. BENDELL A. J. WOOD I. McT. COWAN External Examiner: A. STAKKER LEOPOLD University of California INHERENT RHYTHMS OF ACTIVITY OF THE NORTHERN FLYING SQUIRREL IN RELATION TO ILLUMINATION AND T O LUNAR AND SOLAR PHOTOPERIODISM A B S T R A C T For more than three and one-half years a study was made of the amount of locomotor activity of the northern flying squirrel, Glaucomys sabrinus (Shaw). These nocturnal animals were stud-ied in captivity under both natural climatic (outdoor) and controlled artificial (indoor) environmental conditions. Over a sixteen month period, 1285 observations were made under all kinds of weather upon the time at which flying squirrels became active. The average "awakening" time was 35.4 minutes after sunset. Spontaneous locomotor activity, of both individual and groups of flying squirrels, were recorded under natural climatic conditions by means of activity wheels, a treadle-board activity recorder, and an electronic vibration amplifier. Under these out-side conditions an inverse relationship exists between the level of activity and the intensity of the mocturnal illumination. Locomotor activity was at a high level between the last and first quarter phases of the moon and declined markedly at full moon, or just afterwards. The relationship appeared to be unaltered by temperature, vapor pressure, the season, or the sex of the animal. The internal physiological "clock" governing this activity cycle persisted even after nine months under constant environmental conditions in which only the light was manipulated to produce 2-3 month periods of continuous light, continuous darkness, or light-dark periods in normal or reversed sequences. In later experiments manipulation of artificial moonlight was used to produce in the animals cycles of activity corresponding to lunar cycles of normal duration and lengthened cycles of 40-days duration or shortened cycles as brief as 7-days in duration. Under 8-hours light and 8-hours darkness (a 16-hour day instead of a 24-hour day), responsiveness differed markedly from the previous experiments i. e. the animal's became almost as active under illumination as under darkn'e'ss. Only after two months undex these conditions did daylight activity begin to declined Whether or not the animals could eventually adapt to a 16-hour day was not determined. This study reveals a series of inherent physiological con-trols within the animal which govern the level of the spontaneous activity under varying natural climatic conditions and under con-trolled artificial experimental conditions. The flying squirrel is sensitive to slight changes in light intensity during the dark periods. By observing the responses to varying environmental photoperiods, an attempt was made to understand the inherent rhythms of activity of this species--whether these should be neural, endocrinological, or both. Most nocturnal animals respond mainly to olfactory stimuli. The activity of the flying squirrel is shown by this study to be intimately determined by illumination. GRADUATE STUDIES Field of Study: Zoology Wildlife Biology and Management I. McT. Cowan Comparative Ethology W. S. Hoar and M. D. F. Urvardy Advanced Experimental Zoology W. S. Hoar Terrestrial Zoogeography M. D. F. Udvardy Marine Field Course P. A. Dehnel Other Studies: Courses in Oceanography W. M. Cameron, G. L. Pickard and R. F. Scagel tUbe ptt&ersttg of ^British Ololitmbia Faculty of Graduate Studies P R O G R A M M E OF T H E FINAL ORAL EXAMINATION FOR THE D E G R E E OF DOCTOR OF PHILOSOPHY "t ANDRAS (ANDREW) RADVANYI B. A., McMaster University, 1951 M. Sc., McMaster University, 1955 IN ROOM 187A, BIOLOGICAL SCIENCES BUILDING FRIDAY, APRIL 24, 1959 at 3:30 P. M. COMMITTEE I N C H A R G E DEAN W. H. GAGE: Chairman J. R. ADAMS W. D. KITTS H. ADASKIN G. G. E . SCUDDER J. F . BENDELL A. J . WOOD I. McT. COWAN External Examiner: A. STARKER LEOPOLD University of California INHERENT RHYTHMS OF ACTIVITY OF THE NORTHERN FLYING SQUIRREL IN RELATION TO ILLUMINATION AND T O LUNAR AND SOLAR PHOTOPERIODISM A B S T R A C T For more than three and one-half years a study was made of the amount of locomotor activity of the'northern flying squirrel, Glaucomys sabrinus (Shaw). These nocturnal animals were stud-ied in captivity under both natural climatic (outdoor) and controlled artificial (indoor) environmental conditions. Over a sixteen month period, 1285 observations were made under all kinds of weather upon the time at which flying squirrels became active. The average "awakening" time was 35. 4 minutes after sunset. Spontaneous locomotor activity, of both individual and groups of flying squirrels, were recorded under natural climatic conditions by means of activity wheels, a treadle-board activity recorder, and an electronic vibration amplifier. Under these out-side conditions an inverse relationship exists between the level of activity and the intensity of the mocturnal illumination. Locomotor activity was at a high level between the last and first quarter phases of the moon and declined markedly at full moon, or just afterwards. The relationship appeared to be unaltered by temperature, vapor pressure, the season, or the sex of the animal. The internal physiological "clock" governing this activity cycle persisted even after nine months under constant environmental conditions in which only the light was manipulated to produce 2-3 month periods of continuous light, continuous darkness, or light-dark periods in normal-or. reversed sequences. In later experiments manipulation of artificial moonlight was used to produce in the animals cycles of activity corresponding to lunar cycles of normal duration and lengthened cycles of 40-days duration or shortened "cycles as'brief as'7-da'ys in 'duration. Under 8-hours light-and 8-hours darkness, (a 16-hour-day instead of a 24-hour-day), responsiveness differed markedly from the previous experiments i. e. the animals became almost as active under illumination as under "darkness. Only after two months under these conditions did daylight-activity begin to decline. Whether or not the animals could eventually-adapt to a 16-hour day was not determined. This study reveals a series- of inherent physiological con-trols within the animal which govern the level of the spontaneous activity-under varying natural climatic conditions and under con-trolled artificial experimental conditions. The flying squirrel is sensitive to slight changes in light intensity during the dark periods. By observing the responses to varying environmental photoperiods, an attempt was made to understand the inherent rhythms of activity of this species--whether these should be neural, endocrinological, or both. Most nocturnal animals respond mainly to olfactory stimuli. The activity of the flying squirrel is shown by this study to be intimately determined by illumination. GRADUATE STUDIES Field of Study: Zoology Wildlife Biology and Management _. _ I. McT. Cowan Comparative Ethology W. S. Hoar and M. D. F. Urvardy Advanced Experimental Zoology W. S. Hoar Terrestrial Zoogeography M. D. F. Udvardy Marine Field Course P. A. Dehnel Other Studies: Courses in Oceanography W. M. Cameron, G. L. Pickard and R. F. Soagel INHERENT RHYTHMS OP ACTIVITY OP THE NORTHERN PLYING SQUIRREL IN RELATION TO ILLUMINATION AND TO LUNAR AND SOLAR PHOTOPERIODISM Andrew Radvanyi M.Sc. McMaster University, 1955 A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS POR THE DEGREE OP DOCTOR OP PHILOSOPHY i n the Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OP BRITISH COLUMBIA A p r i l , 1959 INHERENT RHYTHMS OF ACTIVITY OF THE NORTHERN FLYING SQUIRREL IN RELATION TO ILLUMINATION AND TO LUNAR .AND SOLAR PHOTOPERIODISM by Andrew Radvanyi .ABSTRACT For more than three and one-half years a study was made of the amount of locomotor activity of the northern f l y -ing squirrel, Glaucomys sabrinus (Shaw). The d i e l , monthly, and seasonal rhythms in the activity of these nocturnal ani-mals were studied while in captivity and under both natural c l i -matic (outdoor) and controlled a r t i f i c i a l (indoor) environmen-t a l conditions. Over a sixteen month period, 1285 observations were made under a l l kinds of weather upon the time at which flying squirrels became active. The average "awakening time" was 35»^ minutes after sunset. Spontaneous locomotor activity, of both individuals and groups of flying squirrels, were recorded under natural climatic conditions by means of activity wheels, a treadle-board activity recorder, and an electronic vibration amplifier. Under outside conditions an inverse relationship existed be-tween the level of activity and the intensity of the nocturnal i i illumination. Locomotor activity was at a high level between the last and f i r s t quarter phases of the moon and declined markedly at f u l l moon, or just afterwards. The relationship appeared to be unaltered by temperature, vapor pressure, the season, or the sex of the animals. The internal physiological "clock" governing this activity cycle persisted even after nine months under constant environmental conditions in which only the light was manipula-ted to produce 2 - 3 month periods of continuous li g h t , con-tinuous darkness, or light-dark periods in normal or reversed sequences. In later experiments manipulation of a r t i f i c i a l moon-light was used to produce in the animals cycles of activity corresponding to lunar cycles of normal duration and lengthened cycles of 40-days or shortened cycles as brief as 7-days in duration. Under 8-hours light and 8-hours darkness (a 16-hour day instead of a 24-hour day), responsiveness differed markedly from the previous experiments i.e. the animals became almost as active under illumination as under darkness. Only after'two months under these conditions did daylight activity begin to decline. Whether or not the animals could eventually adapt to a 16-hour day was not determined. This study reveals an inherent physiological control mechanism within this species which governs the level of the i i i spontaneous activity under varying natural climatic conditions and under controlled a r t i f i c i a l experimental conditions. The flying squirrel is very sensitive to slight changes in light intensity during the dark periods. By obser-ving the responses to varying environmental photoperiods, an attempt was made to understand the inherent rhythms of activity of this species - whether these be neural, endocrinological, or both. Most nocturnal animals respond mainly to olfactory stimuli. The activity of the flying squirrel is shown by this study to be intimately determined by illumination. In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. Department of TABLE OF CONTENTS PAGE ABSTRACT i INTRODUCTION 1 The Animal 3 Geographical Distribution 3 Periodical Activity of the Flying Squirrel 5 PURPOSE 7 METHODS 8 Apparatus 9 1) Activity Wheels 9 2) Vibration Amplifier Apparatus Unit 1 10 3) Vibration Amplifier Apparatus Unit 2 14 4) Vibration Amplifier Apparatus Unit 3 16 5) Treadle-board Activity Recorder 18 Activity Cages 24 Activity Rooms 26 Temperature Control 27 Light Control 28 i) Light Period 28 i i ) Moonlight 31 Observational Methods 3^ Expt. 1 3^ Experimental. Methods 35 Expts 2 - 22 35-50 RESULTS AND CONCLUSIONS 51 Diurnal Pattern of Activity 51 Monthly Level of Activity 69 Seasonal Levels of Activity 82 PAGE Effect of Light on Patterns of Activity 83 a) Continuous Light 83 b) Continuous Darkness 87 c) Intermittant Light 90 d) Effect of Moonlight on Activity 102 e) Effect of Gonadectomy on Activity 122 DISCUSSION 136 Brief Review of Studies of Periodicities of Activity 136 Effect of Temperature on Activity 1^ 2 Effect of Vapour Pressure on Activity ihh Effect of Oestrous Cycle on Activity lhh Effect of Starvation on Activity 149 Effect of Illumination on Activity 151 , Limitations and Implications of this Study 169 SUMMARY 171 LITERATURE CITED 175 APPENDIX 184 ACKNOWLEDGEMENTS 190 INTRODUCTION Many workers in the past have contributed to the study of photoperiodicities in the activity of animals from practically a l l phyla. In general terms, the major phenomena of the earth are cyclic. These cycles take the form of geological rhythms, cycles in climate, environmental factors, and in population fluctuations. Communities have complex seasonal rhythms, lunar and t i d a l rhythms, and many periodicities associated with the cycles of day and night. Many animals have become morphologically and physio-logically adapted in their a b i l i t i e s to meet the contingencies of their habitat niches during limited portions of the twenty-four hour natural cycles. Such specialization permits one to classify the animals into four major groups. (1) Diurnal animals, which have become adapted to meet or avoid relatively high temperatures, high evaporation rates, a wide range of bright illumination, and decreased con-ductivity of odours by the a i r ; (2) Nocturnal animals which have become adapted to decreased temperatures, high humidities, dim light, and increased conductivity of the air for odours; (3) A third group includes animals which confine their a c t i v i -ties to the dawn and the dusk periods when environmental 2 factors are at neither extreme. These crespuscular a n i -mals inhabit the dawn and dusk simply because they are specialized (Walls, 19^2); (h) F i n a l l y , some animals are active at any time. These animals possess an arhythmic type of ac t iv i ty which r e -sults from (a) their l iv ing in an environment which is re lat ive ly constant because of the absence of fluctuating me-teorological conditions or because the social medium in which they l ive has produced a re la t ive ly constant environment (Park, 19^1 b) or from (b) their being specialized to meet the exigencies of the environment of both the day and night (Walls, 19^2). Among these arhythmic animals might be l i s ted cer-tain species of cave crayfish, log inhabiting social beetles, certain ants and termites, and to a large extent, man. Park (1937, 19^1) has c lass i f ied the ac t iv i ty of a n i -mals according to type and origin as follows: I Periodic Act iv i ty : An ac t iv i ty pattern in which the funda-mental characteristics for a population recur throughout successive d i e l periods. 1) Exogenous Type: Periodic ac t iv i ty in which the pattern is d irect ly induced and controlled by the periodic en-vironmental influences. 2) Endogenous Type: Periodic ac t iv i ty in which the rhythm is inherent in the organism. 3 a) Habitual activity: Endogenous activity that i s the result of induction or previous experiences of the individual, and hence, indirectly induced by the environment. b) Inherent activity: Endogenous activity that is determined by heredity. 3) Composite Type: Periodic activity in which the pat-tern is in part exogenous, and in part endogenous. II Aperiodic (Arrhythmic) Activity: Activity of a species population, the individuals of which do not exhibit the same average pattern with respect to the d i e l time se-quence, but in which each individual exhibits i t s own rhythm of activity and inactivity through successive d i e l periods. The activity of a mammal, as distinct from i t s beha-viour, can be considered at three different l e v e l s — d i u r n a l , monthly, and annual. Most mammals reveal fluctuations in a l l of these levels, but the factors influencing such fluctuations have seldom been studied. In the present study an endeavour has been made not only to determine the pattern of activity of a representative mammal as regarded from such a trip a r t i t e viewpoint but also to reveal a luminosity-activity relationship heretofore rarely portrayed in nocturnal animals. The Animal Geographical distribution: The American flying squirrels comprise two distinct groups. The smaller species, Glaucomys volans, occurs throughout the eastern United States from the Great Lakes and Maine south and from the Atlantic seaboard to approximately the 97th degree of longitude. A second larger species, G^ sabrinus. occupies the Wastern United States and practically a l l of Canada south of the tree line, with the ex-ception of Newfoundland, Antieosti Island, and the islands of the Pacific coast. Gj. sabrinus is also found in southern Alaska and in the New England states. It overlaps the; range of Gj. volans in Minnesota, Wisconsin, Michigan, New York State, Vermont, and New Hampshire. Howell (1918) l i s t s and describes five subspecies in the volans group and nineteen subspecies in the G^ , sabrinus group. Cowan (1937) has detailed the dis-tribution of six subspecies of Gj. sabrinus found in B r i t i s h Columbia. Flying squirrels are circumpolar (Nelson, 1918). In the Old World they occupy forested areas in eastern Europe and nearly a l l of Asia. In the New World they are confined to North America, where they frequent nearly a l l the forested re-gions from the Arctic Circle to the Mexican border. They also occur in forests along the eastern border of the highlands of Mexico and Guatemala. In Asia, the presumed focus of evolution of these rodents, the flying squirrels are more diverse in form and have exhibited more extensive speciation. A l l the flying squirrels used in this study were of the race Glaucomvs sabrinus oregonensis (Bachman) and were l i v e -5 trapped in a wooded area along the edge of the campus of the University of British Columbia. National live traps were used and these were baited with a variety of baits, including nuts, apples, and peanut butter. A flying squirrel caught in one of these traps is shown in Plate I. Plate I . A National live trap used to obtain flying squirrels in the field. Note the V-shaped door apparatus on the right. After being released by the treadle, the right arm of this jams against the roof i f any attempt is made by the animal to push its way out. At the bottom of the V there is a spring which keeps the two arms of V apart. Also note at the left the film casset holder con-taining apple bait. The animal shown is feed-ing on the section of apple used as additional bait. Periodic activity of the flying squirrel; Of the two species of American flying squirrels, the northern species, G. sabrinus, is the hardier and other students of this species found that i t remained active throughout the winter. Bond (1905) maintained, however, that i t was a hibernating animal. The animals I kept in captivity under outside climatic con-ditions did not hibernate. volans, on the other hand, is known to be rather inactive during colder weather (Stone and Cram, 1904; Sollberger, 1940). Most writers who have written about flying squirrels have mentioned the nocturnal habits of these rodents but they have l e f t the nature of this phenomenon unexplored. Remarkably l i t t l e has been learned as to the exact hours during which these animals are active and the degree of their a c t i v i t y dur-ing these hours. Audubon and Bachmann (1846) had the unique experience of watching two hundred of these creatures begin their nocturnal acti v i t i e s "during the half hour before sun-set". Kennicott (1857) observed flying squirrels on cloudy days. Kelker (193D observed a pair mating at 4 p.m. March 12, near Ann Arbor, Michigan. Sollberger (1940) writes of hav-ing watched nesting females emerge from their nests in the evening when there was barely sufficient daylight to see them at a distance of twenty feet, and of being active from the time they emerged u n t i l just before daylight. King (I883) observed two periods of activity in his captives, one beginn-ing at 10:45 at night and one at 03:30 in the morning, each lasting for an hour to an hour-and-a-half. Cahalane (1947), writing of a flying squirrel he kept in captivity, says ".... the animal l e f t his nest box at dark and stayed out only a couple of hours, then went to sleep u n t i l about three in the morning. After scampering about for another couple of hours, he retired again at dawn, which came about five-thirty". Ballantyne (1889) writes of a pet flying squirrel that was ac-tive from two to four o'clock i n the morning only. Sollberger (loc. cit.) writes, however, that he had observed caged ani-mals during every hour of darkness at various times throughout the summer months without noticing any change i n their degree of activity u n t i l just before daylight, when they returned to their nest boxes. Bond (190?) says of a flying squirrel he kept in a small cage and activity wheel: "His wheel is kept going from about eight i n the evening to well on in the morn-ing PURPOSE Thus i t becomes rather apparent that statements in the literature about the time and variations i n the amount of activity of flying squirrels are largely generalizations. The purpose of this thesis is threefold—to determine: 1) What is the pattern of activity of the flying squirrel? 2) What are the factors causing these patterns to occur as they do? 3) The relationship between the amount of activity of flying squirrels and the photoperiodic nature of the envir onment. 8 METHODS Twenty-two experiments ranging in length from as brief a duration as three weeks to as long as almost sixteen months were conducted during the course of this study. For the sake of cl a r i t y these have been summarized in Table I. A l l twenty-two experiments were conducted using captive ani-mals . Table I. List of experiments carried out on captive flying squirrels of this study. OUTDOOR EXPERIMENTS Expt. 1 Study of the awakening times. Expt. 2 Activity under outside climatic conditions. Expt. 3 Activity wheel experiments. Expt. h Treadle-board experiments. INDOOR EXPERIMENTS Expt. 5 Activity under constant light. Expt. 6 Activity under constant darkness. Expt. 7 Activity under normal light-dark sequence. Expt. 8 Activity under reversed light-dark sequence. Expt. 9 Activity under reshifted light-dark sequence. Moonlight Experiments — normal animals Expt. 10 Activity Expt. 11 Activity Expt. 12 Activity Expt. 13 Activity Expt. 14 Activity Expt. 15 Activity Expt. 16 Activity under 28-day lunar cycle. under 40-day lunar cycle. under 21-day lunar cycle. under 18-day lunar cycle. under 14-day lunar cycle. under three 7-day lunar cycles. under 28-day lunar cycle — without nest boxes in cages. .... (cont'd) 9 Moonlight Experiments — gonadectomized animals Expt. 17 Activity under three 28-day lunar cycles. Expt. 18 Activity under 14-day lunar cycle. Expt. 19 Activity under three 7-day lunar cycles. Expt. 20 Activity under 28-day lunar cycle — without nest boxes in cages. Expt. 21 Activity under 16-hour day — normal animals, Expt. 22 Activity under 16-hour day — gonadectomized animals. Apparatus Five major sets of apparatus were used in the course of this study in recording the activity of the flying squirrels under known environmental conditions. These included: 1) Activity wheels. 2) Vibration amplifier apparatus Unit 1. 3) Vibration amplifier apparatus Unit 2. 4) Vibration amplifier apparatus Unit 3. 5) Treadle-board activity recording apparatus. 1) Activity wheels: Two standard 14-inch diameter revolving activity wheels were used in recording the activity of a male and a female flying squirrel (Expt. 3). A cage, 12f,xl0"x8", containing a nest box, was connected to each of the activity wheels and served as both feeding and sleeping quarters for the animals. A strip of glass-cloth wrapped around the attached cage protected the animals from rain and snow while the a c t i -vity wheels were in use on the open roof of the Biological Sciences Building. 10 2) Vibration amplifier apparatus Unit 1; In the design of electronic equipment for the measurement of the physical activity of animals, several factors have to be taken into consideration. The equipment must be inherently stable; pre-set sensitivity must have very l i t t l e variation, changes in operating voltages should not affect the operation, and simi-lar well-known variables must be compensated for. The record-ing of such activity can be carried out in various ways using electronic apparatus. For example: 1) i f one were recording the activity of a bird, a photocell and lamp could be so arranged that every time the bird moved from one part of the cage to another, the light beam would be broken. This could operate a counter, thereby giving a numerical expression of activity of the bird over a unit period of time. 2) E l e c t r i -cal contacts may be placed under strategic platforms. The weight of the bird would operate such contacts and in turn be made to record via one or more counters or stylus recorders. 3) A vibration sensing element may be mounted on the cage. With suitable amplification, vibrations above a certain thres-hold value may be made to activate a suitable counter. This third method was elaborated by Dr. C.G. Lemon, of Pacific Plas-ti c s Limited, Vancouver, B.C. for Unit 1 of the vibration am-p l i f i e r apparatus (Plate 2) used in several of the experiments to be outlined in this study. The sensing head of this appa-ratus consists of a metal box 2"x3,,xV' enclosing a piezoelec-t r i c cartridge with the sensing^ element coupled to a rubber mounted weight. A simplified sketch il l u s t r a t i n g the set-up 11 of this apparatus is shown in Plate 3. Any movement of the animal within the cage on which the sensing element is attached causes a voltage to be developed in the element i t s e l f . The output of this sensing head is taken to an amplifier. In the f i r s t stage of the c i r c u i t , straight amplification is effected by means of a sensitivity control between this and the next stage. The second stage input and output couplings are de-signed with a pass band of 10-100 c.p.s. This avoids record-ing the pickup of extraneous noises. The output of this stage is fed to a heavily biased amplifier and the resultant impul-ses trigger a small thyratron. A suitable relay in the output circuit of this stage operates a counter ranging from 0-99999. There are six such amplifier networks in the equipment allow-ing for operating six sensing heads concurrently. To avoid coupling between channels, each channel has separate voltage control and independent biassing for each thyratron. In operation, the sensing head of the apparatus i s clamped to the cage of the animal whose activity is to be re-corded. The gain of sensitivity is then so adjusted that a count of one pulse i s registered on the counter when a suitable weight i s dropped on the floor of the cage. By a suitable se-lection of gain controls and weights, i t is possible to make the counter responsive to small or large pulses of vibrations. The actual procedure of selecting the sensitivity for each of the six channels of this apparatus w i l l be outlined further in the sections on experiments in which the apparatus was used (see Procedures — Expt. 2). 12 Plate 2. Units 1 and 2 of the electronic vibration amplifier. Unit 1 is on the l e f t and Unit 2 on the right. In Unit 1, note six counters. Below each of these is a (black) d i a l , controlling sensitivity of the counters to electric pulses received from the sensing heads. Leads may be seen (above Unit 2) coming from the sensing heads. They plug into the leftmost plug under each counter of Unit 1. The right-hand plug under each counter con-nects each channel of Unit 1 to the corresponding channel of Unit 2. In Unit 2 the activity of each animal is recorded by one channel, represented by a single vertical row of 6 counters, i.e. the numbers along the top edge of the machine refer to six different sensing heads. For any one channel, each counter may be employed to record for a single hour, two hours, or four hours, depending upon the selection of time unit desired. There are contact points on the face of the clock which switch the recording circuit from one horizontal row of counters to the next below i t , at the time interval selected. The selector d i a l is beneath the sixth channel. By means of the period selector - shown to the left of the clock - one may pre-set the apparatus to start recording at a desired time. 13 Plate 3» Simplified sketch showing recording mechanism on one of six channels of the electronic vibration amplifier apparatus. Vibrations, caused by the movements of the animal in the cage, are picked up by the sensing element attached to the top of the cage. They are then conducted to Unit 1 of the recorder, amplified and transmitted to Unit 2, where the activity pulse is recorded on one of the six v e r t i c a l rows of counters. Each counter in the ve r t i c a l row could be set to record over one-, two-, or four-hour duration. The activity of six animals could be recorded simultaneously and independently on the recording apparatus shown. The activity recorded on each of the six counters of Unit 1 of the vibration amplifier apparatus was done accu-mulatively — i.e. the counters could not be reset to zero once the reading had been taken down. The frequency with 14 which the readings were taken, therefore, determined the time units over which the activity was being recorded. While this presented only mild inconvenience in experiments involving recording over short periods of time, i t led to considerable d i f f i c u l t y when i t was desired to obtain recordings of a c t i -vity in short interval units but over long extended experiments. 3) Vibration amplifier apparatus Unit 2: It was f e l t that rather more interesting information could be obtained i f the recording could be selected at specific times and for specific periods. With this in mind, a time-operated selector switch was designed and connected to the six channel recorder. An electric clock was fi t t e d with contacts and a selector switch to give one pulse at either one, two, or four hour intervals. This was connected to a six bank 25-position positive selector switch which in turn was connected to a bank of 36 five-number counters. Each channel, therefore, had six counters, each of which could be switched into operation for a one-hour, two-hour, or four-hour period of time. In addition, a series of delay positions on the selector switch enabled the recording to commence at any time up to three days later and to continue to record for the required length of time. Upon the completion of the whole cycle of 6-, 12-, or 24-hours (depending on whether the selector switch has been set to record for either 1-, 2-, or 4-hours per horizontal row of counters) the whole equipment automatically switched i t s e l f off. For example, with the apparatus set to record for 1-hour 15 units of time, i t would be possible to set the operating cycle so that the equipment switched i t s e l f on at midnight, recorded a l l activity of six separately caged animals on individual counters along the top row for one hour, switched to the next row of six counters for the next hour, and so on. At the end of the sixth hour, the equipment would switch i t s e l f off. The counters, therefore, would have recorded a l l act i v i t y indepen-dently for each hour from midnight to 6 a.m. Alternatively, with a 2-hour or a 4-hour period selected for each row of counters, the activity would be recorded continuously for 12-or 24-hours respectively. With such equipment the best periods for measuring and recording could be easily selected to match the periods of activity of the animals in question and the convenience of the experimenter. In operation, Unit 1 of the vibration amplifier apparatus could be used in recording activity by i t s e l f , and i f used in this manner, the activity was recorded accumulative-ly — i.e. the activity continued to be added on the same six counters or on as many counters as were being employed. The amount of activity recorded was calculated by subtracting the reading taken at a known time from the latest reading. The difference between these two readings represents the amount of activity which had been recorded in the interval. Unit 2, on the other hand, could not be used by i t s e l f but rather had each i channel of this unit plugged into the corresponding channel of 16 Unit 1. Thus a sensing element attached to the activity cage transmitted impulses caused by vibrations within the cage to Unit 1 where the impulse was amplified and forwarded to Unit 2. Here the impulses were registered on the appropriate row of counters. Here too, the activity was recorded accumulatively, but only over known pre-determined durations of time. As with Unit 1, the amount of activity is obtained by subtracting the numbers occurring on the counters before a six, twelve, or twenty-four hour period from the numbers occurring on the same counters after this time interval. k) Vibration amplifier apparatus Unit 3: In order that even more animals might be employed in the act i v i t y recording experiments at the same time as Units 1 and 2, described above, were being used, a third vibration amplifier apparatus was built for this study by Mr. Robert Butters of the Department of Mining and Metallurgy of the University of British Columbia. This recorder, except for the sensing elements which attached to the activity cages, is shown in Plate 4. Like Unit 1, this too was a six-channel vibration amplifier recorder. The v i -bration sensing element consisted of an electric phonograph pickup cartridge mounted r i g i d l y on the inside of a 2"x3"x1+" metal case in such a way that the phonograph "needle" was in a horizontal plane. A short steel pin with a small weight on the free end replaced the normal phonograph needle. Any sharp vertical movement of the sensing element would thus result in a burst of alternating voltage in the crystal. 17 Plate 4 . Unit 3 of the electronic vibration amplifier. Note the sensitivity dials placed immediately behind the counters in the foreground. The apparatus records in the same manner as Unit 1 (total a c t i v i t y ) . Leads from the sensing heads enter from behind. The burst of electrical "noise" (activity) was then transmitted to the six channel recorder by a 24-foot length of shielding cable. At the recorder the signal was amplified by a two-stage triode amplifier and rectified to produce a posi-tive pulse, which was fed to the grid of a thyratron tube. Upon receiving this pulse, the thyratron tube conducted i t to a mechanical five-numeral counter and caused i t to respond. At the cessation of the i n i t i a l burst of "noise", the whole 18 process stopped and the thyratron reverted to the non-conduc-tive state. Continuous "noise" would produce but one count. Like Unit 1, the sensitivity of this apparatus could be regu-lated to suit the type of cage and animal whose activ i t y was to be recorded. 5) Treadle-board Activity Recorder: Whereas with the use of each of the other apparatuses described, the act i v i t y of each of the animals was recorded while they were completely isolated from others of their kind, the treadle-board was designed and used to record group activity. Such a recorder would not only serve to check on the data obtained using the other recording apparatus, but would also record the activity of these animals under conditions more like those encountered in their natural habitat. In one corner of a large outdoor cage shown in Plate 5 a small wooden platform was attached to one wall 41" above the floor level. A second plywood platform, shown in Plate 6, was fastened to one end of the f i r s t by a 9" wide flexible brass sheet which held the free end of the top platform approx-imately 1" above the lower platform. A contact switch attached to the lower board encompassed the free end of the upper board. Whenever a flying squirrel jumped onto the upper platform, the f l e x i b i l i t y of the brass metal hinge permitted the free end of the upper board to dip, touch the lower platform, and be halted there. As soon as the animal leaped from this corner resting stage, however, the upper platform was caused to spring up 19 approximately one inch at the free end and in doing so, closed an electrical circuit for a fraction of a second. Plate 5 . The large outdoor group-activity cage containing six nest boxes (fruit t i n s ) . The treadle-board recorder is seen just below a couple of nests on the extreme l e f t . From here squirrels could jump to the branches on the right, or onto the wire walls of the cage. On jumping from this platform, they completed an electric circuit connected to a recorder indoors. The outdoor treadle-board was connected by means of two 100' lengths of thin, rubber-coated e l e c t r i c a l wire to the recording device housed indoors. This recording device is shown in Plates 7 and 8. One of the outside leads connected 20 Plate 6. The treadle-board in the outdoor gr oup-activity-cage. When the animal jumps the board w i l l spring up and complete a circuit momentarily beneath the two terminals at the right-hand side. Note the large eye and flattened t a i l of the flying squirrel. with a small transformer and then in turn to a 6-volt electro-magnet. The other connected between the electromagnet and the other terminal of the outside platform contacts. Facing the magnet was a hinged face plate to the center of which a tiny needle had been soldered. To one side of the magnet device, a typewriter ribbon spool was fastened by a center shaft screwed to the same platform as the magnet holder. Onto this spool was 21 Plate 7 . The means whereby the activity of squirrels measured by the treadle-board was recorded. On the right is seen the spool supplying paper-tape. In the center is the 6-volt electromagnet and the face-plate into which the piercing pin is soldered. Above the clock the tape is drawn, by f r i c t i o n , between the drive-wheel attached to the minute shaft of the clock, and a rider-wheel. The paper then runs onto the floor. The time-markers are inked strips of f e l t f i t t e d into s l i t s in the edge of the drive-wheel of the center face of the clock. wound 15 - 20 feet of jjr1' wide paper tape onto which the ac-t i v i t y of the animals in the large cage was to be transferred. Approximately five feet of tape was used during each nightly record by this apparatus. From the spool the paper tape passed 22 through a s l i t cut into a y*ik* piece of thick typewriter pad f e l t stood on edge and placed between the spool and the electromagnet. The f e l t pad served merely to take up slack in the paper tape. The tape then passed between the electro-Plate 8 . Another view of the clock recorder of treadle-board movements. In this the drive-wheel attached to the minute shaft of the clock is more obvious. Note the time-mark on the tape which has just passed by the rider-wheel. The small transformer may be seen on the l e f t . Lead-in wires connecting to the contact points of the treadle-board (Photo 6) are seen entering from the right. magnet and the piercing face plate to be taken up between a second spool attached to the face of a spring-wound alarm 23 clock and a rider wheel resting against the spool of the clock. A small c o i l spring attached to the base of the clock pulled the rider-wheel against the tape and clock-driven spindle. The tape was thus drawn through the recorder without slipping. A paper c l i p weight hooked onto the end of the tape, the free end of which rested over a horizontal portion of the incoming lead wire. As the tape was driven through the recorder by the revolving spindle of the clock, the used portion was permitted to t r a i l over the edge of the platform to the floor —the tape being kept taut by the attached weight at the free end. The recorder was designed to give a record of the time as well as the amount of activity. The spool attached to the face of the clock revolved one complete revolution per hour. This spool had been cut intentionally to provide a 4-inch circumference so that with each revolution of the spool on the clock four inches of tape would be driven through the recorder. Into opposite sides of the spool, two slots were cut. Into each of these a thin piece of f e l t was compressed. Thus, by placing a drop of blue ink on one of these pieces of f e l t and red ink on the other, the recorder could be made to mark out half-hour i n -tervals along the paper tape. Additional slots could have been cut and by using a different coloured ink, the quarter hours could have been indicated as well. Thus a ve r t i c a l ink mark across the width of the moving tape marked the time intervals -the hour marks being four inches apart. As the electromagnet was placed so that there was a four inch length of tape between 2k the point at which the pin pierced the tape and the point at which the tape ran across an inked timer pad in the clock-driven spindle, there was an hour difference between the time marked against a point and the time at which that point was actually recorded. By working back over the length of the used tape, each hour could thus be readily and correctly labelled. The amount of activity recorded was calculated by counting the number of holes punched in the tape as i t was drawn between the pin and the magnet during each time interval marked on the tape. The pin pierced the tape along i t s center l i n e . To avoid flattening out of these puncture marks, the rider wheel was made to press against the tape and the clock-driven spool a fraction of an inch above this center line, thus avoiding the recorded punctures. Activity Cagest A l l the cages except one in which individual flying squirrels were kept in captivity while their a c t i v i t y was being recorded, were similar to those shown in Plates 9 and 10. Of *jr" wire mesh, the cages measured 17"x20,,xl3'!. Several, but not a l l , of the cages were provided with 2" legs at each of the corners. Those cages lacking legs were placed on two nar-row strips of board so that the floor of the cage was slightly raised. Each cage was placed in a sheet metal tray measuring 2*+"x30,,xl" deep and lined with newspaper to f a c i l i t a t e cleaning. The one exceptional cage measured SC^^'xlS". Although this cage was of heavier structural material, this did not appear to have affected the recording obtained as compared with the lighter 25 Plate 9. One of the two shelters on the roof of the Biological Sciences Building showing the arrange-ment of individual squirrel cages. Note the gallon-sized f r u i t tins used as nest "boxes. The sensing elements of the vibration recorders may be seen mounted on 6 of the cages, with leads connecting to the vibration amplifier housed indoors. The shelter is enclosed on three sides by glass-cloth. cages. To the top of each activity cage a flanged metal re-ceptor was bolted. To this was attached one of the six sensing element boxes which picked up the vibrations and transmitted them to Unit 1 of the vibration amplifier apparatus. During the indoor experiments, each of the trays (bearing a cage with a single animal and nest box) was rested on a 2" thick foam Plate 10. Two of the a c t i v i t y cages inside A c t i v i t y Room No. 1. The foam rubber pads designed to pre-vent vibrat i o n of the cages, other than that caused by the s q u i r r e l s themselves, are placed beneath the trays on which the cages r e s t . The sensing heads are seen attached to the top of each page, as i n Plate 9. A piece of f i b e r -board placed between the two cages prevents the two animals from seeing each other. 26 rubber pad. These foam rubber pads were not used during the outside activity recording experiments because they would readily soak up rain which could beat onto the cages from the open side of the shelter and thus change the sensitivity of response in the recording apparatus. The portion of the large outdoor cage in which the activity of seven flying squirrels together was recorded using the treadle-board method (Expt. h) measured 8 ' x5 'x5 l and was shown in Plate 5. This represents one-half of a larger aviary. The seven animals in this portion were provided with a choice of six nest boxes. Several large maple branches were also taken inside the cage and suspended from the ceil i n g . A re-movable board floor permitted one to walk inside the cage in order to feed the animals and to check the treadle-board re-corder. The 13^"x9'i-11 treadle-board already described was l o -cated in one corner and fastened to the sides of the cage. Activity Rooms: The indoor recording of the activ i t y of flying squirrels was a l l carried out in a room in a small de-tached building on the University of British Columbia campus. Inside this large room, a smaller activity room (Activity Room No. 1) was constructed and i t was in this smaller room that most of the indoor experiments were conducted. The activity room, built of ^ M fiber board panels bolted on a dexion frame, measured S'x^'xS^-1. Along the inside length of one wall, two shelves were built, each to support three of the activity cages which had been used in the outdoor experiments. Vertical fiber 27 board panels obscured the cages visually from one another.on the shelves. The activity room was made light-proof by taping a l l the corners, by providing a blackened light trap over the ventilation opening, and by lining the edge of the door into the room with f e l t weather stripping. Temperature Control: During a l l indoor experiments ex-cept the last (Expt. 21 and 22) — during which time a record heat wave was experienced in the city, the temperature within the above-described room was maintained between 68 and 70°F. The temperature was controlled by means of a Fenwall thermostat hung in the center of the room. The thermostat was in circuit with two 15" e l e c t r i c a l strip heaters mounted on a dexion frame, one above the other, near the floor of the room. The thermostat was also connected to a V' el e c t r i c a l fan which blew cool air into the activity room from underneath the building through a 5" square hole made in the floor in one corner of the activity room. This air passed through two 8" circular water-cooled radiator cores like those found in the heating systems of B r i t i s h cars. During a l l but the hottest days, the strip heaters functioned alternatively with the fan under the floor about every four to six minutes. As soon as the temperature in the room was raised to the proper pre-set level, the strip heaters cut off and the fan came on and remained on u n t i l the room had been cooled by one or two degrees, at which time the floor fan switched off and the strip heaters came back on. A second small fan inside the activity room was kept running con-tinuously, blowing the cooled air from the circular radiator 28 cores across a second and larger water-cooled car radiator and then around the room. A narrow opening near the roof at the opposite end permitted air drawn into the room to leave via a light trap and enter the larger room outside. Air from this large outer room was drawn to the outside of the building by a 10" fan placed in front of a window from which a sheet of glass had been removed. Both the window and the fan were pro-vided with a light trap so that the large room was darkened even while the fan to the outside was running. A 50' garden hose circulated cold water from a tap outside the activity room through the three cooling radiators and then back to a drain sink also outside the activity room. The cold water c i r -culating through the radiators helped cool the room quite ef-fectively. The second activity room was a duplicate of the f i r s t and opened onto the same large room inside of which Activity Room No. 1 had been bu i l t . Light Control: i) Light Period — Light in the activity room was provided by a single 100-watt blue tungsten daylight bulb attached to the center of the wall facing the two rows of cages. This light source was directly opposite the top middle cage. At this point a reading on a Photovolt 22 Photometer gave an intensity value of 6 ft.-candles. Cages to either side and be-low received slightly lower light intensities. The average for the six readings taken in front of the cages was 3.3 ft.-candles. 29 In order to simulate outside l i g h t conditions more accurately, a l i g h t control mechanism was designed which would not only provide l i g h t and dark periods of pre-set duration, but would also accord a r t i f i c i a l sunrise and sunset conditions. The l i g h t control mechanism i s shown i n Plate 11. The con-t r o l l e r consists e s s e n t i a l l y of two slow-speed motors, two microswitches, and a variax, a l l attached to a metal pane. The f i r s t motor, geared to turn one revolution per day, turned a f l a t face plate. The two halves of this face plate had di f f e r e n t diameters.' As the face plate was turned, the greater diameter forced down a plunger on the f i r s t microswitch and started the second motor running. The second motor was geared to turn a second face plate (attached to this second motor and also having d i f f e r e n t h a l f diameters) at the rate of one-half revolution i n two hours. At the end of this time, the smaller diameter of i t s face plate would release the plunger on the second microswitch and the motor would stop u n t i l i t was started again by the f i r s t motor. In making the h a l f revolution over the two-hour period, the second motor turned a variax by means of a thread and weights pulley system from the " o f f " to a near maximum "on" position or vice versa. Thus, the output of elec-t r i c a l current available to a t r i p l e socket e l e c t r i c a l plug also f i x e d onto the panel board and connected with the variax was gradually increased or decreased. A 7-watt clear glass p i l o t bulb was screwed into one part of the t r i p l e socket, ex-tension cords from the 100-watt daylight bulbs i n each of the a c t i v i t y rooms were plugged into the other two sockets of t h i s 30 Plate 11. The light control mechanism used in the indoor experiments to simulate solar illumination. The device controlled the duration of the a r t i f i c i a l sunlight used in the activity room and produced gradual changes in light intensity corresponding to sunrise and sunset. The wheel at the lower l e f t was turned counter clockwise by a motor behind i t at the rate of one revolution per day. The larger half diameter of the wheel caused the microswitch immediately below i t to start a second motor behind the large center wheel. This latter wheel was turned at the rate of one-half revolution during two hours in a clockwise direction after which time i t turned off. In making the half revolution, the wheel turned on, by means of a thread attached to i t , a variax situated to the right of the large center wheel. The variax controlled the strength of e l e c t r i c a l current supplied to a tr i p l e socket at the top. The solar bulb in each of the activity rooms was plugged into two of these three sockets while a pilot bulb was screwed into the third. 31 light controller. Thus the controller, with proper gearing, gave 12-hours light and 12-hours darkness with almost two hours of waxing and waning of the light from the 7 and 100-watt "bulbs. The pilot light on the face of the controller panel enabled the writer to know what light condition existed inside the activity rooms without opening the doors and there-by disturbing the animals inside. Whenever the pilot light was on, the light inside the large room in which Activity Room No. 1 had been built could be turned on for the purpose of taking down records from the vibration amplifier apparatus. If the pilot light was off, however, records were taken in the darkened large room by using a pin-source of light from a shielded flashlight. In both circumstances, records could be taken without the animals being aware that anyone had entered the main room. i i ) "Moonlight" — There is considerable uncertainty in the literature about the intensity and quality of illumin-ation reaching the surface of the earth from the moon. The intensity of this light depends upon several well-known factors — the time of year, the time of night, location of the ob-server, the height of the moon above the horizon, the phase of the moon, cloud or other interference, the latitude and a l t i -tude of the observer. Dice (194-5), basing his values on data collected by the Smithsonian Institute (1918) and his own readings in 1939, maintains that the light from the zenithal f u l l moon on a clear night in November in Michigan may be taken 32 to be 0.02 ft.-candle. Dice also gives quarter moon light intensity as 0.002 ft.-candle and starlight, alone, as 0.000,08 ft.-candle. Mr. R.M. Petrie, Director of the Dominion Astro-physical Observatory, Royal Oak, B.C. informed me (in l i t t . ) that the intensity of illumination of the f u l l moon for an altitude of about 50° above the horizon is 0.1 ft.-candle. This angle is about the maximum that the moon attains above the horizon at the latitude of Vancouver, B.C. and the value de-creases quite sharply as the phase of the moon changes from f u l l moon toward the quarters. I have taken readings on a f u l l y moonlit night in early September using a Photovolt Model 520-M Electronic Photometer and obtained an average reading of 0.05 ft.-candle. This latter value was used as maximum inten-sity for the a r t i f i c i a l f u l l moon light in the later experi-ments of this study. A r t i f i c i a l "moonlight" was produced by enclosing a 60-watt frosted electric light bulb and socket inside a 6"x6"x9" asbestos-lined wooden box into the l i d of which had been set a sheet of opal glass. The a r t i f i c i a l moon was attached to the wall of the activity room near the "sun" bulb and the light emitted from i t was cast onto the ceiling of the activity room. The reduced illumination of the different moon phases of the a r t i f i c i a l moon was accomplished by inserting two thin sheet-metal plates over the opal glass. From the lower permanent plate, a funnel-shaped portion had been cut away. By sliding the upper plate over the lower, varying degrees of illumination 33 were obtained. When the upper plate was so adjusted that light could pass only through the opal glass and the narrow portion of the funnel cutout, low intensities of light were emitted into the activity room and corresponded to early and late phases of the moon. By pulling the upper plate back to expose more and more of the funnel aperture, more light was cast onto the ceiling inside the activity room. By using the same Photovolt Model 520-M Electronic Photometer as used i n taking readings on the f u l l moon outside, the a r t i f i c i a l moon was calibrated for maximum illumination of 0 .05 ft.-candle when the sensing element of the light meter was placed in front of the top center cage in the activity room. As this reading corresponded to a value of 50 on the 1,000-scale of the photometer, the position of the upper sliding plate of the a r t i f i c i a l moon was marked as a setting of 50. The intensity of moonlight drops off rapidly on either side of the f u l l moon period. To simulate this drop-off, arbitrary positions of 40, 25? 5> 3? 1 and .3 were selected for the lunar scale. The moonlight bulb was unplugged to leave the activity room in com-plete darkness at the moonless phases. The moonlight settings, therefore, corresponded to decreasing illumination values of 0 .05 , 0.04, 0 .025 , 0 .005 , 0 .003 , O.OOl, 0 .000.3 and 0 f t . -candles respectively. It is known, of course, that sunlight, moonlight and a r t i f i c i a l bulb lights have different wave lengths and d i f f e r -ent polarization. Furthermore, the light arriving from the moon 3^ on the earth has greater polarization value at the f i r s t and last quarters. However, no attempt could be made to reproduce the correct wave length or polarization qualities of the moon in this experiment. Nor was an image of the moon per se in its various phases projected onto the ceiling of the act i v i t y room. The a r t i f i c i a l moonlight developed as described above was in effect as natural as the bulb used in the a r t i f i c i a l d i e l cycle experiments. A l l that was done in this experiment was to produce and maintain over a long period a light of very low intensity. While moonlight experiments were being conducted, the "moonlight" was l e f t on during both the light and dark periods of the day. A l l changes in the setting of the a r t i -f i c i a l moonlight intensity were made during the light period of the experimental day, generally while the animals were being fed. Methods — Observational Experiment 1 - Study of the "Awakening time" of flying squirrels. In order to learn at what time the flying squirrels in captivity emerged from their nest boxes and commenced their nightly a c t i v i t i e s , I made checks almost every night for six-teen months on a l l animals on hand by direct observation. Ap-proximately an hour before sunset, I went out on the roof of the Biological Sciences building where the activity of these animals was being recorded and sat very s t i l l on a chair placed 35 approximately twenty-five feet in front of the shelter housing the individually caged animals. In the course of this study 1,285 individual observations were made on the time at which the flying squirrels l e f t their nest boxes for the f i r s t time in the evenings. During the early months, only one animal was being checked. Is more animals were live-trapped, the data were based on a larger number of individuals. The maximum num-ber of individuals checked on any one night was fifte e n . As each animal emerged from i t s nest box, the time — taken to the nearest minute — was recorded. Note was also made of the general cloud conditions. A continuously operating temperature recorder was kept within the shelter beside one of the cages. Observations were begun on January 16, 1955, and were continued through to Apri l 22, 1956. Observations were made in a l l kinds of weather — sun, cloudy, rain, wind, snow, freezing, and fog. Winter observations generally required one and a half to two hours before the last animal emerged from its nest box. During the summer months, however, I frequently waited for more than four hours a night to obtain the data. While an attempt was made to check the emergence time of these animals on a l l occasions, due to other commitments this was not always possible. Methods — Experimental Experiment 2 - Recording acti v i t y under natural climatic conditions. ^ In recording the act i v i t y of flying squirrels under 36 natural climatic conditions, Units 1 and 2 of the vibration amplifier apparatus previously described were used. A small metal box containing a sensing element was attached to the out-side ceiling of each of the cages housing an animal whose ac-t i v i t y was to be recorded. A 25-^foot shielded cable ran from each of six cages placed in an outside shelter to Unit 1 of the vibration amplifier being housed indoors at the same level of the building. During the early months of this study, only Unit 1 was available. As the activ i t y was recorded accumula-tively on the counters of this unit, to obtain hourly records of the activity registered would have meant returning to the apparatus each hour of the night to record the counter numbers. Instead, only three readings were taken each day — at 9:00 a.m., just before activity was due to commence in the evening, and again at midnight. With the addition of Unit 2 of the v i -bration amplifier apparatus, six consecutive hourly records could be achieved with one resetting of the apparatus. Thus the apparatus could be started in operation at any time during the late afternoon, be re-checked and the numbers recorded at 10:00 p.m. and again at 1:00 or 2:00 a.m. By the time the six hours of recording after the f i n a l resetting of the day had expired, dawn would have arrived and the animals ceased their activity. The apparatus would continue to record u n t i l 7*00 or 8:00 a.m. and then turn i t s e l f off. As the recording apparatus — except for the sensing elements and the connecting cables — was a l l indoors and completely out of sight and sound from the animals whose activity was being recorded, the counter numbers could be 37 taken down and the apparatus reset without the slightest d i s -turbance to the animals by the observer. A simplified sketch illustrating how one of the cages i n the outside shelter was connected to Units 1 and 2 of the recording apparatus housed indoors was shown in Plate 3. The activity of five additional flying squirrels could be simultaneously and independently recorded on the same recorder. Perhaps a brief description would be appropriate here concerning the procedure used in determining the sensitivity settings used in the vibration amplifier apparatus. The sen-s i t i v i t y of recording on each of the six channels could be ad-justed independently of each of the other channels. While uniformity of sensitivity response on each of the channels would have been desirable, this could not be achieved merely by setting each of the sensitivity dials at a chosen position. Too many variables prevented such a simple solution. The cages in which the flying squirrels were being kept — although of the same general size and structure — were not identical in a l l respects. The animals, too, differed in size and weight and thus could affect the sensitivity of the apparatus in vary-ing degrees. Also the type of activ i t y which each animal ex-hibited within the cage generally differed from that of others. Some flying squirrels would repeat hour-after-hour a three point movement pattern, leaping from the floor of the cage to one side, to the ceili n g , and then back to the floor. Others would merely perform rapid backward summersaults landing on the 38 same spot, while s t i l l ethers merely ran either around the walls of the cage or else around the c e i l i n g . Thus the sensitivity of each channel of the recording apparatus had to be adjusted to the characteristic pattern of activity of each animal and the nature of the cage being used. The setting chosen was determined by gently tapping on the top of the cage and turn-ing the sensitivity d i a l up or down u n t i l the recorder regis-tered a count of one pulse only for each time the cage was tapped. Final adjustment was later made in accordance with the pattern of movement of each animal. Slow and gentle move-ments such as when the animal was feeding on the floor of the cage were not registered. Only when the animal moved with a momentum above the selected threshold value was acti v i t y re-corded. The count of one pulse for each such movement was the basis for the UNITS OF ACTIVITY in which the locomotor ac t i v i t y of the flying squirrels was represented in the figures accom-panying the results of most of the experiments. Once the sen-s i t i v i t y settings had been determined over a t r i a l period, they were l e f t at these settings as long as the same animals were being used. Whenever the apparatus had to be dismantled for repair, i t was again set for sensitivity in the standard manner just described. Experiment 2 was continued from January 22, 1955 un-t i l A pril 23, 1956 and thus encompassed almost sixteen months of near continuous recording. 39 Experiment 3 - Activity wheel experiments The activity of only two flying squirrels was re-corded using activity wheels. On August 15, 1955, a male f l y -ing squirrel (Fej) was placed in a small cage attached to an activity wheel and transferred to the roof of the Biological Sciences Building. On August 19th, a second flying squirrel — a female (FQ) — was similarly placed in a second acti v i t y wheel situated on the same roof. Readings of the revolution counter were taken only once a day — during daylight hours, at a time when the animals were inactive and food could he placed into the cages without unduly disturbing the animals. The activity wheels were placed near the center of the roof in f u l l view of the moon. The nest box of each activity wheel was sheltered from rain by a strip of glass-cloth wired over i t . The activity of F5 was recorded u n t i l October 20th, at which date i t escaped from the cage. Recording on the female flying squirrel FQ continued u n t i l December 15, 1955. The ex-act time at which these two animals l e f t their nest boxes to enter the connecting cage between the nest box and the ac t i v i t y wheel was often also recorded by direct observation as part of the data obtained in Experiment 1. F5 had been permitted to run in the activity wheel for more than a month before being transferred to the roof of the Biological Sciences building for this experiment. F8 had no previous conditioning period. Experiment k - Treadle-board experiments y In order to ascertain whether the acti v i t y pattern 40 of several flying squirrels kept together i n a large cage d i f -fered from that of individually retained animals, the combined activity of seven male Glaucomys was recorded using the treadle-board apparatus already described under the section on Apparatus. The experiment was carried out during two periods of the year — from November 1 to December 22, 1957 and from May 23 to August 10, 1958. Experiment 5 - Activity under conditions of constant light. During mid-February, 1957, two male and one female flyin g squirrel (F 2, F^, and F Q respectively) were taken with their cages from the roof site of the previous experiments i n -to the indoor experimental room. Here, after more than a week of acclimation under conditions of continuous light i n this Activity Room No. 1, recording was commenced of the activity of these animals. The temperature within this activity room was kept constant within two Fahrenheit degrees (68-70°F.) while the relative humidity was kept between 45 and 55$. The animals were fed every other day and the time of feeding was staggered as much as 12 hours in order that the animals should not become accustomed to one feeding hour and alter their ac-t i v i t y accordingly. Activity recordings were commenced on Feb-ruary 26, 1957, and continued under these environmental con-ditions until May 2, 1957. The activity was recorded using Units 1 and 2 of the vibration amplifier apparatus previously described. The activity of these animals was recorded i n one-hour time intervals from 8:00 a.m. until the following midnight hi or 1:00 a.m. at which time the recorder was adjusted to record activity in two-hour intervals per row of counters for the re-mainder of the night. The recorder was set hack to the one-hour time interval setting when the f i r s t reading was taken in the morning. Experiment 6 - Activity under conditions of constant darkness. At the same time that Expt. 5 was being conducted, the activity of another three flying squirrels — two males ( F 5 and F]_i.) and one female (Fa. ) — was recorded under condi-tions of continuous darkness on the remaining three channels of the vibration amplifier apparatus. These animals were being kept in separate cages and housed in Activity Room No. 2 — a ventilated, light-proof storage closet of approximately the same size as Activity Room No. 1. Slightly greater fluctua-tions in temperature and relative humidity occurred in this second activity room. The temperature fluctuated between 68° and 72°F.; the relative humidity between hO and 58$. Like the previous experiment, recording under conditions of continuous darkness ran between February 26 and May 2, 1957. Experiment 7 - Activity under normal light-dark sequence Following the completion of Expt. 5 and 6, the three flying squirrels from Activity Room No. 2 were transferred to the lower shelf in Activity Room No. 1. The light conditions during the present experiment were governed by the light control mechanism described under the section on Apparatus. During the hours between 8:00 a.m. and 8:00 p.m. the 100-watt bulb in the 4-2 activity room was on. During the remainder of the d i e l period i t was off. The transition between the two light conditions was not abrupt but rather effected over a period of almost two hours — thus simulating somewhat the conditions encountered at sunrise and sunset, even to the extent of the red colour of the light as the current was reduced to a low l e v e l . Shortly after 6:00 a.m. the controller began to increase the current to the daylight bulb and by 8:00 a.m. the light had reached f u l l intensity. During the dark period, no light existed in or could enter the activity room. As in the previous experiment, the activity of the six animals was recorded in one-hour time intervals between 8:00 a.m. and either midnight or 1:00 a.m. Following this f i n a l reading for the day the apparatus was set to record for two hours on each counter before automatically switching over to the next row of counters. The animals were again fed at staggered hours during the light period every other day. The experiment was commenced on May 2 and continued u n t i l July 21, 1957. Experiment 8 - Activity under reversed light condition. A part of the building in which the indoor experiments were being conducted was being used by other personnel as of-fices and laboratories. The question became raised: "To what extent was the daily activity pattern of the flying squirrels being influenced by possible vibrations or sounds caused by ^3 other people in the same building? Were these animals actually responding to an innate biological clock mechanism or were physical clues in the form of sounds or vibrations actually determining the time and extent to which the animals were ac-tive?" To obtain an answer to these questions, the light se-quence in Activity Room No. 1 was completely reversed. The dark period now f e l l between 8:00 a.m. and 8:00 p.m. The two-hour gradient between the light and dark periods was retained, as were the conditions of constant temperature and near-constant relative humidity. Experiment 8 was commenced July 22 and was carried on u n t i l November 24, 1957. The same six animals were used in this experiment as i n the previous one. With the dark period now between 8:00 a.m. and 8:00 p.m., the activity during the entire dark period could be recorded using hourly time' units. Final readings were s t i l l taken at either midnight or 1:00 a.m. at which time the apparatus was reset to record for the two-hour intervals per counter u n t i l 8:00 a.m. Experiment 9 - Activity under reshifted light-dark sequence. In this experiment the same procedures were followed as in the previous one except for the change made in the light regulating mechanism to give a dark period inside the activity room between the hours of 1:00 p.m. and 1:00 a.m. instead of tne former 8:00 a.m. and 8:00 p.m. The activity of the six kk flying squirrels was again recorded during the entire dark period using one-hour intervals. Experiment 9 commenced on September 30 and continued through to November 2k, 1957. With the completion of Experiment 9 more than nine months had passed during which the four male (F2, F 3 , F 5 , and F l l ) a n d t n e two female (Fg and Fg) flying squirrels had not seen either sunlight or moonlight. They had been subjected to (1) two months in continuous light or continuous darkness, and (2) the remainder of the time in 12-hours light and 12-hours darkness at altered times within the 24-110^ cycle. What had been established so far; as w i l l be seen shortly, was a relationship between light intensity and the level of activity, and between activity and the duration of the dark period. But nothing was yet known about the relation-ship, i f any, between the duration of the lunar cycle and the level of activity. Altering the length of the lunar cycle might indicate that the 28-day lunar period was controlling ac-t i v i t y directly, as well as indirectly through phasic light i n -tensity variations which i t incidentally produces, i.e. that the 28-day cycle of activity is stable. What was required was to find out i f there was also a 28-day "biological clock" or rhythm within the neuroendocrine system of the animals. If not, then their phasic behaviour must simply be the product of the varying light intensities of the phases of the moon. . h5 Experiment 10 - Activity under 28-day lunar cycle. Experiments 10 to 15 were conducted i n order to de-termine what response normal flying squirrels would show to the light emitted by an a r t i f i c i a l moon hand-operated on a natural and an unnatural cycle duration. The a r t i f i c i a l moon was calibrated with settings 50, 40, 25, 5, 3, 1, 0.3 and 0 and these settings gave light values of 0.05, O.O1*, 0.025, 0.005, 0.003, 0.001, 0.000,3 and 0 ft.-candle respectively when readings were taken at the top center cage in the acti v i t y room. A more detailed description of the a r t i f i c i a l moonlight source, i t s calibration and comparison to that of the ce l e s t i a l moon has been described under the section on Apparatus. In the present experiment the locomotor activity of the same four male and two female, flying squirrels was recorded as in the previous experiments and using the same vibration am-p l i f i e r apparatus. The animals were kept in their individual cages inside Activity Room No. 1 under the same environmental conditions as in the previous experiments except that a r t i f i c i a l moonlight was introduced and was effective throughout the dark periods. In order that the relationship between the intensity of the lunar illumination and the corresponding level of a c t i -vity of the flying squirrels may be more apparent, tables of the lunar cycles used for each of the following experiments w i l l be given-in the section on results rather than i n the pro-cedures. In the present experiment the a r t i f i c i a l moonlight was gradually increased in intensity over the f i r s t two weeks and then gradually decreased, completing the f u l l cycle in 28 46 days. Maximum intensity of the a r t i f i c i a l moonlight during this lunar cycle was timed to occur at the same date of the month as that of the ce l e s t i a l moon, although the dark periods of the experiment continued to occur between 1:00 p.m. and 1:00 a.m. The experiment was conducted between November 25 and December 22, 1957. Experiment 11 - Activity under 40-day cycle. , In the previous experiment the maximum intensity of the a r t i f i c i a l moonlight had been made to coincide with the date of the f u l l moon. To determine whether maximum a r t i f i c i a l moonlight had to occur at the same time as f u l l moon in nature in order that a light intensity-activity level relationship is shown, the lunar cycle in the present experiment was altered (1) by having the maximum intensity of a r t i f i c i a l moonlight occur at least a week after the time of f u l l moon outside, and (2) by lengthening the lunar cycle, to 40 days instead of the usual 28 days, i.e. nearly one and a half times the duration of the natural lunar month. The experiment ran from December 24, 1957 to February 1, 1958. Experiment 12 - Activity under 21-day lunar cycle. In this experiment using the same animals and appara-tus as before, the schedule of the a r t i f i c i a l moonlight inten-sit i e s was shortened to 21 days, or three-quarters that of the natural lunar month. The experiment ran from the 4th to the 24th of February, 1958. hi Experiment 13 - Activity under 18-day lunar cycle. Between March 10 and March 27, 1958, the light se-quence of the a r t i f i c i a l moonlight being provided the four male and two female flying squirrels was shortened even more than in the previous experiment to accord an 18-day lunar cycle. Experiment Ih - Activity under l1*-day lunar cycle. By changing the diaphragm position of the a r t i f i c i a l moonlight source by one calibration unit each day, a lunar cycle one-half the length of the natural cycle was achieved for Experiment ih running between A p r i l 2 and A p r i l 15, 1958. No other aspect of the experiment was changed. Experiment 15 - Activity under three 7-day lunar cycles. By omitting several of the possible light intensity settings, three consecutive experiments of 7-day lunar cycles were conducted on the above-mentioned animals between A p r i l 19 and May 16, 1958. These were lunar cycles of only one-quar-ter the duration experienced outdoors. Experiment 16 - Activity under 28-day lunar cycle — without nest boxes. In a l l the previous experiments, the animals were able to sleep in nest boxes or retreat to these boxes whenever they wished to avoid more unfavourable conditions such as bright ligh t . Such a nest box being tied in a corner of the cage four or five inches off the floor, cast a shadow beneath i t thus ac-cording to the animals a limited area of the cage outside the nest box where they could eat in subdued l i g h t . To determine X 1+8 whether such nest boxes and such shadows played any marked role in the activity rhythms, the nest boxes and a l l nesting material was removed from the cage of each of the flying squirrels. Another 28-day lunar light sequence was conducted on these ani-mals between May 21st and June 17th, 1958. Experiment 17 - Activity under three 28-day lunar cycles - Gonadectomized animals. To ascertain whether any connection existed between the reproductive cycle of flying squirrels and their activity cycles, the gonads of an additional three male (F ]_Q , F20 F 2l ) and three female flying squirrels ( F ^ Q , F ^ , F ^ S ) were removed. The operations were performed by a qualified veterinarian dur-ing the last week of November, 1957 and the animals were per-mitted almost a f u l l month to recover and to become acclimated to the new environment (Activity Room No. 2) before recording * of their activity was attempted. Each gonadectomized animal was then placed in a separate cage mounted on a tray supported by a 2-inch thick foam rubber pad much in the same manner as that of the normal animals in a l l indoor experiments to this point of the study. The locomotor activity of the gonadecto-mized animals was recorded using Unit 3 of the vibration am-p l i f i e r apparatus. This six unit recorder had only one counter per channel and the activity of the animal on each of these channels was recorded accumulatively. The light i n this second activity room was regulated by the same light controlling mech-anism as that governing the light cycle in Activity Room No. 1. ^9 Readings were taken on this apparatus once a day — at 8:00 a.m., and as in the other experiments, these animals too were fed only every other day. Commencing on December 24, 1957, the gonadectomized animals were subjected to two 28-day lunar cycles each of which paralleled the phases of the outside ce l e s t i a l moon. A third 28-day lunar cycle was then introduced one-half a month out of phase with the c e l e s t i a l moon. No moonlight was provided dur-ing the dark periods of the two week period required to place the a r t i f i c i a l lunar cycle out of phase with that of the natural cycle. The experiment ended March 31, 1958. Experiment 18 - Activity under 14-day lunar cycle -Gonadectomized animals. After Expt. 17 and at the same time as the activ i t y of the six normal flying squirrels was being recorded in Expt. ih, the activity of the six gonadectomized animals was recorded under the same light conditions in the second activity room. No. *r0-, 21- , and 18-day lunar cycle experiments were conducted using the gonadectomized animals. Experiment 19 - Activity under three 7-day lunar cycles - Gonadectomized animals. This experiment paralleled Expt. 15 and was carried on at the same time. As before, these three brief experiments followed one after the other without an intervening period. Experiment 20 - Activity under 28-day lunar cycle without nest boxes - Gonadectomized animals. ^ In this experiment the same light sequences were used on the gonadectomized animals as had been employed in Expt. 16, 50 using the normal flying squirrels. The nest box was removed from each cage thus eliminating shadows from within the cages. Experiment 21 - Activity under 16-hour days - Normal animals. For this experiment the light regulating mechanism was re-geared to provide light and dark periods of 8-hour dur-ation each instead of the natural 12-hour periods. The same r sunset and sunrise gradients were retained as before. Thus two light and one dark or two dark and one light period were provided during each 24-hour day. After almost two weeks of acclimation, recording of the locomotor activity of the four male (F 2, F3, F5, F J J . ) and two female (F3, Fg) flying squirrels was commenced on June 26, 1958. During the dark 8-hour periods, a r t i f i c i a l moonlight corresponding to changing moon phases was provided and the f u l l sequence of moon changes was carried through in 18 days (July 2 - 21, 1958). A second lunar month of shortened light and dark periods was conducted on the same animals between July 23 and August 10, 1958. Experiment 22 - Activity under 16-hour days. -Gonadectomized animals. Light and dark 8-hour periods and a r t i f i c i a l moonlight intensities used i n Expt. 21 were simultaneously duplicated in the second activity room for the gonadectomized flying squirrels. The locomotor activity of these animals was recorded during two abbreviated lunar months. 51 RESULTS AND CONCLUSIONS While the sequence of experiments i n the section on Methods followed to a large degree the chronological order i n which the experiments were carried out, deviations from this orderly system w i l l be made in order that the results might be given in accordance with the tri p a r t i t e viewpoint mentioned under Purposes of the Study — i.e. that evidence may" be pre-sented for diurnal, monthly, and seasonal levels of ac t i v i t y . Activity of flying squirrels at one or more of these levels were found to occur in most of the individual experiments and for this reason any one experiment might be drawn upon to sup-port evidence of ac t i v i t y at the d i e l , monthly or seasonal level. In order that the evidence might conform as near as possible to the activity of these animals i n their natural habitats, those experiments carried on under outside climatic conditions w i l l be cited f i r s t to support these three levels of a c t i v i t y — Expts. 1-U-. The time at which activity of f l y -ing squirrels commenced in the evenings throughout the year was studied in Expt. 1; the hour at which activity ceased i n the early hours of the morning is drawn from data of Expt. 4; evidence of the monthly rhythm of activity is seen in Expts. 2 , 3 and h\ and for the seasonal levels of acti v i t y Expt. 2 and h are cited. Diurnal Pattern of Activity "Awakening time" of flying squirrels: The time at which 52 flying squirrels being kept in captivity on the roof of the Biological Sciences Building came out of their nest boxes was checked by direct observation for almost sixteen months (January, 1955 to A p r i l , 1956). During this interval, 1,285 observations on emergence time were made. The results of 1,033 of these observations made during 1955 are shown i n Figure 1. The remaining 252 observations made during the f i r s t four months of 1956 are summarized i n Table II. In Figure 1 the o f f i c i a l time of sunset is represented by a straight line running through the length of the figure. Time, indicated as minutes before and minutes after sunset, is represented along the ordinate below and above the sunset line respectively. Each of the double bar units is based upon a variable number of observations of emergence time made within consecutive 5-day periods throughout the year 1955. The mean of this awakening time within the five-day periods is represented by the triangle and line symbol (>- ) passing through the center of the clear bars, and is based on whatever number of observa-tions were made during those particular five days. The range in the number of observations within a five-day period extended from a low of 3 observations (on July 20-24, 1955) to a high of 64 observations (Oct. 28-Nov. 1, 1955). The right-hand black bars represent the range of this awakening time during the same 5-day periods while the left-hand open bars indicate twice the standard error based on these observations. The 53 undulating line running across the page was obtained by taking a 5-unit running average of the mean awakening times. The number of animals whose emergence time was being checked and the number of observations made during each of the 5-day periods varied throughout the duration of Experiment 1, which meant that various sections of the graph are hot directly comparable. The variations i n the number of animals involved and the number of observations, as well as the mean awakening time, the range and two standard errors have been summarized on a monthly basis in Table III. During the f i r s t four months of the experiment, the awakening time was checked on only one flying squirrel (Fj). As more animals were live trapped and included in the experi-ment, the greater number of awakening time observations were based on a larger number of animals. The greatest number of animals obtained for this experiment was 15 individuals, each housed in an activity cage visually separated from each of the other animals. As seen in Figure 1, the time at which flying squir-rels leave their nests in the evening to commence their nightly activity depends very much upon the number of animals under ob-servation. Considering f i r s t of a l l only the averages of the awakening times over the 5-day periods, this value, with very ,few exceptions, f a l l s between 40- and 50-minutes after sunset during January, February and March. During A p r i l , there is an 5h FIGURE 1 Awakening time of a variable number of flying squirrels (Jan. - Dec. 1955). From January u n t i l the end of A p r i l , 1955 only a single animal was observed. From May to July, three or four animals were observed. Nine animals were observed in August and from September to December the number was between 13 and 15 animals. A l l observations are plotted over five-day periods. The black columns show the overall v a r i a b i l i t y in "awakening" time of a l l the animals during each five-day period. The t r i -angle and horizontal line across each white column is the mean of the awakening times of a l l the animals observed in each five-day period, and the height of the white column above and below this midpoint shows the value of two times the Standard Error. The undulating line is the running average of the mean of five five-day periods. For interpretation of this graph see text. Total number of observations upon which the graph is based is 1,033 awakening times. >Table II. Additional data on awakening times, of 13 flying squirrels during 1956 5-day Periods Number of Mean Awakening Time 2 Standard Errors Range i n Minutes Observations (in Minutes after about Mean (in after Sunset Sunset, P.S.T.) Minutes) Early Late Jan. 11 - 15 20 29.9 i 6.72 (-1) • - 50 16 - 20 18 28.8 5.05 9 - h? 21 - 25 9 22.8 7.30 (-1) • - 37 31 - 26 - 30 19 39.5 6.09 (-1) • - 55 31 - Feb- 4 16 42.6 6.17 20 - 63 5 - 9 10 38.3 8.34 5 - 55 10 - 14 32 44.6 4.95 18 - 72 15 - 19 7 37.1 13 A5 12 - 67 20 - 24 10 40.7 9.79 15 - 57 25 - 29 10 37.1 7.15 12 - 52 Mar. 1 - 5 15 37.1 6.74 16 - 59 6 - 10 10 ^7.8 9.69 21 - 66 11 - 15 16 ^3.9 4.34 29 - 59 16 - 20 5 36.0 9.23 24 - h7 21 - 25 9 37.3 7.25 21 - 5h 26 - 30 5 1+6.4 6.83 40 - 57 31 - Apr- 4 l i 39.7 7.17 19 - 58 5 - 9 10 52.3 8.91 32 - 72 10 - 14 5 50.8 13.21 31 - 71 15 - 19 9 38.8 12.63 12 - 66 20 - 24 6 29.2 9.33 11 - 41 56 even greater delay i n the time at which flying squirrels leave their nests. Then during May and June, the squirrels come out earlier and earlier after sunset each night. During July and August as the days shorten, the animals come out progressively rather later and reach the 4-0-minute after sunset level by early September. During the f a l l and winter the running av-erage of mean awakening times centered around the 30-minutes after sunset level but by the following February was once more at the 4-0 minutes after sunset level as i t had been dur-ing 1955. As mentioned, the averages for the month of January, February, March and Apr i l (1955)) are based oh data from only one animal (F^). One might ask whether these data are repre-sentative and comparable to the picture which might have been presented had a greater number of flying squirrels been checked during these months of the year. As seen in Table III, from data based on observations of thirteen flying squirrels in 1956, the mean awakening time during the latter part of January and through February and March once more fluctuated only slightly about the 4-0-minutes after sunset level — as had been the case when only the one animal was being checked. The delay in the awakening time during the early weeks of Ap r i l , 1955, seen in Figure 1, occurred again the following year and was again followed by weeks during which the animals began coming out earlier and earlier each evening. Table III. Monthly summary of the awakening time of flying squirrels. Month (1955) Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. (1956) Jan. Feb. Mar. Apr. No. of Animals Checked 1 1 1 1 2 h 9 15 15 14 13 13 13 13 13 No. of Ob-servations Record ed 16 27 29 27 78 95 80 93 200 233 126 29 75 76 66 35 Mean Monthly Awakening Time (Minutes after Sunset, P.S.T.) 42.8 46.7 45.9 55.9 h3.3 22.5 26.3 41.4 32.0 31.6 35.3 39.1 33. ^ 40.8 41.8 42.9 Two Standard Errors (in Minutes) ±1.58 3.34 3.42 2.48 3.98 5.16 6.06 4.54 2.06 1.1+6 2.1+8 5.14 3.36 3.26 2.92 5.64 Range (Minutes after Sunset) Early Late 38 25 30 44 -20 -53 -25 • 2 -10 :l 8 - 1 J 11 48 P 63 68 6 8 92 117 68 58 67 63 72 66 71 Total 1,285 Average 35.4 ±2.12 58 Not only do flying squirrels come out much earlier i n the evenings during the summer months, hut they also show the greatest v a r i a b i l i t y i n their time of emergence during these same months. In midsummer these animals often become active even before the sun had set. Indeed, during the hot-test days the flying squirrels in the cages in the shelter of-ten came out of their nests to l i e on the floor of the cage along the side nearest the open edge of the shelter. When the awakening time of each individual animal was plotted, no significant differences from the pattern shown for the whole group could be seen. Each showed a characteristic earlier emergence during the summer months, although some individuals did persist in beginning at a late or early hour. The sexes do not differ noticeably in this respect. Activity Cessation Time: The time at which the activity of the flying squirrels ceased in the early hours was, for ob-vious reasons, only periodically observed. These data were, however, readily obtained in part by a l l night direct obser-vations and in part from the activ i t y recorded on the moving paper tape of Expt. h. This experiment was conducted in two parts ~ Nov. 1 to Dec. 22, 1957 and from May 23 to Aug. 6, 1958 — thus providing data from mid-winter and mid-summer months. These data are presented in Tables XIX and XX in the Appendix. In Table IV below are given the time of sunrise, sunset, and the corresponding length of the night during these two periods. 59 It is interesting to consider what factors might serve to bring about such a characteristic pattern in the time at which these animals begin and end their nocturnal activity. Despite great variations in the cloud cover from night to night at the time these observations were being conducted, the variations in the light intensity thereby produced did not appear to have a direct governing influence in determining the precise time at which an animal would leave i t s nest box. Often the same animal would come out at almost the same time on a cloudy night as on a following clear night. Nor do tem-perature variations appear to cause v a r i a b i l i t y i n the awaken-ing time. Sudden cold periods lasting one or more weeks during mid-winter are not accompanied either by earlier or later times of emergence. The phase of the moon does not ap-pear to be correlated with variations i n the awakening time of the flying squirrels. One factor which does show at least an inverse cor-relation with the awakening time pattern and the continuance of nightly activity is the duration of nightly darkness. Dur-ing the equinox the light and dark periods are of approxi-mately equal duration — each being roughly 12-hours duration. During the winter months, for example on or shortly before December 21, the sun set in Vancouver shortly after 4:00 p.m. and rose soon after 8:00 a.m. This gave approximately 16 ,hours of night. During the same time of the year the acti v i t y 60 Table IV. Approximate time of sunset, sunrise and duration of night during interval of Expt. h ( a l l times are Pacific Standard Time). Date Sunrise Sunset Duration of night Oct. 27 1957 6:51 Nov. 1 7:00 6 7:07 11 7:15 16 7:23 21 7:31 26 7:38 Dec. 1 7:^5 6 7:51 11 7:56 16 8:01 21 8:04 __ n n 13 hr. 41 min. 17:00 l k oo 16:51 14 16 16:44 2.h 31 16:37 i4 46 ,„., ^ 16:30 15 oi S i n t e L 16:24 H Xt Recording 16:21 il P4 P e r l 0 d 16:17 34 i ^ 1 ? 15 41 16: l*t 15 .^7 May 20 1958 25 3P June 4 9 14 19 24 29 July h 9 ih 19 24 29 Aug. 3 /. 8 4:24 4:18 4:14 4:10 hiO? 4:07 4:07 4:08 4:10 4:13 4:17 4:22 4:28 ht$h 4:40 4:47 4:5^ 19 20 20: 20: 20 20 20 20 20 20 20: 20 20 20 19 19 19 5h 00 06 ;11 15 17 19 20 20 19 17 13 08 02 ?6 40 8 24 8 14 8 04 7 56 7 52 7 50 7 9^ 7 50 7 53 7 58 8 05 8 15 8 26 8 38 8 51 9 05 Summer Recording Period 61 of the flying squirrels was distributed over 13 of these 16 dark hours — from 5:00 p.m. to 6:00 a.m. Similarly, during the summer (June 21, for example) the sun rose shortly after 4:00 a.m. and set at 8:20 p.m. thus providing only about 8 hours of darkness. The flying squir-rels were intensely active over a period of six hours (9:00 p.m. - 3*°0 a.m.) compared to the thirteen hours noted during the winter months. In their natural habitat, where food is less abundant than i t was i n captivity, flying squirrels would require a certain minimal number of hours In which to find suf-fic i e n t food to sustain them. This could possibly be the rea-son for their becoming active even before sunset during summer months when the night has become so much shortened. During the winter, the flying squirrels revert to a habit of becoming active at a later hour, in relation to the time of sunset, when darkness affords greater safety. At the same time suf-fic i e n t hours of darkness prevail to enable adequate time for foraging, in comparative leisure. It thus becomes apparent that the ac t i v i t y of flying squirrels is complex. The time at which the animals become active appears to be governed by a precise internal physio-logical clock which is altered but gradually and i n keeping with the major environmental changes -- for example, the sea-sons. The diurnal rhythm i s , therefore, pliable over long /periods of time. 62 The average of the 1,285 observations on the awaken-ing time of the fif t e e n flying squirrels under observation during the sixteen months of this study was 35.4- - 2.12 minutes after sunset. This value differs during the different months of the year and appears to be governed by some stimulus within the animals rather than by prevalent light conditions. Comparison of the beginning times of nocturnal ac-t i v i t y of flying squirrels with that of other animals which restrict their activities to the darkened period of the 24-hour natural cycle i s of interest. Falls (1953) found that Peromyscus in activity wheels began their a c t i v i t y 30 minutes after sunset during June and July. These animals became active when the illumination was about equivalent to or a l i t t l e brighter than that provided by a f u l l moon. Neal (1958) found a striking parallel between the time of sunset and the time at which badgers emerged, particularly during the periods March to May and August to November. During these months bad-gers became active approximately one-half hour after sunset. As in the case of the present study of flying squirrels, bad-gers tended to come out i n much broader daylight after May. Neal suggests this is due to the shortening of the night, thus necessitating an earlier start to feeding. During the winter months, with the longer hours of darkness, emergences became more regular. During periods of bright moonlight, bad-gers came out much later than usual. Such was not found to be x the case with the flying squirrels. 63 Attention is now turned to the hourly distribution of the nocturnal activity of the flying squirrels. This can best be shown by further examination of the data compiled i n Expt. k in which the combined acti v i t y of seven male animals was recorded under outside climatic conditions using the treadle-board apparatus. The mechanism of the treadle-board and moving tape activ i t y recorder has been described. It need only be added here that this recording device is intended to give an index of the gliding and leaping activity as well as a measure of the running which accompanies these movements. A record is made only when an animal leaps from the small platform s i t u -ated i n the large outdoor cage. The results of the winter treadle-board experiment is shown in Table XIX of the Appendix; that of the summer months experiment appears in Table XX. Here the total number of pin holes punched into the moving tape — indicating the number ofotimes that flying squirrels had leaped from the treadle-board — is shown for each hour of the night. No re-cord was attempted during heavy downpour of rain or during violent wind storms and hence the repeated breaks in the winter records. Either element could possibly have caused bridging of the e l e c t r i c a l contacts at the movable end of the treadle-board . 7< 64 In Table V below, an attempt has been made to sum-marize even further the winter-collected data presented in Table XIX. F i r s t , the hourly a c t i v i t y — i.e. the number of pin holes recorded during each hour of the night on the moving paper tape — were listed for each of the 43 nights on which records had been made. Next, the hour on any one night during which peak activity for that night had occurred was assigned a magnitude value of 1; the hour during which the second highest value of activity of the night occurred was assigned a magnitude value of 2, and so on. In cases where equal amounts of activity had been registered during two or more hours of the same night, equal magnitude values were assigned to each of these hours, and then one magnitude (or more) was omitted from the count for each double value in order that the hour of least amount of activity could s t i l l be assigned a value corresponding to the number of hours over which activity had occurred. The assigned magnitude values were then summed for similar hours of the night over the 4-3 nights and these sums in turn assigned to the proper magni-tude level, i.e. so many l ' s , so many 2's, and so. on. Fin-a l l y , the frequency with which each magnitude value occurred during each hour of the 4-3 nights is expressed as a percentage figure and appears in Table V. The data in Table XX of the Appendix dealing with the summer treadle-board data have been similarly treated and / appear as an expression of magnitude distributions of activity x-Table V. Percentage distribution of hourly magnitudes of activity of seven male flying squirrels recorded on the treadle-board apparatus. Data based on 43 nights of recording between October 31 and December 22, 1957. Magnitude 1 (Ml) represents hour of peak activity. Hours Ml M2 M3 M4 M5 M6 M7 M8 M9 M10 Mil M12 M13 Ml4 4 I 7 8 9 10 11 Mt. 1 2 I I 5 p.m. 6 p.m. 7 p.m. 8 p.m. 9 p.m. 10 p.m. 11 p.m. Mt. 1 2 : I - 5 - 6 - 7 a .m. a.m. a.m. a.m. a.m. a.m. a .m. 14. 23. 2. 8. 4. 12. 12. 2. 8. 4. 4. 2. 2.1 — -- — 2.9 4.8 — 9.5 7.4 — 14.3 50.0* — 9 17.6* 9.7 8.7 2.5 5.7 4.8 2.8 — 3.7 15.4 — — — 4* 8.5 4.9 8.7 7.5 ~ 9.5 5.6 19.6* 7.4 — -1 6.4 9.7 2.2 10.0 11.4 16.7* 5.6 9.5 3.7 7.7 — — 100.0* 5 2.1 4.9 6.S 2.5 2.9 2.4 5.6V 9.5 3.7 15.4 14.3 50.0* — 2 2.1 — 15.2* 5.0 11.4 4.8 13.9* 4.8 3.7 — 14.3 — — 8 6.4 7.3 15.2*10.0 14 .3 s 2.4 8.3 4.8 — — 14.3 — 8 12.8 17.1* 6.5 2.5 8.6 9.5 8.3 4.8 — 7.7 1 12.8 2.4 13.0 12.5 8.6 11.9 2.8 k.Q 11.1 -5 10.6 14.6 4.3 10.0 5.7 11.9 11.1 9.5 — — -- — 2 14.9 9.7 2.2 12.5 8.6 — 2.8 — 14.8 — 14.3 — — 7.3 8.7 17.5* 2.9 7.2 11.1 — 18.5* 15.4 4.2 4.9 2.2 5.0 14.3* 7.2 13.9*15.7 3.7 23.1* ~ 2 — 4.9 6.5 2.5 2.9 4.8 5.6 4.8 11.1 7.7 28.6* — — 1 — 2.4 — 2.5 — 2.4 2.8 4.8 11.1 7.7 -No. of Nights 47 47 41 46 40 35 42 36 21 27 13 7 2 1 Ml - Ml4 indicates decreasing magnitudes of locomotor activity. K indicates the hour of the highest percentage distribution of activity at each of the indicated magnitudes. 66 in Table VI. In this table, the act i v i t y of the seven male flying squirrels over 7^ nights of recording between May 23 and August 10, 1958, has been summarized as percentage figures. The table is read, as for example — on 52.6 per cent of the nights in question, the peak of the activity (magnitude 1) occurred between the hours of 10:00 and 11:00 p.m. (P.S.T.). On 18.4- per cent and 17.1 per cent of these same nights, peak activity occurred between 9:00 and 10:00 p.m. and between 11:00 p.m. and 12:00 midnight respectively. The greatest percentages of each of the decreasing magnitude values (1, 2, 3, , 8) as indicated by the asterisk suggests that this supplementary activity is concentrated later and later than the 10:00 - 11:00 p.m. peak just described for magni-tude 1. Second magnitude activity is greatest between 11:00 p.m. and midnight, and third magnitude more or less evenly distributed between 11:00 p.m. and 1:00 a.m. This shift of the supplementary activity to the right is worthy of study i n view of i t s possible relation to various other ac t i v i t i e s (e.g. feeding, grooming, play). In general, flying squirrels become active shortly before 9*00 p.m. during the summer in the Vancouver area, and the peak of activity occurs between 9:00 p.m. and midnight — but most frequently between 10:00 and 11:00 p.m. " Only one major peak of activity occurs during the summer nights follow-ing which there is a gradual decline in the intensity of loco-motor activity. The animals cease their movements shortly x Table VI. Percentage distribution of hourly magnitudes of activity of seven male flying squirrels recorded on the treadle-board apparatus. Data based on 7k nights of recording between May 23 and August 1 0 , 1 9 5 8 . Magnitude 1 (Ml) represents hour of peak activity. Hours Ml M2 M3 M4 M5 M6 M7 M8 8 - 9 p.m. 1.32 — 1.33 5.33 9.21 1 8 . 6 7 4 5 . 2 8 * 11 .11 9 - 10 p.m. 18.4-2 2 0 . 8 3 2 2 . 6 7 14-. 67 1 7 . 1 1 4 .00 1.8.9 — 10 - 11 p.m. 52.63* 23.61 IO .67 2 . 6 7 2 . 6 3 2 . 6 7 1 . 8 9 5.56 11 - Mt. 17.11 31.95* 2 8 . 0 0 * 1 0 . 6 7 6.58 2 . 6 7 -- 5.56 Mt. - 1 a.m. 5.26 16.67 2 8 . 0 0 * 3 0 . 6 7 * 14-. 48 2 . 6 7 I . 8 9 — 1 - 2 a.m. 5.26 6.94- 6.67 30.67* 36.84* 9.33 1 .89 — 2 - 3 a.m. 2 . 6 7 5.33 10.53 5 6 . 0 0 * 2^.53 — 3 - 4 a.m. 1.33 2 . 6 3 2 . 6 7 20.75 .83.33* 4 - 5 a.m. 1.33 1 . 8 9 No. of Nights 76 72 75 75 76 75 53 18 Ml - M8 indicates decreasing magnitudes of locomotor activity. X indicates the hour of the highest percentage distribution of activity at each of the indicated magnitudes. 68 after 3:00 a.m. by which time the f i r s t indications of dawn become apparent with sufficient intensity as to cause the animals to retreat to their nest boxes for the daylight hours. On only two occasions did activ i t y continue u n t i l after 4:00 a.m. In one of these instances at least, rain had fall e n in the earlier part of the night, thus delaying the time at which activity commenced. During the long winter nights (comparatively speak-ing) in the Vancouver area with i t s almost twice the number of hours of darkness, the activ i t y in turn is distributed over a correspondingly greater number of hours. Both the to-t a l count for the night and the counts for individual hourly units were, however, but a fraction of that recorded over corresponding hours in mid-summer — generally about one-tenth that of the summer values. The peak of act i v i t y again occurred during the third hour after activity commenced. At this time of the year the peak f a l l s between 6:00 and 7:00 p.m. Not only is this peak less pronounced — magnitude 1 percentage for peak hour in winter being only 23.^ as compared to 52.6 during the summer - but there appears a tendency for a second lesser peak to occur during the early hours of the morning — the two being separated by a marked decline of ac-t i v i t y between 7s00 and 10:00 p.m. Whether this second peak is brought about by a need for additional food to last through-out the long winter night can only be conjectured here. As during the summer months, acti v i t y commences and ceases within 69 approximately an hour after sunset and before dawn respectively. Monthly Level of Activity Expt. 2 Activity under outside climatic conditions. That flying squirrels are nocturnal has been verified by numerous authors — Audubon and Bachmann (18^-6), Howell (1918), Seton (1929), Sollberger (1940), McKenny (1954), and Cowan and Guiguet (1956) — and although reference has been made to their a c t i v i t i e s , the literature on this aspect of these animals has been conspicuously vague. Nowhere does there appear to be a description of the extent of the noctur-nal activity of flying squirrels, i.e. the intensity and duration of locomotor activity. Nor is there a description of the relationship of environmental factors such as maximum and minimum temperatures, humidity, or nocturnal illumination which might influence the activity of these animals in demon-strable fashion. Using the vibration amplifier apparatus (Units 1 and 2) the activity of several flying squirrels was recorded under outside climatic conditions on the roof of the Biological Sci-ences Building for almost sixteen months (January 22, 1955 -April 23, 1956). At the commencement of the experiment only one flying squirrel, (FT.), had been live trapped for this pur-pose. As others were captured, they were included into the ex-periment. Because of the more extended records made on F ] _ , i t s activity pattern alone is being used to illustr a t e the monthly rhythm of locomotor acti v i t y present in this species. 70 The records of other flying squirrels, of either sex, while recorded over somewhat shorter and less continuous periods, did not differ appreciably or in a consistent manner from that being illustrated for F j . The acti v i t y of F j over a period of thirteen lunar months is shown in Figure 2. The level of activity is i n d i -cated along the ordinate in Hundreds of Units as outlined under Procedures (Expt. 2). Along the abscissa, the phase of the moon and date (via the f i r s t letter of the month and the calendar number) are indicated at the base of each double column. The activ i t y of this animal has been grouped into two periods: 1) activity which occurred from the time the animal f i r s t became active shortly after sunset u n t i l mid-night (black columns), and 2) activity from midnight u n t i l dawn (open columns). While the recorder was kept in operation throughout the whole day for several weeks at the beginning of the experiment, vi r t u a l l y no acti v i t y was recorded during the bright daylight hours and so recording was ceased during these hours. The results of the act i v i t y recording are shown separated into lunar month units. In the figure the average of each of five nights, of activity have been grouped about each of the four calendar phases of the moon. The five nights have been selected so that i t i s the third night on which the precise phase of the moon is indicated on the calendars. The activity unit used is a count of one pulse on the vibration amplifier counters for each movement of the animals above the 71 FIGURE 2 Activity of one male squirrel (F-^ ) during part or whole of thirteen successive lunar months under natural climatic conditions. In 1955» part of the months of June, September and December were not recorded. Months are indicated by their i n i t i a l letters, and the numbers indicate the calen-dar date of the lunar phases indicated. Activity over f i v e -night periods has been averaged and centered about each of the lunar phases. N.M. = New Moon; F.Q. = F i r s t Quarter; F.M. = F u l l Moon; L.Q. = Last Quarter. Black bars indicate 5-night average of activity occurring between sunset and midnight. Open bars indicate average of activity from midnight to dawn over the same five nights. Note repeated decrease in activity at time of f u l l moon. Also greater portion of the nightly activity occurs during the f i r s t part of the night. A C T I V I T Y HUNDREDS OF UNITS 72 predetermined intensities of movement. The sensitivity of the apparatus was preset by the method already described. When the total sum of the activity of the male f l y -ing squirrel Fi_ is plotted for night after night against such environmental factors as maximum or minimum temperature or averages of the relative humidity for these same time units, no clear cut correlation can be determined between any of 0 these factors and the sum of the activity. When this same nightly total i s plotted, however, against the phases of the moon, a strong correlation becomes evident. During dark nights of l i t t l e or no moon, i.e. between last and f i r s t quarter phases, the activity of flying squirrels is at a r e l -atively high level. As the moon waxes, however, and the i n -tensity of the lunar illumination increases, the activity of these same animals declines markedly to a minimum at the period of f u l l moon. This low level may be one-half to one-twentieth that of the former high level of ac t i v i t y . Then, as the moon wanes, the amount of activity again increases. There thus occurs a rhythmicity i n the total of the nightly activity of flying squirrels the periodicity of which closely parallels the 28-day rhythm of the lunar phases. As w i l l be seen later, this monthly rhythm is amazingly stable and con-tinues to persist even after the animal is placed under highly unnatural and varied environmental conditions for as long as nine months. This rhythm which correlates the nightly sum of the activity of individual or groups of flying squirrels 73 with the intensity of the nocturnal illumination, whether this he of a natural or of an a r t i f i c i a l source, is one which w i l l be found to be evident i n each of the experiments to be discussed from here to the end of the study. As seen i n Figure 2 , the greater portion of the total activity of flying squirrels occurs in the period be-tween sunset and midnight, after which activity f a l l s off. Exceptions to this general rule do occasionally occur but the instances are few. Because of several breaks i n the continuous sequence of these recordings, i t is not intended that the absolute totals represented by the vertical bars in Figure 2 should be used for other than general comparisons of the activ i t y levels over widely separated times of the year. Activity was not re-corded during one or more of the moon phases (e.g. June, Sep-tember and December, 1955) and they are omitted from the figure. When the apparatus was used after these interruptions, i t was again set for sensitivity i n the standard manner. De-clines in activity at the time of f u l l moon continued to be registered and i t was assumed that the apparatus was again working satisfactorily. Thus, superimposed upon the d i e l rhythm of 24-hours, there is an equally exact lunar rhythm which governs the amount of total activity exhibited by individuals of this species over approximately 28-day periods. The responses of the animal 7h to the nocturnal illumination of this rhythm is i n an i n -verse relationship. Expt. 3 Activity wheel experiments In part that i t might serve as a check method of re-cording as compared to that using the vibration amplifier apparatus, the locomotor activity of two flying squirrels was recorded using activity wheels. The animals, a male (F^) and a female (Fg), were placed inside nest cages attached to i n -dividual activity wheels and placed approximately thirty feet apart on the roof of the Biological Sciences Building i n f u l l view of the sun and the moon. F5 had been given almost a month and a half previous opportunity to run: i n the wheel be-fore the experiment was considered to have started. Fg had no such training. Records were kept of the number of revolutions run by F^ nightly from August 15 u n t i l October 20, 1955. The nightly activity of Fg was recorded from August 19 u n t i l De-cember 15 , 1955. A portion of the activity record of the female flying squirrel Fg is shown in Figure 3. As the figure shows, considerable variation in the number of revolutions run from night to night was exhibited. Such variation might be readily expected i n the total activity level of any animal. Considering only the general trend, how-ever, the same picture established in Expt. 2 again becomes evident. During the nights of l i t t l e or no moonlight the number 75 FIGURE 3 Number of revolutions run by one female squirrel (F8) in an activity wheel from early October to early December, 1955. Activity during the period October 25-31 i s greater than expected from knowledge of response to lunar phase illumination, because of considerable overcast con-ditions. From November 2-^f, activity was almost total l y inhibited by rain. From November 8-15 i t was very cold and foggy. At this time a rise in ac t i v i t y should be anticipated, but did not materialize. Thus the rhythm of acti v i t y during the f i r s t month was upset bywaather conditions. In the second month, however, the usual decline i n activity at the time of f u l l moon was observed. 76 of revolutions run by the flying squirrel was considerably more than on clear nights at the time of or near f u l l moon (20,107 revolutions on the night of the f i r s t quarter moon on October 23; and only 657 revolutions on the f i r s t clear night one day after the f u l l moon of October 31). Nights with clear sky prevailed during the f i r s t quarter phase of the moon and the activity of Fg began to decrease with i n -creasing lunar illumination. Had the clear sky condition continued, i t is assumed that the activity would have con-tinued to decrease. From the 25th of October to the end of the month, however, dense and complete overcast conditions prevailed and to a large degree n u l l i f i e d the effects of nocturnal illumination. The number of revolutions run nightly once more rose to approximately the level of those incurred during new moon. The sky cleared on the night after the f u l l moon and the level of activity expressed by the number of revolutions run f e l l dramatically from 25,378 to 657 from one night to the next. From November 2nd to the M;h rain f e l l during part of the night and the act i v i t y continued to drop. From the 5th to the 8th of November cloudy conditions again prevailed and the activity showed a temporary increase. From the 8th to the 15th the weather became extremely cold (10° to 15°F.) and dense fog set in during the greater part of both day and night. The activity again f e l l to a low level but rose when the temperature ameliorated and skies cleared after the 18th of November. A similar decrease in activity at the 77 time of f u l l moon at the end of November was recorded but again the activity was kept at a low level on successive nights by almost continuous drizzle and rain. Considering the activity of this one flying squir-r e l , one might conclude that 1) i t s activity was influenced by the intensity of the nocturnal illumination causing a de-crease of the running activity at the time of f u l l moon, and 2) that the activity wheel is a satisfactory method of re-cording the locomotor activity of these animals provided the method is supplemented with additional observations. The use of this method of recording activity did not prove satisfac-tory for the second flying squirrel, F^. While under almost identical environmental and experimental conditions in another wheel, i t was found that F5 was registering three to five times as many revolutions per night as Fg. A check was made by direct observation to determine the cause for such a dis-crepancy. The reason soon became apparent. F5 had developed the habit of entering the activ i t y wheel, causing the wheel to gain momentum by running in i t and then hopping out into the adjoining cage to watch the wheel revolve by i t s e l f for another fifteen to twenty revolutions. As the wheel began to slow down, this flying squirrel would again hop inside, run only long enough to regain the"lost momentum and then once more hop out to watch. The results of this animal were not included in the experiment. 78 Expt. h Treadle-board experiments The recording of the activ i t y of flying squirrels by means of the treadle-board method already described was designed to serve three important functions: 1) To provide a record of the activ i t y of a group of animals i n a record-ing device which alters the normal locomotory habits of the animals as l i t t l e as possible. Gliding plays a prominent role i n the locomotor activity of flying squirrels, as does running and climbing. Activity wheels by their inherent shape and mechanism do not permit either gliding or climbing, and for this reason are of questionable value as a recording device for locomotor potential of this species. 2) To allow the recording of activity of a number of flying squirrels as a group or community unit. Gregariousness is in fact common in the wild i n this species. With the use of the treadle-board recording apparatus, the combined activity of seven male animals was obtained. 3) To provide yet another means of recording the locomotor activity as a check upon other re-cording apparatus which were being used. Data from these experiments conducted during both winter and summer months have been drawn to illustrate the nightly hours of activity on the 24-hour level. As might be expected, minor fluctuations in the total activity level from night to night are seen to occur. Considered on the monthly level, however, the general trend is much the same as had been 79 found using the vibration amplifier apparatus (Expt. 2) or the activity wheel (Expt. 3). With the increase i n illumin-ation during the nocturnal period — i.e. as the f u l l moon approached — there was a marked decrease in the activity of the group of flying squirrels. Figure ha shows two such de-clines i n locomotor activity, each occurring during evenings close to the date of winter f u l l moons. A second period of recording using the treadle-board apparatus was carried out during the summer and extended over almost three lunar months. These results are shown i n Figure Hb. As in the winter experiment, there occurred a distinct decrease in activity during the period of f u l l moon — the activity during the period of new moon to f i r s t quarter being two to three times greater than that of the f u l l moon period. These declines in the total a c t i v i t y at the time of f u l l moon — as seen in Tables XIX and XX resulted not by a decrease in the number of hours during which activity would normally occur from night to night within a lunar month, but rather by means of a general decrease in activity during each of the hours during which activity normally occurs. Whether this decrease in activity at f u l l moon is proportion-ately equal for a l l hours of the night is d i f f i c u l t to ascertain. Apparently both the diurnal and the 28-day rhythms of locomotor acti v i t y in Glaucomys vary during the different Reasons of the year. The hours over which activity occurs (diurnal rhythm) coincide roughly with the number of hours of 80 FIGURE ha Activity of seven male squirrels recorded together i n a large outdoor cage by the treadle-board recorder (Nov. 1 - Dec. 22, 1957). A decline in act i v i t y is noticeable at the time of, or just after, f u l l moon. The units along the ordinate are the number of punches in the moving paper tape each night. 81 FIGURE 4b Summer activ i t y of seven male squirrels recorded together in a large outdoor cage by the treadle-board recorder (May 23 - Aug. 6, 1958). There are low points in activity at the time of three successive f u l l moons. The low activity i n late July (as compared with similar lunar phases in May and late June) is due to a prolonged heat wave i n July, 1958, which depressed the activ i t y of the animals, even at night. Units along the ordinate as in Fig. U-a. A C T I V I T Y - TREADLE-BOARD COUNTS 82 darkness available. During the summer months when available hours of darkness are inadequate for the needs of the animal, activity is extended into the daylight hours. The amount of activity over each of these hours, on the other hand, may be determined by the energy which need be expended to search for food. This, in turn, may be influenced by the act i v i t y -inhibiting characteristic of brighter nocturnal illumination during the lunar cycle — particularly at time of f u l l moon. Seasonal Levels of Activity of Flying Squirrels While the monthly rhythm is the most outstanding feature i n the acti v i t y of the flying squirrels, there is evidence of a seasonal rhythm i n this activity as well. At no time of the year did these animals show signs of hiber-nating. Even under near blizzard winter conditions, the f l y -ing squirrels in Expt. 2 continued to be active throughout much of the dark period of the 24-hour day. As seen in Expts. 1 and 4 there is a marked relation-ship between the time flying squirrels begin and end their activity and the length of the nightly dark periods through-out the year. During the mid winter months there exist in the Vancouver area more than twice as many hours of darkness than during mid summer months. The nightly activity is dis-tributed over correspondingly shortened hours with the onset of summer and may even extend somewhat into the daylight hours as seen i n Figure 1. The level of this activity, however, may x be three to four times as great during a spring or summer night 83 than that of a winter night (Compare Figures ha and hb showing nightly counts on activity using the treadle-board recorder in mid winter and mid summer respectively). Northern flying squirrels breed but once a year and the marked increase in the activity during the third week in March (Expt. 6) may have been associated with this phase of the animals' behaviour. Effects of Light on Patterns of Activity. a) Continuous_Lightj. Whether the vibration amplifier apparatus (Expt. 2), activity wheels (Expt. 3)» or treadle-board recording apparatus (Expt. h) had been used to record the locomotor acti v i t y of individual or groups of flying squir-rels, a marked decrease in the total nightly act i v i t y with the approach of the f u l l moon had been registered. This was f o l -lowed by a recovery with the waning of the lunar phase. Sev-eral pertinent questions arise from this discovery: 1) Is this decrease in activity merely an inverse response to light intensity alone? 2) Is i t associated with other fluctuating environmental variables such as temperature, relative humidity, or duration of the night, or 3) Is this an endogenous activity pattern, |. and i f so, to what degree is i t persistent 84 under prolonged periods of uniform environment? Expt. 5 Activity under constant light An attempt was made to find an answer to some of these questions and attention was turned to recording the ac-t i v i t y of flying squirrels indoors, where at least some of the important environmental factors could he controlled over prolonged periods. Two small activity rooms in which temp-erature, light and humidity could he controlled were used for this purpose. In Activity Room No. 1 two male (Ev, and F^) an& o n e female (F g) flying squirrel were subjected to continuous light (averaging 3.3 ft.-candles in front of the three cages), constant temperature (68-70°?.), and relative humidity (45-55%), The three animals were i n separate cages and visually separated from one another. They were kept under continuous light from February 26 to May 2, 1957. The vibration ampli-f i e r recording apparatus, Units 1 and 2, were used. Record-ing of the activity was made over one-hour intervals from 8:00 a.m. until midnight and two-hour intervals from midnight to 8s00 a.m. Averages of the combined total activity registered on three channels of the vibration amplifier apparatus by these animals i s shown as 24-hour histograms i n Figure 5. Activity from midnight to midnight was considered in the calculation of t 85 FIGURE 5 Average activity of three squirrels under conditions of continuous low intensity illumination from February 26 - May 2. 1957. The histograms each cover a 24-hour period from midnight to midnight. It i s probable that the low value of ac t i v i t y during the f i r s t two weeks of recording was due to the slow accommodation of the animals to the new extreme environmental conditions; they had only been placed under continuous illumination for two weeks before recording was started. The wavy line is a five-day running average of activity. The decline in activity at f u l l moon, found in earlier experiments, occurred i n the second month of record-ing under continuous illumination. The illumination was not as great as daylight, but was rather of a twilight intensity (averaging 3.3 foot candles). { A C T I V I T Y HUNDREDS OF UNITS * 86 these averages. Units of activity were essentially the same as those of Expt. 2 — a count of one unit for each movement above a predetermined intensity or force. The undulating line run-ning through the 24-hour histograms i s based on a 5-day running average of the average activity of the three animals. The phases of the moon, depicted along the top of the figure, are those which were occurring outside the building at the time of the experiment, but the animals were being kept in a lightprodf room inside a larger room which was in continuous darkness. Thus the animals had no visual clues as to the phase of the moon prevalent at any time during the two months this experiment was being conducted. Y et even after two months under such conditions of constant light, the flying squirrels — both as individuals and as a group — continued to show the distinct characteristic decrease i n activity at the time of f u l l moon, even though both the monthly lunar and the di e l cycles of the environment were being denied them. The low level of locomotor activity registered at the beginning of the experiment was probably due to too short a period' of acclimation of the animals to experimental conditions after removal from the outdoor environment before the recording of the present experiment commenced. On the basis of the 24-hour cycle, the peak activity of each animal continued to occur during the outside night period although there did occur a general shift of this peak from the early evening hours to some time between midnight and 87 8:00 a.m. Brief bursts of activity by one or another of the three animals also occurred throughout almost any hour of the d i e l cycle, but these bursts were inconsistent and small compared to the major hours of activity. There is thus evidence that the squirrels were main-taining both the lunar and the diurnal rhythm of the normal environment despite the absence of clues, b) Continuous_Darkness_ Expt. 6 Activity under conditions of constant darkness At the same time (February 26 - May 2, 1957) that the three flying squirrels in Expt. 5 were being subjected to two months of continuous light, another group consisting of two male (F^ and FTJ_) and a female ( F Q ) flying squirrel were housed i n the second activity room and maintained for a corresponding period under essentially the same constant tem-perature and relative humidity as the f i r s t animals. These were kept, however, under continuous darkness during the whole of the two lunar months. Even when the animals were to be fed, the lights in the large outer room where the recording apparatus was kept, were turned off before I entered this ac-t i v i t y room. Feeding was done in complete darkness. The loco-motor activity of these animals was recorded on the same v i -bration amplifier apparatus as was that of the three flying squirrels being kept in continuous light, and was done at the same time. 88 The average activity of the three flying squirrels kept i n continuous darkness i s shown as 24-hour histograms in Figure 6. Each histogram is based on activity occurring between consecutive midnight hours. The lunar phases shown at the top of the figure are those occurring outdoors during the duration of the experiment, although at no time was the day or night sky visible to the animals. As i n Expts. 2, 3, ^, and 5, marked decreases i n activity coincided with each natural f u l l moon period. An exceptionally high level of activity (reaching an average peak of 3,064 pulses over the 24-hour period on March 23, 1957) was recorded by each of the three flying squirrels during several days of the third week i n March, 1957. Whether this coincided with the annual mating period of these animals was not determined, but there is a record of copulation being observed in G^ , volans on March 12, 1930 i n Michigan (Kelker, 193D which i s sugges-tive of the possibility. Following this period of high ac-t i v i t y there occurred a decline almost as great as that coin-ciding with the decrease usual at the f u l l moon. No explan-ation based on the existing data can be offered to account for this marked decline at time of new moon when i t is to be expected that the acti v i t y would have remained at a high level. An even greater and more persistent low in activity level occurred two weeks later coincident with the time of f u l l moon. f 89 FIGURE 6 Average activity of three squirrels under conditions of continuous darkness from February 26 - May 2. 1957. Notations as i n Figure 5. The high level of activity in the third week of March may be coin-cident with the annual rut. 90 No clear-cut pattern of locomotor acti v i t y of the three flying squirrels i n continuous darkness was apparent on an hourly "basis. While activity occurred at each hour of the outside night and day during one d i e l period or an-other, yet the greater part of the total activity continued to occur just before or just after actual midnight outdoors. Activity during the outside daylight hours occurred occas-ionally but was sporadic and of low magnitude, c) Inter mi tt ant _Light__and_Dark Expt. 7 Activity under 12-hours light and 12-hours darkness. Normal sequence. Following completion of Expt. 6, the three flying squirrels whose activity had been recorded under conditions of continuous darkness were transferred with their cages to the larger of the two activity rooms. Here, together with the flying squirrels studied in Expt. 5» the animals were subjected to the same conditions of temperature and humidity as before but the lights in the activity room were now me-chanically controlled to provide twelve hours of light (8:00 a.m. to 8:00 p.m.) and twelve hours of darkness (8:00 p.m. to 8:00 a.m.). The change between the two light conditions was not abrupt, but rather graded over a two hour period governed by the light regulator previously described. No acclimation period was provided between this experiment and the last. The activity of these six flying squirrels recorded •f. under twelve hours light and twelve hours total darkness is 91 shown in Figure 7. The experiment was conducted between May 3 and July 21, 1957. Each of the histograms in the figure represents an average of the activity of the four male (F2, F^, F,j, F^) and two female (Fg, F^) flying squirrels over consecutive 24-hour periods from midnight to midnight. The lunar phases shown at the top of the figure are those which were occurring outdoors during the interval of the experiment, although at no time was either the day or night sky visible to the squirrels. Two and a half months had passed since the animals had last seen moonlight prior to the commencement of the present experiment. Three f u l l moon periods occurred outside in the course of this experiment. During each of these periods, as i n the case of each previous experiment, marked declines in the level of average activity occurred at or just after the f u l l moon. The monthly rhythms continued, therefore, to persist despite the lack of external clues. In the diurnal rhythm, however, the distribution cf the activity of each of the six flying squirrels differed some-what from each other. While the activity was now largely confined to the dark period of the night, the peak of this ac-t i v i t y did not occur at the same hours in a l l six animals. Nor did i t occur at the same hours for individual animals throughout the course of the experiment. Two male flying squirrels, F 2 and F^, generally exhibited peak activity during , the third and fourth hour after commencement of the dark period. 9 2 FIGURE 7 Average activity of six squirrels (previously used in Expts. 5 and 6 ) when returned to a d i e l period with 1 2 hours total darkness and 1 2 hours illumination almost coincident with conditions outdoors. Notations as in Figs. 5 and 6. A lunar periodicity of acti v i t y can s t i l l be demonstrated even after two and a half months of previous experimentation in which lunar periods were denied the animals. ACTIVITY HUNDREDS OF UNITS J i- 1 1 I.- I I. I 1.. -1 1 1 , I 1 • ' • -93 Another male, F5, and two females, Fgand F9, generally con-fined the major portion of their activity to either the f i r s t or second of the two-hour recording intervals after midnight. The sixth animal, a male, F - Q , concentrated i t s acti v i t y on either sides of the midnight hour. With the provision of the 12-hours light and 12-hours darkness sequence, the diurnal rhythm of the flying squirrels in this experiment was once more strongly estab-lished and activity during the light periods ceased. Except for a slight decrease just after the new moon (on June 27, 1957), the lunar rhythm continued to be reflected in the i n -verse relationship between light and activity levels even though the animals had received no clues as to the outside moon phases for five months. Expt. 8 Activity under reversed light conditions. Darkness from 8:00 a.m. to 8:00 p.m. As previously mentioned, other people inhabited the building in which the experiments were conducted and i t was possible that vibrations within the building could be affect-ing the activity patterns of the flying squirrels. A small electric fan kept continuously running inside the activity rooms to circulate the air inside caused a low background humming noise so that a person speaking in moderate tones im-mediately outside the activity room could not be discernably heard inside. To test i f human activ i t y was affecting the animals, the light regulating mechanism was altered to provide 94-a complete reversal of the light-dark sequence. Darkness now extended from 8:00 a.m. to 8:00 p.m. The near 2-hour sunrise and sunset gradients used earlier were retained. The same four male and two female flying squirrels as in the pre-vious experiment were again used and the experiment ran from July 22 u n t i l September 29? 1957* In order to record the response of these animals to reversal of the light sequence, the experiment was considered as started immediately at the time of the light change rather than allow the animals sev-eral days for acclimation. The average of the activity of the six flying squir-rels calculated on a midnight to midnight basis throughout the course of the experiment is shown in Figure 8a. The line running through the graph is again based on a five-day run-ning average of the daily values. 4s i n previous experiments, activity was recorded using the vibration amplifier apparatus. Activity was registered in one-hour intervals per counter from 8:00 a.m. to midnight and in 2-hour intervals per counter from midnight u n t i l the following 8:00 a.m. With the reversal of the light-dark periods, the complete dark period of each day was covered using 1-hour recording intervals. Two complete lunar cycles occurred outside during the course of this experiment. Yet, although the animals had seen neither sun nor moon during five months prior to this ex-periment, s t i l l the characteristic peaks of activity of the 95 FIGURE 8a Average activity of the six squirrels previously used in Expts. 5, 6 and 7? under a d i e l period with 12 hours total darkness and 12 hours illumination, in reverse of the conditions outdoors. Notations as in Fig. 5. A lunar periodicity of a c t i v i t y was s t i l l exhibited even after five months of previous experimentation in which lunar periods were denied the animals. f A C T I V I T Y HUNDREDS OP UNITS 96 28-day monthly rhythm continued to occur during the darkness, and decreased activity at the time of f u l l moon continued to persist, even though the dark period of the day had been altered for the animals so as to f a l l during the outside day-light hours. During the second lunar cycle of the present experiment, the average activity for the six flying squirrels at the time of the outside f u l l moon was less than one-thir-teenth of that which had occurred for these same animals just after the new moon period two weeks before. Several weeks passed before the animals under the reversed light sequence altered the time of their locomotor activ i t i e s and completely confined their movements to the 8:00 a.m. - 8:00 p.m. dark period. Although the diurnal rhythm in this species is pliable, nevertheless this response to a change i n the environment requires several weeks to be brought about. The diurnal rhythm of locomotor activity of the male flying squirrel, F 2 , immediately before and during the f i r s t few weeks of the present experiment is shown in Figure 8b . The pattern is representative of the behaviour of most of the other animals during the light reversal period. The beginning and the end of the dark period appear to be of considerable importance in the locomotor activity pattern of these animals. Before the light reversal, the peak activity of F 2 occurred early i n the dark period — just before true midnight, when a dark period from 8:00 p.m. to 8:00 a.m. was being provided. 97 FIGURE 8b Experimental alteration of the diurnal rhythm of acti v i t y of the male flying squirrel (F2) just before and after a 12-hour shift in the experimental light sequence. In the top trace, the dark period occurred between 8:00 p.m. and 8:00 a.m. and the peak of activity f e l l shortly after the commencement of the dark period. The remaining traces, taken at six day intervals, are based on the dark period occurring between 8:00 a.m. and 8:00 p.m. Almost three weeks were required for the animal to gradually shift i t s peak of activity back to occur shortly after the commencement of the experimen t a l dark period. •f-98 After the light reversal (Note that i n Figure 8b, 6:00 p.m. is at the l e f t of the graph on the July 14 trace, and at the right in the other traces) the time of the peak acti v i t y was found to be shifted to the end of the dark period. From the second trace onward, the activity of F 2 is shown at six-day intervals immediately after the light sequence had been re-versed. The peak hour of act i v i t y then gradually began to be shifted forward in respect to the beginning of the dark period u n t i l after three weeks i t once more occurred as be-fore the light sequence had been reversed, within the f i r s t few hours of darkness. Peak activity again occurred at the third or fourth hour of darkness, even though with the re-versed light condition this was to f a l l just before noon. It becomes apparent, therefore, that i f any vibra-tions or noise from the rest of the building i n which the experiments were being carried out were being transmitted to the animals, these were not of sufficient intensity to affect noticeably either the diurnal or monthly rhythm of activity in the animals being used. Also, even though the diurnal activity patterns of the flying squirrels can be completely reversed by a reversal of the light dark relationship, i t is s t i l l at the beginning of the dark period rather than at the end that the peak of the activity f a l l s and this occurs re-gardless of when this darkened phase of the 24-hour d i e l cycle fshould occur i n relation to the outside condition. A similar 99 activity-dark period relationship was seen i n the records of the activity of flying squirrels using the treadle-board recording apparatus under outside conditions (Expt. 4). It is further remarkable that l i t t l e or no disrup-tion occurred in the monthly rhythm of activity even while the light-dark sequence was being completely reversed. This may suggest that the 28-day rhythm is just as stable as the 24-hour rhythm. Expts. 10 to 20, as w i l l be seen, suggest that this is not necessarily so. Expt. 9 Activity under re-shifted light conditions. Darkness from 1:00 p.m. to 1;00 a.m. A second alteration in the light sequence to provide a dark period from 1:00 p.m. to 1:00 a.m. (instead of from 8:00 a.m. to 8:00 p.m. as i n Expt. 8) was made on September 30 and the activity of the same six flying squirrels was re-corded under these conditions u n t i l November 24, 1957. Once more the animals altered their diurnal rhythm of activity to conform to the new light regime. With this second shift in the light sequence, however, the animals re-quired only about one-half the time to alter their activity accordingly — one and a half weeks as opposed to nearly three weeks required in Expt. 8 for the animals to resume the same activity-dark period relationship. This shortening of the readjustment time may have been due in part to 1) a {less drastic change having been attempted i n this dark period shift (only a shift of five hours as compared to a twelve hour 100 FIGURE 9 Average activity of six squirrels (used in Expts. 5, 6, 7 and 8) under a d i e l period with 12-hours illumination and 12-hours darkness extending from 1:00 p.m. to 1:00 a.m. Notations as in Fig. 5« These animals had been under experimental conditions for seven and a half months prior to commencement of this experiment. f 101 shift i n Expt. 8), and 2) a possible learning process which may have occurred wherein more frequent and slight changes in the light sequence would bring about more rapid and more complete adjustments in the diurnal activity rhythm. The average of the total nightly activity of the six flying squirrels under conditions of 1:00 p.m. to 1:00 a.m. darkness is shown in Figure 9. While declines i n ac-t i v i t y at, or just after, the time of f u l l moon did occur, the monthly rhythm of activity of the animals is seen to be less precise than i t had been in Expt. 8. It is not surpris-ing when one considers that the animals had been kept under controlled a r t i f i c i a l environmental conditions of constant temperature and relative humidity and under highly aberrant light sequences for almost eight months prior to this experi-ment. During this time the animals had seen neither sun- nor moonlight. Without such clues for reinforcement, the physio-logical clock mechanism governing the level of locomotor ac-t i v i t y of these animals might well have become less precise and more random In i t s nature. While variations in the level of activity are s t i l l seen in Figure 9, these are neither uniform nor rhythmical. Only during the second f u l l moon period did the low level of activity coincide. Had time per-mitted, the present experiment might have been continued for several more months to determine whether the activity cycle would have eventually become completely random. 102 d) Effect_of Moonlight on_Activit^ Expt. 10 Activity under 28-day a r t i f i c i a l lunar cycle. A photometer reading on the f u l l moon i n early September had given a value of 0 .05 ft.-candle illumination, or a reading of 50 on one of the scales of the sensitive instrument being used. It was convenient, therefore, to assign the value of 50 to the a r t i f i c i a l moonlight apparatus setting when this apparatus was so adjusted as to produce light with a value corresponding closely to 0 .05 ft.-candle. As the intensity of moonlight f a l l s rapidly with the waning of the moon, the values chosen a r b i t r a r i l y to correspond to this waning on the a r t i f i c i a l moon were 50, 40, 25 , 5, 3 , 1, 0.3 and 0 — the instrument being unplugged to obtain the latter value i n the lightproof ac t i v i t y rooms. The date and the various light values used in the 28-day cycle of a r t i f i c i a l moonlight employed in Expt. 10 are listed i n Table VII below. The average of the locomotor activity of the four male (F 2, F^, F^, and F^) and the two female (Fg, F Q) normal flying squirrels recorded from midnight to midnight during the present experiment is shown i n Figure 10a. In Figure 10b the same data are presented by plotting the average activity against light intensities at which the activity had been registered. Open circles indicate that the intensity of the a r t i f i c i a l moonlight was being increased while closed circles represent levels of activity during that part of the lunar cycle when the a r t i f i c i a l moonlight was being 103 Table VII. A r t i f i c i a l moonlight values used i n Expt. 10 Date Setting Date Setting Nov. 25, 1957 0.3 Dec. 10 hO 26 1 11 hO 27 1 12 25 28 3 25 29 3 lh 5 30 5 15 5 Dec. 1 Fuse blown 16 3 2 25 17 3 3 25 18 1 4- ho 19 1 5 hO 20 0.3 6 50 21 0.3 7 50 22 0 8 50 9 50 decreased according to the values listed in the above Table VII. The line through the graph i s based on an average of the values for each of the light intensities. There i s considerable day by day variation i n the locomotor activity of the six flying squirrels. Such variation can be expected in any population of animals. A portion of this v a r i a b i l i t y may be attributed to the fact that the ani-mals were being fed only every other day. This, however, is not the sole cause for the somewhat saw-tooth pattern seen in Figure 10a, for i f i t were, one would expect to find a con-sistent rise or f a l l of activity every other day. Such is not the case. Nor does a slight increment of light always bring ^ about a corresponding decrease in activity. 104 The general trend of the activity over the total period of the experiment, however, closely parallels the monthly patterns recorded in practically a l l the experiments conducted so far — under both outside and inside conditions. As the intensity of the light provided during the 12 hours of darkness was gradually increased from the .3 setting (corres-ponding to 0.000,3 ft.-candle intensity) to the 50 setting (corresponding to 0.05 ft.-candle and equivalent to f u l l moon light) the activity decreased to almost a quarter of the i n i t i a l value. This maximum setting of the a r t i f i c i a l moon-light took place at the same time that f u l l moon occurred outdoors, although the dark experimental periods occurred be-tween 1:00 p.m. and 1:00 a.m. The lowest point on the a c t i -vity curve, however, does not correspond with the maximum moonlight intensity used, hut occurs instead at the second highest value. This may be a question of relative change. A change from a condition of no light to light of low intensity may constitute to the animals a greater alteration i n illumin-ation than would an even greater increase at the brighter end of the scale. Whether accommodation is involved i s another matter. The distribution of both closed and open circles in Figure 10b suggests that light intensity is important i n de-termining activity i n both the waxing and waning phases. The hourly distribution of the locomotor activity i n the diurnal rhythm of the six animals under conditions of a r t i f i c i a l moonlight closely resembles records obtained out-105 FIGURE 10a (Left) Average activity of six squirrels (used in Expts. 5. 6. 7. 8 and 9) under a 28-day a r t i f i c i a l moonlight periodicity. The a r t i f i c i a l lunar illumination applied daily is listed i n Table VII. Response to these illumin-ations is apparent (see Fig. 10b). A 24-hour d i e l rhythm was employed — the dark period running from 1:00 p.m. to 1:00 a.m. FIGURE 10b (Right) The data i n Fig. 10a is plotted here against the light intensity applying at any one time. The figures for light intensity are not foot candles, but the units explained in the text. The figure 50 corresponds to .05 ft.-candle , which represents f u l l moon intensity In September. Open circles indicate averages of activity at each intensity during the waxing of the "moon". Dark circles indicate av-erage activity at each intensity during the "waning" process. x ACTIVITY HUNDREDS OF UNITS 106 doors — peak activity occurring primarily within the f i r s t several hours after darkness commenced and a second mode occurring during the last hours of darkness. Expt. 11 Activity under 40-day lunar cycle The brightest period of a r t i f i c i a l moonlight of the previous experiment f e l l at the same time of the month as the f u l l moon was present outside. Some uncertainty arises, therefore, whether 1) the decrease in activity of the six flying squirrels at that time was due to the a r t i f i -c i a l moonlight, or 2) was the monthly lunar rhythm of ac-t i v i t y previously demonstrated being maintained as had been the case for almost a year without the animals being exposed to any sort of moonlight at a l l . It was important to find out whether the 28-day cycle is intrinsic and unchangeable or whether i t is a plastic rhythm which can be altered under simulated light conditions. To test this, the animals were subjected' to an a r t i f i c i a l lunar month of kO days, the f u l l moonlight intensity of which f e l l six days after f u l l moon had occurred outdoors. The light intensities used during the dark 12-hour periods of the cycle are as listed i n Table VIII. As in the previous experiment, the a r t i f i c i a l moonlight setting of 50 corres-ponded to a value of 0.05 ft.-candle illumination which, i n turn, was equivalent to the photometer reading obtained for the f u l l moon in September. 107 Table VIII. A r t i f i c i a l moonlight values used in Expt. 11 Date Setting Date Setting Dec. 24, 1957 .3 Jan. 13, 1958 40 25 .3 14 40 26 .3 15 40 27 1 16 25 28 1 17 25 29 1 18 25 30 3 19 5 3 1 3 20 5 Jan. 1, 1958 3 21 5 2 5 22 3 3 5 2} 3 4 5 24 3 5 25 25 1 6 25 26 l 7 25 27 1 8 4o 28 .3 9 40 29 .3 10 40 30 .3 11 50 31 0 12 50 Feb. 1 0 The average activity of the six flying squirrels subjected to the above intensities of a r t i f i c i a l moonlight is shown in Figure 11a. The same data plotted against light i n -tensity are shown i n Figure l i b . Notations are the same as in Figure 10a and b (Expt. 10). The activity pattern during the 40-day lunar cycle follows the characteristic phasic decline and rise seen i n each of the experiments to this point. With increasing inten-sity of the a r t i f i c i a l moonlight, the total of the locomotor activity registered by each of the animals on the vibration amplifier apparatus declined. At the f u l l moon setting of 50 108 FIGURE 11a and b Average activity of six flying squirrels (used i n Expts. 5-10) under a ^O-day lunar cycle using a r t i f i c i a l lunar illumination during the 12-hour dark periods. Notations as in Figs. 10a and b. X ACTIVITY HUNDREDS OF UNITS 109 the average activity is approximately one-quarter that regis-tered at the lower end of the light scale. Lengthening the a r t i f i c i a l lunar cycle caused a corresponding lengthening of the activity cycle. This suggest that although the 28-day pattern is f a i r l y stable under out-door conditions or under conditions of continuous darkness or continuous light — that i s , in the absence of visual clues — i t is pliable when a varying source of light (corresponding roughly to the low intensities of normal moonlight) i s intro-duced during the dark period. Under outside conditions this 28-day rhythm, i f not actually caused by cyclic variations i n moonlight illumination, is at least supplemented and kept in phase by this repeating stimulus over long periods of time. Expt. 12 Activity under 21-day lunar cycle. Lengthening the a r t i f i c i a l lunar cycle had brought about a corresponding lengthening of the activity cycle of the flying squirrels. It remained to be seen i f the shortening of the lunar sequence would bring about abbreviation of the ac t i v i t y cycle. A r t i f i c i a l moonlight intensities used in a 21-day experiment to test such a hypothesis are listed i n Table IX below. The average of the activ i t y of the six flying squir rels during the 21-day lunar cycle is shown in Figure 12a and again i n Figure 12b. As i n the previous a r t i f i c i a l moonlight experiments, the activity followed an approximate inverse re-lationship to the light provided during the dark periods. In the present experiment, although the lowest point of the cycle 110 Table IX. .A r t i f i c i a l moonlight values used in Expt. 12. Date Setting Date Setting Feb. 4, 1958 1 Feb. 15, 1958 40 5 1 16 40 6 3 17 25 7 3 18 25 8 5 19 5 9 5 20 5 10 25 21 3 11 P 22 3 12 40 23 1 13 40 24 1 14 50 occurred just before the maximum light of f u l l moonlight i n -tensity was introduced, the ac t i v i t y declined again after a brief rise with decreased illumination. The slope of the av-erage line in Figure 12b is somewhat more horizontal than i n the previous experiments, suggestive perhaps that a limit is being approached to the rate at which the moonlight intensity can be changed and s t i l l be effective i n influencing the ac-t i v i t y of these animals. Another factor one must also con-sider is the interval of time allowed between two consecutive experiments. During such time the animals are not provided with a r t i f i c i a l moonlight in the dark periods. If more than one or two days are allowed to intervene, i t may be that while the animals s t i l l continue to respond to the low illumination being used here during the dark periods, nevertheless, the de-gree of response may have been influenced by the previous his-tory (i.e. during the period between experiments). I l l FIGURES 12a and b Average activity of six flying squirrels (used in Expts. 5-11) under a 21-day lunar cycle using a r t i f i c i a l moonlight illumination during the 12-hour dark periods. Notations as i n Figs. 10a and b. ACTIVITY - HUNDREDS OF UNITS 112 Expt. 13 Activity under 18-day lunar cycle. In this experiment the a r t i f i c i a l lunar cycle was shortened to 18 days. The light values used during the dark portions of the 24-hour cycles are listed i n Table X below. Table X. A r t i f i c i a l moonlight values used i n Expt. 13 Date Setting Date Setting March 10, 1958 1 March 19, 1958 '50 11 3 20 40 12 3 21 25 13 5 22 25 14 5 23 5 x? 25 24 5 16 25 25 3 17 40 26 3 18 50 27 1 The average of the d i e l locomotor activity of the four male and two female flying squirrels is depicted i n Figure 13a while the same data plotting this average level of activity against i t s corresponding light intensity are shown in Figure 13b. With the shortening of the lunar cycle of light the overall range i n the level of the average nightly ac-t i v i t y has been considerably reduced. Also the saw-tooth pattern in the day to day values of activity is more apparent. The flying squirrels were fed on even-numbered days during the course of this experiment and while a surplus of food was a l -ways maintained within the cages, less activity appeared to be ^recorded on days when the animals were fed than on the inter-113 Figures 13a and b Average activity of six flying squirrels (used in Expts. 5-12) under an 18-day lunar cycle using a r t i f i c i a l moonlight illumination during the 12-hour dark periods. Notations as in Figs. 10a and b. ACTIVITY - HUNDREDS OF UNITS o i o * 0 > o > o r » Z o > 5 i i i i i i ' ' • ' i i i i i i 1 1 i _ 114 vening days. In Figure 13b the average line is even more horizontal than i n Figure 12b. The shortening of the lunar cycle involved more drastic changes i n the light intensities being used. The animals, i n turn, were expected to adapt their activity more rapidly. Instead they tended towards an even level of activity throughout the cycle, perhaps due to failure of responsive process. Alternatively, i t may be ar-gued that the animals are becoming more independent of the lig h t . Expt. 1)+ Activity under 14-day lunar cycle. Next, the four male and two female flying squirrels were subjected to a complete cycle of a r t i f i c i a l moonlight within 14 days. The light sequence followed in the experiment is listed i n Table XI below. Table XI. A r t i f i c i a l moonlight intensities used i n Expt. ih Date Setting Date Setting April 2, 1958 0 A p r i l 9, 1958 ?° 3 1 10 40 4 3 11 25 5 5 12 5 6 25 13 3 7 40 14 1 8 50 15 0 The average of the activity of the six flying squirrels during the 14-day lunar cycle is shown in Figure 14a, while the a c t i -* vity related to the light intensities employed i n the dark 115 FIGURES 14-a and b Average activity of six flying squirrels (used in Expts. 5-13) under a Ik-day lunar cycle using a r t i f i c i a l moonlight illumination during the 12-hour dark periods. Notations as i n Figs. 10a and b. ACTIVITY - HUNDREDS OF UNITS 116 periods is shown i n Figure 14b. Even i n this period corres-ponding to only one-half the length of the outside lunar cycle, the flying squirrels reacted much in the same manner recorded while they were being kept under natural climatic conditions. As in several of the previous experiments, there was a lag be-tween the period of maximum illumination and that of minimum activity. The low point of the activity cycle occurred sev-eral days (April 11) after the maximum light had been used. Even under outside conditions and under continuous light or continuous darkness, this low point frequently occurred after the time of f u l l moon. Activity during the second half of the 14-day a r t i f i c i a l lunar cycle was lower at each of the light intensities used than i t was during the f i r s t half a l -though the differences were but slight. Two suggestions as to why the records i n this experi-ment approximate more to Expt. 10 than Expt. 13 may be pro-posed: 1) While the 28-day cycle appears to be of basic dur-ation in nature, i t may become evident only when shorter-termed cycles reinforce one another at 28-day intervals. There is also a suggestion of a 14-day cycle i n Glaucomys but this has not been adequately investigated, 2) From March 27 to Ap r i l 1, 1958, the animals had been removed from the influence of any "moonlight", thus allowing a recuperating period dur-ing which activity level increased. 117 Expt. 15 Activity under three 7-day lunar cycles. In this experiment the a r t i f i c i a l lunar cycle has been abbreviated to one quarter the natural phase and the ex-periment was repeated three times. The light intensities used are listed in Table XII below. Table XII. .Ar t i f i c i a l moonlight intensities used in Expt. 15 Date Setting Date Setting Date Setting 1st week 2nd week 3rd week April 19, 1958 1 April 30 1 May 10 1 20 5 May 1 5 11 5 21 25 2 25 12 25 22 50 3 50 13 50 23 25 h 25 Ih 25 2h 5 5 5 15 5 25 1 6 1 16 1 The activity of the six flying squirrels is shown as average values i n Figure 15a and 15 b. Several days were allowed to lapse between the three cycles. During these days no a r t i f i -c i a l moonlight was provided during the dark periods. Although the activity pattern exhibited i n the f i r s t of the three short cycles differed somewhat from the second and third, yet i n each there occurred a marked decrease in ac-t i v i t y during those days when a r t i f i c i a l f u l l moon illumina-tion was provided i n the activity room during the dark periods. f Also with the shortening of the lunar cycles the range of the 118 FIGURES 15a and b Average activity of six flying squirrels (Used i n Expts. 5-140 during three 7-day lunar cycles, using a r t i f i c i a l moonlight illumination during the 12-hour dark periods. Notations as i n Figs. 10a and b. ACTIVITY - HUNDREDS OF UNITS O i o * a » 0 o r e Z < n 5 I 1 1 1 1 1 1 1 1 1 i i i • ACTIVITY HUNDREDS OF UNITS —i 1 1 " 1 ' 1 1 1 1 1 1 1 i • 4** * <> op. 4 it XX ' <f 0 I 1 t ui ro w : i < • • sr 119 activity levels has become considerably reduced. No attempt was made to shorten the lunar cycle even further. It is readily apparent, therefore, while the 28-day monthly rhythm of activity is the one which is repeatedly reinforced in the animals under outside conditions and is the one which is retained by the animals while under constant en-vironmental conditions, this same cycle is malleable under changing light conditions. Expt. 16 Activity under 28-day lunar cycle without nest boxes. Following the series of experiments i n which the animals had been subjected to lunar cycles of normal, lengthened, and shortened durations, the nest box and a l l nesting material was removed from each of the cages i n order to ascertain what effect the lack of shadows within the confines of the ca-ges might have on the activity of the flying squirrels. The 1:00 p.m. to 1:00 a.m. dark period was retained, but once more the animals were subjected to the 28-day lunar cycle of a r t i -f i c i a l moonlight during these dark periods. The light values used i n this experiment are given in Table XIII below. The av-erage values of the activity of the four male and two female flying squirrels from whose cages the nest boxes and nesting materials had been removed are shown in Figures l6a and l6b. Removal of the nest boxes had two major effects on the locomotor activity of the flying squirrels i n this experi-f- ment. During the days of no light or weak illumination i n the 120 FIGURE 16a and b Average activity of six flying squirrels (used i n Expts. 5-15) deprived of nest boxes and under a 28-day lunar cycle using a r t i f i c i a l moonlight illumination during the 12-hour dark period. Notations as i n Figs. 10a and b. See discussion in text. ACTIVITY HUNDREDS OF UNITS 121 Table XIII. A r t i f i c i a l moonlight values used i n Expt . 16 Date Setting Date Setting May 21, 1958 0 June 5, 1958 40 22 .3 6 40 23 .3 7 25 24 1 8 25 25 1 9 5 26 3 10 5 2? 3 11 3 28 5 12 3 29 5 \3 1 30 25 14 1 31 25 15 .3 June 1 40 16 .3 2 40 17 0 3 50 4 50 dark periods, act i v i t y again rose to a much higher than usual level. This increased activity was partly due to the animals moving about the cages during a greater number of hours of the dark period (diurnal rhythm) and partly due to a higher level of activity during these hours. As the a r t i f i c i a l moonlight was increased i n intensity, however, the act i v i t y f e l l to an even lower level than usual. This may have been due to tlhe lack of shelter or shadows into which the animals could re-treat periodically. The recovery period after the a r t i f i c i a l moon was more gradual than the original decline of activity. While basically the same activity pattern was shown by these animals without the nest boxes as they had followed i n a l l the previous experiments when nesting material was provided, the flying squirrels appeared to show signs of stress and c h i l l i n g . 122 During the light periods, they would back into one corner of the cage and wrap the broad, f l a t t a i l about their head thus shutting out some of the light from the eyes or try to con-serve body heat by rol l i n g into a b a l l , e) Effect_of Gonadectomy on_Ac t i v i t y,. Expt. 17 Gonadectomized Animals — Activity under three 28-day lunar cycles. To determine whether or not the gonads or their products were i n some way responsible for the ac t i v i t y pat-terns seen i n the experiments to this point, three males (FIQ, F20» F2l) were castrated and three females (F T _ D , F17, Fl8) spayed. After several weeks to allow recovery from the operations, the six flying squirrels were established in the second acti v i t y room under light, temperature and relative humidity conditions comparable to those being experienced by the flying squirrels in Activity Room No. 1. The activity of these animals was recorded on Unit 3 of the vibration am-p l i f i e r apparatus. While the light and dark periods were governed i n this second activity room by the same regulator mechanism as that controlling the light i n the f i r s t a ctivity room, and was done at the same time, the intensity of the ar-t i f i c i a l moonlight could be, and was, set independently i n the two rooms. The activity of the six gonadectomized animals was recorded under three 28-day cycles of a r t i f i c i a l moonlight, the f i r s t two cycles of which coincided with the ce l e s t i a l moon outside. The third cycle was made to occur one-half out 123 of phase with the cel e s t i a l moon. The intensities of a r t i -f i c i a l moonlight used i n the three cycles were as listed i n Table XIV. Table XIV. A r t i f i c i a l moonlight intensities used i n Expt. 17 Date Setting Date Setting Date Setting Dec. 25, 1957 26 1 22 0 5 .3 27 1 23 .3 6 .3 28 29 30 31 Jan. 1, 1958 2 .3 Jan. 21 0 Mar. h 0 1 22 0 5 < 1 23 .3 6 * 3 h .3 7 1 3 25 1 8 1 5 26 1 9 3 5 27 3 10 3 25 28 3 11 5 25 29 5 12 5 hO 30 5 13 25 hO 31 25 Ih 25 50 Feb. 1 25 15 ho hO 2 ho 16 ho hO 3 ho 17 50 25 h 50 18 50 25 5 50 19 ho 5 6 ho 20 hO 5 7 ho 21 25 3 8 25 22 25 3 9 25 23 5 1 10 5 2h 5 1 11 5 2? 3 .3 12 3 26 3 .3 13 3 27 1 0 Ih 1 28 1 0 15 1 29 0 16 .3 30 Tube blown 31 0 18 0 5 6 7 8 9 10 11 12 13 Ih 15 16 17 18 19 .3 20 0 16 .3 30 .3 The average of the activity of the six gonadectomized flying squirrels during the three a r t i f i c i a l lunar months is shown in Figure 17. Other than remaining at a lower absolute 124-level than that for the normal flying squirrels, the activity of the gonadectomized animals does not differ notably from that of their non-operated counterparts. The activity con-tinued to be at a relatively high level during the f i r s t dark periods, decreased as the a r t i f i c i a l moonlight was increased in intensity and reached a low point at or just after the brightest a r t i f i c i a l moonlight. It then gradually climbed as the moonlight diminished. Whether the a r t i f i c i a l moon-light cycle was in or out of phase with that of the celestial lunar cycle does not appear to have made any demonstrable d i f -ference upon the activity cycle. The animals were responding to the levels of illumination in the activity room and not to the outdoor phase of the moon. Whereas the activity of these animals was recorded on the six counters of the Unit 3 apparatus and readings were taken only once a day, no data were obtained concerning the hourly distribution of their activity. Expt. 18 Activity of gonadectomized animals under 14-day lunar cycle. The intensities of the a r t i f i c i a l moonlight used in the 14—day lunar cycle and the average of the activity of the six gonadectomized flying squirrels occurring at each of these light intensities are listed in Table XV below. The response of the gonadectomized flying squirrels to the abbreviated a r t i f i c i a l moonlight cycle, as seen in the 125 FIGURE 17 Average activity of six gonadectomized squirrels during three 28-day lunar cycles, under a r t i f i c i a l lunar illumination. The animals were provided with nest boxes. The f i r s t two lunar periods were coincident with the natural lunar period, the third was one-half period out of phase. 8 126 Table XV. A r t i f i c i a l moonlight intensities and resulting activity of gonadectomized flying squirrels. Date Light Intensity Average Activity 2, 1958 0 350 3 1 1,246 3^ 0 4 3 5 5 308 6 25 180 7 40 203 8 50 204 9 po 252 10 40 63 11 25 108 12 5 89 13 3 85 14- 1 84 15 0 712 above table, closely resembles that recorded by the normal animals (Cf. Figures l4a, b of Expt. 14). As i n many of the other experiments, the lowest level of the activity occurred after, arid not at, the period of brightest moonlight. Why this lag exists between the highest light intensity and the lowest level of activity is not known. Expt. 19 Activity of gonadectomized animals under three 7-day lunar cycles. In Table XVI are listed the light intensities used in three 7-day lunar cycles and the average of the activity of the. six gonadectomized flying squirrels at each of these light intensities. Although a decline in activity corresponding with increase in the a r t i f i c i a l moonlight occurred in each of the 127 Table XVI. A r t i f i c i a l moonlight intensities and resultant average activity. Date Light Intensity Average Activity May 19, 1958 1 1, 148 20 5 784 21 25 556 22 50 126 23 25 138 24 5 V 25 l 80 30 l 953 1 5 709 2 25 240 3 50 253 4 25 72 5 5 202 6 l 66 10 l 173 11 5 65 12 25 82 13 50 .42 14 25 15 5 61 16 l 151 7-day lunar cycles depicted above, nevertheless, with such shortening of the lunar cycle, much of the regularity of form characteristic of lengthier cycles is lost. The recovery period was late and each successive cycle began at a lower level than the previous one. It is anticipated that had the 7-day cycles been repeated several more times, l i t t l e or no fluctuation in activity level would have occurred and the cycle characteristic would no longer have prevailed. The experiment suggests therefore that there is a limit within which the 128 inherent rhythmic activity pattern may he molded by new en-vironmental conditions over a short evolutionary period. Expt. 20 Gonadectomized animals — Activity under 28-day lunar cycle without nest boxes. A r t i f i c i a l moonlight intensities used i n this 28-day lunar cycle without nest boxes for the gonadectomized flying squirrels were identical to those employed in Expt. 16 for the normal animals, and were conducted at the same time. The average values of the activity of the six operated ani-mals for each of the light intensities is shown i n Figure 18. The i n i t i a l introduction of a r t i f i c i a l moonlight into the experiment, even though very slight — from 0 to 0.000,3 ft.-candle — caused an appreciable drop i n the ac-t i v i t y . Activity then rose by the third night even though the light intensity had been further increased. It is as-sumed that the activity of the animals was inhibited at the start of the experiment. Low intensities of moonlight were s t i l l being employed. After this early accommodation, the inverse light-activity relationship followed and the lowest point of activity i n the cycle was reached even before maxi-mum intensity of moonlight was used. Again the recovery period was slow and only at the lowest light values did the activity return to a high level. Removal of the nest boxes and nesting material from the cages appeared to cause some stress to the gonadectomized animals. Although the temperature within the second acti v i t y 129 FIGURE 20 Average activity of six gonadectomized squirrels (used i n Expts. 17. 18 and 19) deprived of nest boxes and under a 28-day lunar cycle using a r t i f i c i a l lunar illumination. The intensity of the a r t i f i c i a l moonlight was gradually increased to a maximum value on June 3rd and 4th and then again decreased. Gonadectomized animals responded to the light intensities i n an inverse manner, as did normal animals i n Expt. 16. o 130 room was maintained between 68 - 72°F., the animals appeared to suffer from c h i l l . Their pelage appeared matted and lost i t s lustre. Several declined to feed even when nuts were supplied and on June 12, one of the animals died, i t s stomach nearly empty. (The activity during the last five days of the experiment shown i n Figure 18 is based on five animals i n -stead of the six up to that date.) During the light periods the animals would remain i n a corner of their individual cages and tightly wrap the broad, f l a t t a i l about the head, partly to shut out the light and partly, or possibly, to con-serve body heat. Practically no activity was registered on the recording apparatus during the light hours. The counter numbers on the recording apparatus checked for instance at 2:00 a.m. near the start of the light period read the same when checked again shortly before the start of the dark period. It is of interest to compare the results of this experiment using gonadectomized animals with results of the normal animals whose activity was being recorded at the same time i n Activity Room No. 1. Even though the two sets of animals were in separate environmentally controlled rooms, the peak of the lunar cycle of activity i n each occurred on the same date, May 24-. The peak of the activity of the normal animals was, however, more than twice as high as that of the gonadectomized squirrels (3>139 as opposed to 1,402). The low point in each cycle (93 pulses for the normal animals and 85 for the gonadectomized), although occurring on different 131 nights, nevertheless did occur at the same light intensity. The second peak of activity at the end of the cycle again was nearly twice as high for the normal animals than for the gonadectomized (normal peak of 2,316 vs. gonadectomized peak of 1,258) and although these peaks as well did not occur on the same night, they did both occur at the same light inten-sit y . Therefore, while gonadectomy may have caused a decrease in the absolute amount of activity i n each of the animals, i t did not change the overall pattern of this a c t i v i t y i n i t s relation to the intensity of nocturnal illumination. Expt. 21 Activity of normal animals under a 16-hour day, (o hours light and 8 hours dark). The total (not the average as in previous experiments) summed activity of the six flying squirrels (males F2, F 3 , F 5 , F l l , and females F8 and Fa) recorded under conditions of 8 hours light and -8 hours darkness is shown in Table XVII be-low. The experiment was run through two 28-short day lunar cycles between July 1 and August 10, 1958. The intensity of the a r t i f i c i a l moonlight used during each of the dark periods is also shown in the table. The animals had been under the 16-hour d i e l sequence for a week before the experiment was commenced. Vibration amplifier apparatus Unit 1 and 2 were used i n the recording of the act i v i t y . In practically a l l the indoor experiments up to this point activity of the flying squirrels has been recorded under conditions of 12 hours light and 12 hours darkness. The animals 132 Table XVII. Total activity of four male and two female flying squirrels under 16-hour "days" CYCLE 1 16-hr.day Moonlight intensity Total activity Total activity number during dark period under 8-hr. light under 8-hr. dark i 130 25 .3 73. 1H-3 .3 h 48 79 h 51 202 12 241 76 13 55 109 10 108 126 8 78 114 3 84 75 18 94 88 23 128 95 37 108 129 18 366 277 41 180 293 27 357 79 145 169 498 260 584 82 762 .3 242 800 .3 37 2,784 316 2,169 1 0 128 1,785 2 .3 104 853 3 .3 85 2,128 4 1 77 1,588 5 1 17k 256 6 3 76 430 7 3 11 1,044 8 5 129 149 9 5 20 716 1 0 2 3 4 1 5 1 6 3 rj 3 8 5 9 5 10 25 11 25 12 40 !3 40 14 50 15 50 16 40 17 40 18 25 19 25 20 5 21 5 22 3 23 3 24 1 25 1 26 27 28 0 CYCLE 2 cont, Table XVII continued 133 10 25 21 518 11 25 115 731 12 ko 118 162 13 ko 96 233 14 50 177 72 15 50 137 219 16 ko 262 216 1? ko 147 3>k7 18 25 104 31* 19 25 200 793 20 5 276 22? 21 5 61 1,684 2A33 22 3 77 2 ? 3 51 676 24 l 102 1,230 25 l 17 3,577 438 26 .3 96 27 .3 76 5,614 976 28 0 38 had generally avoided a l l activity during the light periods and exhibited an inverse relationship to the lunar intensities of natural and a r t i f i c i a l moonlight, thus maintaining a char-acteristic d i e l and monthly pattern of activity. With the change to a 16-hour day (involving 8 hours darkness and 8 hours l i g h t ) , however, the d i e l pattern of ac-t i v i t y of the animals became greatly altered. The animals showed some activity throughout each of the light periods, in addition to that occurring i n the darker moonlit periods. This activity during the "day" periods, however, gradually began to diminish throughout the second lunar cycle of the ex-periment. On eight of the twenty-eight l6-hour days i n Cycle 1, the total of daylight activity for the six animals was 13^ greater than that i n the corresponding dark periods. In Cycle 2, on only two occasions was activity during the light period greater than during the following dark period. The animals did not appear to be able to adjust to the 16-hour day in as short a time as had been attempted i n the experi-ment. The 24—hour d i e l cycle was s t i l l dominant, even i f t h i necessitated being active during the light period. It is pre sumed that the animals would have to be carried through many more months of experimentation before activity during the light period would be eliminated altogether on the basis of a 16-hour day. Whether flying squirrels could eventually adapt to such a shortened d i e l period was not determined. When the total activity for the six animals during each dark, but moonlit, period,of this experiment is con-sidered alone, then once more the inverse relationship betwee the intensity of the a r t i f i c i a l moonlight and the level of activity becomes apparent — particularly during the second of the lunar cycles. While the animals had failed to adapt to the l6-hour d i e l period by avoiding activity during the light 8-hour portion, they did, nevertheless, continue to re-spond (at least i n the amounts of nightly activity) to the variations in the low light intensities provided during the dark 8-hour portions — much in the manner shown in a l l the previous experiments. Expt. 22 Activity of, gonadectomized animals under / a 16-hour day. Table XVIII shows the activ i t y of the five gonadect 135 mized flying squirrels on the 8-hours light and 8-hours dark-ness regimen. (The sixth animal i n this group had died in the course of Expt. 20). For the purpose of recording using Unit 3 of the vibration amplifier apparatus and for conven-ience in changing the lunar intensities, the acti v i t y periods were made to consist of 48-hour intervals consisting of three light and three dark periods each. The animals were under these experimental conditions for a week prior to the be-ginning of the records shown. Table XVIII. Total activity of five gonadectomized animals over three light and three dark 8-hour periods (48 hours) in relation to light intensities used for moonlight i n the dark periods. CYCLE 1 • CYCLE 2 ^-hour Moonlight Total 48-hour Moonlight Total units intensity settings Activity units intensity settings Activity 1 .3 386 1 .3 1,787 2 3 438 2 3 2,276 2,036 3 5 700 3 5 4 40 2,469 4 40 1,818 5 50 881 5 50 544 6 25 523 6 25 671 7 5 1,282 7 5 562 8 1 952 8 3 1,353 9 .3 2,293 1,73^ 9 1 2,027 10 0 During the f i r s t lunar cycle above, the animals show no distinct alteration i n activity with changes in moonlight Intensity. Through the second cycle, however, there is a 136 marked decrease in activity at intensity 50 and this low ac-t i v i t y persisted for 288 hours — u n t i l after the lunar setting of 5 had been completed. The response to the intensities of moonlight were being shown even while the animals were sub-jected to 8-hours light and 8-hours darkness. The lunar re-sponse of the gonadectomized animals did not differ s i g n i f i -cantly, therefore, from that of the normal animals. Activity which may have occurred during the 8-hour light periods were not recorded separately but rather included i n the 48-hour recording intervals. DISCUSSION Brief Review of Studies in Periodicities of Activity. Kalabukhov (194-0) and Calhoun (194-5-46) have re-viewed much of the pertinent literature on the d i e l cycles of many animals. Walls (19*+2) postulated that the time of ac-t i v i t y of animals i s related to the structural adaptations of the eyes. Southern (19540 believes that i t is associated with the twenty-four hour rhythm of light and darkness. Ac-cording to the same writer, short-term cyclic variations of activity — with periods of only one or few hours duration — have been demonstrated in many small mammals which tend to be arhythmic with respect to the 24-hour cycle of night and day. These periodicities are probably related to feeding. •i 137 The observed activity of any species is generally a composite one showing the influence of both the 24-hour d i e l and short-termed periodicities (of only 2 - 4 hours duration) and is sufficiently labile to be modified to meet temporary ecological requirements. Calhoun (loc. c i t . ) considers the short-term rhythm i s more basic because i t alone has been found in the young of several species studied. 4s the young animal is repeatedly exposed to light and dark-ness, the d i e l a c t i v i t y cycles gradually develop and become superimposed on the short-term rhythms. Such is the case i n many animals from the temperate zones where the conspicuous contrast between illumination of day and night is a d i e l occurrance. In the Arctic region, on the other hand, where over months at a time the light differences are not so great, the short-term cycles may be more conspicuous. Short-term rhythms have been shown to exist i n num-erous small mammals. They have been studied in Microtus agrestis by Davis (1933); ochrogaster by Calhoun (19^5); M. pennsvlvanicus by Hatfield (19^0) and in Clethrionomys glareolus by Miller (1955). Short-term cycles of oxygen con-sumption, and therefore of activity by inference, have been shown to exist in Microtus pennsvlvanicus, Clethrionomys gapperi and Pitymis pinetorum by Pearson (19*+7) and Morrison (19^8). The average period of these cycles was two to four hours. Nicholls (1922) found short-term rhythms of rest and >/ activity during night and day in the guinea pig kept at high temperatures. 138 Crowcroft (195*0 studied three B r i t i s h species of shrews, Heomys fodiens, Sorex araneus. and Sorex minutus and found each to exhibit short-term cycles of activity. Morrison (1948) inferred short-term rhythms i n the activity of Sorex cinerus and Blarina brevicauda from their oxygen consumption. Smith (1957) has shown the act i v i t y of lemmings during both day and night to occur i n short periods punctuated with brief periods of quiescence. Most of the small mammals shown to exhibit a short-term rhythm of act i v i t y during the night and day are found to be either herbivorous rodents, or shrews which are carni-vorous. Ecologically speaking, they live largely i n burrows or runways or at least under dense cover and must eat large quantities of food i n relation to their weight i n order to survive. Microtines, being vegetarians, ( consume a large bulk of green food containing much water. Davis (1933) suggested that the capacity of their stomach limits the size of each meal. They must eat, therefore, at frequent intervals through-out the twenty-four hours to obtain sufficient food to sur-vive. Shrews, also noted for their high metabolic rate, must have a high food intake to maintain themselves (Morrison and Pearson, 194-6). "Nocturnal mammals form two-thirds and diurnal mam-mals only one-third of the species of North America. (Park, 1940). Clark (1914-) suggested that as the day is the time of 139 greatest climatic and thermal diversity, many new animal forms would arise from diurnal species. If successful and adaptable, crepuscular and nocturnal variants would eventually develop. It i s this stage that the rodents and lepidoptera of the pre-sent day have reached. New types arising subsequently would follow the same course, and in doing so, would extirpate the diurnal species upon the food supply of their more efficient rivals only at night. Among those animals which have been studied and found to be almost completely nocturnal in habit are: Peromyscus spp. (Johnson, 1926, 1939; Behney, 1936; Hatfield, 19^0; Morrison, 19^8); the house mouse, Mus musculus (Southern, 1954); Anodemus svlvaticus (Elton et a l . , 1931; Kalabukhov, 1940) and Glaucomys sp. (Audubon and Bachmann, 1846; Stone and Cram, 1904; Seton, 1929; Sollberger, 1940; Morrison, 1948). In general, these animals are active throughout the night or exhibit great acti v i t y between dusk and midnight and again in the hours just before dawn. During the active period they tend to be less dependent on cover than microtines, being active on the forest floor, beaches, i n trees. These habits are pro-bably related to the decreased danger of predation during the night. Many of these animals tend to eat more concentrated foods than do the microtines. Peromyscus eat principally i n -sects and seeds (Hamilton, 19^1). Elton et a l . (193D fed nuts to Apodemus and found that they ate the equivalent of two s'tjomachs-full in a night. From this observation they suggested 140 that the bimodal acti v i t y patterns found during nights repre-sented the activity involved in obtaining two meals, with a period of quiescence to allow digestion of the f i r s t meal intervening. Pearson (1947) showed that the nocturnal species had the widest daily fluctuations i n metabolic rate, due i n most cases to a low resting level. The possible advantages and limitations of a noc-turnal environment have been reviewed by Crawford (193*+) • Ac-t i v i t y of nocturnal animals has come to be controlled i n part by variations in the environmental stimuli operating at night. These inherent rhythms of activity can be established in re-lation to light intensity, lunar periodicity and other factors Foremost among the advantages of a nocturnal habit is the avoidance of enemies i n the daytime. Furthermore, ther is a reduction in competition for food and for s t r i c t l y guarde territories and shelter sites. Animals engaged in feeding are apt to be especially vulnerable to their natural enemies. Among the mammals, bats, rats, mice,.and flying squirrels are forms which may find activity at night a means of avoiding carnivores which hunt by day. For many predatory animals, however, the preferred food is more easily acquired at night. Night allows for the i n v i s i b i l i t y of the hunter as well as the prey and there is greater ease of detecting victims by the sense of smell. Odours remain longer i n the air at night due to greater humidity and the relative absence of upward air lkl currents. Thus predators, scavengers, and general feeders may-a l l he able to find food with more ease at night owing to better conditions for the use of the olfactory sense. L i t t l e is to be found i n the literature concerning predation upon flying squirrels. Domestic cats have most fre-quently been reported as taking them. Man himself is probably the'most serious enemy on account of his logging operations and the f e l l i n g of old and rotten trees, thereby removing many of their nest sites. Other enemies of Glaucomys are listed by Seton (1929) as owls, foxes, martens, and weasels. He mentions a case of one being taken by a trout. As might be expected, most of these predators are largely nocturnal. Although the l i s t is doubtless incomplete, It is nevertheless l i k e l y that the animal has fewer enemies than i t would were i t a diurnal species. Although flying squirrels may have adopted a nocturnal l i f e to attain greater freedom from pre-dators, this cannot be proven now since the whole behaviour and adaptive nature of the animal has been altered. Attention is now turned to a brief consideration of the possible influence of several environmental factors upon the activity of flying squirrels and other small mammals. Among the more important of these influences to be considered as affecting activity of these mammals are temperature, va-pour pressure, the oestrous cycle, starvation, and then that wliich appears to be the prime factor as far as flying squirrels are concerned — illumination. 142 Effect of Temperature on Activity. While temperature, particularly that of extreme high and low values, may he of utmost importance as a factor influencing the activity of diurnal animals, i t does not share the same place of prominence in controlling, or at least influencing, the activity of nocturnal animals. The night is characterized by a greater uniformity of temperatures and is associated with higher humidity and a general decrease in wind velocity. No clear-cut correlation could be seen when the daily maximum and minimum temperatures were plotted against the activity registered by three male flying squirrels re-cording individually on the vibration amplifier activity re-cording apparatus. Even when the temperature f e l l to between 8 and 10 degrees above zero Fahrenheit for several weeks dur-ing February, 1956, water bottles attached to the activity cages froze solid and s p l i t , and snow almost covered the ca-ges, the flying squirrels continued active each night. While the total activity registered nightly during these cold spells was slightly less than that of shortly before, this slight de-cline in register might well have been brought about by a dampening effect caused by snow piled on and about the a c t i -vity cages. The animals did not appear to the observer to have slackened the intensity of their activity. X Because of their nocturnal habits, flying squirrels would unlikely be tolerant of the high temperatures of the day 1^ 3 period. Uniform temperatures characterize the night environ-ment more so than the day. During the heat wave of the summer of 1958, when diurnal temperatures reached into the upper 80's, the flying squirrels were repeatedly seen to leave the nest boxes in the outdoor shelter to l i e i n the shaded portions of the activity cages. Their fur appeared matted and blotched with sweat, and the blood vessels of the ears were swollen and prominent. The temperatures encountered during the out-door recordings seldom went into the extremes (below 25°F. and above 80°F.). The amount of data on the effects of tem-perature upon activity of these animals has, therefore, been limited. Possessing a thick coat of fur, the flying squirrel is well able to withstand low temperatures and remains active throughout the year. Further, the gregarious habit of these animals results in several members of a family unit sometimes sharing the same nest hole during the non-reproductive season and the combined warmth would undoubtedly aid each to meet the rigors of winter temperatures. The indoor experiments on flying squirrels during this study were conducted at temperatures between 68 and 70°F. and, therefore, this factor was considered to have been held constant throughout Expts. 5 - 2 2 . No indoor experiments were conducted to study the effect of extreme temperatures upon flying squirrels while other factors were being held controlled. Effects of Vapour Pressure on .Activity. The effects of variations in vapour pressure upon activity of animals has received scant attention i n studies reviewed i n the literature. Smith (1957) found that vapour pressure had no measurable effect on the duration of activity of lemmings at least at temperatures up to 25°. It the 31.5° to 35° temper-ature, range, there was a definite decrease i n the duration of activity i n drier a i r . No precise correlation could be found between vapour pressure fluctuations and the level of activity of flying squirrels. No attempt was made to design experiments in which the vapour pressure and level of locomotor acti v i t y were to be the only two variables. Effect of Oestrpus Cycles on Activity In mammals cyclic changes in the ovaries and uterus are reflected by simultaneous changes in the vaginal epithelium. Examination of the cellular composition of vaginal smears or lavages are frequently used i n diagnosing the stage of the oestrous cycle. The cells to be found at each stage in the oestrous cycle of the rat have been described i n de t a i l by Asdell (19^6) and Maximow and Bloom (19^2). The oestrous cy-cle has also been described in several other animals — the house mouse (Snell, 19^1), Peromyscus (Clark, 1936), Microtus oeconomus (Hoyte, 1955), lemmings (Smith, 1957) and for several other mammals (Asdell, 19^6). 145 Several workers (Long and Evans, 1922; Slonaker, 1924) have shown that the amount of activity of the female white rat reaches sharp peaks regularly about every fourth night. These peaks of activity coincide with increases in the number of cornified cells i n the vaginal epithelium. Asdell (loc. citO stated that the voles, Clethrionomys. are polyoestrous and that the sequence of changes in the vaginal cells are similar to those of the white rat. Hoyte (1955) found the oestrous stages in Microtus oeconomus of arctic Norway varied from six to eleven days. An exceptional case has been found in the Mg_ guentheri of Palestine for Zondek and Sulman (1940), taking vaginal smears of ten females of this species twice a day over long periods, found neither proestrous nor cornification. Bodenheimer and Sulman (1946) later concluded that no oestrous cycle occurred i n M^ guen-theri and that this species must be included among those mam-mals i n which ovulation can normally be induced during the period of oestrous only by the stimulation of copulation (as in the rabbit - cat - ferret group). Colton (1933) after studying female wood rats (Neotoma mexlcana pinetorurn) in ac-t i v i t y cages from early May to October found that the activity patterns did not d i f f e r notably from that of the males of the same species. Colton concluded that wood rats probably had only one period of oestrous in the spring because they bear only a single l i t t e r each year (in April or early May). 146 Riehter (1927) found that the amount of running in female rats was at a very low level i n young animals or adult females during pregnancy. The four-day cycles of high acti v i t y became evident only after puberty at seven to eight weeks of age. This cycle was also shown to be dependent on the presence of the ovaries and independent of the presence of the uterus. Bugbee and Simond (1926) injected f o l l i c u l a r extracts from pigs into ovariectomized rats and caused their ac t i v i t y to increase rapidly. They inferred that the sub-stance which brings about the increase i n running that coin-cides with the peak of cornified cells is produced in the ovaries. The morpholojteal changes in the vaginal epithelium up to the time of ovulation have since been shown to be brought about by an oestrogenic hormone (°c oestradiol) which is produced i n the ovaries (Bullough, 195D. Smith (1957) found no apparent relationship between the level of running activity and the oestrous cycle i n female collared lemmings, Dicrostonyx groenlandicus, and postulated three possible reasons for this: 1) the oestrogenic hormone did not effect running activity i n the lemming, 2) the peak concentration of the hormone at oestrous may have remained below the threshold for the stimulation of activity 3) o c oestradiol brought about an increase i n a type of activity other than running — a type which might have shown up had an-other type of activity recording apparatus been used. Earys (f954) found that the four-day activity rhythm associated with 14-7 the oestrous cycle in white rats was less marked in s t a b i l i -meters than in the revolving drums. No activity rhythm corresponding to the four-day cycle of the female white rats was found to occur i n the f l y -ing squirrels while the activity was recorded using activity wheels, treadle-board or vibration amplifiers. When the ac-t i v i t y of individual male and female flying squirrels was plotted separately on the same graph, the pattern for the two sexes did not differ appreciably. Nor was that of one sex consistently higher or lower than that of the other sex. Northern flying squirrels breed once a year — dur-ing March or Apr i l — and with a gestation period of approxi-mately 4-0 days, young are born in May or June. It may be that they exhibit exceptionally high levels of activity at the time of rut. The markedly high level of activity shown in Figure 6 of the present study (during the third week in March) may have been accentuated by the occurrence of the oestrous cycle in the female at that time. The figure represents, however, the average activity of two male and one female flying squir-r e l and the level of activity i n each of the animals did not differ appreciably from that of the others. No vaginal exam-ination of the female was made at the time. Nor is i t known for certain whether or not increased activity i n the female may have been a stimulus for increased activity i n the males. The animals were housed in separate cages in a completely 148 darkened room and maintained at constant temperature and r e l -ative humidity. The possibility of stimulation of one another by vocalization exists but was not determined. In experiments involving the recording of activity under outside climatic conditions and indoors under conditions of continuous light or continuous darkness or under a 12-hour light sequence, a marked inverse relationship has been seen between the level of locomotor activity of flying squir-rels and the prevailing intensities of nocturnal illumination as reflected by the lunar phases. The same relationship was found to occur in flying squirrels from which the ovaries or testes had been removed. It would appear unlikely, therefore, that the near-monthly cycle i n the activity level of these animals i s governed by a hormonal substance originating from these tissues. If i t were, the mechanism might be the effect of the hormone upon sensitivity to lig h t . But altering the length of the lunar phase failed to produce chaotic activity patterns, which would have been the case had such a hormone substance been altering the sensitivity of these animals to light. Thus there appears to be no evidence that the lunar rhythm reflects and is influenced by the sexual cycle of f l y -ing squirrels. There i s , however, an increase in activity i n March which coincides with the season of rut. 149 Effect of Starvation on Activity. Whereas the flying squirrels kept in captivity dur-ing the course of this study were fed each day during the out-door experiments and every other day during the indoor experi-ments, no data were obtained on the effects of prolonged starvation on the activity of these animals. During the i n -door experiments minor fluctuations were seen to occur in the level of total activity recorded during consecutive 24-hour periods and although these levels were frequently slightly lower on days on which the animals had been fed, this relationship was not consistently adhered to on a l l occasions. While pre-ferred foods were generally eaten during the f i r s t night after feeding, nevertheless there was always a surplus of balanced ration rat pellets and carrots i n the cages even after the second night. The effects of possible starvation were fur-ther reduced by the hoarding tendency of the flying squirrels. Only one animal — a female — died during the course of the activity recording experiments. The ovaries had been removed from this animal more than six months before and i t was sub-jected to alternating 12-hours light and 12-hours darkness with a r t i f i c i a l moonlight on a 28-day lunar periodicity. The nest boxes had been removed from each of the cages which caused further distress to the animals. Although the stomach of the animal in question was nearly empty at the time of her death, her activity had not deviated from the general pattern being followed by each of the animals i n response to the inten-sities of a r t i f i c i a l moonlight being employed in that particular 150 experiment. Nor did food appear to be the primary incentive causing the animals to leave their nest boxes for the f i r s t time each evening (Expt. 1). Almost always the animals would dart out to urinate, defecate, or both, and then return to the nest box or s i t and groom before starting to eat even the most favoured food — a p p l e s . Generally each animal spent considerable time and energy in darting about the cage before pausing to eat during the early part of the evening. Smith (1957) found that lemmings deprived of food did not in most cases continue running for more than 2h to 36 hours. Starvation tended to bring about an i n i t i a l increase and then a subsequent decrease in activity, and culminated in death. Richter (1927) found that white rats had a 3 - h hour" cycle of general activity and quiescence when food was available. When the animals were deprived of food, the period-i c i t y of the rhythm was reduced to 1 or 2 hours. Richter re-viewed a number of studies on the periodicity of the stomach contractions, hunger sensations, and general body movements in man and inferred that the period of bodily activity in rats was associated with periods of gastric movements and hunger. Munn (1950) f e l t that although stomach contractions and hunger cycles i n the rat are related, i t could not be 151 assumed that the former were the ultimate cause of the latter. He cites several references in which i t was shown that the removal of the stomach or cutting of the connections between the stomach and the central nervous system did not alter the periodicity of the activity rhythm. Behney (1936) and Stinson (1952) have demonstrated that the lack of food w i l l cause the activity of Peromyscus to extend into the daylight period. Calhoun (1945) found that the activity of the noc-turnal rodent, Sigmodon. i n the southern United States occurred several hours earlier each day i f the animal was deprived of food. Effect of Illumination on Activity. Perhaps more than any other single factor i n the en-vironment, illumination effects the behaviour of flying squir-rels at both the d i e l (24-hour), the lunar (28-day) and the seasonal levels of activity. The nocturnality of the flying squirrel has been f r e -quently mentioned. During almost four years of live-trapping only once did I observe a free flying squirrel during daylight hours (9s00 a.m. on a cloudy morning i n mid-March). The only times that flying squirrels i n captivity were seen to leave their nest boxes during mid-afternoons were i l e the animals were suffering from prolonged heat encoun-tered during mid-summer. 152 In large measure the time at which flying squirrels f i r s t become active i n the evenings appears to be influenced by the illumination, the time of year, and hence the length of the night. The average value for the awakening time of f l y -ing squirrels was found in this study to be 35*^ - 1.2 minutes after the o f f i c i a l time of sunset. Glaucomys are very active throughout almost the whole of the dark period but are sel-dom, i f ever, seen to be active during even the cloudiest of days. Thus the food taken in a pre-dawn meal presumably allows them to remain i n an inactive state throughout the day with-out exposing themselves to predation in searching for food in the open forest by daylight. Bu dusk, however, the stom-ach is again empty and the observed intense period of a c t i -vity during the f i r s t few hours of the night probably repre-sents efforts to obtain the next meal. The intensity of nocturnal illumination has a marked effect on the level of locomotor activity exhibited by f l y -ing squirrels. Several nocturnal illumination values i n na-tural habitats are given by Dice (1945) and are quoted here. He maintains that the light from a zenithal f u l l moon f a l l i n g to the earth on a clear November night in Michigan is 0.02 ft-candle. Light f a l l i n g to the earth on a moonless night i n -cludes starlight, auroral luminosity and zodiacal light and averages 0.004 ft.-candle. Clouds reduce the sky light reach-ing the earth's surface to between one-tenth and one thirty-second of the cloudless values, depending on the nature and 153 thickness of the cloud cover. With the reduction to one-tenth caused "by cloud cover, the intensity of light f a l l i n g on the earth under a f u l l moon would be 0.0C2 f t .-candle; under a quarter moon i t would be 0.000,2 ft.-candle; and on a cloudy moonless night i t would average approximately 0.000,04 f t . -candle. Under heavier clouds giving a reduction of light to one thirty-second, the light intensity f a l l i n g on the earth would be approximately 0.006 ft.-candle at f u l l moon and only 0,000,012 ft.-candle on a moonless night. The light values given to this point are those oc-curring i n wide clearings. In the habitats in which terres-t r i a l mammals usually l i v e , the light that comes to the earth from the sky is further reduced by shade cast by various ob-jects, particularly vegetation. In moderately dense oak-hick-ory woods near Ann Arbor, Michigan, i n September, while the trees were i n f u l l leaf, Dice (loc. c i t . ) found that the light intensity under the shade of these trees was reduced to one per cent of the value in the open. Under dense clumps of shrubs the reduction of the light may be as great as to one two-hundredth of the value in the open. Assuming a reduction to one per cent, therefore, the light of the f u l l moon would be reduced to 0.000,2 ft.-candle due to the shade of deciduous trees in summer, while on clear moonless nights i n summer the light f a l l i n g on the ground in deciduous forests would be re-duced to 0.000,004 ft.-candle or less. On cloudy moonless X nights i n summer the light reaching the forest floor often 1*4 f a l l s to 0.000,000,4 ft-candle, i f one assumes a reduction by a factor of ten due to clouds and by a further reduction fac-tor of 100 due to shade cast by trees. Coniferous trees pro-bably cast even heavier shade and because they do not drop their leaves in winter, they reduce light intensity at a l l seasons of the year. Vtfhen the spontaneous activity of flying squirrels i n captivity was recorded under outside conditions, a distinct relationship became evident between the level of this activity and the phases of the moon, hence illumination, to which the animals were subjected. During nights of l i t t l e or no moon-light — at new moon — the flying squirrels were extremely active and registered comparatively large totals on the re-cording apparatuses as indices of the nocturnal activity. With the waxing of the moon, however, a marked decrease in the activity of these animals was recorded during each hour of the night and the total for the entire night was only a small fraction of the former level. With the later waning of the moonlight at the last quarter and the new moon stages, the level of activity once more resumed the intensive manner. The pattern was essentially the same for either sex and for gonadectomized as well as normal animals. The a c t i v i t y of a group was shown to have much the same pattern as that of single animals. / The inverse relationship of the activity of flying squirrels to moonlight continued to persist more or less in 155 phase with the c e l e s t i a l moon for almost nine calendar months, while the animals were being subjected to continuous light, continuous darkness, 12-hours light and 12-hours darkness in normal or reversed sequences. Only during the last of this series did i t tend to become arhythmic. The inherent 28-day, lunar rhythm is deep-seated (but not entirely unchangeable) in the neuro-endocrine mechanism governing the activity of this species. When a r t i f i c i a l moonlight was introduced into the indoor experiments, however, i t was found that the level and pattern of the activity of each of the animals could be cor-rectly governed and predicted. The characteristic pattern of the activity established under outside conditions could be lengthened to 4-0 days instead of the normal 28 days or shortened to as brief a period as 7 days, as long as the 24-hour d i e l periods were being retained. Similar results could not be repeated when the animals were subjected to 8-hours light and 8-hours darkness during which the same sequence of a r t i f i c i a l moonlight was used as before — at least not within the dur-ation of the experimental periods applied. Gonadectomy had no apparent effect on the overall pattern of activity in six animals subjected to such an operation. The literature concerning the effect of length of day and illumination upon animals i s voluminous, complex and r/apidly growing. A decrease in activity corresponding to an 156 increase in illumination has been reported for Peromyscus by Blair (1943, 195D, Stinson (1952) and Falls (1957). The effect of illumination was found to be more pronounced when the activity was being recorded on open beaches than in dense vegetation. Falls maintains that the effect of light on ac-t i v i t y can only be obtained using an apparatus in which there are no dark places. Where shadows and dark nest boxes are available to the mice, this effect is reduced or absent. Such has not been the case in the experiments described in the present study. Each flying squirrel had been supplied with a dark nest box which i n turn cast shadows at least into one corner of the activity cage during a l l experiments except two — Expts. 16 and 20. Nevertheless, with each increase in illumination, a marked decrease in activity did occur and con-tinued to occur even after the animals had been placed for several months under continuous light or continuous darkness. Johnson (1939) recorded the activity of Peromyscus leucopus noveboracensis under continuous light of a low inten-sity (0.25 to 25.0 ft.-candle), and noted a striking progres-sive shift in the time at which activity commenced and ended over the 24-hour period. The rate of shift of the daily ac-tive period varied with the intensity of the light being em-ployed, and was greater with high intensities of illumination, but i t was always i n the form of a delay over the previous day, i.e. their active period f e l l slightly more than 24 hours apart. Light from a diffuse source was found to have more 157 effect on the rate of shift of the activity period than light of the same intensity from a more concentrated source. As soon as the continuous light was. removed, the shift i n the, ac-t i v i t y period ceased, activity beginning every 2h hours. Such a shift in the acti v i t y period under contin-uous light was not found to occur in the activity records of flying squirrels under continuous light of the intensity used in the present study. The activity of these animals continued to occur during approximately the same hours at which i t had occurred when the animals were f i r s t subjected to the contin-uous light. The a r t i f i c i a l moonlight used in the experiments was a diffuse light and no "moon" per se was visible to the animals. Experimental reversal of diurnal rhythm has been ac-complished in several animals, although not successfully in man (Freeman and Hovland, 193k; Wolker, 1926). Most reversals have been made by exposure to light at night and dark in the daytime. Browman (1937) reported repeated reversals i n the activity rhythm of albino rats under continuous l i g h t . He de-scribed their rhythm of activity under outdoor conditions as having a peak every 5 - 6 days but under continuous light an intermediate peak was noted. Hemmingsen and Krarup (1937) after keeping albino rats in continuous light found that the activity was delayed each day on the average about two hours, so that after about 12 days, and again after 2h days, i t occurred f again at the original time. Such a cumulative delay in the time 158 of the active period in continuous light may perhaps he a key to the repeated reversals of activity reported by Browman. Neither the mechanism by which a diurnal rhythm i s maintained under constant conditions, or how i t may be modi-fied i n continuous light, is f u l l y understood. Browman (loc. cit.) reported tests on albino rats in which removal of the eyes or cutting of the optic nerves prevented reversal of diurnal activity rhythm by light, although an individual with both lenses and humours of both eyes removed but with retinae uninjured, did show the same reactions to light stimulation as did rats with normal, unoperated eyes. It would appear then that light affects the daily ac t i v i t y rhythm, at least in part, through action on the eyes. Retinal function is based on photochemical responses i n a multitude of photosen-sitive cells — the rods and cones — one or other, or both, of which may be found i n different vertebrate species (Walls, 1942). The number of these cells which respond increases with increasing light intensity u n t i l a l l have been stimulated, and i f these quantities are represented graphically, the re-sultant curve is roughly sigmoid. There are several explanations of how some nocturnal animals can make their way about their territories or within the confines of activ i t y cages at very low intensities of light. Southern (1955) notes that many animals active at night.have no obvious adaptations of sight or hearing to help 159 them move about in darkness and he believes that such animals, including man, possess a kinesthetic sense which guides them in moving about a familiar territory. Once such animals have become thoroughly familiar with every aspect of their t e r r i -tory (just as a normal or blind man becomes acquainted with every turn and item within his house) they are able to move throughout their domain with utmost speed and without hesi-tation even in the dark. The nearly complete lack of light constitutes pos-sibly the greatest single alteration in the nocturnal, as con-trasted with the diurnal, environment. A brief review of the adaptations i n the eyes o f nocturnal animals would be, there-fore, appropriate here. Nocturnal animals need large eyes, but merely to en-large the eyes in order that more light may enter them is not enough. Doubling the diameter of the eye doubles the diameter of the retinal image (Walls, 194-2). This reduces the illumin-ation per unit area of retina to one-fourth. If the pupil is enlarged in proportion to the whole eye, doubling the d i -ameter would increase, by four times, the amount of light i t admits. The illumination of the retina has thus the same strength i n a l l or any eyes whose proportions are exactly the same, regardless of their absolute sizes. Enlarging the pupil even more, out of proportion of /%he eye, w i l l brighten the image. To enlarge the pupil, 160 however, the lens must be broadened too, i f spherical aber-r a t i o n i s not to occur, k proportionately thicker lens w i l l i n turn necessitate an increase i n the absolute size of the eye i f i t i s to remain mechanically and b i o l o g i c a l l y i n b a l -ance. Enlarging the lens out of proportion to the eye moves the optic center of the cornea-lens apparatus backwards. When the curvature of the cornea, lens, or both, i s sharpened to keep t h i s image from receding behind the r e t i n a , the an-t e r i o r chamber becomes deepened and the image reduced, there-by brightening the image while allowing the eyes to operate i n dimmer l i g h t . Thus nocturnal eye development may incur the development of one or more of the following c h a r a c t e r i s t i c s : 1. R e l a t i v e l y large eye for the size of the a n i -mal, and absolutely large i f there i s room for i t i n the head. It may even be altered i n shape ('tubular' eyes of owls) i f there i s not space enough for an orthodox eye. 2. Eye provided with r e l a t i v e l y large anterior segment, making room for a widely opening p u p i l and a proportionately large lens which i s 3. more nearly, or even quite, spherical and set far back from the cornea (which, where conven-ie n t , i s less sharply curved), so that the an-t e r i o r chamber i s often deepened and k. the o p t i c a l center i s f a r back within the eye C r e s u l t i n g i n a smaller and brighter r e t i n a l Image. 161 The nocturnal eye tends to have a larger anterior segment and a r e l a t i v e l y smaller fundus than the d i u r n a l eye. The eye i s , therefore, somewhat tubular i n some species as the anterior segment has become enormous (owls, lemuroids, deep-sea f i s h e s , and f l y i n g s q u i r r e l s ) . The small size of the r e t i n a i n tubular nocturnal eyes tends to make more nar-row the angle which embraces the v i s u a l f i e l d outside of the eye. This demands considerable r o t a b i l i t y of the eyeballs i n the orbits i n order that the animal can see about him through a safely wide angle. Where such r o t a b i l i t y i s pre-vented — as i n the tubular eyes of owls — i t i s compensated for by the extraordinary rotating power of the head upon the axis of the body. S t r i c t l y d i u r n a l hawks can rotate the head about 180° while owls can revolve t h e i r s through 270°or more. A l t e r n a t i v e l y , some nocturnal forms have retained spherical eyes which have not been greatly enlarged (bats, most rodents and rodent-like opposums) by evolving a lens larger i n proportion than In the tubular eyes. Such a spheri-c a l lens negates the need for voluntary eye movements, par-t i c u l a r l y i n those forms which lack an area c e n t r a l i s . Since there i s no reason to aim any p a r t i c u l a r r e t i n a l spot at the object under scrutiny, there i s a nearly concentric r e t i n a and an image which i s small but equally good whatever the d i r e c -t i o n i t i s cast on the r e t i n a . Hence, the eye with a spheri-c a l lens sees an object about as w e l l i n the periphery of the re t i n a as i n the fundus. 162 While much has been written on the advantages of s l i t pupils as opposed to round ones as a nocturnal adaptation, i t i s a c t u a l l y a d i u r n a l adaptation, for the s l i t p u p i l can be more nearly closed i n b r i l l i a n t l i g h t than can the round. Although the s q u i r r e l s include strongly nocturnal forms (the f l y i n g s q u i r r e l s ) , they a l l have round or s l i g h t l y oval (horizontal) pupils (Walls, 1942). Walls (1931) notes that there i s a close c o r r e l a -t i o n between the depth of yellow colour of lens and the ac-tiveness of the species; those forms which are swift and pur-sue swift prey have the yellowest lenses. Yellow lenses markedly increase v i s u a l acuity by absorbing the highly r e -frangible v i o l e t end of the spectrum thus greatly reducing the natural chromatic aberration of the eye and sharpening the v i s i o n . Such lenses have been noted by Walls i n an adult red s q u i r r e l , Sciurus hudsonicus loquax. i n a p r a c t i c a l l y full-grown fox s q u i r r e l , Sciurus niger r u f i v e n t e r . and i n an immature Lyster chipmunk, Tamias s t r i a t u s l y s t e r i . The lens of an adult striped ground s q u i r r e l , C i t e l l u s t . tridecem-lineatus. was found to be appreciably deeper yellow than i n the above animals, while that of a two-thirds grown grey squir-r e l , Sciurus carolinensis l e u c o t i s , was decidedly paler. These var i a t i o n s , Walls maintains, are i n accord with the habits of the various species, as the more deeply coloured lenses are found i n most di u r n a l forms. In f l y i n g s q u i r r e l s , Glaucomys volans. the lens was found to be quite colourless, as would 163 be predicted from the above theory. The r e t i n a l cones of frogs, l i z a r d s , t u r t l e s , birds, and non-placental mammals contain brightly-coloured o i l drop-l e t s whose significance has not been c l e a r l y understood. Such o i l droplets are absent i n snakes and s q u i r r e l s , t h e i r place being taken by the yellow lenses. None of the animals with yellow lenses possess the coloured o i l droplets (Walls, 193D. Diurnal animals, with their cone-rich eyes, have an acuity of v i s i o n which makes the eyes their best sensory i n -strument. Nocturnal forms, on the other hand, being cone-poor, have less clear v i s i o n and can make more accurate iden-t i f i c a t i o n of enemies and food with the nose than with the eyes. Nocturnal animals on the whole have thinner retinae than d i u r n a l groups and have much more slender optic nerves. It i s not at a l l unusual for several thousand rods to be connected by ganglion c e l l s to one optic nerve f i b e r . The r e t i n a l adaptations for s e n s i t i v i t y , both within the v i s u a l c e l l s themselves and i n t h e i r r e l a t i o n s h i p to optic nerve f i b e r s , render the receptive tissue of a nocturnal animal very sensitive to l i g h t and l i a b l e to be damaged by strong i l l u m -i n a t i o n . ^ The presence of a tapetum i s almost c h a r a c t e r i s t i c of a nocturnal animal. This structure behind the ret i n a r e f l e c t s 164 back the l i g h t entering the eye, causing the well-known shin-ing of the eyes i n the dark. The structure of the tapetum varies among the d i f f e r e n t groups of animals. According to Crawford (1934) the colours of glow i n tapetal r e f l e c t i o n s are probably due to surface colours and interference pheno-mena. In f l y i n g s q u i r r e l s i t i s a d u l l red or orange glow when spotlighted i n the beam of a f l a s h l i g h t . A c t i v i t y under very low i n t e n s i t i e s of l i g h t may not involve the eyes at a l l , but other sensory organs such as v i b r i s s a e . Olfactory organs may take over the function of orienting movements. These alt e r n a t i v e organs, when operative, permit a c t i v i t y to occur i n complete darkness. Although i t was not carried out i n the course of t h i s study (and no r e f -erence to i t has been found i n the l i t e r a t u r e ) , i t would have been informative to determine how well the f l y i n g s q u i r r e l s could orient themselves i n complete darkness i f the vibrissae had been removed. Whether the normal d a i l y a c t i v i t y rhythm of f l y i n g s q u i r r e l s (and presumably a concurrent metabolic rhythm) i s based on a pacemaking d i e l rhythm i n the endocrine or nervous system has not been determined. These animals appear to have exceptionally substantial and durable physiological clocks which continue to run over long periods of time. Whether con-d i t i o n i n g plays any part i n the production of said rhythms i s unknown. 165 It i s not clear how one should account for the de-crease i n the t o t a l n i g h t l y a c t i v i t y of f l y i n g s q u i r r e l s at or near the time of each f u l l moon. Henstock (1952) records a circumglobal decrease i n the minimum night temperature at or near the date of f u l l moon. No such regular decline i n temperature with each f u l l moon was noted from the constant recording temperature scribe operating next to the a c t i v i t y cages during the outdoor experiments. Furthermore, the i n -door experiments were maintained at constant temperature. They reveal that temperature, at lea s t i n the ranges used, was unimportant i n af f e c t i n g the a c t i v i t y rhythms of these animals. Undoubtedly, either very high or very low tempera-tures would influence a c t i v i t y of a l l homeotherms, but thi s aspect was not studied. Although as yet unproven, one hypothesis i s suggested here which may to a notable degree explain, or at least sug-gest, how the monthly rhythm of locomotor a c t i v i t y i n f l y i n g squirrels may have originated. It has been repeatedly shown that l i g h t has an i n -h i b i t o r y e f f e c t on the a c t i v i t y of some nocturnal animals. In the experiments i n which the a c t i v i t y of f l y i n g squirrels was being recorded outdoors, the peak hours of a c t i v i t y were seen to occur generally three or four hours afte r sunset. Dur-ing those nights on which the moon i s i n the new or dark phase, the moon, i f v i s i b l e , i s low i n the western sky and the peak a c t i v i t y during the t h i r d or fourth hour afte r sunset i s 166 achieved nigh uninhibited. By the time peak a c t i v i t y would normally occur, the moon may have already set. As the moon waxes toward the f i r s t quarter, both the sun and moon are i n the sky at the end of the day and the a c t i v i t y of f l y i n g squir-r e l s becomes inhi b i t e d somewhat by both sources of l i g h t . By the time the sun sets, and the animals leave t h e i r nests to become active, the moon i s already nearing the zenith. By the t h i r d or fourth hour of the night, i t w i l l have neared the western horizon and although the moonlight during the e a r l i e r part of the evening may have caused a s l i g h t decrease i n the amount of a c t i v i t y , i t w i l l s t i l l not have reached i t s maxi-mum i n h i b i t i n g value. With, or shortly after the f u l l moon period, however, the f u l l i n h i b i t i n g impact of the moonlight f a l l s upon the animals at pr e c i s e l y the hours at which peak a c t i v i t y would occur. By the time the animals have become ac-tiv e for the evening, the f u l l moon has r i s e n above the horizon and although s t i l l low i n the sky, the increased diameter, and therefore i l l u m i n a t i o n , i s adequate to make i t s e f f e c t s f e l t even from an early hour i n the evening. The moon continues to be i n the sky during the after-midnight hours, thus, so to speak, i n h i b i t i n g a possible s h i f t of the peak hours of a c t i -v i t y to a l a t e r period i n the night. F i n a l l y , during the l a s t quarter phase, the moon again r i s e s late i n the evening, by which time the peak a c t i v i t y for the night w i l l already have occurred and thus the t o t a l amount of a c t i v i t y for the night w i l l again be on the r i s e . 167 From this i t is clear that during those nights in which no moon appears in the sky, flying squirrels are subject only to the very weak lumination accorded by other sources such as starlight, auroral luminosity and zodiacal light. Ac-t i v i t y at this time is at a high level during practically the whole of the night and reaches i t s peak in the third or fourth hour. As the moon waxes and the consequent light to which the animals are.subjected becomes brighter and brighter, the activity may increase at f i r s t , but then rapidly declines as approximately the 0.001 ft.-candle level is reached. From then on u n t i l the f u l l moon stage or even shortly after, the amount of activity exhibited by these animals tends to decline and remains at a low level during each hour of the night. Dur-ing the nights of f u l l moon intensity the flying squirrels may remain inactive for several hours in the middle of the night, thus giving a bimodal nature to the d i e l activity curve. As the moon wanes, the inhibitory influence is removed and ac-t i v i t y again returns to a high level. Y/hether this cyclic d i e l nature of the activ i t y of flying squirrels has been brought about by narrow tolerance of light variations or is a protection against nocturnal pre-dators, remains to be proven. To reduce the amount of ac-t i v i t y to a bare minimum required to obtain adequate nourish-ment during the nights of bright moonlight, would certainly be of distinct survival value. Dice (1945) has calculated yc that the light f a l l i n g on the floor of a deciduous forest on 168 a cloudy moonless summer night may he as low as 0.000,000,4-ft.-candle. Light reaching the upper branches of such a forest where f l y i n g s q u i r r e l s would frequently be found would be of considerably higher ftrcandle value. Horned owls, barred owls, and long-eared owls, which may be included among the predators of f l y i n g s q u i r r e l s , have been shown to be able to see and approach prey d i r e c t l y from a distance of six feet or more under an i l l u m i n a t i o n calculated to be as low as 0.000,000,73 ft.-candle. (Dice, l o c . c i t . ) . It would thus appear that a f l y i n g s q u i r r e l g l i d i n g across a forest c l e a r -ing on even a cloudy, moonless night, i s susceptible to pre-dation and t h i s s u s c e p t i b i l i t y i s greatly enhanced during clear moonlit nights. Whether f l y i n g s q u irrels spend more time i n the lower l e v e l s of the forest during periods of f u l l moon and only reach the upper canopy on darker nights, i s not known. No attempt has been made to estimate the extent to which wavelength, p o l a r i t y , or energy content of solar and lunar l i g h t determine the preference of f l y i n g s q u i r r e l s for nocturnal (or tw i l i g h t ) a c t i v i t y and depress t h e i r a c t i v i t y i n bright moonlight. Maximum p o l a r i z a t i o n of moonlight occurs during the time of f i r s t and l a s t quarter phases. If t h i s q u a l i t y of the nocturnal i l l u m i n a t i o n was of b i o l o g i c a l im-portance i n depressing the a c t i v i t y of the f l y i n g s q u i r r e l s , one would expect two declines i n each of the lunar months / during which a c t i v i t y was being recorded under outside cl i m a t i c conditions. Such was not the case. 1 6 9 Limitations and Implications of this Study. While the results of this study have proven excit-ingly new and stimulating in the field of animal behaviour, several limitations are readily acknowledged. These reser-vations in no way invalidate the observed results and are mentioned in order that the reader might be cognizant that such limitations have been recognized and accepted. First , the study by its inherent characteristics i s , as i t was anticipated that i t could only be, incomplete. Ac-tually the results may be considered as the broad and general basic concepts of a much wider-scoped study of nocturality. Such a wide range investigation might have a comparative as-pect and entail the study of behaviour patterns of a host of nocturnal animals living within a community. One might ask: How do these animals f i t into the community as a whole? What correlation, i f any, is there between the activity patterns of these nocturnal forms i f one is a predator and another its prey? What physiological adaptations do each of these possess which enable them to survive successfully as a nocturnal spe-cies? To what degree do the major environmental factors in-fluence the behaviour and activity pattern of each of these nocturnal inhabitants? While the present study was conducted entirely upon captive flying squirrels, there is l i t t l e evidence to suggest that the general behavioural pattern trends unveiled are in any significant way different from that which might be expected 170 to occur i n these animals In t h e i r natural habitats. To have attempted a similar study e n t i r e l y i n the f i e l d would have been nigh impossible or at least extremely d i f f i c u l t . The number of indivi d u a l s studied was admittedly low from a s t a t i s t i c a l point of view and-but were to a large degree limited by the capacity of the recording apparatus. While to have conducted the study on a much larger number of i n d i v i d -uals might have given more s i g n i f i c a n t l y r e l i a b l e r e s u l t s , yet i t i s dubious whether the basic concepts would have d i f -fered appreciably. To a large degree each of the experiments of the study emphasized the factor of the nocturnal i l l u m i n a t i o n as influencing the behaviour pattern of these animals. To com-plete the picture, several other factors — s i n g l y and i n com-bination — ought to be treated i n a similar manner to deter-mine the i r potential influence upon the behaviour of these animals. P r a c t i c a l l y nothing was attempted i n the present study i n the l i n e of a ph y s i o l o g i c a l approach to the problem of nocturnal behaviour. This i s another entire and basic study i t s e l f and one which w i l l ultimately need to be i n v e s t i -gated before a complete picture can be obtained. F i n a l l y , and perhaps most important of a l l , while the present study was conducted using f l y i n g s q u i r r e l s , these animals might best be considered not only as subjects of a 171 study into t h e i r particular species, but rather as a vehicle for a much broader i n t e r p r e t a t i o n of c o r r e l a t i o n between en-vironmental factors and the behaviour of nocturnal animals as a whole. This i s not to imply that a l l nocturnal animals would be influenced by such factors as nocturnal i l l u m i n a t i o n as are f l y i n g s q u i r r e l s , but may be taken to emphasize a new approach to a c t i v i t y rhythms i n many other animals which have received but scant attention i n the past. SUMMARY 1. This laboratory and, to a limited extent, f i e l d i n v e s t i g a -t i o n was conducted during the period January, 1955 to August, 1958 on the campus of the University of B r i t i s h Columbia, Vancouver, B.C., Canada. 2. The northern f l y i n g s q u i r r e l , Glaucomys sabrinus oregonensis (Bachman) was the object of t h i s i n v e s t i g a t i o n and s p e c i a l attention was paid to the duration and i n t e n s i t y of the locomotor a c t i v i t y of these animals and the factors i n the i r natural environment which would a f f e c t t h i s a c t i v i t y to the greatest amount. 3. The animals studied proved to be active throughout the year and except for a b r i e f period i n mid-summer avoided a c t i v i t y during daylight hours. h. A t o t a l of 1,285 observations on up to f i f t e e n captive and individually-caged f l y i n g s q u i r r e l s at one time were made 172 over a sixteen-month period under outside conditions. These observations gave an average value f o r the time at which f l y i n g s q u i r r e l s commenced the i r n i g h t l y a c t i v i t y as being 35.^ - 2.12 minutes afte r sunset. 5. The f l y i n g s q u i r r e l s — as shown from continuous record-ing experiments — cease a c t i v i t y generally within an hour prior to sunrise. 6. When the t o t a l n i g h t l y locomotor a c t i v i t y , either of i n d i -viduals of either sexes or as groups of males only, are plotted against such environmental factors as maximum or minimum temperatures or r e l a t i v e humidity, no clear-cut r e l a t i o n s h i p i s found. When t h i s same data i s plotted against i n t e n s i t i e s of nocturnal i l l u m i n a t i o n as expressed by the phases of the moon, a strong inverse c o r r e l a t i o n i s seen between the two. During nights of l i t t l e or no moonlight (New Moon) t o t a l n i g h t l y a c t i v i t y i s at a high l e v e l . This t o t a l decreases with the waxing of the moon and reaches i t s lowest point at or just a f t e r f u l l moon. With the waning of the moon to l a s t quarter and new moon again, the a c t i v i t y l e v e l returns to a high l e v e l . This monthly rhythm of a c t i v i t y was evident whether the a c t i -v i t y was being recorded using either the el e c t r o n i c v i -bration amplifier recorders, a c t i v i t y wheels, or the treadle-board a c t i v i t y recording apparatus. 7. Both the d i u r n a l and the monthly patterns of a c t i v i t y were retained for more than two months while the animals were 173 kept under constant conditions of temperature and r e l a t i v e humidity and under either continuous l i g h t (at an average of 3*3 ft.-candles) or under continuous and t o t a l darkness. 8 . Under conditions of 12-hours l i g h t and 12-hours darkness, the animals r e s t r i c t e d t h e i r a c t i v i t y e n t i r e l y to the dark period and when t h i s l i g h t regimen was reversed, the a c t i -v i t y period was reversed accordingly. At the same time, the monthly rhythm of a c t i v i t y continued to persi s t i n the animals and i n phase with the outside c e l e s t i a l moon de-spite the absence of v i s u a l clues. 9. When a r t i f i c i a l moonlight was introduced into the a c t i v i t y rooms during the dark portions of the d i e l periods, the f l y i n g s q u i r r e l s responded to i t much i n the manner that they had to the natural moon — showing high l e v e l s of ac-t i v i t y during periods of weakest i l l u m i n a t i o n and decreas-ing t h e i r a c t i v i t y markedly when t h i s i l l u m i n a t i o n corres-ponded approximately with that of f u l l moon i n t e n s i t y . Un-der constant conditions of i l l u m i n a t i o n , the low point of the monthly a c t i v i t y cycle of the animals had l a r g e l y co-incided with the f u l l moon period outside. With the i n t r o -duction of a r t i f i c i a l moonlight, however, the low i n the in t e n s i t y l e v e l coincided with the highest i l l u m i n a t i o n of the a r t i f i c i a l moon whether th i s was i n or out of phase with the outside moon. 1 0 . Prolongation of the a r t i f i c i a l moonlight cycle to kO days f or gradual shortening of i t to as b r i e f as 7 days caused similar adjustments in the act i v i t y rhythms of the flying squirrels. 11. Flying squirrels deprived of their nest box and hence shadows within the confines of the activity cage, continued to show the same trends in activity level i n respect to nocturnal illumination as before removal of the nest boxes. 12. The animals could not be made to adapt to a 16-hour d i e l period consisting of 8-hours light and 8-hours of moonlit darkness during the duration of two a r t i f i c i a l lunar cycles of 28 days each. 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The occurrence of colored lenses i n the eyes of snakes and s q u i r r e l s , and t h e i r probable s i g n i f i c a n c e . Copeia 1931 (2): 125-127. 1942 The vertebrate eye and i t s adaptive r a d i a t i o n . Cranbrook Inst, of S c i . B u l l . No. 19, pp. 1-785. Zondek, B. and F. Sulman. 1940 Vaginal cycle of Microtus guentheri and i t s response to estrogenic and gonadotropic hormones P r o c Soc. E x p t l . B i o l . & Med. 43 (1): 86-88. APPENDIX r Table XIX. Hourly distribution of activity of seven male flying squirrels recorded in large outdoor cage using treadle-board recorder (Expt. 4) Date Weather Moon 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-Mt. Mt.-ll -2 2-3 3-h 4-5 5-6 6-7 Total Tape of even- Phase Taken ing of Off record (No. of pinholes punched in moving tape during above hours Nov. 1/57 Cloudless _ _ — 3 1 — 13 10 1 4 29 26 18 105 2 Cloudless — 3 40 27 27 36 22 84 46 6 4 26 321 3 Cloudless — 4 — 7 3 14 4 Cloudless No record 5 Cloudless — 6 48 3 1 28 25 8 10 2 — — 131 6 Foggy -- — 7 3 — — 9 2 1 22 7 Foggy F.M. — k 13 13 — — 2 2 3 21 1 59 8 Foggy — 2 — 1 — 1 1 5 9 Foggy No record 10 Rain No record 11 Rain No record 12 Rain 1 — — 40 9 — 13 40 52 -- 145 13 Rain No record 78 14 Clear L.Q. — 13 5 3 10 3 14 11 1 6 11 1 15 Clear — 9 23 1 — 4 2 1 21 1 — 8 70 16 Rain No record 17 Rain No record 18 Rain No record 14 19 Clear 6 33 11 3 7 21 28 39 7 — 7 17 10 8 211 20 Clear — 9 32 10 1 3 13 18 — 8 23 3 — — 123 21 Overcast N.M. 4 16 6 4 7 h7 27 9 20 13 2 8 — -- 163 22 Overcast — — 11 15 1 -- 8 13 7 8 13 4 4 • 2 — 86 23 Overcast — 15 17 5 1 12 15 10 12 7 11 4 2 1 — 112 24 Overcast — -- 26 11 — — 11 17 4 3 13 2 7 4 — 98 25 Overcast -- k 17 15 1 — 16 12 8 46 37 — 5 6 — 167 26 Windy No record 16 62 27 Cloudy — 4 - 9 3 .1 6 — 3 9 5 4 — 1 Table XIX.continued Nov. 28/58 Clear 29 Clear 30 Rain Dec. 1 Rain 2 Cloudy 3 Cloudy 4 Windy 5 Clear 6 Cloudy 7 Clear 8 Clear 9 Clear 10 Clear 11 Clear 12 Cloudy Cloudy 14 Clear 15 Clear 16 Cloudy 17 Rain 18 Rain 19 Rain 20 Clear 21 Rain 22 Rain F.Q. F.l L.Q. N.M. 1 28 18 h -- 21 21 7 1 13 1 — —- 5 Ih h 25 2 — 3 7 13 3 3 7 7 — 10 5 7 13 20 8 12 — 19 18 . h h 8 — — 2 2h 2 7 36 20 29 10 18 6 1 2 1 — 1 — 8 1 5 9 1 2 3 3 10 3 5 1 2 1+ 11 h — 6 1 — — — — 2 — 10 16 l — — 5 4 1 5 2 5 2 — 6 2 l — l 6 — 5 18 i 3 — — 4 — h 3 l 13 5 10 12 1 33 52 h6 26 8 l 4 8 26 — 20 23 33 — 18 20 27 33 22 14 8 2 5 — — 3 3 — 2 1 — 7 7 2 1 1 — — 1 5 2 3 6 17 30 — — 7 32 22 — — 1 2 3 1 — 3 — 1 110 3 6 — 11 7 2 — 63 11 16 — 9 1 2 — 96 4 6 3 2 4 41 5 17 1 3 4 1 — 106 8 9 17 2 1 3 — 93 31 16 4 10 10 2 2 198 1 8 2 3 53 — 2 5 6 3 9 — 5h 6 6 5 4 6 — 66 — — 5 1 1 1 — 12 1 2 — — 5 1 1 19 5 15 4 56 l — — 1 — — 21 7 27 — — 3 — 2 -- — 36 5 39 9 1 102 3 '4 — 8 6 3 3 198 — 18 4 11 147 20 16 31 12 221 10 2 1 7 — 2 8 26 3 2 — 1 3 4 • 3} 22 37 38 20 3 — 12 196 — 6 31 6 1 6 2 114 H 00 >Talle XX. Hourly distribution of activity of seven male flying squirrels recorded in large outdoor cage using treadle-board recorder (Expt. 4) Date Tape Weather of evening Moon 8-9 9-10 10-11 11-Mt. Mt.-l 1-2 2-3 ?>-k Evening Taken off of record Phase Total (No. of pinholes punched in moving tape during above hours) May 23/58 Warm, cloudless N.M. 21 97 99 84 76 5k 12 — 451 24 Warm, clear 18 5k k3 23 26 8 1 — 173 25 Warm, clear F.Q. 3 80 99 66 ^3 9 3 — 303 26 Warm, clear, s t i l l 28 98 111 89 76 58 13 — ^73 27 Warm, clear 3 66 9* 88 64 18 9 — 3k2 28 Intermittent showers 6 k6 35 25 8 5 5 - 130 29 Partly cloudy, but bright moon 5 65 71 38 20 4 4 — 207 .30 Partly cloudy, rain just before dawn 1 53 88 68 29 15 5 - 229 31 Few clouds, bright moon, rain at dawn 1 *3 18 20 k5 21 7 — 155 June 1 Partly cloudy F.M. — 7 26 31 15 86 2 Bright f u l l moon 7 27 79 5k 17 12 7 2 205 3 Bright moonlight 1 22 k3 Ik 13 7 6 1 107 Table XX. continued June 4/58 Partly cloudy & dark t i l l after Mt. 1 h2 26 44 13 9 5 — 140 5 Hazy sky, but moon bright; 3 6h 114 108 98 39 8 — h3h 6 Very s t i l l , warm, clear moon nearing L.Q., bright ~ 53 9*f 119 28 20 5 — 319 8 Dark, warm, no moon 3 60 114 72 24 21 — 388 9 Partly cloudy, dark, calm. L.Q. 3 59 100 104 81 32 8 — 387 10 Dark, cloudy, no moon. — 7 145 130 79 36 17 — 414 11 Dark, cloudy, drizzle at dawn. 5 5h 13 3 42 14 2 - - 133 12 Dark, cloudy, no moon. 11 71 101 73 7 9 4 1 277 13 Dark, clear sky, no moon. 2 12 48 89 53 12 10 — 226 14 Dark, cloudy, no moon. — 61 120 80 92 22 5 2 382 15 Clear, warm, no moon. h 92 122 84 96 46 9 - - - 453 .. 16 Clear, warm, no moon. 8 104 104 83 51 27 2 — 379 17 Clear, warm, no moon. N.M. 8 41 90 124 135 46 444 Table XX. continued June 18/58 Clear, warm, no moon. 2 24 19 Clear, warm, no moon — 88 20 Clear, warm, no moon 1 3*+ 21 Clear, warm, no moon 4 14 22 Clear, warm, no moon 9 74 23 Clear, warm, no moon — 50 24 Partly cloudy, rain starting at 4 a.m. F.Q. 5 35 25 Light drizzle, dark 2 44 26 Cloudy, no moon t i l l 1 a.m. — 36 27 Overcast, int. drizzle 1 36 28 Dark, int. drizzle t i l l Mt. 2 20 29 Dark, int. drizzle t i l l Mt. 1 23 July 1 Overcast, but light moon above F.M. 2 34 2 Clear bright moon — 23 4 Clear ybright moon — 24 125 121 101 56 37 — 466 140 118 140 103 3 — 592 87 61 115 35 1 — 33^ 60 48 59 25 4 1 215 126 127 125 149 26 — 636 121 103 98 73 23 1 469 55 78 52 38 13 5 331 53 12 4 ,9 — — 124 55 42 37 42 6 — 218 ^9 7 40 10 4 1 148 14 17 9 12 5 1 80 22 6 17 5 7 — 81 40 10 32 11 9 — 138 48 >*9 42 17 6 1 186 V3 10 21 27 8 1 13^ Table XX. continued July 5/58 Clear bright moon 6 Clear, bright moon, warm 7 Clear, bright moon 8 Partly cloudy t i l l Mt. L.Cj. 9 Cloudy, but no rain 10 Partly cloudy, very late moon. 11 Clear sky, dark, warm 12 Clear sky, dark, no moon. 13 Clear, no moon 14 Clear, no moon 15 Clear, no moon 16 Clear, no moon N.M. 17 Clear, no moon 18 Clear, no moon 19 Clear, dark, cloudy by^dawn. 27 20 1 2 3 2 73 13 3 5 8 — — 57 53 42 29 22 11 — 190 36 52 *3 11 -- — 167 60 38 24 9 — — 176 67 3^ ^9 23 5 — 200 60 32 26 58 16 1 229 36 26 19 13 2 — 108 39 48 26 18 3 — 176 65 75 19 18 12 — 208 66 82 33 64 12 1 280 88 61 36 5h 8 2 296 84 60 3^ 36 29 6 251 42 h5 41 15 7 — 202 k7 96 65 31 7 270 Table XX. continued July 20/58 Clear sky, dark 5 21 Clear, crescent N.M. in sky 3 22 Clear, crescent N.M. in sky 15 23 Clear, crescent N.M. in sky F.Q. — 24 Clear, crescent N.M. in sky 8 25 Clear, moon bright 5 26 Clear, moon bright 10 30 Hazy sky, practically f u l l moon. ( F.M. 6 1 31 Hazy sky. 2 Aug. 1 Clear sky, bright moon. 9 2 Clear, bright moon 9 3 Clear, few clouds, rain 7 a.m. 7 4 Mainly clear. 6 5 Mainly clear. 8 6 Cloudy night. 24 64 80 50 53 37 6 1 296 48 73 4l 23 38 19 1 246 68 101 70 24 17 3 — 298 71 86 69 53 15 9 — 303 38 99 61 30 28 18 2 284 30 57 31 20 38 13 2 196 53 67 61 57 23 16 3 290 29 — 14 3 7 5 — 64 35 1 4 8 1 5 2 56 30 4 39 9 10 16 3 120 58 29 .1 8 8 8 3 124 50 25 4 8 4 4 4 106 36 8 ^3 56 8 5 4 166 32 7 25 9^ 52 5 1 179 70 65 46 35 14 5 1 260 Table XX. continued Aug. 7/58 Rain t i l l 7 p.m. L.Q. ~ 17 1 25 12 50 12 19 136 8 Mainly clear 18 73 71 67 28 ^5 12 2 316 9 Clear sky . 12 79 63 24 38 10 15 4 245 10 Clear sky . , .. 15 75 93 55 23 37 32 3 333 11 (activity of 16 squirrels) 67 115 111 101 98 80 78 32 682 190 ACKNOWLEDGEMENTS . The writer wishes to point out that many persons'" contributed i n one way or another to make t h i s study possible. The data on the preceding pages were gathered on the campus of the University of B r i t i s h Columbia and the writer benefited during three of the summers covered by t h i s study from t h i s University's research funds. Dr. Ian McT. Cowan deserves pa r t i c u l a r mention for his suggestion of t h i s f a s c i n a t i n g f i e l d of research, and for his continued guidance and encouragement throughout the course of the experiments and i n the reviewing of the r e s u l t s . Mention i s thankfully accorded to those numerous individuals who from time to time were called on and so w i l l i n g l y gave of t h e i r assistance at the oddest hours of the night i n order that the experiments might continue uninterrup-ted and under as near natural conditions as p r a c t i c a l . The assistance of Dr. Ann Curier, Dr. M. A l i , Harold M i t c h e l l , and others did much to achieve the re s u l t s recorded herein. A p a r t i c u l a r vote of thanks i s due to Mr. Robert Butters of'the Department of Mining and Metallurgy, University of B r i t i s h Columbia, who so w i l l i n g l y gave of his time and assistance i n the buil d i n g , wiring and maintenance of the ac-t i v i t y rooms and recording apparatuses and i n achieving the 191 photographic i l l u s t r a t i o n s . Dr. C.G. Lemon of P a c i f i c P l a s t i c s , Vancouver, designed, b u i l t and on several occasions serviced Units 1 and 2 of the v i b r a t i o n amplifier apparatus used so extensively i n the study. The writer wishes to express his appreciation to Drs. W..4. Clemans, P. Larkin and J . Bendell of the University s t a f f and to M.T. Myres — each of whom contributed i n point-ing out improvements i n the e a r l i e r writings of t h i s study. In conclusion I would wish to express sincere appre-c i a t i o n to my wife for the many and late hours of assistance i n taking readings, the typing and re-typing of e a r l i e r drafts of t h i s thesis and for her extreme patience when so often the experimental animals were to be given f i r s t preference and consideration.
Thesis/Dissertation
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Zoology
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Inherent rhythms of activity of the northern flying squirrel in relation to illumination and to lunar and solar photoperiodism
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