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UBC Theses and Dissertations

A study of the growth and reproduction of the beaver (Castor canadensis Kuhl) correlated with the quality… Pearson, Arthur M. 1960

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A STUDY OP THE GROWTH AND REPRODUCTION OP THE BEAVER (Castor canadensis Kuhl) CORRELATED WITH THE QUALITY AND QUANTITY OF SOME HABITAT FACTORS * y Arthur M. Pearson B.Sc., University of British Columbia, 1958 A THESIS SUBMITTED IN PARTIAL FULFILMENT OP THE REQUIREMENTS FOR THE DEGREE OF MASTER OP SCIENCE in the Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1960 I n 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 a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree t h a t t h e 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 o f 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 o r 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 . Department o f "2-00£ 0 6 V  The U n i v e r s i t y o f B r i t i s h Columbia, Vancouver $, Canada. i ABSTRACT This study was concerned with analysis of the habitat of beaver (Castor canadensis Kuhl). The hypothesis that an animal's condition r e f l e c t s the adequacy of i t s environment was used as a basis for the evaluation. The growth rates of beaver on two d i f f e r e n t habitat types i n Prince Albert National Park, Saskatchewan, are compared and the habitats are c l a s s i f i e d accordingly. Beaver were raised under experimental conditions at the University of B r i t i s h Columbia and the growth rates and feed consumptions were recorded. The bioenergetics of the beaver are calculated and the r e s u l t s , combined with q u a l i t a t i v e and quantitative measures of the habitats on the study areas, are used to elucidate the energy r e l a t i o n s of the natural colonies of beaver under study. The r e l a t i v e growth of some organ weights and body measure-ments are described. Unsuccessful attempts are made to derive ..m a condition index f o r beaver by using a l l measurements available and subjecting them to various analyses. F i n a l l y , the sequential measurements of beaver on the study areas are compared for both summer and winter seasons. These studies indicated that the condition of a beaver, whether measured by growth rate or r e l a t i v e growth, accurately designates the value' of i t s habitat. Differences i n condition of beaver occurred most prominently during the winter as a re s u l t of the s t r i c t l i m i t a t i o n s i n the quality and quantity of available food. Fourteen beaver l i v e r s were analyzed to determine whether a chemical change of l i v e r tissue accompanies a change i n the condition of the animal. Over the period studied, May 2 to October 15, no progressive change could be found. The reproductive rates of beaver from Elk Island National Park, Alberta, and Prince Albert National Park, Saskatchewan, are compared. Beaver from the former park showed a s i g n i f i -cantly higher reproductive rate. This was correlated with habitat differences between the two areas i n d i c a t i n g that the reproductive rate i s another attribute of the animal which w i l l r e f l e c t the adequacy of the environment. i i i . TABLE OF CONTENTS PAGE GENERAL INTRODUCTION 1 GROWTH RATES 6 I n t r o d u c t i o n . . . . 7 D e s c r i p t i o n of Study Jtreas 10 N a t u r a l Growth 15 M e t h o d s . . . . . 15 R e s u l t s and D i s c u s s i o n 16 E x p e r i m e n t a l Study of Growth 23 Methods and T e c h n i q u e s . . . . 23 Growth Pat te rns 24 B i o e n e r g e t i c s 32 RELATIVE GROWTH AND CONDITION 43 I n t r o d u c t i o n 44 Methods 46. R e s u l t s and D i s c u s s i o n 47 LIVER ANiiLYSlS 61 M e t h o d s . . . . . 62 L i v e r W a t e r . . . . . •• 63 L i v e r Fat 66 P r o t e i n L e v e l • « 69 C o n c l u s i o n s 73 REPRODUCTIVE RATES . 75 I n t r o d u c t i o n • • • • 76 Genera l F e r t i l i t y •'• 76 Number of ova s h e d . . . . . . . . . . . . . . . . . . . . . 76 iv PAGE Number of ova fertilized •;. 77 Number of embryos developing to bir th . . 77 Energy Considerations of Beaver Reproduction 78 Methods . 79 Results and Discussion 80 Elk Island National Park ? 80 i -Prince Albert National Park 83 Comparison of Two Areas 86 i Conclusions 89 SUMMARY AND DISCUSSION • 91 LITERATURE CITED 100 V LIST OF TABLES TABLE . . PAGE 1 L i s t of plant species collected from Transition Zone - Prince Albert National Park. (Potential summer food f o r beaver).-... 12 2 Description of feed- beds on- the two study areas 14 3 Comparison of average absolute growth rate- of beaver from two areas i n Prince-Albert National Park. 18 4 Composition of U.B.C*-rat-ion- 16^ -57.......,. 32 5 Comparison of estimates of maintenance . requirements of beaver - figures .in d i g e s t i b l e Calories per day 33 6 Bioenergetics of growing beaver 35 7 The proximate analyses of food used by beaver during winter months 36 8 Calculation of average d i g e s t i b l e Calories available from branches of trees u t i l i z e d by beaver i n winter •. 38 9 Calculated maintenance requirements for beaver colonies over winter (October 15-May 1) 39 10 Weight changes of beaver over winter on study areas, Prince Albert National Park 41 11 Relationship of v i s c e r a l organ weights to body weight of various mammals 52 12 Relationship of heart weight to body weight of mammals 53 v i TABLE PAGE 13 "R" values and an analysis of variance of hind foot - body weight re l a t i o n s h i p of natural beaver 59 14 »p« values f o r comparisons of means of "R" values f o r beaver i n study 60 15 Results of chemical analyses of beaver l i v e r collected i n Prince Albert National Park.... 64 16 Reproduction data for a l l years' study i n Prince Albert National Park, Saskatchewan... 87 17 Results f o r analyses of a l l comparisons carried out (Null hypothesis: there i s no difference between mean number of young per reproductive female i n areas being compared). 90 v i i LIST OF FIGURES FIGURE PAGE 1 Pattern of beaver growth on area 1, Spruce River, Prince Albert'National Park........... 20 2 Pattern of beaver growth on area 2, Rabbit Creek, Prince Albert National Park....'..;... 21 Diagram 1 Plan View of beaver pen ... 25 Diagram 2 V e r t i c a l cross section view of pen 25 Diagram 3 Feed tray and bracket 25 Photograph 1 Beaver pens, U.B.C 26 Photograph 2 Den cavity 26 3 Growth pattern of beaver maintained i n c a p t i v i t y 1959-60...... ,. 28 4 Average growth rate of beaver 29 5 Regression of heart weight and body weight for type D data of beaver.... 48 6 Regression of kidney weight and body weight for type D data of beaver.. 49 7 Regression of l i v e r weight and body weight for type D data of beaver 50 8 Regression of circumference of furred part of t a i l and hind foot length of beaver 54 9 Regression of body weight and hind foot length of beaver . 56 10 Regression of body weight and hind foot length for beaver with body weight over 30 pounds 58 v i i i FIGURE PAGE 11 Relation of per cent f a t content to per cent water content of beaver l i v e r <> 65 12 Regression of dry f a t free l i v e r weight and body weight of beaver 71 13 Regression of l i v e r nitrogen and body weight of beaver I 72 14 Relation of maintenance requirements of nitrogen' (2*mgms./Kcal.) and l i v e r " n i t r o g e n available f o r metabolism (about"40$) . 74 15 Regression of l i t t e r size and weight o f females f o r a l l samples!. ".I.. '..... ».. 81 16 Regression of number of young per l i t t e r and weight of female f o r Elk Island National Park, 1958 84 17 Regression of number of young and weight of female beaver for Prince Albert National Park, 1954 '. 88 i x ACKNOWLEDGEMENTS Many thanks are due Dr. I. McT. Cowan, Department of Soology, and Dr. A.J. Mood, Department of-Animal Science, for their understanding and guidance shown throughout this study, and to Dr. J.R. Adams and Dr. J.F. Eendell who read and c r i t i c i z e d this manuscript i n i t s rough form. To the Canadian W i l d l i f e Service, under whose employ the f i e l d research was carried out, are extended grat e f u l appreciation for their assistance. I am p a r t i c u l a r l y indebted to Mr. D.R. Flook, mammalogist f o r Western Canada Parks, whose aid and c r i t i c i s m while i n the f i e l d , was a major fac t o r i n making the study a success. .......... The author i s indebted to the many-students who helped ideas and moral support while the thesis was being written. F i n a l l y , appreciation i s "due the s t a f f of Prince Albert National Park, who supplied physical assistance during the f i e l d aspect of the problem. The f i n a n c i a l "support"'for research during the university term of 1959-60 was supplied by Canadian Industries Ltd, and was greatly appreciated. GENERAL INTRODUCTION Habitat is an ecological term which has been defined as the place in which an animal lives. As such, i t includes the animal community, vegetation, and physical factors (Elton, 1957). Such divisions as major and minor habitats have been described but do not delineate the concept, in fact, they border on the ridiculous when practical application of the terms is attempted. A habitat cannot be considered properly unless i t is associated with a particular animal species. When analyzing and evaluating an area with regard to a species, two evident possibilities occur. Either i t is a habitat at present or else the environmental factors are such that a potential habitat exists, i . e . the animal is either present or absent. It is further axiomatic that for the purpose of wildlife management the latter situation is useless without a knowledge of the former. Such a view has not always been held and consequently the f irs t method of habitat evaluation was to describe the vegetation on an area without too much con-sideration of the animals' biology (Hamilton J r . , 1959; Hall , 1928). This method considers essentially the gross energy available in an area. The accuracy of the evaluation varies with the knowledge the investigator has of the biology of the animal and his ability to integrate that knowledge with the vegetative analysis. Most of the variables are qualitatively expressed and no standardization can be attained between i n -vestigations. A marked advance in technique occurred when quantitative measures of the vegetation were initiated. This, at least, gave figures which were comparable to other findings although their 3 absolute significance was s t i l l in doubt. When investigators finally turned to the animal i tself as an indicator of the value of the habitat upon which i t was l iving, the modern concept of habitat evaluation began. At f i r s t , an animal's condition was classified as good, poor, fat, lean, etc, each having a vague connotation, (Harper, 1958; Bradt, 1947) . Finally, a quantitative measure of an animal's condition was recorded. Growth rate, relative growth rate, relative size, reproductive success and other absolute attributes gave a method whereby animals could be compared on a level that would eliminate error due to human judgement, (Brandborg, 1955; Hogdon and Hunt, 1955;and Taber and Dasmann, 1958) . Besides the attributes of the individual a measure of the population success on a partic-ular habitat could be used as a quantitative measure of the value of the habitat. The measurement of the effect of the habitat as a whole rep-resented a most complex interaction of factors. So many combin-ations existed that i t has been found almost impossible to separate the reasons for one habitat being better than another. This led to the final step of analysis in which the absolute measures of an animal on a natural habitat are compared to the corresponding measures of an animal on control conditions. The controls could be other natural populations or experimentally raised animals. The effect of each variable can now be separated and compared to evaluate the habitat. The last method has been extended to further elaborate the effects of the environmental factors. The activity of the animal is investigated on a bioenergetic basis in which the 4 relations of energy intake and output are compared and the success of each net energy level recorded. The purpose of this study was to use a combination of the habitat evaluation methods heretofore elaborated in order to compare colonies of beaver, Castor canadensis Kuhl. The problem was attacked along several lines of study, each bearing in mind that the animal is a reflection of i ts environment. (1) The growth rate was used as a quantitative measure of the beavers1 condition. The natural growth rate of beaver on two study areas in Prince Albert National Park, Saskatchewan, were compared during 1958 and 1959 and the results were explained on general ecological considerations. (2) The growth rate and energy relations of experimental beaver kept at the University of British Columbia during 1959 and 1960 were recorded. The bioenergetics of the experimental beaver were combined with quanti-tative measures of the natural food available on the two study areas to deduce the energy relations ex-isting thereon. The results were used to support conclusions of habitat evaluation set forth in the f i rs t section based upon inspection of the conditions found in the f ie ld . (3) The relative grov/th rate and condition (relative size) of beaver from the study areas in Prince Albert National Park were compared. The results were employed to test evidence of the value of the habitats found by measuring growth rates. (4) I t was thought that as an animal i n c r e a s e s i n c o n d i t i o n a chemica l change of the body mass should o c c u r . To t e s t t h i s h y p o t h e s i s f o u r t e e n beaver l i v e r s were c o l l e c t e d d u r i n g the season o f open water at P r i n c e A l b e r t N a t i o n a l P a r k . Bach l i v e r was analyzed f o r w a t e r , f a t , p r o t e i n , and ash content . (5) The number of l i v e b i r t h s o f an animal i s an a t t r i b u t e which r e f l e c t s the adequacy of i t s environment. A l a r g e amount o f data on r e p r o d u c t i v e r a t e o f beaver was c o l l e c t e d from E l k I s l a n d N a t i o n a l P a r k , A l b e r t a , i n 1958 and from P r i n c e A l b e r t N a t i o n a l Park i n 1954, 1956, 1957, 1958, 1959. T h i s i n f o r m a t i o n was analyzed and the r e s u l t s of the v a r i o u s years compared. The h a b i t a t s o f the two areas were d e s c r i b e d and each type was eva luated on b a s i s o f the r e p r o d u c t i v e r a t e o f the beaver l i v i n g upon i t . The s tudy was s t a r t e d as p a r t o f a r e s e a r c h program of the Canadian W i l d l i f e S e r v i c e which have been i n t e r e s t e d i n beaver problems i n Canadian n a t i o n a l parks f o r many y e a r s . I t was a l s o a c o n t i n u a t i o n of experiments on beaver c a r r i e d out at the U n i v e r s i t y o f B r i t i s h Columbia i n 1956 by Stephenson and i n 1958 by C u r r i e r . 6 GROWTH RATES 7 INTRODUCTION '"There has been much discussion of the various techniques for describing and/or explaining growth (Krebs, 1959; Parker and Larkin, 1959). The value of some mathematical technique for describing growth is not disputed. However, much controversy has arisen over the problem of whether a growth equation is empirical or biological (i .e.) the constants are merely functions relating size and time or else they imply a biological meaning of a process underlying growth. If a true biological equation or growth formula is obtained i t must follow that i t is the only one that will accurately describe and explain the data. The ultimate goal would seem to be a mathematical equation relating growth of individual organisms (and perhaps numbers of organisms) to biological factors which are measureable and upon which growth depends. Growth (defined as biologic synthesis) is prop-ortional to the interaction of factors that may be categorized as follows: Growth cx body size c x caloric intake (net energy) O growth impulse (inherent physiological) mechanism Much experimental research has been performed which showed the effect of the various categories: body size (Minot, 1908; Eckles and Swett, 1918; Benedict and Talbot, 1921; Brody, 1927); caloric intake (Eckles and Swett, 1918; Benedict and Talbot, 1921; Joubert, 1954; Bandy, 1955); growth impulse (Eckles and Swett, 1918; Simpson, 1924; Brody, 1927; Pitt , 1941; von Bertalanffy, 1949; Bandy, 1955; Buckley and Libby, 1955). 8 On an empirical approach many authors have developed growth equations which relate growth to only one of the above categories (most prominent is body size). They make no mention of the other factors and i t is left to assume that they are always constant i f the growth equation is to be valid. In natural conditions which are encountered in ecological studies, two instances with the animals having the same size, nutrition, and growth impulse would probably never be found. The growth of each animal wil l depend upon a steadily fluctuating interaction of the three factors. Even though growth is proportional to the three factors simultaneously an equation relating growth to them a l l could s t i l l not be considered a true biological formula. The effect of each general factor is dependent upon hundreds of smaller and more basic categories, e.g. hormone level, enzyme balance, photoperiodicity, etc. In order for a growth equation to singul-arly f i t a set of data i t must consider a l l those smaller units. It would therefore follow that at our present stage of knowledge of the biological fundamentals of growth, an equation can only have biological implications to varying degrees. A true biological formula cannot be presented. A l l the factors upon which growth depends are not known and many that are known are not measureable. If and when it is accepted that a l l equations are empirical and that a biological equation would involve infinitesimal constants, more valuable work on the description of growth will be obtained. The explanation of the growth data will depend upon a 9 combination of deductive and inductive reasoning. There will be no mathematical equation from which the reasons for different growth can be extracted. It was decided that growth can only be defined as a measure-able attribute. Simple body weight was chosen as the attribute showing the effect of a l l reactions involved. Depending upon the accuracy of weighing, a few or many of the reactions may be left out of the results. Since description is the only purpose of a growth equation, the simplest equation to relate the variables will be the most practical. If a standard technique of description is decided upon, making results comparable, then the causes of the varied growth patterns can be obtained by inductive reasoning. In view of the above discussion, the simplest formulae relating body weight and time were considered as possible tools for analyzing the data: (1) Average absolute growth rate K = W9 -The result is expressed in pounds gain per unit of time. This method gives results that do not infer a biological explan ation of growth. If the time periods are uniform, then the results are comparable. (2) Average relative growth rate K = Wg -v1 the result is expressed in gain of pounds relative to the i n i t i a l weight,and K = ¥2 -i- (w2 + w x ) 10 the result being in gain in pounds relative to the mean weight of the animal. If the gain be large in relation to the i n i t i a l weight then the resulting figure will be unnaturally high. (3) Instantaneous relative growth rate K = lnWp - InW These results are expressed in gain in pounds per pound per unit of time. This method is not applicable to describe rate of growth over the seasonal periods for which beaver data are available. The fact that Brody's MK" has a very definite meaning (the instantaneous relative rate of growth for a given unit of time) means i ts use would imply conclusions not warranted by the paucity of the data. With due consideration to each of the methods and their merits and restrictions, and keeping in mind the purpose of this study i t was felt that the average absolute growth rate would best describe the data. DESCRIPTION OF STUDY AREAS The two study areas were located on the southern portion of Prince Albert National Park, Saskatchewan. As such, they were within the general biome termed Transition Zone which was essen-t ial ly a poplar (Populus sp.) forest. However, differences in habitat occurred with regards to beaver and they will be explained below. Area 1 consisted of a creek running through a valley with a relatively level floor extending from 50 - 1000 feet on both sides of the water way. A major portion of this was a flood plain which was under water for some time of the year and was 11 always very damp and spongy underfoot. Because of i t s tolerance of poorly aerated conditions, the willows (Salix sp.) formed the dominant vegetation. Willow clumps collected large amounts of humus under them forming mounds. The subordinate vegetation was of t y p i c a l flood p l a i n species which require moist conditions; (Carex sp., Ranunculus sp., Mentha sp.). In areas where the bank of the v a l l e y came down close to the water the better drainage enabled good aspen habitat to develop. However, the beaver had occupied t h i s area f o r a considerable time and had cut i n years past, almost a l l the available trees. Such areas were now covered only by shrubs and herbs (Rosa sp., Amelanchier sp., C a s t e l l e j a sp., Rubus sp. , Aster sp. , Hieracleum sp. , Smilacina sp., Galium sp., P o t e n t i l l a sp., and others). The second area was one i n which the banks of the small v a l l e y descended p r a c t i c a l l y to the edge of the creek. There was no flood p l a i n . In thi s habitat large poplars were growing abundantly along with various willows. The understory was of shrubs and herbs of a t y p i c a l aspen forest (Rosa sp., Amelanchier sp., Symphoricarpos sp., Betula glandulosa, Prunus sp., Equisetum sp., Agropyron sp., Aster sp., and others). The summer habitats of the two areas were e s s e n t i a l l y of equal r a t i n g with regards to beaver food. There was no shortage of lush, green vegetation and many of the species recorded f o r the areas have been recorded as beaver food (Currier, 1958). Table I l i s t s a l l the species collected but i s not complete. During the summer when the vegetation i s so lush, beaver should be able to survive almost anywhere there i s ample water. In f a c t , they do, as the colony becomes a very scattered unit -•TABLE I - List of Plant Species Collected Prom Transition Zone -' Prince Albert National Park. (Potential summer food for beaver) SPECIES SPECIES SPECIES Trees Populus tremuloides Populus balsamifera Picea glauca Salix petiolaris Salix Bebbiana Salix discolor Betula papyrifera Alnus rugosa Shrubs Betula glandulosa Amelanchiar alnifolia Cornus stolonifera Prunus melanocarpa Ribes americanum Rubus americanum Rubus idaeus Rosa woodsii Symphoricarpos occidentalis Artemesia ludoviciana Corylus americana Herbs Agropyron trachycaulum Poa palustris Bromus tectorum Calamagrostis canadensis Glyceria striata Glyceria grandis Calamagrostis purpurascens Phalaris arundinaceae Koeleria cristata Beckmannia syzigachne Carex aquatilis Carex diandra Carex bebbii Carex rostrata Carex antherodes Scirpus microcarpus Aster ciliolatus Aster ericoides Aster novae-angliae Aster ptarmicoides Aster daevis Achillea millifolium Achillea sibirica Achillea lanulosa Bidens cernua Solidago canadensis Agoseris glauca Prenanthes racemosa Petasites aagittata Viburnum opulus Campanula rotundifolia Galium boreale Galium septentrionale Plantago major Orthocarpus luteus Castelleja miniata Mentha canadensis Gentiana amarella Pyrola sp. Arctostaphylos uva-ursi Cicuta bulbifera Hippuris vulgaris Myriophyllum exalbescens Epilobium angustifolium Viola rugulosa Rharanus alnifolia Callitriche palustris Lathyrus ochroleucus Vicia sp. Geum macrophyllum Pragaria sp. Potentilla norvegica Potentilla fruticosa Parnassia multiseta Ranunculus circinatus Thalictrum venulosum Anemone canadensis Axyris amaranthoides Polygonum amphibium Rumex mexicanus Commandra richardsiana Urtica gracilis Smilacina stellata Hedysarum MacKenzeii Agastachi foeniculum Potomogeton richardsonii Sparganium multipedunculatum Sparganium angustifolium Huracium umbellatum Equisetum hiemale Equisetum pratense 13 and beaver are found wandering up and down a l l waterways. There are no special feeding areas and the animals are conse-quently more difficult to trap. Therefore, i f a difference in growth rate is to be found, i t was concluded that i t must be due to differences in the winter food supply when strict restric-tions on quantity and quality of food occur. The feed bed on Area 1 reflected the relative availability of woody vegetation. The composition by numbers Was..,found to be 91 per cent willows, 5 per cent white poplar (Populus tremuloides) and 4 per cent black poplar (Populus balsamifera). Measurements taken from the surface of the pond revealed a pile approximately 38 feet long by 17 feet wide and 7 feet deep. Prom trapping results i t was estimated that six beaver overwintered on that supply. There was no trace of a store in the spring which indicated that i t had a l l been used. Likewise the feed bed of Area 2 was composed of about 55 per cent willow, 25 per cent white poplar, and 20 per cent black poplar with a trace of other shrubs. The pile was 60 feet long by 15 feet wide by 5-10 feet d.eep. An estimated 11 beaver over-wintered off this store. In spring there were only a very few branches left uneaten. Table II compares feed beds of two study areas. In both areas freeze-up occurred near November 1st and lasted until May 1st, a total of seven months. TABLE II - Description of Feed Beds on the Two Study Areas. Vol. (Composition by Numbers) Location (ft.) Lgjth. (ft.) Width (ft.) Depth # Beaver Willow Aspen Black Poplar Misc. Area (1) 38 17 7 4522 6 91 5 4 Spruce River Area (2) Rabbit Creek 60 15 7.5 6750 11 55 20 25 Trace Rosa sp. Betula sp. Cornus sp. Alnus sp. 15 NATURAL GROWTH METHODS The technique employed was one of live trapping, ear tagging, release, and retrapping. At each capture the animal was weighed and measured. The trapping was done with Bailey purse-type traps set in shallow water along the creeks. Each area was trapped intensively for one week and then let rest a week. The traps were checked in the evening and again in the morning. Any beaver caught were removed and the data recorded immediately.-. Each animal was i n i t i a l l y tagged by ketchum ear tags, one per ear. As an additional check the webs of the hind feet were punched with a leather punch. Over the two years no trouble was encountered in identifying previously captured beaver. Weights were recorded by means of a 100 lb . Hanson spring scale. When one animal was caught two or more times, a record of the growth, as indicated by an increase in weight, was obtained. It was also felt that, when an animal was caught close to the same location at various intervals throughout the year, i t was indicative that that animal lived within the area under study. Many animals were caught in early spring and summer but not recaptured. In as much as most of these animals weighed about 30 pounds, the weight generally reached by 2 year olds, i t was concluded that they represented two year old beaver which had left their maternal colonies to search for an area in which to establish new colonies. Results of such captures were useless in the study of growth. 16 The summer habitats of the areas in question were nearly-identical with reference to beaver food species so only a general survey of species present was taken. The winter feed beds of both areas were analyzed as accur-ately as possible without disturbing them. The size and compo-sition was estimated independently by two investigators and the results showed such close agreement that i t was felt an accurate estimate was obtained. Samples of bark and twigs were removed from the beds in late f a l l and dried to constant weight to find moisture content. They were then sent to the Research Laboratory of the Department of Agriculture for proximate analysis. Only a few results have been obtained at the writing of this thesis. RESULTS AND DISCUSSION Most of the live trapping of beaver was carried out in May and early June and again in late August and September. It is realized that during that time interval i t was unlikely that a constant rate of growth occurred. However, because of the difficulty of catching wild beaver at regular, frequent intervals to obtain a true picture of growth rates, the data were treated as a constant growth rate from f i rs t capture in spring until the last capture in the f a l l . The same technique was used for analyzing growth from f a l l to spring. If any errors were involved they would be constant between populations as both were analyzed similarly. It was therefore felt that on a comparative basis such methods were justifiable. The animals were classified as kits , yearlings and two year olds. A beaver was a kit through the f i r s t winter but became a yearling the following spring. It was a yearling through the 17 second winter whence i t became a two year old. The values for average absolute rate of growth for beaver on the two areas are presented in Table III. Data were not obtainable for kits on area 1 but since yearlings on the two areas weighed about the same in the spring, i t was assumed that the growth patterns were similar. There appeared to be a difference in summer growth rates of the yearling beaver from the two areas. The mean rates of i n -crease were .071 and .099 pounds per day on areas 1 and 2 respec-tively. However, the mean weights of beaver on area 1 at June 1 and October 15 were 20 pounds and 31 pounds while on area 2 they were 21 pounds and 32 pounds. This difference between mean weights was not as great as the variation on each area. There-fore, the difference in mean growth rate probably results from the preponderance of figures from area 2 which were taken from beaver measured late in the spring and early in the f a l l and thus measured only the accelerating part of the summer's growth. On area 1 the figures were recorded in early spring and late f a l l . The average rate took into consideration the growth plateaus in early spring and late f a l l before and after the accelerating phase of growth. It was concluded that there was no true differ-ence between the rates of growth during the yearling summer on the two areas. The winter growth rates of yearlings shov/ed marked differ-ences. Beaver on area 1 uniformly showed a loss of weight during the winter, a mean loss of .013 pounds per day. On area 2 there was a reduction in the rate of increase from the summer but the beaver s t i l l gained weight at a mean rate of .025 pounds per day. TABLE III - Comparison of Average Absolute Growth Rate of Beaver Prom Two Areas in Prince Albert National Park. Area kii Summer rs Winter YEARI Summer INGS Winter 2 YR. Summer OLD Winter 3 YR. Summer OLD Winter i .0709 .0752 .0667 -.0044 -.0184 -.0159 .0737 .0645 .0769 .0729 ..0677 .0833 -.0217 -.0041 -.0192 .1059 .1081 ...071 -.013 .072 -.015 .106 '.$521 .0091 .0293 .0882 .0982 .1071 .0932 .0606 .0893 .1205 .1333 .0252 .0238 .0649 -.0270 ;029 '.699 .025 .065 .027 (Figures mean the average gain in pounds per day) !9 An interesting phenomenon was apparent when the summer rates of two year old beaver were compared. The growth rates on both areas increased sharply with the advent of summer. The results presented in Table III were few and their significance might be doubted. However, when those figures were compared with the general trends shown in Figures 1 and 2 i t appeared that they were a good representation of the true situation. The beaver on area 1, which had lost weight during the preceding winter and weighed less than their counterparts on area 2, gained weight at a greater rate than those on area 2. This tendency to regain lost weight and reach a set size has been termed "compensatory growth". It has been described many times (Eckles and Swett, 1918; Maynard, 1947; von Bertalanffy, 1949) for various animals. The situation described above could perhaps be explained on the basis of maintenance to body weight relationships. Supposedly animals on both areas were getting X Calories per day. The heavier animals on area '2 would require a greater percentage of X for maintenance than the lighter animals on area 1. This would result in more Calories for growth for area 1 and a corresponding increase in gain per unit time should result. If this explanation holds then when beaver on area 1 reached the weight of beaver on area 2 the growth rates should be equal. The data obtained were not sufficient to verify or disprove this theory. The limited data for winter rates of the two year old beaver showed a wide difference between areas. Area 2 showed an increase while a l l samples from area 1 decreased. Figures 1 and 2 give a schematic presentation of growth patterns from area 1 and 2 respectively. The scatter diagram 20 22 records the actual weight-time relationships of beaver handled during the study. The line was drawn by eye. A l l the phenomena described in the preceding paragraphs can be read easily from the figures. There could be numerous factors causing differences in growth patterns. Some of those will, be discussed with reference to the recorded results. The growth rate of an animal is influenced by its genetic make-up. The variability within a single subspecies group is a function of individual variation. Correction for such variation can only be carried out by taking large samples of each group. In the animals in question there is no reason to suppose a greater genetic influence between populations than within a single one. Growth, as affected by size, has been discussed in the introductory remarks. The data from natural studies indicated that the rate of increase in weight decreased as the animals grew larger. This can be seen by comparing successive summers on area 2. (On area 1, the phenomenon of compensatory growth confuses the data). Seasonal fluctuations in growth rate apparently occur in a l l animals in natural conditions. In some cases, like the beaver, they are self-imposed by an inherent physiological mech-anism which causes a decreased food consumption (Stephenson, 1956; present study). In others, they are imposed on the animal by a food shortage"which may be quantitative or qualitative. The reason for differences in growth rate on the two areas can only be explained by differences of habitat types. Beaver 23 living on an area provided with available aspen show a better growth performance than those depending upon.willows. This correlation will be shown to be cause and result in the bioenergetic analysis of the colonies. EXPERIMENTAL STUDY OF GROWTH METHODS AND TECHNIQUES It was planned to obtain pregnant female beaver in the early spring and. follow the growth curve of their kits from birth. That failed, so young were captured in the wild as soon as possible after birth. Two young were captured around August 1 at a weight of five pounds. One died shortly after without any growth data being recorded. Two more were captured on August 20 at 11 pounds weight. The three were shipped by air to the University of British Columbia where pens were being prepared for them. Until November 5, a l l three were kept in a cement room with only a washtub of water. They were fed U.,B.,G:. Ration 16-57 which was the standard rabbit pellet. Food consumption was not recorded but the animals were weighed at two week intervals to obtain growth data. On November 5, the animals were moved to their outdoor pens. Each beaver was housed separately,in a cement tank 8 feet long, 3 feet wide, and 4 feet high. Each tank was divided into two sections joined by a dive hole under the level of the water. The outside cavity was open at the top and the water was free from obstructions. This was the swimming or exercise pen. The den cavity was covered by \ inch plywood sheeting which was easily removable. A platform was placed just above water level to serve n as a nest site. There was a narrow strip of unobstructed water leading to the dive hole. Diagrams 1 and 2 show a plan and vertical cross section view of the pens. Photographs 1 and 2 show an external view of a l l three pens and a plan picture of one den cavity respectively. The animals were fed U.B.C. Ration 16-57 in an enamel dish covered by an aluminum top with a hole 6 inches in diameter through which the beaver could pick up the pellets. Spillage was thus negligable. The trays were held in place by fM steel strip bracket which could be removed easily and facilitated feeding. Diagram 3 demonstrates this feeding device. A day after the beaver were moved one animal appeared i l l and died shortly. A respiratory infection, possibly related to a change from normal to cold conditions, was believed to have caused death. The other two beaver reacted favorably to the new pens. They ate regularly and accurate records of food consumption were obtained. The animals were weighed to the nearest l / l6 pound every ten days. Calculations of the bioenergetics of beaver were deduced from those records. GROWTH PATTERNS The growth patterns found in captive beaver showed great similarity to those found under natural conditions. A rapid increase in weight during the summer was followed by a sharp break and a levelling of the weight - time relationship. The break in the rate of increase occurred in both beaver about January 10. Activity cavity - 25 . DIAGRAM 1 Den cavity 2 WATER Wooden Platform Underwater diva>^*i hole between cavities f row -drain Harbetween pens f I PLAN VIEW OF BEAVER PEN t^ DRAI W ^0> \ 1 T" 1 foot J DIAGRAM 2 Plywood top on den cavity * * Hater level Feeding tray r en platfom Underwater dive hole DRAIN VERTICAL CROSS SECTION VIEW OP PEN A 7\ / / DIAGRAM 3 C FEED TRAY AND BRACKET 26 Photograph 1 Den Cavity 27 Beaver #1 gained weight during the f i rs t phase at an average rate of .090 pounds per day. After the January 10 break and up until cessation of the experiments on March 9, the average rate of gain was .015 pounds per day. Beaver #3, which was a larger animal, gained at an average rate of .096 pounds per day up until January 10 and .007 pounds per day thereafter. The marked decline in growth rate was not a simple matter of more energy expenditure for maintenance, temperature control, etc. The decline was caused by a sharp decrease in food consumption. Figure 3 demonstrates the correlation between rate of growth and food consumption. The weight - time points are actual measurements of the beaver. The curvilinear lines are drawn by eye and rep-resent only the general pattern of the growth. Food consumption shows the pounds of food consumed per day for each beaver. Each point represents the average of three days feed consumption. Interesting comparisons can be made with similar data from Michigan and Russia. Bradt (1939) recorded the increase in weight of four beaver raised in captivity from birth to one year of age. He took weights at monthly intervals. The beaver recorded showed no change in rate of growth between summer and winter. They grew at an average rate of .058 pounds per day. This rate resulted in beaver which weighed less than the present beaver in the f a l l but by spring they were of equal weight. Figure 4 demonstrates this phenomenon. Also included are data of Lavroff (1952) on rate of growth of seven beaver raised in Russia. Neither Bradt nor Lavroff give any details of the conditions under which the young were reared. WEIGHT IN POUNDS 30 It has been shown that the break in the growth curve is a result of decreased food consumption by the beaver. The mechan-ism which controls the decrease in food consumption is the problem. Brody's growth inhibiting substance which can only act once a certain threshold of weight has been attained appears as a possible explanation when Viewing the experimental evidence. However, such a theory could not be accepted as one to occur in natural beaver populations. It has been assumed by the author that the reason for a decrease in food consumption is an inherent trait associated with survival and the limited amount of food available during the winter. The beaver is even more limited than other animals. Once freeze-up occurs the animals are wholly dependent upon the food stored under the ice. It follows that some sort of behavioral mechanism must exist to ensure that surplus food is stored, or that consumption is based upon potential food available. The results of our observations indicate that the f i rs t is not always the case. The amount of food stored is dependent upon a number of factors. First , i t is dependent upon the availability of suitable food7 trees (both quantitatively and qualitatively). The other main factor is the amount of time and industry the beaver put into cutting their supplies. The stimulus to begin storing food is unknown but i t does not seem to be the same for a l l colonies. Some take weeks of cutting while others prepare the feed bed in a few days. If predators, bad weather, human interference, etc. should harass the beaver, then the time for cutting would be considerably reduced. An early freeze could catch beaver with only 31 the start of a feed pi le . If a high food consumption were maintained after freeze-up, i t is quite feasible that the entire feed bed could be consumed before the winter is half over. If such were the case the beaver in the colony would certainly die. It is suggested that there is a definite physiological threshold that is "aimed for" by the beaver. In the f i r s t year i t would be equivalent to about 25 pounds. However, the decreasing photoperiod together with a complete behavioral change influence the pattern and cause a reduction in food consumption. Those influences cannot completely depress the effect of the physiol-ogical threshold as is evidenced by the fact that small beaver, animals that have not achieved the 25 pound threshold weight, grow during the winter but at a slower rate than during the summer. The extent of decrease in food consumption seems to support such a theory. If a beaver has reached the physiological thresh-old then food consumption usually decreases to bare maintenance needs. A smaller beaver will continue to grow slowly indicating that food consumption is maintenance plus. It is admitted that a great many assumptions are involved in such a theory but until further information is uncovered this seems to explain the phenomenon best. 32 BIOENERGETICS Beaver maintained throughout the experiment were fed exclusiv ely on U.B.C. ration 16-57. Table IV shows the composition of the diet. TABLE IV - Composition of U.B.C. Ration 16-57. Constituent p.p. 2000 T.D.N. {%) Ground oats 400 65 Ground wheat 400 80 Ground barley 300 70 Wheat bean 250 57 Mollasses 100 71 Dried grass 100 60 Soya meal 100 78 Linseed meal 100 77 Fish meal 160 76 Bone meal 20 15 Iodized salt 20 72 Irradiated yeast 0.5 — Stabilized fat 50 225 The total digestible nutrients in per cent were taken from Tables of Feed Composition, 1959, for non-ruminant animals. Stephenson (1956) performed digestibility trials on a similar feed and found an overall 70 per cent digestibility. The empirical cal-culations for Ration 16-57 yield a 72.7 per cent digestibility factor. Currier (1958) presented a table of proximate analyses of ration 16-57. From her figures an apparent gross energy of 1907 Calories per pound was obtained. However, the present diet contained an additional 11 grams of stabilized fat per pound of food. Using Brody's figures of 9.45 Cal . /g . of fat this would add 104 gross Calories per pound. The total gross energy was then determined to be 2011 Calories per pound as fed. Using a 70 per cent digestibility factor results in 1408 digestible Calories per pound of food. 33 The maintenance requirements of beaver can now be calcu-lated by converting food intake to digestible energy intake over the period when the beaver did not change weight. This was done and the results were compared to previous findings and empirical calculations. The Missouri Agriculture Station related basal metabolic rate to body weight for mature animals by the formula: B.M. dig. = 70.5 (Gals. ) ,0.73 (kgms.) Subsequent investigations have found such a figure to be quite reasonable. Brody (1945) used as a working approximation of maintenance needs, twice the basal Calories in digestible energy terms. Cowan, Wood, and Kitts (1957) performed feeding trials on beaver at U.B.C. and provided another estimate of maintenance requirements. Table V compares Brody's theoretical maintenance require-ments with data from the present study and from 1957. The figures represent digestible Calories per day. TABLE V - Comparison of estimates of maintenance.requirements of Beaver - figures in digestible Calories per day. (kgms. ) Wt. of Beaver Maintenance 2 x 70.5 B . W . 0 , 7 5 U.B.C. I960 U.B.C. 1957 9.41 724.4 703.9 (1.95 x B.M.) 9.42 724.8 838.0 (2.31 x B.M.) 11.26 825.6 763.3 (1.85 x B.M.) 13.51 943.0 1058.6 (2.25 x B..M.) 13.93 964.4 952.0 (1.97 x B.M.) 15.10 1023.2 1051.2 (2.05 x B?.M.) 34 The d i s c r e p a n c y between c a l c u l a t i o n s i s not g r e a t but as the techniques employed i n t h i s s tudy were the most advanced to date and the data should show the l e a s t e r r o r , a f i g u r e of 1.90 X the b a s a l m e t a b o l i c requirements w i l l be used to est imate maintenance needs. The e f f i c i e n c y and b i o e n e r g e t i c s of beaver growth were c a l c u l a t e d from data on feed consumption and growth r a t e d u r i n g November and December. Table VI shows that the s m a l l e r beaver was more e f f i c i e n t at c o n v e r t i n g feed to body w e i g h t . The d i g e s t i b l e C a l o r i e s r e q u i r e d f o r one pound g a i n of body weight a l s o showed that the s m a l l e r beaver was more e f f i c i e n t . The C a l o r i e s r e q u i r e d above maintenance f o r one pound g a i n were s i m -i l a r and depended upon the type o f t i s s u e which the one pound g a i n r e p r e s e n t e d . A mean of 4529 d i g e s t i b l e C a l o r i e s was r e q u i r e d . I n order to eva luate the energy r e l a t i o n s h i p s of the beaver the food h a b i t s and the q u a n t i t y and q u a l i t y o f . t h e food eaten should be known. I t was assumed that summer food c o n s i s t e d of l u s h v e g e t a t i o n found abundant ly a l o n g the edge of the waterway. The w i n t e r food was r e s t r i c t e d to bark and twigs of t rees s t o r e d i n the feed p i l e s , which have a l r e a d y been d e s c r i b e d . Cowan et a l . (1950) and C l a r k e and T i s d a l e (1945) l i s t e d n u t r i t i v e v a l u e s f o r food used by moose and c a t t l e r e s p e c t i v e l y . A few samples of w i l l o w were analyzed i n the course of the present s t u d y . Table V I I presents the p e r t i n e n t d a t a on forage comp-o s i t i o n from the three s o u r c e s . The d i g e s t i b l e C a l o r i e s per pound of dry matter was c a l c u -l a t e d by m u l t i p l y i n g grams of f a t X 9 . 4 5 , grams p r o t e i n X 5 . 6 5 , TABLE VI - Bio energetics of growing., .beaver. (1) lbs. Wt. (2) Gain lbs./day (3) Gain ¥ 2 - ¥ 1 (4) Intake' lbs. (5) Intake Dig. lbs. (6) Intake Dig. Cals. (7) Eff ic . (3)/(5) x 100 (8) Cals. req'd. for one lb. gain (9) Cals. Above Mainten. for one lb. gain (1) 15..75 .091 4.7 38.5 27.0 54000 17.2$ 11600 4830 (2) 20.1 .088 4.5 39.8 27.9 56000 16.1$ 12400 4228 3 6 TABLE VII - The proximate analyses of food used by beaver during winter months. % Dry Matter H20 Protein Crude fat N.P.E. Crude fiber Ash T.D.N. per lb.. dry matter Salix sp. twigs (Cowan et al.) 48.25 6.12 4.72 58.55 27.93 3.41 1169 Salix sp. twigs (Present study) 35 13.32 1.85 52.38 28.10 4.35 1133 Salix sp. 1st yr.twigs (Cowan et al . ) 43.10 7.22 4.32 54.10 31.73 2 .63 1141 Salix sp. 2nd yr.twigs (Cowan et al.) 43.10 5 .69 2.70 50.20 38.72 2 .69 1 0 5 3 Salix sp. average 42.36 8.09 3.40 53.81 31.62 3.27 1124 Aspen twigs (Cowan et al .) 46.34 7.10 7.71 52.95 28.07 4.16 1205 Aspen bark (Cowan et al .) 40 12..66 14.21 43.07. 24-24 5.81 1350 Black poplar twigs (Cowan et al .) 48.21 6.08 15.26 51.17 24.07 3.42 1368 Salix sp. leaves (Clark and Tisdale) 75 17.93 5.84 53 15.84 7.39 Aspen leaves (Clark and Tisdale) 75 18.23 4.57 53 17.36 6.84 37 and grams of carbohydrate X 4.10 (Brody, 1945) and using digest-i b i l i t y factors of 70$ for protein, fat, N.F.E. , (Stephenson, 1956) and 30$ for fiber (Currier, 1958). Samples of willow, aspen, and black poplar branches were removed from.the feed piles and the wet weight of bark and 1st and 2nd year twigs from each was measured. From Table VIII we can estimate that each log of aspen stored contained,on the average,5.87 times as many digestible Calories as a log of willow. Similarly, each black poplar log contains 5.60 times as many digestible Calories as willow. This can be seen to result from a combination of column 3 and 4 in Table VIII. The average aspen and black poplar have more dry matter than the average willow and each unit of dry matter contains more Calories. The bioenergetics of each colony can now be calculated and the theoretical results compared with the actual. Area 1 supported six beaver over the winter. Those beaver stored a feed pile 38 X 17 X 7 feet composed of 91 per cent willows, 5 per cent aspen, and 4 per cent black poplar. Maintenance per day for each beaver was calculated as 1.90 times the Calories for basal metabolism. The period of winter sustance was set from October 15 until May 1, a period of 197 days. From Table IX i t can be seen that the six beaver would have re-quired 1.16 digestible mega Calories in order to maintain them-selves for that period. Each willow branch stored contained on the average, 539 digestible Calories. Similarly each aspen had 3162 and each black poplar 3018 digestible Calories (Table VIII). Solution by simple algebra results in an estimate of 1500 TABLE VIII - Calculation of average digestible Calories available from branches of trees utilized by beaver in winter. (1) (2) (3) (4) (5) (6) (7) Wet weight % H20 Dry matter Av. dig. nut. per gm. dry matter Cals. Total dig. Cals. per branch Mean dig. Cals. per branch stored Aspen Bark only 2321.3 40 1392.8 2.77 4137 4137 3162 Bark Twigs 800.1 534.8 40 46..3 480.1 287.2 2.97 2.65 1426 761 2187 Black Poplar Bark only 2131.9 41.6 1245.0 3.39 4221 4221 3018 Bark Twigs 590.2 370.7 41.6 •48.5 344.7 190.9 3.39 3.39 1169 647 1816 Willows Bark 242.5 42.-4 139.7 2.48 346 539 539 Twigs 134.8 42.4 77.6 2.48 193 TABLE IX - Calculated maintenance requirements for beaver colonies over winter (October 15 - May 1). AREA 1 Mean Mean Mean basal metabolic Mean Maintenance Weight Weight requirement Maintenance for winter (lbs.) (kgms.) (dig. Cal. per day) (1.9 X B.M.) (Maintenance X 197) 41 18.614 594.4 1129 222483 39 17.706 574.5 1092 215124 33 14.982 508.7 967 190444 28 12.712 451.1 857 168829 31 14.074 485.9 923 181872 29 13.166 462.8 879 173226 Total Digestible Calories 1151978 AREA 2 41 18.614 594.4 1129 222483 45 20.430 637.7 1212 238691 40 18.160 585.2 1112 219064 34 15.436 519.8 988 194636 32 14.528 497.3 945 186165 34 15.436 519.8 988 194636 19 8.626 339.8 646 127262 13 5.902 257.6 489 96333 18 8.172 326.8 621 122337 18 8.172 326.8 621 122337 18 8.172 326.8 621 122337 Total Digestible Calories 1846881 40 branches having to be stored: 1365 willows, 75 aspen, and 60 black poplar. Similar calculations for area 2 on which 1.85 digestible mega Calories were required for maintenance of 11 beaver and the feed bed was 55 per cent willow, 25 per cent aspen, and 20 per cent black poplar resulted in an estimate of 1092 branches stored: 601 willows, 273 aspen, and 218 black poplar. Performance of beaver on area 2 indicated that they not only maintained themselves but added weight during the winter. It was previously calculated (Table VI) that, on the average, for each pound gain in weight, 4529 digestible Calories above mainten-ance were required. Table X records the performance of beaver on both areas over the winter. Assuming that the adult beaver did not change, a sixty-four pound gain was recorded. This represents an addition-al 290,000 digestible Calorie requirement.., The total digestible mega Calories required by area 2 for the winter was 2.14. The total number of branches in the feed bed must have been close to 1264: 695 willows, 316 aspen, and 253 black poplar. The outside measurement of the feed bed was 60 X 15 X 7.5 feet or 6750 cubic feet. Assuming that each species occurs in equal density, on the average, each cubic foot would contain about .187 branches. It was estimated that willows were packed twice as densely as the other species. Prom that assumption the density of willow branches was established at .272 branches per cubic foot and .136 branches per cubic foot for aspen and black poplar. The feed pile on area 1 was 38 X 17 X 7 feet or 4522 cubic feet and composed of 91 per cent willow, 5 per cent aspen, and 41 TABLE X - Weight changes of beaver over winter on study areas, Prince Albert National Park. AREA 1 AREA 2 [Pall Spring Pall Spring 41 ? ? 41 S 40 45 e ? 41 •? 36 36 & 31 38 8. 41 31 37 30 <3 26 33 * 29 29 a 36 29 $ 28 31 37 11 * 26 12 ? 14 15 # 20 15 9 22 11 24 42 4 per cent black poplar. Using the density figures found above a total of 1125 branches: 1024 willows, 56 aspen, 45 black poplar, would compose the food pile on this area. It was previously estimated that for maintenance requirements of the beaver 1500 branches with 91:5:4 ratio must be stored. The expected result would be that beaver on area 1 would not main-tain themselves and in fact would lose weight. That this did occur can be ascertained from the performance of beaver in Table IX. The beaver lost a total of 20 pounds. If we assume that this was a l l fat, a resulting 76,000 Calories would be produced. The total Caloric exchange on area 1 was 864,000 + 76,000 = 940,000 digest-ible Calories. The deviation between this and the estimated 1.15 digestible mega Calories is small when considering the possible places for errors. 43 RELATIVE GROWTH AND CONDITION 44 INTRODUCTION The concept of r e l a t i v e growth has been reviewed v e r y t h o r -oughly by Krebs (1959). H i s d i s c u s s i o n was based on an i n t r i c a t e a n a l y s i s o f the problem by Kavanagh and R i c h a r d s (1942). The l a t t e r authors c l a s s i f y f o u r types of r e l a t i v e growth s t u d i e s and d i s c u s s the s i g n i f i c a n c e of each. Al t ho u gh the a n a l y s i s o f r e l a t i v e growth i n t h i s t h e s i s i s not d i r e c t l y con-cerned w i t h the g e n e r a l concept , the theory o f the advantages and r e s t r i c t i o n s o f the v a r i o u s types of d a t a must be known. TYPE A - Simultaneous measurements of two v a r i a b l e s are taken from time to time on a s i n g l e organism d u r i n g the course of i t s g r o w t h . TYPE B - A group of i n d i v i d u a l s i s chosen to be as homo-geneous as p o s s i b l e w i t h r e s p e c t to c a u s a t i v e f a c t o r s , e s p e c i a l l y age, and one set o f measure-ments i s taken on each i n d i v i d u a l . TYPE C - A s e r i e s o f TYPE B measurements i s taken on the same group^of animals at s u c c e s s i v e i n t e r -v a l s o f t i m e . TYPE D - Measurements are taken on a group of organisms without r e g a r d to d i f f e r e n c e s between d e v e l o p -mental s tages of the i n d i v i d u a l s . TYPE E - A set o f TYPE A curves i s prepared f o r a group of i n d i v i d u a l s and the r e s u l t s combined. The problem i s whether s u f f i c i e n t d a t a are a v a i l a b l e on beaver to g i v e any e s t i m a t i o n at a l l of r e l a t i v e growth . Meas-urements o f Type A , Type D , and Type E , are a v a i l a b l e but a l l have many f a u l t s which prevent accurate a n a l y s i s . 45 For purposes of relative growth i t was decided to express various organ v/eights as a function of total body weight for TYPE D data. It is realized that this does not represent a good estimate with regard to conceptual theory but i t is the only type of data available for organ-weight relationships. A similar method has been used by Brody (1945) and Stephenson (1956) . The main problem of this section of the study is an eval-uation of condition of the beaver (actually i t is an expression of relative size of body parts). Two methods were tried: the regression of body weight on hind foot length as described by Bandy et a l . (1956) ; and the regression of circumference of furred part of t a i l on hind foot length. Both are based on the same assumptions, namely (a) the length of hind foot is least affected by nutritive state, growing slowly at a constant rate throughout l i f e and (b) the body weight or circumference of t a i l express the condition of the animal and fluctuate directly with nutritive status. In other words the hind foot length, depicts age, an independent variable, and the other measurements are the dependent variables. The larger the dependent variables relative to the hind foot length, the better should be the condition of the animal. One other type of analysis was carried out involving only the animals for which sequential measurements were avail-able. A function was used which shall be called R. R = W 2 - W-L Ef 2 e x R, here, wall represent the increase in body weight per unit of hind foot size for time t 9 - t-,. This analysis cannot 46 be i n t e r p r e t e d on an abso lu te s c a l e . A beaver growing n o r m a l l y , showing no i n c r e a s e i n c o n d i t i o n , w i l l show 3.51 per cent i n -crease i n body weight f o r a 1 per cent i n c r e a s e i n h i n d f o o t l e n g t h . ( F i g u r e 9 ) . Therefore a p o s i t i v e f i g u r e f o r R does not n e c e s s a r i l y mean an i n c r e a s e i n c o n d i t i o n or c o n v e r s e l y an R f i g u r e o f zero does not i m p l y that a change of c o n d i t i o n d i d not o c c u r . The R v a l u e obta ined w i l l be b i a s e d i f the h i n d f o o t l e n g t h s o f the v a r i o u s samples are not the same or i f the amount o f change between HFg and HP^ i s not the same f o r each sample. I n the ana lyses i n q u e s t i o n these seem to be extraneous v a r i a b l e s and do not b i a s the d a t a . The e f f e c t was equal on a l l f o u r samples. To remove some e r r o r o n l y animals hav ing a mean h i n d f o o t l e n g t h between 6.5 and 7.5 inches were u s e d . METHODS Every beaver k i l l e d was weighed to the nearest pound on a s p r i n g s c a l e , a measurement o f h i n d f o o t l e n g t h and c i rcumference of f u r r e d p a r t of t a i l was taken to the neares t e i g h t h of an i n c h , and the animal was a u t o p s i e d . The body organs were removed, washed and wiped f r e e o f s u r f a c e water . The h e a r t , l i v e r , lungs and k i d n e y s were weighed to the nearest t e n t h of a gram on a t r i p l e beam b a l a n c e . The lungs showed such a l a r g e v a r i a t i o n i n weight tha t r e -g r e s s i o n a n a l y s i s was not c a r r i e d o u t . The other organ weights were p l o t t e d a g a i n s t body weight on a l o g - l o g s c a l e and the l i n e o f best f i t drawn by the l e a s t squares method. A s i m i l a r method of l i n e a r r e g r e s s i o n was used to r e l a t e body weight to h i n d f o o t l e n g t h and c i rcumference o f t a i l to h i n d f o o t l e n g t h . A s e r i e s of Type B; measurements were taken on a l l beaver 47 weighing over 30 pounds ( s i g n i f i e s a d u l t b e a v e r ) . The sample was s u b d i v i d e d i n t o s p r i n g trapped and f a l l trapped a n i m a l s . A l i n e o f best f i t was c a l c u l a t e d f o r both s u b d i v i s i o n s r e l a t i n g body weight to h i n d f o o t l e n g t h . I t was intended to compare the s u b d i v i s i o n s by a n a l y s e s o f covar iance but p r e l i m i n a r y t e s t s i n d i c a t e d that such m a n i p u l a t i o n s would be u s e l e s s as the r e -g r e s s i o n l i n e s were v e r y s i m i l a r . For purposes of comparing R v a l u e s the areas were d i v i d e d i n t o seasonal e f f e c t f o r each. The summer c l a s s i f i c a t i o n was c o -i n c i d e n t w i t h the p e r i o d o f open water a t 54° n o r t h and the w i n t e r season w i t h the i c e d - i n p e r i o d . The summer R was the d i f f e r e n c e i n r a t i o s between f i r s t capture i n the s p r i n g and l a s t capture i n the f a l l . C o n v e r s e l y the w i n t e r R was equal to the d i f f e r e n c e i n r a t i o s from f a l l to s p r i n g . Such s u b d i v i s i o n s p e r m i t a t y p i c a l 2 x 2 f a c t o r i a l a n a l y s i s . The da ta a v a i l a b l e were compl ica ted by n o n - o r t h o g o n a l i t y , caused by unequal sample s i z e i n the b l o c k s . The method of comparison f o r such da ta was worked out w i t h the g r a c i o u s h e l p o f D r . Nash o f the U . B . C . Mathematics Department. RESULTS AND DISCUSSION The r e g r e s s i o n s o f organ weight and body weight are shown i n F i g u r e s 5 -7 . I n each case the growth r a t e o f the organs cannot be deduced. The equat ion f o r l i n e of best f i t enables the p r e d i c t i o n o f the average organ weight f o r any g i v e n body w e i g h t . Such a technique may prove u s e f u l i n d e t e r m i n a t i o n of p a t h o l o g i c a l c o n d i t i o n s . Brody (1945) s tated? "Without e x c e p t i o n the v i s c e r a l organ weights i n mature -animals o f d i f f e r e n t s p e c i e s i n c r e a s e w i t h a f r a c t i o n a l power of body w e i g h t , tha t i s , the weights of v i s c e r a l KIDNEY WEIGHT - GRAMS 51 organs do not i n c r e a s e as r a p i d l y as the "body as a w h o l e . " T h i s was found to h o l d f o r the beaver where the l i v e r i n -creased .90 per cent and the k i d n e y s .83 per cent w i t h a 1 per cent i n c r e a s e i n body w e i g h t . Those f i g u r e s compare w e i r w i t h o ther f i g u r e s f o r beaver (Stephenson, 1956) and f o r o ther mammals (Brody, 1945) as shown i n Table X I . On the other hand, Brody (1945) s t a t e d that the hear t weight tends to v a r y d i r e c t l y w i t h body s i z e because of i t s c o r r e l a t i o n w i t h the e x e r c i s e l e v e l of the body which v a r i e s d i r e c t l y w i t h body w e i g h t . Stephenson (1956) found a f i g u r e much below u n i t y f o r r e -l a t i n g hear t weight and body w e i g h t . T h i s supposedly i s a r e s u l t of the a q u a t i c h a b i t o f the beaver and weight r e l a t i o n s i n v o l v e d . However, the more e x t e n s i v e da ta obta ined i n t h i s s tudy would i n d i c a t e tha t Stephenson's f i g u r e s o n l y averaged the t rue p i c t u r e and that there are two s tages i n the r e l a t i o n s h i p of heart weight to body s i z e . I t i s seen from F i g u r e 5 tha t up u n t i l m a t u r i t y a 1 per cent i n c r e a s e i n hear t weight i s a s s o c i a t e d w i t h a .49 per cent i n c r e a s e i n body w e i g h t . A f t e r m a t u r a t i o n a 1 per cent i n c r e a s e i s r e l a t e d to a 1.33 per cent i n c r e a s e i n body w e i g h t . The p h y s i o l o g i c a l reason of t h i s break i s unknown but the o r i g i n of the r e l a t i o n s h i p i s t h a t a f t e r m a t u r i t y the heart cont inues to grow at the same r a t e as before m a t u r i t y w h i l e the r a t e o f body weight i n c r e a s e i s r e t a r d e d . A s i m i l a r phenomenon has been r e p o r t e d f o r growth of a d r e n a l g land and k i d n e y of guinea p i g s (Brody, 1945) . Table X I I r e p o r t s some of the equat ions r e l a t i n g heart weight and body weight i n mammals. F i g u r e 8 r e l a t e s c i rcumference o f f u r r e d p a r t o f the t a i l to h i n d f o o t l e n g t h of beaver . The f u n c t i o n of t h e i r r e l a t i o n -52 TABLE XI - R e l a t i o n s h i p o f V i s c e r a l Organ Weights to Body Weight o f V a r i o u s Mammals. Organ E q u a t i o n Animal Organ ( kgms.) M (kgms.) L i v e r L = 34.81 Beaver ( t h i s s tudy) L = 53.25 Beaver (Stephenson, 1956) L = 137 w 0 . 6 1 Horses (from Brody, 1945) L = 64 Dogs (from Brody , 1945) L = 52 ¥ 0 . 7 0 S t e e r s (from Brody , 1945) L = 33.3 ¥ 0 . 8 6 7 Mature mammals (Brody, 1945) Kidney K 5.225 Beaver (one k i d n e y , present s tudy) K = 17.0 Beaver (two k i d n e y s , Stephenson, 1956) K 6.5 Rats ( from B r o d y , 1945) K = 11.5 ¥ 0 . 7 0 Dogs (from Brody , 1945) K = 8.6 w 0 . 6 3 Cats 6 ( from Brody , 1945) K 7.7 Cats ? ( from Brody , 1945) K = 36.8 ¥ 0 . 5 1 S t e e r s (from Brody , 1945) K 24 .3 ¥ 0 . 6 6 Horses (from Brody , 1945) K 7.32 ¥ 0 . 8 4 6 Mature mammals (Brody, 1945) 53 TABLE XII - Relationship of Heart Weight to Body Weight of Mammals. Equation Animal Heart ' (gms,) a¥ /, \ (kgms.) -H = 9.908 .49 W immature Beaver, present study H = 1.079 W 1 * 3 3 adult H = 7.26 W 0 . 7 0 Beaver, Stephenson, 1956 H = 2.9 w 0 . 8 0 Rats (from Brody, 1945) H = 3.0 Guinea pigs (from Brody, 194-5) H = 4 .3 Gats (from Brody, 1945) H = 7.6 Dogs (from Brody, 1945) H - 5.7 Monkeys (from Brody, 1945) H = 16.2 ¥ ° - 6 3 Hogs (from Brody, 1945) H = 5.9 ¥ 0 - 9 8 4 Mature mammals (Brody, 1945) 55 ship is close to unity and shows a small standard error. From such results one would conclude that both are measures of skeletal growth. This is not the actual case as the circumfer-ence of ta i l varies greatly with nutritive state. This only points to the inadequacy of TYPE D data and the reserve one must show in interpreting results. The circumference of t a i l showed reactions to nutritive state very similar to those of body weight. Because hind foot to body weight relationships have been analyzed for other mammals the evaluation of beaver condition in this study were a l l based on the body weight - hind foot relationships. Similar calcu-lations on circumference of tai l - hind foot length relationships would have shown the same results. Figure 9 shows the relation of body weight and hind foot length. It can be seen that a 1 per cent increase in hind foot length corresponds to a 3.51 per cent increase in body weight. Stephenson (1956) found an increase of 3.04 per cent with a 1 per cent increase of hind foot length. Le Cren (1951) evaluated the condition of fish on the basis of the length to weight ratio of the fishes. He calculated the line of best f i t relating a l l length-weight measurements for a species and concluded that a fish showing such proportions was in an average state of condition. He developed a condition index by dividing the expected weight at a certain length into the actual weight at that length. This was tried as mature beaver from the two study areas were compared to the average regression line of Figure 9. The data from the different areas did not show a significant difference because of the wide variation (measurement error) involved in both measurements involved. 57 A second method v/as tried to determine the feasibility of using TYPE D regression lines to evaluate condition. Figure 10 records the regression lines for a l l beaver captured in spring and f a l l . The averaging of the figures resulted in a non-significant difference between the lines. It was concluded that by grouping relative size data an evaluation of beaver condition could not be obtained. The final method of calcu-lating MRM values for individual beaver, each captured several times, essentially involves TYPE A measurements which are combined to form TYPE E data. Table XIII presents the results of "R" calculations. An analysis of variance is also carried out on the data. The data was divided into a 2 X 2 factorial analysis and individual comparisons performed for most of the combinations. It can be seen from Table XIV that a l l the significant differ-ences resulted from the low value found for the Spruce River winter rates. It was concluded that the relative rate of growth of body weight to hind foot length was less for those animals on Area 1 during the winter than for a l l the other groups. This evidence supports data reported in previous chapters where i t was found that the beaver on that area during the winter were on a lower plane of nutrition than otherwise occurred. Scheffer (1955) found that the body size of the Alaska fur seal (Callorhinus  ursinus) was smaller as the number of animals increased. This he related to a lower plane of nutrition due to the greater distance which had to be travelled to obtain food. 59 TABLE XIII - "R" Values and an Analysis of Variance of Hind foot - Body Weight Relationship of Natural Beaver. SPRUCE RIVER (Area 1) RABBIT CREEK (Area 2) Summer Winter Summer Winter .325 -.603 1.135 .857 1.370 .182 -.090 .770 1.100 -.808 .520 .764 1.164 -.582 .042 1.177 .372 -.305 .507 1.240 -.552 .957 . 341 .184 .828 -.241 .533 .363 .840 1.295 1.010 1.528 1.069 9.122 -2.667 7.269 3.569 .8292 - .4445 . 6057 .8922 9.032 .1.784 7.986 3.298 7.564 1.185 4.403 3.184 1.468 .599 3.583 .114 Source of Variation d.f. s . s . - Mean Square Total 32 13.03774 .4074 Between Means 3 7.27511 2.42504 Within Means 29 5.76263 .19877 (Individual) 60 TABLE XIV - "F" Values For Comparisons of Means of yR" Values ForSBeaver in Study. SUMMER ' WINTER 11 12 Area 1 5c = .8292 x = -.4445 n = 11 n = 6 21 22 Area 2 x = .6057 x = .8922 n = 12 n = 4 1 Z ' A i 2 ) +2( AJ?) 1 # m e a n square c o e f f i c i e n t of means making up the comparison population mean (x estimates i t ) number of values i n means being compared Where "X= COMPARISON *.05 ( u u + u 1 2 ) - ( u 2 1 + u 2 2 ) = 0 1 0 . 5 4 4.18 ( u n + u 2 1 ) - ( u 1 2 + u 2 2 ) = 0 8.29 4.18 (3u1 2) - < ull + u21 + u22) = 0 34.93 4.18 (3u2 2) " < ull + u 1 2 + u 2 1 ) = 0 5.52 4.18 (3u u ) - ( u 1 2 u2 ]_ + u 2 2 ) = 0 7.85 4.18 (3u2]_) - < ull + u 1 2 + u 2 2 ) = 0 1.167 4.18 - u 1 2 ) = 0 31.68 4 .54 ( u 1 L - u 2 1 ) = 0 1.45 4.32 ( u l x - u 2 2 ) = 0 .06 4.67 ( u 1 2 - u 2 1 ) = 0 22.19 4.49 ( u 1 2 - u 2 2 ) = 0 21.57 5.32 ( u 2 1 - u 2 2 ) = 0 1.24 4.60 61 LIVER ANALYSES 62 METHODS As another facet of the evaluation of animal condition a sample of l i v e r s was col l e c t e d from beaver k i l l e d i n Prince Albert National Park during the summer of 1959. It was a n t i c i -pated that an increase of protein and fat storage would be found as the animals increased i n condition. A t o t a l of fourteen l i v e r s was c o l l e c t e d , the e a r l i e s t on May 9 and the l a s t on October 15. To ensure homogeneity of sample the r i g h t l a t e r a l lobe of the l i v e r was collected i n each case. They were frozen from the time of c o l l e c t i o n u n t i l analyses were begun i n November. The l i v e r s were made into sub-samples with wet weights ranging from 11 grams to 42 grams. Each sub-sample was placed i n a p e t r i dish and dried to constant weight i n an oven at approxi-mately 100°G'. The per cent water content was calculated. The f a t content of each ground l i v e r sample was determined by repetative extractions with 30-40 ml. aliquots of petroleum ether u n t i l no further weight loss of the samples took place. This was accomplished i n f i v e washings. The difference i n sample weight before and after extraction represented the f a t content of the l i v e r . The dried, f a t free samples were then processed f o r nitrogen content using the micro Kjeldahl technique as described i n A.O.A.C. 1950. The standard digestion and d i s t i l l a t i o n with NaOH was completed and the boric acid containing ammonia was t i t r a t e d against a .0102 N. concentration of HC1. The standard acid was obtained by d i l u t i o n of an ampule of .IN solution purchased from Anachemia Chemicals Ltd. (Acculute Standard Volumetric Solution). 63 The acid was standardized against a known alkali which was, in turn, standardized by titration against a known normality solu-tion of potassium acid phthalate. The results are recorded in Table XV. It was found generally that a much larger sample of the population than was available would have been required to establish unequivacally dependent changes upon a l l the collected variables which can affect the chemical composition of the liver. Each of the three constituents measured, water content, fat level, protein level, will be discussed separately and the results interpreted on the basis of known results in experimental animals. LIVER WATER There are no special properties of the liver regarding water content. However, being a tissue of an animal body, the water would constitute the largest per cent by weight of the organ. It has been shown, however, that water content of the liver can vary inversely with the fat content (Deuel, 1937), and further, that there is a gradual reduction in the water content of a l l animal tissues with increasing age. figure 11 relates the association of liver water to fat level in the beaver. The water content of rats on a stock diet was 68$ while that on a high fat diet for 14 days declined to 47%. Correspondingly, rats fasted for several days experienced an increased liver water content. The values of 72% were obtained for stock rats fasted for 5 days, and 51% for the rats previously on the high fat diet for 14 days then fasted for 5 days. The water content of beaver liver is similar to that reported for the rat. The average recording for beaver was 67%, the range TABLE XV - Results of chemical analyses of beaver liver collected in Prince Albert National Park. (Dry. Basis) Date Body (kgms.) Length Hind Foot (ins.) Liver (gms.) % H20 Dry wt. -% Pat Protein (N-.x6.25) Ash •* H?0 % CHp 1 May 27/59 ¥ 7.264 6 181.2 • 62.8 67.4 11.9 61.2 2 May 12/59 9 7.718 6 1/8 217.6 69.4 66.6 6.9 68.8 3 May 29/59 9 10.442 6 1/2 255.4 68.0 81.7 12.9 57.8 4 May 29/59 9 12.712 7 1/4 369.2 64.1 132.5 13.3 59.9 5 May 12/59 9 14.074 6 1/2 362.2 70.2 107.9 6.1 69.1 6 May 14/59 9 15.436 7 1/8 387.9 65.3 134.6 17.8 . 57.9 7 May 9/59 d 19.976 7 - 71.5 - 3.1 -8 Aug.25/59 $ 10.896 7 242.6 67.7 78.4 6.4 65.3 9 Sept.2/59 9 14.074 6 3/4 333.3 66.3 112.3 8.4 64.3 10 Sept.9/59 S 14.528 . 7 1/8 413.8 66.1 140.3 11.0 64.3 11 Sept.6/59 % 15.890 7 1/8 398.6 63.9 143.9 19.4 52.4 12 Sept.6/59 $ 15.890 7 1/4 384.3 65.4 133.0 16.4 57.9 13 Oct.15/59 9 8.614 7 5/8 566.1 69.6 172.1 3.5 71.9 14 Sept.6/59 ? 19.976 7 5/8 455.5 66.6 152.1 8.5 65.9 Mean - 67.6 10.4 62.8 3.9 3.1 19.8 WATER CONTENT 66 from 63-71%. FAT LEVEL The liver plays an important and unique role in the 'metabolism of l ipid components. Newly absorbed fat is altered in the liver to conform to the specific structure of the organism in question. Besides fat anabolism,fat shifting and fat catabolism occur:: . in the liver . In the present analysis the fat was considered as an abstract, homogenous entity. It was realized that perhaps more significant than total fat changes were the changes in ratio of the essential fats to the neutral fats. These divisions were not segregated and the interpretation of results was correspond-ingly limited. Deuel (1955) stated that the liver of most mammals contained 3-5% of total l ipids. Such a figure must be relative to wet weight of l iver . Williams et a l . (1945) recorded a figure for total l ipids, of 21.26 per cent of dry liver weight for new born rats. Assuming approximately 70% water in liver , the latter figure is somewhat above Deuel's range. Since a species, age, sex, nutritive state, hormone, miscel-laneous factor, and even a diurnal effect have been proposed as influences upon the liver fat content, the interpretation of any figure becomes extremely diff icul t . The essential l ipid decreases constantly with maturation of the animal. However, the neutral fats reveal a range of variation that makes i t impossible to detect any regular pattern with age. A sex difference in fat content has been suggested but nowhere authenticated. Feeding rats a high fat diet for fourteen days can increase 67 liver fat content from 4% up to as high as 40% of wet weight (about 80% of dry weight). Degradation of fats is a major function of the liver and consequently starvation, causing mobilization of fat reserves, results in an increase in liver fat content. The mouse shows amazing fat turnover under fasting conditions. The content of liver can rise from 16 per cent to 38 per cent in two days and in two more days drop to 10 per cent. In larger animals, the pattern is the same but takes longer and does not show such wide changes. An additional variable has been interjected into the results obtained in the present study. The turnover of liver fat is very high and as a result the conditions encountered during capture would undoubtedly influence the fat level. As each finding;/ is discussed this factor will, be considered. The lowest fat contents recorded were from mature animals, numbers 7 and 13 , taken in early May and late October respectively. The figure of 3 and 4 per cent fat on dry basis has been inter-preted as representing the amount of essential fats in mature beaver. The October caught animal had been exposed to winter feed conditions for about a month preceeding the capture. This was ample time for a l l the labile fat (neutral fat) in the liver to be used up. The May animal had had about a week preceeding capture during which the spring conditions prevailed. Fresh feed was obtainable. The lush vegetation was not yet present, however, so increase in content could not occur rapidly. Animals 2 and 5, caught only three days later, showed a doubled fat content and animal 6, taken five days later, showed a six fold increase. 68 Such variation must be explained on the basis of several variables. Animal 7 had been enclosed in a live trap for several hours with subsequent struggle to get free. It had then tipped the trap over and gradually been submerged under the water until i t was pinned under and drowned. The long hard struggle could use up stored fats so that only essential lipids were left . Animals 2 and 5 were trapped in dead traps and drowned but this entailed being caught for only a short time before drowning with result-ingly less struggle. Both animal 2 and 5 were younger than animal 1 and i t could be that the essential fat level is higher in these younger animals meaning that a figure of 6 per cent could be very close to their essential fat level. The level found in animal 6 probably represented the amount of fat found in a mature animal which had been well fed for at least a week before sampling. It had been exposed to about two weeks of spring conditions during which time the neutral fats could be stored. The animal was trapped and killed with very l i t t l e exposure or struggle resulting. Animals 1, 3, and 4, showed very similar figures. A l l three figures were probably reduced from the actual by the method of capture. They were a l l live trapped during the night and could have been penned up to twelve hours without food before being ki l led . Some struggle to escape obviously occurred. Beaver 8 demonstrated well the effect of depletion on liver fat content. That animal's figure of 6 per cent probably depicted the level of essential fat or very close to i t . It had been in captivity for a period of 85 days before being killed and was fed on a diet of aspen and willow branches. During that time the body 69 weight of the animal was reduced eleven pounds. The l i v e r weight had probably decreased as much as 150 grams. The f a t content, being expressed i n per cent, indicated that the amount of fat decreased by a greater r e l a t i v e amount than the body weight. The low figure f o r animal 9 cannot be explained on basis of the known factors a f f e c t i n g the animal. The same applied for animal 14. Animals 10, 11, and 12 formed a representative sample of beaver i n good condition showing a high l i v e r f a t content. PROTEIN LEVEL The l i v e r as a protein storage organ has been recognized for many years. It i s usually referred to as a dispensible store which varies d i r e c t l y as intake. I f a s p e c i f i c protein or amino acid i s not supplied i n the diet then the reserve i s c a l l e d upon to provide i t . The factors a f f e c t i n g l i v e r protein l e v e l are not well documented. More work has been done on the effect of plane of n u t r i t i o n and as that i s e s s e n t i a l l y what this study i s concerned with, i t alone w i l l be discussed. Addis et a l . (1936) performed depletion experiments with r a t s . They found that l i v e r was the most dynamic organ with regard to protein changes. In a two day f a s t 20% of the o r i g i n a l protein content of l i v e r was l o s t (Addis et a l . , 1936). In seven days of f a s t i n g 40% of the o r i g i n a l was l o s t (Addis et a l . , 1936a). Repletion of the stores does not occur as r a p i d l y as depletion but on an adequate protein diet a 20% depletion can be repleted i n four days. Luck (1936) experimented with the effect of dietary protein lev e l s on l i v e r protein contents. He determined that muscle 70 protein of a high protein diet rat was 10 per cent higher than a corresponding low protein diet r a t . The comparable figure for l i v e r protein was 120 per cent. His figures for protein content were 22.6 per cent of wet l i v e r weight on high protein diet and 16.6 per cent on low protein d i e t . The comparable per cents of dry matter are 75% and 55% respectively. The micro-Kjeldahl technique yielded figures f o r nitrogen content ranging from 10.4 to 11.9 per cent of the f a t free dry l i v e r . Multiplying by the conventional 6.25 fig u r e to give protein we got a range from 65 to 74 per cent protein on a f a t free dry basis. It has often been suggested that growth can best be measured by recording the protein synthesized. For this reason a regression analysis was carried out on the f a t free dry weight of l i v e r to body weight. The l i n e obtained on arithmatic paper was straight but f o r three points. Because of the wide (abnormal) deviation of those three they were l e f t out of the c a l c u l a t i o n of l i n e of best f i t . Figure 12 records the points and the l i n e of best f i t . The l i v e r nitrogen was regressed against body weight i n a similar manner. Figure 13 presents those r e s u l t s . Of i n t e r e s t i s the fact that spring k i l l e d beaver and f a l l k i l l e d beaver of equal weight have approximately the same amount of protein i n the liver'. It was concluded, therefore-, that f o r the time i n t e r v a l tested, May 9 to October 14, there was no appreciable store of protein observed i n the l i v e r . L I V E R N I T R O G E N - GMS. I [_ i i r i i i t 73 CONCLUSIONS The level of water in beaver liver showed an inverse relation-ship with liver fat. There was no progressive change during the time interval that the beaver were taken. It is therefore un-likely that any change in fat/water ratio of the liver occurs with an increase in condition of the animal. The liver protein was higher than that reported for mice or rats raised on stock laboratory diet. Again there did not seem to be a storage of protein as the condition of the animal increased. If we assume that the beaver is similar to other rodents and can deplete 40 per cent of the liver protein for emergency needs, then the length of time each beaver could supply mainten-ance requirements from liver protein store is shown in Figure 14. It is assumed that 2 mgms. of nitrogen are required per Calorie used. This strongly suggests that the liver is not a storage region of any importance in so far as long term fasts are concerned. BODY WEIGHT - KGMS. 18 19 75 REPRODUCTIVE RATES 76 INTRODUCTION GENERAL FERTILITY In 1899, Herbert Spencer developed a theory regarding re-production which he applied at the i n t r a s p e c i f i c l e v e l . It was stated that the individuation and the genesis of the animal vary inversely, i . e . i f more energy were spent i n da i l y processes of l i v i n g then the reproduction would be reduced. He used his theory to explain the low reproductive rate of bats as compared to the equal sized mice. His theory probably applies best on an i n t r a -s p e c i f i c l e v e l . I f there i s ample food and a favourable environ-ment then the necessary expenditure of energy compared to intake i s s l i g h t r e s u l t i n g i n or correlated with an increased reproductive rate. The number of l i v e b i r t h s experienced by an animal i s the product of ovulation rate, f e r t i l i z a t i o n rate, and s u r v i v a l to p a r t u r i t i o n . The f i r s t and the l a s t are dependent upon conditions of the females while the second concerns mainly the males. Number of ova shed The pot e n t i a l f e r t i l i t y of the female i s determined by the number of ova ripening at each estrus and this i s , i n turn, controlled d i r e c t l y by the hormones i n the blood. The hormones may be considered the proximate f a c t o r . The ultimate factor w i l l be of the environment and i s the mechanism to be investigated. Age or chronological time w i l l be considered as an ultimate factor. Young animals have less gonadotropic hormone i n the blood and subsequently have fewer young (Hammond, 19^9; Parkes, 1952). The "middle years" show the highest rate of reproduction followed i n old age by a reduction i n the number of young produced. 77 The number of ova shed i s g r e a t l y a f f e c t e d by the plane of n u t r i t i o n ( M i l l e r , 1942; F o l l e y , 1949; P a r k e s , 1952). The o v u l a t i o n r a t e i s d i r e c t l y p r o p o r t i o n a l to both energy and p r o t e i n i n t a k e a l though i t i s not known how the e f f e c t i s imposed. M a l n u t r i t i o n causes break down of g r a f f i a n f o l l i c l e s i n the ovary (Loeb, 1917). Number of ova f e r t i l i z e d There i s a p o s s i b i l i t y tha t the number of ova f e r t i l i z e d may be i n f l u e n c e d by f a c t o r s a f f e c t i n g ascent and p r o l o n g a t i o n of l i f e o f the sperm i n the female t r a c t but no exper imenta t ion has been per formed. Hammond (1949) s t a t e d that under maintenance c o n d i t i o n s , l i t t e r s i z e i n r a b b i t s v a r i e d d i r e c t l y w i t h d e n s i t y of sperm i n semen. I t was a l s o found that the d e n s i t y v a r i e d d i r e c t l y w i t h the amount o f p r o t e i n i n g e s t e d by the male (Wal ton , 1949). Number o f embryos d e v e l o p i n g to b i r t h F o l l o w i n g f e r t i l i z a t i o n the f a t e of a zygote can be a f f e c t e d at two s tages . Defec ts i n the mechanism of i m p l a n t a t i o n or decrease of hormones necessary to m a i n t a i n pregnancy can prevent an embryo from r e a c h i n g f u l l t e rm. Both are r e s u l t s of hormonal u p s e t s . The g e n e r a l p lane of n u t r i t i o n may i n f l u e n c e the d e v e l o p -ment of the embryo i t s e l f i n that the young w i l l be born i n a r e t a r d e d c o n d i t i o n and soon d i e . I t i s known that a l a r g e p r o p o r t i o n o f f e r t i l i z e d eggs p e r i s h i n an e a r l y stage of development. Hammond (1955) quoted a f i g u r e o f 25% i n c a t t l e . Osborn (1953) r e p o r t e d a 27% r e s o r p t i o n i n Wyoming beaver . Provost (1958) found 15% r e s o r p t i o n i n Washington beaver . The l a t t e r author concluded that embryo r e s o r p t i o n 78. increased as habitat condition decreased. No resorption was found after beginning of hair growth. He found no difference i n the ovulation rate of ovaries of beaver from good or poor areas. ENERGY CONSIDERATIONS OF BEAVER REPRODUCTION In unfolding the complicated mesh of i n t e r r e l a t i o n s of energy expenditure of animals the reproductive rate should hold important stature. N u t r i t i o n can have a profound and recognize-able e f f e c t on the reproductive processes. Although many other considerations influence reproduction, they are a l l f a i r l y easy to measure or dispose of i n analyses. The reproductive rates of populations, therefore, present an e f f i c i e n t and r e l a t i v e l y easy method of comparing the condition of the populations. Population i n t h i s sense refers to the animals under study and does not imply.a b i o l o g i c a l d i v i s i o n . In monestrus species, such as the beaver, the drain of energy imposed by the reproductive cycle n a t u r a l l y occurs only once a year. The most important time, nutrition-wise, should therefore be the weeks immediately preceeding ovulation, the period of gestation and the period of l a c t a t i o n . The beaver has, as many animals, not evolved so that this important period occurs during the time of most lush vegetation. The r e s u l t of such a s i t u a t i o n being that the general, yearly condition of the animal becomes much more s i g n i f i c a n t i n determining the reproductive success. The beaver has imposed upon i t s e l f another obstacle. With the onset of winter and subsequent freezing the entire feeding habits must change which should place additional s t r a i n on the animals' system. The Calories available to the beaver during the winter are much r e s t r i c t e d as compared to summer, and depend upon 79 the industriousness of the beaver and the a c c e s s i b i l i t y and quality of the deciduous trees i n the area. A l l those factors influence reproduction through their effect on the n u t r i t i v e state of the animals. Beaver have a ninety day gestation period (Provost, 1958). Back calcul a t i n g from average date of b i r t h of June 1, i n f e r s a date of ovulation around the end of February. At that time the ponds are frozen s o l i d and the animals have been l i v i n g on bark and twigs from the winter feed bed f o r four months. The c r i t i c a l factor i s again found to be the quality and quantity of the winter food. No matter what the condition of the animal entering the winter, i f the subsequent four months provide poor n u t r i t i v e conditions, the animal w i l l be i n poor condition by the time of ovulation. METHODS The estimation of reproductive rates i n this study depends upon two sources of data. A l l females k i l l e d during the period of gestation were examined fo r young i n utero. Animals k i l l e d subsequent to p a r t u r i t i o n were examined for placental scars. The second type of data may d i f f e r from the f i r s t by the extent of loss through resorption of embryos. The i n t r a uterine f e t i counts were a l l nearly f u l l term which would rule out the p o s s i b i l i t y of resorption which might have occurred a f t e r the count was made. In analyses of covariance, when body weight of the females was correlated with the number of young, the figures from i n t r a -uterine data would tend to be s l i g h t l y biased towards a lower value. This could have been corrected by subtracting the weight 80 of the f e t i from the weight of the female and cor r e l a t i n g the corrected figure with the number of young. It was not f e l t that such manipulations would present a clearer picture so they were not performed. Beaver were collected i n Prince Albert park i n 1954, 1956, 1957, 1958, 1959, and a single sample was taken i n Elk Island park i n 1958. The data were analyzed f i r s t by c o r r e l a t i n g number of young to the weight of the females for a l l areas together, as shown i n Figure 15. A c o r r e l a t i o n for each sample was then performed and the r e s u l t s compared by analysis of covariance. The covariance method w i l l adjust the analysis so as to eliminate the effect of weight of female on the number of young, leaving only the influence of external f a c t o r s . The r e s u l t s were interpreted i n view of population status of the beaver and most important the serai stage of plant succ-ession at which each population of beaver was l i v i n g . RESULTS AND DISCUSSION ELK ISLAND NATIONAL PARK The area, i n general, although being of l a t i t u d e to be included i n aspen parkland, cannot be c l a s s i f i e d as a parkland type. It i s situated on the north end of a major moraine area. The climax vegetative type i s a white spruce (Picea glauca) forest but frequent burnings prevent this climax type ever being reached. There i s evidence that the entire park was burned i n the l a s t s i x t y years. As a r e s u l t the area i s blanketed by a mature ( f i f t y years old) forest of aspen poplar (Populus tremuloides) and balsam poplar (Populus balsamifera) i n the r a t i o of 4:1. LU N or UJ h-WEIGHT - POUNDS :8:2 White spruce i s l o c a l l y concentrated hut generally sporadic i n d i s t r i b u t i o n . A l l beaver sampled were taken from the major lake, Astoten, located north c e n t r a l l y i n the park. The lake has a perimeter of approximately seven miles and i s completely surrounded by the poplar association. Numerous authors have shown the great dependence of beaver on poplar. Beaver were absent from that area i n 1945 but moved i n shortly thereafter. A census taken by Holsworth i n 1959, i n -dicated 10 active lodges i n the park. Four of these were on Astoten Lake. Thus the population of beaver had r i s e n from two to f i f t y i n approximately ten years. Such an increase does not indicate a rapid increment rate. It i s easy to explain such a slow increase i n an area having a l l the attributes of an excel-lent environment. F i r s t , the age of the i n i t i a l introduced beavers i s unknown. It seemed most l i k e l y that they were two year olds of about 30 pounds. The f i r s t couple of years they would produce small l i t t e r s and each l i t t e r would take two years to reach sexual maturity. Second, the absence of waterways interconnecting the various areas of the park now inhabited by beaver renders i t certain that colonization involved long pass-ages over land with the attendant exposure to loss by predation. This also may have contributed to the r e l a t i v e l y slow increase during the f i r s t 13 years. F i n a l l y , i n 1958, when the sample of reproduction tracts was obtained, a t o t a l of t h i r t y beaver were coll e c t e d from Astoten Lake. The low population and the abundance of available food and space would indicate that i n 1958 the beaver population on Astoten §3 Lake was i n a state of rapid increase. Population increase can be brought about by high n a t a l i t y , low mortality, immigration, or a combination of the three. Immigration was impossible i n Elk Island park and no inform-ation was available as to the mortality rate. Evidence from the reproductive tracts d e f i n i t e l y indicate a high reproductive rate for beaver i n 1958. The animals were collected at a late stage of pregnancy (end of A p r i l ) i n which hair f o l l i c l e s were present on most young. Eight females were found pregnant out of thirteen females of 30 pounds or more. A weight of 30 pounds was a r b i -t r a r i l y chosen as size of animals sexually capable of reproduction (2 years or more). The eight females produced forty-nine young or on the average 6.125 per pregnant female. Further c a l c u l a t i o n revealed 9.49 pounds mass of pregnant female per young produced. A. l i n e a r regression was established between number of young and weight of female (Figure 16). The c o e f f i c i e n t of co r r e l a t i o n was .739 ( s i g n i f i c a n t at .05 l e v e l ) . PRINCE ALBERT NATIONAL PARK This area i s of l a t i t u d e to be included i n the coniferous forest biome. The southern border l i e s twenty-five miles north of the aspen parkland. As a r e s u l t , the southern sections contain some large forests of aspen poplar and balsam poplar. There are, however, very few waterways along which th i s assoc-i a t i o n can s t i l l be found. Either they have a l l been cut and white spruce i s invading, or else the beaver have formed a flood p l a i n area, i n which only willows (Salix sp.) and sedges (Carex sp.) occur. In the southern area the succession i s generally the same as i n Elk Island National Park but the ser a i stage i s much 8 5 closer to the climax of white spruce. The heaver collected f o r reproductive data were from no one area so exact c o r r e l a t i o n with habitat type cannot be made. However, the fac t that there i s no s i g n i f i c a n t difference between the reproductive rate of the various years would indicate that there was a general uniformity over the entire park. Thus, the res u l t s recorded below ref e r to the general or mean for the Prince Albert park habitat as described above. Beaver were introduced into the park i n 1929. Simultaneously, immigration occurred along the west, south, and east borders of the park. A l l the streams leaving these areas eventually f i n d their way to the Saskatchewan River. It i s possible that immigration also occurred from the north where the r i v e r system f i n a l l y l i n k s up with the Ch u r c h i l l River. By 1935 the estimated beaver population was 500. There was a massive eruption i n la t e r years r e s u l t i n g i n a population maximum by 1950. A e r i a l counts were made i n 1954, (Tener), 1955, (Tener), 1956, (Radvanyi), 1957, (Plook), 1958, (Plook), 1959, (Plook).- There was an apparent increase i n numbers from 1954 to 1956 but i t was i n t e r -preted as f l u c t u a t i o n about a high i n population s i z e . Since 1956 the numbers have decreased. This can be,correlated with two f a c t o r s : the u t i l i z a t i o n of most of the available food and the drying up of many potholes. When reproductive studies were i n i t i a t e d i n the park the population of beaver had already reached the carrying capacity of the habitat. As such, a low reproductive rate could be expected. The data for a l l years i n Prince Albert Park are shown on 36 Table XV/I. Correlation between size of female and number of young proved s i g n i f i c a n t only i n the case of the 1954 data (Figure 17). As a consequence, a simple " t " test comparison of means was used i n place of covariant analysis i n order to compare reproductive success of the various years. To compen-sate f o r the effect of large variance i n the body weights of females i n some samples, only the number of young produced by females within the weight range of the smallest sample were used. The only s i g n i f i c a n t difference was found between number of young i n 1954 and 1956, with the 1956 figure being lower. This would appear to be an a r t i f a c t rather than a true difference, a re s u l t of the small sample size i n 1956 and the large variance i n number of young f o r any weight class. No s i g n i f i c a n t difference was found between the number of young per female (homogeneous samples for weight of female) i n years 1954 and 1 9 5 7 , 1958, 1959. COMPARISON OP TWO AREAS A correlation between body weight of females and number of young was found s i g n i f i c a n t for both 1954 Prince Albert National Park and Elk Island so the analyses of covariance was used. For comparison of other years of Prince Albert park with Elk Island park a simple " t " test was used. S i g n i f i c a n t differences were found at the .05 l e v e l of significance and i t was concluded that a d e f i n i t e difference i n reproductive rate had occurred with Elk Island having the higher rate. Table XVII gives analyses data for a l l comparisons carried out. No s i g n i f i c a n t difference between number of capable females 87 TABLE XVI - Reproduction data for a l l years* study i n Prince Albert National Park, Saskatchewan. Year Mean Wt. of reproductive female Mean No. of young per reproductive female n Pounds mass of productive female - per young produced 1954 46.06 4.24 25 10.86 1956 49.00 3.17 6 15.47 1957 45.50 3.50 4 13.00 1958 45.80 3.00 5 15.27 1959 55.00 2.67 3 13.13 WEIGHT OF FEMALE - POUNDS 89 bearing young was found between the two parks. The f i g u r e f o r i n f e r t i l e females being about 30% i n each park. CONCLUSIONS The reproductive rate of animals i s an important t r a i t with which to evaluate the r e l a t i v e condition of the animals. The condition of the animals i n turn suggest the value of the habitat of the area on which they are l i v i n g . Beaver i n Elk Island National Park i n 1958 showed a s i g -n i f i c a n t l y higher rate of reproduction than those i n Prince Albert National Park which showed uniformly low reproductive rate f o r years 1954, 1956, 1957, 1958 and 1959. By using appropriate analyses to correct f o r variance i n body weight of females i n the sample, i t was concluded that the habitat of Elk Island Park was much better than Prince Albert Park. The reasons for the r e l a t i v e l y low index f o r Prince Albert Park was due to a large extent to the a c t i v i t y of the beaver themselves which had reached a peak i n numbers and had u t i l i z e d most of the available feed. The Elk Island population was i n the i r r u p t i n g state of growth because the environmental factors which tend to decrease population growth had not yet become l i m i t i n g . The mechanism whereby the superior conditions influenced number of young was either at number of ova shed or number of ova f e r t i l i z e d and implanted. Prom l i t e r a t u r e references, i t would appear most l i k e l y that the number of ova shed was the factor which was instrumental i n this s i t u a t i o n . The effect being produced by a change i n hormone le v e l s which i n turn was influenced by plane of n u t r i t i o n . 90 TABLE XVII - Results for analyses of a l l comparisons carried out (Null hypothesis: there is no difference between mean number of young per reproductive female in areas being compared). Comparison n t.05 t Conclusion 1954-1956 P. A.N.-P. 15 2.160 2.83 reject N.H. -*see text 1954-1957,'58,'59 P.A.N.P. 35 2.035 2.007 cannot reject N.H.; .*. no difference 1956-1957,'58,'59 P.A.N.P. 11 2.262 .053 cannot reject N.H.; .*. no difference 1958 E.I.N.P. 1956 P.A.N.P. 12 2.228 4.697* reject N.H. .*. difference significant 1958 E.I.N.P. 1957,'58,'59 P.A.N.P. 12 2.228 5.515* reject N.H. .*. difference significant n P.05 P 1958 E.I.N.P. 1954 P.A.N.P. 33 4.17 4.45* reject N.H. .". difference signifi cant 91 SUMMARY AND DISCUSSION The problems of habitat analysis have been outlined. The evolution of thought on the subject was traced and i t was decided to attack the problem with the basic theory that the condition of an animal i s a r e f l e c t i o n of the adequacy of i t s environment. The condition of the animal was measured by several d i f f e r e n t quantitative measures and the r e s u l t s of each analysis compared. As part of a Canadian W i l d l i f e Service research programme and as a continuation of recent work at the University of B r i t i s h Columbia, the Canadian beaver (Castor canadensis Kuhl) was chosen as the animal on which the study was based. The f i e l d work was carried out i n Prince Albert National Park, Saskatchewan, during the summers and f a l l s of 1958 and 1959 and i n Elk Island National Park, Alberta i n the spring of 1958. Two experimental animals were shipped to the University of British'Columbia i n the f a l l of 1959 and t h e i r growth and food consumption followed u n t i l the spring of I960. In the f i e l d the condition of beaver was measured i n terms of growth rate and r e l a t i v e growth on two areas i n Prince Albert Park. The reproductive rate of beaver i n Prince Albert Park was compared to that i n Elk Island Park. A sample of beaver l i v e r s was collected from animals k i l l e d during 1959. The l i v e r s were frozen and taken to the University of B r i t i s h Columbia where they were analyzed for water, f a t , protein, and ash content i n order to investigate the p o s s i b i l i t y of a chemical change i n composition as the condition of the animal changed. The experimental animals were housed i n s p e c i a l l y constructed cinder block pens which were supplied with constantly circulating water one foot deep. One animal was housed per pen. The beaver were fed U.B.C. ration 16-57 in J inch pellet form. Daily records of food consumption were registered and the animals were weighed at 10 day intervals. The results of the investigation are recorded below in point form. 1. Study area 1 in Prince Albert National Park involved a beaver colony situated in a slow moving creek which was surrounded by a typical flood plain. The main tree avail-able for winter food was willow (Salix sp.). A great abund-ance of lush vegetation was present as a source of summer food. The 1958 winter feed bed for the colony of six beaver measured 38 X 17 X 7 feet and was composed by numbers of 91 per cent willows, 5 per cent aspen (Populus tremuloides), and 4 per cent black poplar (Populus balsamifera). 2. Area 2 in Prince Albert National Park was a slow moving creek at the bottom of a shallow ravine. In most places the slope of the ravine ran right to the edge of the creek. The feed bed for the 1958 winter was 60 X 15 X 7.5 feet in size and supported eleven beaver throughout the winter. It was composed by numbers of 55 per cent willow, 25 per cent aspen, and 20 per cent black poplar. 3. Beaver growth in the wild is divided into two phases, summer and winter. The summer coincides with the ice free period and the v/inter the period when beaver are dependent upon their stored food as the only source of energy. The average absolute growth rate was calculated for the summer as the 93 weight at l a s t capture i n the f a l l minus the weight at f i r s t capture i n the spring divided by the time, i n t e r v a l i n days between captures. For the winter rate the weight at l a s t capture i n the f a l l was subtracted from the weight at f i r s t capture i n the spring. 4« Beaver were grouped into age classes as follows: beaver were k i t s through t h e i r f i r s t winter and became yearlings the following spring. They were yearlings through to the end of their second winter. S i m i l a r l y , two year olds became three year olds i n the spring aft e r their t h i r d winter. 5. Average absolute growth rates were calculated f o r the various seasons within each age class on the two areas. K i t s on area 2 grew during the winter at an average rate of .029 pounds per day. No data were available for k i t s on area 1. The summer rate of growth f o r yearlings on the two areas showed no s i g n i f i c a n t difference*, an average rate of .071 pounds per day on area 1 and .099 pounds per day on area 2. The rate of growth of yearlings during the winter was -.013 on area 1 and .025 on area 2 which resulted i n s i g n i f i c a n t l y heavier two year old beaver on area 2_ i n the spring. The summer growth of two year olds was .072 and £>65 pounds per day on area 1 and 2 respectively. The compensatory growth of the beaver on area 1 resulted i n beaver of equal weight on both areas for two year olds i n the f a l l . Two year olds on area 1 l o s t weight during the winter while a s l i g h t gain was recorded on area 2. The average absolute rate of growth decreased as the beaver * see text became larger. 6. Studies on food consumption and growth of experimental beaver resulted in an estimate of maintenance requirements of beaver. Using the Missouri equation for basal energy requirements as a starting point, a formula was derived that related maintenance to body weight in beavers 0 7^ Maintenance requirements / n Q l o \= 1.9 X 70.5 W/7 „ \ ^oais.) ^Kgms.} It was found that smaller beaver were more efficient at turning food intake into weight gain. A 16 pound beaver obtained .172 pounds of gain per pound of digestible Calorie intake. Similarly, a 20 pound beaver derived a .161 pound gain. A total of 4530 digestible Calories above maintenance was required for each pound of gain in beaver. 7... The average willow branch stored in the feed beds in Prince Albert National Park contained 539 digestible Calories. Similarly the average aspen contained 3162 and the black poplar 3018 digestible Calories. 8. It was estimated that the colony of six beaver on area 1 required 1.15 digestible mega Calories for maintenance for the period from October 15, 1958 to May 1, 1959. The eleven beaver on area 2 required 1.85 digestible mega Calories for the same period. 9. The beaver on area 2 showed a total of 64 pounds gain during the winter. This represented an energy requirement of 290,000 digestible Calories. The total energy required by beaver on area 2 for the winter was 2.14 digestible mega Calories., Using the outside measurements and composition of the feed bed and the average number of digestible Calories per log in 95 the feed p i l e , i t was estimated that the energy was supplied by 1264 branches: 695 willows, 316 aspen, 253 black poplar. I t was assumed that willows were packed i n the feed bed twice as densely as the other species. 10. I t was assumed that the branches i n the area 1 feed p i l e were packed at the same density as i n area 2. Prom the outside measurements and composition of the feed bed and the density of each type of branch i n the p i l e i t was c a l -culated that the area 1 feed bed contained 1125 branches: 1024 willows, 56 aspen, and 45 black poplar. This supplied 864,000 dig e s t i b l e Calories but f o r maintenance i t was previously estimated that the colony required 1.15 digest-i b l e mega Calories. Because of this shortage of energy the beaver on area 1 l o s t a t o t a l of 20 pounds during the winter. 11. The i n t r i n s i c pattern of beaver growth i s characterized by a rapid increase during the summer months followed by a l e v e l i n g of the weight-time curve. The break i n the growth rate i s a r e s u l t of an inherent decrease i n food consumption. The timing of this mechanism i s unknown, but certain specu-l a t i o n s were made. Experimental beaver 1 grew at an average rate of .090 pounds per day u n t i l the break around January 10 and thereafter grew at a rate of .015 pounds per day. Beaver 3 showed corresponding gains of .096 and .007 pounds per day. 12. Organ weights were regressed against body weight by the simple allometric equation. The equation was calculated from a log-log plot of the data. Liver, kidney, and heart 96 weight before maturity a l l increased with a f r a c t i o n a l power of body weight (0.91, 0.83, 0.49 re s p e c t i v e l y ) . Mature beaver showed a 1.33 per cent increase i n heart weight with a 1 per cent increase i n body weight. 13. The hind foot length of beaver was regressed against body weight and circumference of furred part of t a i l f o r a series of Type D data. The hind foot length and body weight were related by the equation: Hind f o o t ( i n s - ) = .055 W ^ J . , The circumference of the base of t a i l and hind foot showed a near unity r e l a t i o n s h i p , i n d i c a t i n g that both had attained about the same percentage of adult size at b i r t h . The circumference of t a i l , however, showed great variations i n size depending upon the plane of n u t r i t i o n while the hind foot length did not. 14. I f hind foot length was independent and body weight dependent upon the plane of n u t r i t i o n then a comparison of the r e l a t i o n -ships of the two attributes between beaver caught i n the spring ( r e l a t i v e l y poor condition) and those caught i n the f a l l (good condition) should res u l t i n a s i g n i f i c a n t l y higher allometric l i n e for the f a l l beaver. No s i g n i f i c a n t difference was found betv/een the two l i n e s . The reason for the deviation from expected was a large measurement error as well as the inadequacy of Type D data. 15. A condition f a c t o r , R, was calculated f o r beaver on the two study areas f o r both summer and winter. R = f2 M-^  = increase i n weight r e l a t i v e to hind - foot length hTJ h f 1 97 A 2 X 2 f a c t o r i a l analysis was carried out on the following, mean R values: area 1 summer = .829; area 1 winter = -.445; area 2 summer = .606; area 2 winter = .892. A l l s i g n i f i c a n t comparisons were a resu l t of the low value f o r area 1 winter. 16. Analyses were carried out on fourteen beaver l i v e r s collected during 1959. The mean chemical composition was as follows: water 67.6%; dry matter 32.4%; on a dry basis:-fat 10.4%; protein 62.8%; ash 3.9%; moisture 3.1%; nitrogen free extract 19.8%. 17. It was found that the f a t content of the l i v e r varied inversely as the water content. This had been reported for other animals. 18. No progressive change of l i v e r composition was evident with a change of the animals' condition. Spring animals had the same r e l a t i v e chemical composition as those k i l l e d i n the f a l l . A regression of dry f a t - f r e e l i v e r weight and body weight showed a very high correlation but f o r three points. Those three were omitted from the cal c u l a t i o n of li n e of best f i t . Liver w e i g h t ( g m a - ) = 6.56 body w e i g h t ( k g m s < ) + 8.23 r = .991 I f the beaver are similar to the r a t and can deplete 40% of the l i v e r protein for emergency conditions then the beaver studied would be able to survive for three days on their l i v e r protein store (range 2-4 days). 19. The reproductive rate of beaver from Elk Island National Park, Alberta i n 1958 was compared to that of Prince Albert National Park i n 1954, 1956, 1957, 1958, 1959. Both areas have an aspen forest type of vegetation. Beaver have reached a population peak i n Prince Albert Park and consequently have f i l l e d a l l the available habitats and, i n f a c t , have reduced the quality of them by using most of the available aspen. Elk Island Park supports a beaver population which i s i n a state of rapid increase as none of the environmental factors have as yet become l i m i t i n g . Large amounts of aspen abound along the waterways. 20. A s i g n i f i c a n t c o r r e l a t i o n was found between size of the female and the number of young produced i n the beaver studied. They were related by the equation: Number of young i n l i t t e r = .124 weight of female - 1.66 The Elk Island Park beaver had more young per l i t t e r than the beaver from Prince Albert Park. 21. A s i g n i f i c a n t difference i n number of young per l i t t e r was found between Elk Island Park 1958, and a l l years studied i n Prince Albert Park. No difference was found between the & d i f f e r e n t years i n Prince Albert Park.* 22. No difference was found i n the number of i n f e r t i l e female beaver i n the two parks - about 30 per cent i n each. It was concluded that the adequacy of an environment can be measured i n terms of the success of the animals l i v i n g upon i t . The success could be measured by the number of animals supported by the area or the condition of each animal. Usually the two factors cannot be separated and the better habitats support more animals with better condition, growth rate, etc. than the poorer areas. Asdell and Cromwell (1935) have shown * see text 99 that neither growth nor sexual a c t i v i t y takes precedence over the other, thereby making either attribute an equally good measure of success. Beaver i n a population that i s rapidly expanding i n numbers show a higher reproductive rate than otherwise. I t i s suggested that the reason f o r this phenomenon i s a greater number of ova shed at each ovulation due to the better n u t r i t i v e state of the animals. It was further concluded that the qua l i t y and quantity of the winter food i s the major factor a f f e c t i n g the success of beaver i n Prince Albert National Park and i n Elk Island National Park. 100 LITERATURE CITED Addis, T. , L . J . Poo, and W. Lew. 1936. Protein loss from liver during a two day fast. J . Biol . Chem. 115(1): 117-118. 1936a. The quantities of protein lost by the various organs and tissues of the body during a fast. J . Biol . Chem. 115(l)s 111-116. Asdell, S.A. and M.P. Crowell. 1935. The effect of retarded growth upon the sexual development of rats. J . Nutrition 10: 13-24. Association of Official Agricultural Chemists - Official methods of analysis, 7th Ed. , A.O.A.C. Wash. D.C. , 1950. Bandy, P.J. 1955. Studies of growth and nutrition in the Columbia black-tailed deer (Odocoileus h. columbianus). Master's thesis, University of British Columbia. — , i . McT. Cowan, W.D. Kitts, and A.J . Wood. 1956. A method for the assessment of the nutritional status of wild ungulates. Can. J . Zool. 34: 48-52. Benedict, E.G. and F.B. Talbot. 1921. Metabolism and Growth from Birth to Puberty. Carnegie Inst, of Wash. Bradt, Glen W. 1939. Breeding habits of beaver. Jour. Mamm. 20(4): 486-489. 1947. Michigan Beaver Management. Game Division, Mich. Dept. Cons., Lansing, Mich. Brandborg, S.M. 1955. Life History and Management of the Mountain Goat in Idaho. State of Idaho, Dept. Pish and Game Wildlife Bull . No. 2. Brody, S. 1927. Growth and development. I l l Growth rates, their evaluation and significance. Univ. Mo. Agr. Exp. Stat. Res. Bull . 97. . . 1945. Bioenergetics and Growth. Reinhold Publishing-Co. , New York. Buckley, John L. and W.L. Libby. 1955. Growth rates and age determination in Alaskan beaver. Trans. N.A. Wildl. Conf. 20: 495-505. Clarke, S.E. and E.W. Tisdale. 1945. The chemical composition of native forage plants of southern Alberta and Saskatchewan in relation to grazing practices. Dept. Agric. Tech. Bull . 54. ' Cowan, I. McT., W.S. Hoar and J . Hatter. 1950. The effect of forest succession upon the quantity and upon the 101 n u t r i t i v e values of woody plants used as food by moose. Can. J . Research 28(5): 249-271. Cowan, I. McT. , A.J. Wood, W.D. K i t t s . Peed requirements of deer, beaver, bear, and mink f o r growth and maintenance. Trans. M.A. Wi l d l . Conf. 1957. 179-188. Crampton, E.W. (ed.). 1959. Joint United States and Canadian Tables of Peed Composition. National Academy of Sciences, N.R.C. Publ. 659. Currier, A.A. 1958. A preliminary study of ce l l u l o s e digestion i n the beaver (Castor canadensis). Master's thesis, University of B r i t i s h Columbia. Deuel, H.J. J r . 1955. The L i p i d s . Vol. I I : Biochemistry Digestion, Absorption, Transport and Storage. Inter-science Publishers, Inc., N.Y., London. . , Li'P. Hallman and S. Murray. 1937. Studies on ketosis. XL The r e l a t i o n of f a t t y l i v e r s to f a s t i n g ketonuria i n the r a t . J . B i o l . Chem. 119(1): 257-268. Eckles, CH. and W.W. Swett. 1918. Some factors influencing the growth of dairy h e i f e r s . Univ. Mo. Agr. Exp. Stat. Res. B u l l . 31. P i t t , A.B. 1941. Seasonal Influence on Growth, Punction and Inheritance. N.Z. Council f o r Educational Research. Plook, D.R. 1957. A e r i a l census of beaver colonies, Prince Albert National Park, Sask. Report to Canadian W i l d l i f e Service, Ottawa, Ont; . 1958. A e r i a l census of beaver colonies, Prince Albert National Park, Sask. Report to Canadian W i l d l i f e Service, Ottawa, Ont. . 1959. A e r i a l census of beaver colonies, Prince Albert National Park, Sask. Report to Canadian W i l d l i f e Service, -Ottawa, Ont. Polley, S.J. 1949. Nut r i t i o n and female f e r t i l i t y . B r i t . Jour. Nut. 3: 91-96. H a l l , E.R. 1928. Notes on the l i f e history of the sage brush meadow mouse (Lagurus). Jour. Mamm. 9(3)J 201-204. Hamilton, W.J. J r . 1939. American Mammals. McGraw-Hill Co. N.Y. & London. Hammond, J . 1949. Physiology of reproduction i n r e l a t i o n to n u t r i t i o n . B r i t . Jour. Nut. 3:79-83. 102 Hammond, J . 1955. The effects of nutrition on f e r t i l i t y in animal and human populations. In "The Numbers of Man and Animals" ed. Cragg & Pirie; Oliver & Boyd. Harper, F. 1955- The Barren Ground Caribou of Keewatin. Univ. Kansas Press. Hodgdon, K.W. and J .H. Hunt. 1955. Beaver Management in Maine. Game Division Bull . ; 3.. State of Maine Department of Inland Fisheries and Game. Joubert, D.M. 1954. The influence of winter nutritional de-pressions on the growth, reproduction and production of cattle. Jour. Agric. Sci . 44(1): 5-60. Kavanagh, A.J . and O.W. Richards. 1942. Mathematical analysis of the relative growth of organisms. Proc. Rochester  Acad. Sci . 8: 150-174. Krebs, C.J. 1959. Growth studies in the reindeer (Rangifer tarandus) with an analysis of population changes in the MacKenzie Delta herd over the period 1938-1958. Master's thesis, University of British Columbia. LeCren, E.D. 1951. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch (Perca  f l u v i a t i l i s ) . Jour. Animal Ecol. 20(2): 201-219. Loeb, Leo. 1917. The concrescence of fol l ic les in the hypotypical ovary. Biol . Bull . 33(3): 187-195. Luck, J.M. 1936. Liver proteins. I. The question of protein storage. J . Biol . Chem. 115(2): 491-510. Maynard, L.A. and J.K. Loosli. 1956. Animal Nutrition. McGraw-Hill Book Co. New York, Toronto, London. Miller , R.F. , G.H.* Hart and H.H. Cole. 1942. Fert i l i ty in sheep as affected by nutrition during the breeding season and pregnancy. Bull . Calif . Agric. Exp. St.. No. 672. Minot, C S . 1908. The Problem of Age, Growth, and Death. New York. Osborn, D.J. 1953. Age classes, reproduction, and sex ratios of Wyoming beaver. Jour. Mamm. 34: 27-44. Parker, R.P. and P.A. Larkin. 1959. A concept of growth in fishes. J . Fish. Res. Bd. 16(5): 721-745. Parkes, A.S. (ed.). 1952. Marshall's Physiology of Reproduction Vol. II. Longmann and Green Co., London, N.Y., Toronto. 103 Provost, Ernest E. 1958. Studies on reproduction and population dynamics i n beaver. Ph.D. thesis, State College of Washington. 85 pp. Radvanyi, A. 1956. A e r i a l census of beaver colonies, Prince Albert National Park, Saskatchewan. Report to Canadian W i l d l i f e Service, Ottawa, Ontario. Scheffer, V.B?. 1955. Body size with r e l a t i o n to population density i n mammals. Jour. Mamm. 36(4): 493-515. Simpson, S. 1924. The effect of thyroidectomy on growth i n the sheep and goat as indicated by body weight. Quart. Jour. Exp. Physiol. 14(1): 161-183. Stephenson, A.B-. 1956. Preliminary studies on growth, n u t r i t i o n , and blood chemistry of beavers. Master's thesis, University of B r i t i s h Columbia. Taber, R . D i and R.P. Dasmann. 1958. The Black-tailed Deer of the Chapparal. Game B u l l . 8. State of C a l i f o r n i a , Dept. of Pish and Game. Tener, J.S. 1954. A e r i a l census of beaver colonies, Prince Albert National Park, Saskatchewan. Report to Canadian W i l d l i f e Service, Ottawa, Ontario. . 1955. A e r i a l census, of beaver colonies, Prince Albert National Park, Saskatchewan. Report to Canadian W i l d l i f e Service,'Ottawa, Ontario. von Bertalanffy, L. 1949. Problems of organic growth. Nature 163: 156-158. Walton, A. 1949. Spermatogenesis and n u t r i t i o n . B r i t . Jour. Nut. 3: 83-86. Williams, H.H.,'N; Galbraith, M. Kaucher, E.Z. Moyer, A.J. Richards and I.G. 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