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Flight speeds and energetics of seven bird species Kolotylo, Rebecca Ann 1989

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FLIGHT SPEEDS A N D ENERGETICS OF S E V E N BIRD SPECIES  By REBECCA ANNKOLOTYLO  B.Sc, The University of British Columbia, 1987  A THESIS S U B M I T T E D  IN PARTIAL F U L F I L L M E N T O F  THE REQUIREMENTS  FORTHE DEGREE OF  MASTER OF SCIENCE  in THE FACULTY OF GRADUATE  STUDIES  ( D e p a r t m e n t of Zoology)  We accept this thesis as conforming to the required standard  T H E UNIVERSITY  OF BRITISH  COLUMBIA  A u g u s t 1989  © Rebecca Ann Kolotylo, 1989  In presenting this thesis degree  at the  in partial fulfilment  of the  requirements  for an advanced  University of British Columbia, I agree that the Library shall make it  freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes department  or  by  his  or  her  may be granted  representatives.  It  is  by the  understood  that  head of my copying  or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department of The University of British Columbia Vancouver, Canada  DE-6 (2/88)  ABSTRACT Flight speeds of seven bird species, the Tree Swallow (Tachycineta bicolor), Mountain Bluebird (Sialia currucoides), White-throated Swift (Aeronautes saxatalis), European Starling (Siurnis vulgaris), Black Tern (Chlidonias nigra), Pigeon Guillemot (Ceppkus columba), and Red-necked Grebe (Podiceps grisegna), were recorded using a Doppler radar handgun. Velocities were measured of adult birdsflyingto and from foraging areas while rearing young, and totalled 1178 records. Morphological measurements were also made on some of the species and were used, along with literature values, to construct curves of estimated total power required for flight versus flight velocity for each species. The mean observed flight speed, V b , for each species was then compared to the minimum power 0  s  speed, V m p , and the maximum range speed, V , on the power curve. For five of the mr  seven study species, the V b was significantly greater than V , and thus appeared to be 0  e  mr  independent of morphology, foraging methods and habitats. The V bs of the other two 0  species was found to be between V  mp  and V  mr  for the Pigeon Guillemot and less than V  mp  for the Red-necked Grebe. In a more detailed study of the Tree Swallow and the Mountain Bluebird, V b was 0  s  determined to be fairly constant over the recording period. Individual power curves were constructed for five female Mountain Bluebirds and three female Tree Swallows, since both morphological measurements andflightspeeds were recorded for these individuals. In each case, V be was significantly greater than V mr . For the bluebird, it was also found that the 0  number of visits to the nest per hour per nestling did not appear to increase with the age of the nestling. The rate of feedings, however, was quite variable for both the Tree Swallow and Mountain Bluebird. By setting the observedflightspeed, V b , equal to. a predicted 0  e  optimal speed, V t, the net rate of energy gain during foraging by the parents could be op  determined. Comparing this energy gain with estimates of nestling energy requirements for both species resulted in the conclusion that the observed speed could not be the same as the optimal speed, and that in order to meet nestling requirements, the parents may increase their feeding rate during other parts of the day not under observation.  ii  TABLE OF CONTENTS ABSTRACT  ii  LIST O F T A B L E S  iv  LIST O F F I G U R E S  vi  ACKNOWLEDGEMENTS  viii  CHAPTER ONE GENERAL INTRODUCTION  1  CHAPTER TWO OBSERVED VERSUS PREDICTED FLIGHT SPEEDS 2.1 Introduction  13  2.2 Materials and Methods  15  2.3 Results  28  2.4 Discussion  51  CHAPTER THREE D E T A I L E D OBSERVATIONS OF T W O SPECIES 3.1 Introduction  55  3.2 Materials and Methods  59  3.3 Results  62  3.4 Discussion  76  CHAPTER FOUR G E N E R A L DISCUSSION A N D CONCLUSIONS 4.1 General Discussion  89  4.2 Conclusions  92  REFERENCES  93  APPENDIX  102  iii  LIST OF TABLES TABLE I. Radar Calibration  19  TABLE II. Morphological Measurements  23  TABLE III. Power Curve Input Values  27  TABLE IV. Results Of Flight Speed Measurements  29  TABLE V. Comparison Of Observed And Predicted Speeds  41  an  TABLE VI. Values of C£>( ra) d Cl>(pro) Required To Accept The Null Hypothesis H : V = V  42  TABLE VII. Summary Statistics For Measurement Groups And One-Way ANOVA Between Groups  43  pa  0  obs  mr  TABLE VIII. Tukey Test Results For Tree Swallow, White-throated Swift, Pigeon Guillemot  44  TABLE IX. Two-Way ANOVA Test Results For Mountain Bluebird, Tree Swallow  46  TABLE X. Mann-Whitney Test Results For Black Tern  47  TABLE XI. Previously Recorded Flight Speeds  53  TABLE XII. Individual Female Power Curve Input Values  61  TABLE XIII. Summary Of Nest Visits For The Mountain Bluebird And Tree Swallow  63  TABLE XIV. Regressions Of Nestling Age Versus Adult Flight Speed And Visits To The Nest (For All Bluebird Nests)  68  TABLE XV. One-Way ANOVA Test Results For Differences Between Flight Speed Recording Days  72  iv  TABLE XVI. Comparisons Of Observed Speeds With Predicted Speeds For Individual Female Birds TABLE XVII. Mountain Bluebird Nestling Energy Requirements  73  .84  TABLE XVIII. Tree Swallow Nestling Energy Requirements  85  TABLE XIX. Comparisons Of Nestling Energy Expenditure For One Nestling  86  v  LIST OF FIGURES FIGURE 1. Map of Study Locations  18  FIGURE 2. Wing Shapes And Aspect Ratios  25  FIGURE 3. Flight Speed Frequency Histograms  31  FIGURE 4. Tree Swallow Power Curve  33  FIGURE 5. Mountain Bluebird Power Curve  34  FIGURE 6. White-throated Swift Power Curve  35  FIGURE 7. European Starling Power Curve  36  FIGURE 8. Black Tern Power Curve .  37  FIGURE 9. Pigeon Guillemot Power Curve  38  FIGURE 10. Red-necked Grebe Power Curve  39  FIGURE 11. Flight Speed Versus Time Of Recording For The Mountain Bluebird  49  FIGURE 12. Flight Speed Versus Time Of Recording For The Tree Swallow  50  FIGURE 13. Age Of Young Versus Feeding Rate For All Bluebird Nests  66  FIGURE 14. Age Of Young Versus Feeding Rate For Individual Bluebird Nests  67  FIGURE 15. Age Of Young Versus Adult Flight Speed For AU Bluebird Nests  70  FIGURE 16. Age Of Young Versus Adult Flight Speed For Individual Bluebird Nests  71  vi  FIGURE 17. Mountain Bluebird Growth Curve..  75  FIGURE 18. Determination of P the Mountain Bluebird  78  gain  FIGURE 19. Determination of P the Tree Swallow  ga  in  for  for •  vii  79  ACKNOWLEDGEMENTS I would like to thank my supervisor, Dr. R. W. Blake, for his advice and support, as well as my committee members, Dr. L. Gass and Dr. J. Gosline, for their helpful comments. I would also like to thank Anna Roberts and my family for assistance in the field work at the Cotton Ranch and Clive Welham for the data on Black Terns. I would like to thank everyone in the Animal Locomotion Lab for their assistance over the past two years, especially Horacio de la Cueva and Mrigesh Kshatriya for their help in analysis. I also appreciate the help of Alistair and Joerg at the B.D.C.. I am grateful to the Riske Creek Cattle Company for allowing me to work on the Cotton Ranch and to the Creston Valley Wildlife Management Area, the Scout Island Nature Centre, the Burke Museum at the University of Washington, the Vertebrate Museum (Dick Cannings) at UBC, and to Alice Cassidy and Wes Hochachka for their help on Mandarte Island.  viii  CHAPTER GENERAL  ONE  INTRODUCTION  Bird flight can be studied using many different approaches, including investigations of anatomy, morphology, and physiology. General principles of avian morphology (including the evolution of flight, the central nervous system, the cardiovascular system, the respiratory system, and structural adaptations for flight) are discussed by King and King (1979) and a general discussion on energy expenditures and intakes can be found in Wolf and Hainsworth (1978). Detailed analysis of the anatomy involved in locomotion can be found in Raikow (1985). The metabolic costs of flight have been studied extensively by Tucker (1968, 1972, 1973) and others (e.g. Bernstein et al, 1973; Torre-Bueno and Larochelle, 1978; Hails, 1979; Hails and Bryant, 1979; Bryant and Westerterp, 1980; Flint and Nagy, 1984; Westerterp and Bryant, 1984; Rothe and Nachtigall, 1985; Rothe et a/., 1987). Respiratory mechanics, gas exchange, circulation, temperature regulation, water loss and energy turnover in migratory flights are discussed by Berger and Hart (1974). Specific classification of avian muscles and muscle fibre types can be found in George and Berger (1966) and Rosser and George (1986). The aerodynamic approach concentrates mainly on how physical design influences the cost of flight. Early work on flight mechanics was mainly descriptive (e.g. Brown, 1948, 1953). Estimations of the varing aerodynamic costs of flight with changing flight speeds come from the momentum jet theory (Pennycuick, 1968a,b, 1969, 1975, 1989) as well as from the vortex theory (Rayner, 1979a,b,c). Records of flight speeds range from early estimates using speedometers in automobiles and airplanes (Cooke, 1933; Meinertzhagen, 1955) to more accurate measurements using ornithodolites (Pennycuick, 1987) and radar (Schnell 1965, 1974; Schnell and Hellack 1978, 1979; Blake et ai., 1989). The speed at which a bird flies depends upon the reason for the flight as well as environmental conditions such as food supply, time, and predation risk. Curves of the aerodynamic power required for flight versus flight velocity indicate optimal speeds in 1  particular circumstances, but collections of flight speed data (Gill, 1985; McLaughlin and Montgomerie, 1985; Rayner, 1985b; Pennycuick, 1987; Blake et ai., 1989, and others) indicate a pattern of flight speeds that is, as yet, unclear. The objectiveof this study is to compare a large sample of flight speed data from a range of bird species under similar conditions to predicted speeds. Chapter Two will compare observed flight speeds of seven species to optimal speeds derived from power curves, while Chapter Three will concentrate on two of the species.  A. P R I N C I P L E S O F P O W E R E D F L I G H T  Flight can be categorized into several modes - passive flight, powered forward flight, and hovering. Passiveflight,which includes gliding and soaring, involves minimal wing movement and is thus a low cost form of locomotion (Pennycuick 1971, 1972, 1982). This type offlightis common in larger birds such as albatrosses, eagles, vultures and gulls as well as others with opportunities to exploit updrafts, thermals, or winds (Pennycuick, 1971, 1972, 1982). Intermittentflightinvolves bothflappingand non-flapping flight (Rayner, 1977, 1985a). Bounding intermittent flight is found mainly in small birds while undulating intermittentflightis employed by larger birds such as woodpeckers, gulls, and crows (WardSmith, 1984a,b). Other patterns offlightinclude formation flight (Hummel, 1983) and flying in ground effect (Withers and Timko, 1977; Blake, 1983, 1985). Steadyflappingflight requires more energy input than passive flight in terms of aerodynamic power. There have been many attempts to describe the aerodynamic power required for flight (Pennycuick 1968a,b, 1969, 1975, 1989; Tucker, 1973; Greenewalt, 1975; Rayner, 1979a,b,c). Pennycuick (1968a,b, 1969) developed the momentum jet theory, which has been modified several times (Tucker, 1973; Pennycuick, 1975, 1989). Greenewalt (1962, 1975) based his approach toflighton scaling techniques and comparisons between groups offliers(passerines, non-passerines, hummingbirds, shorebirds, waterfowl, bats and insects).  2  In this study, aerodynamic power required for flight has been determined based mainly on the model developed by Pennycuick (1968a,b, 1969, 1975, 1989). Aerodynamic power can be divided into four components; parasite power P power Pi d and basal metabolic power,  profile power P  ,  pro  induced  Parasite power overcomes the pressure drag  Pmet-  n  ra,  pa  and skin friction of the bird's body, which increases with increasing flight velocity. It can be written as:  Ppara = ^pV* A C { ara) p  where p, V, A , and p  a r e  Cr>( ra) pa  D  P  (1)  air density (kgm~ ), forward flight velocity of the z  2  bird (ms~ ), frontally projected area of body (m ), and the parasite drag coefficient, 1  respectively.  P r pa  a  is measured in Watts  (W).  The frontally projected area of the body can be determined if the diameter of the body at its widest point is known, using  (2)  A = <- )  2  P  2  where d is the body diameter at widest point (m). Alternatively, A can be determined by p  2 3  A = 0.00813M / p  (3)  Pennycuick (1989, program 1), where M is the body mass (kg). The parasite drag coefficient, Cr)(  c a n D e pa  r )i a  number, R , of the body; e  3  estimated based on the Reynold's  where I is a characteristic length, V is the free stream velocity, and fi is the viscosity of the fluid. R can be estimated as e  1 2  R = 125000M /  (5)  e  (Pennycuick, 1989). If the body Reynold's number is less than 50,000, timated as 0.4. If R  e  >  200,000,  C ( a) D  is  par  Cr)( ra) pa  taken to be 0.25 (Pennycuick  Pennycuick, 1989). Values of R between 50,000 and 200,000 result in a Cr)( e  et al, a)  par  is es-  1988,  according  to  C ( ara) D  Profile power,  P -, pro  is  P  = 1-57 - (0.108lnR )  (6)  e  the power required to overcome the profile drag of the wings  and is proposed to be constant by Pennycuick, (1969, 1975, 1989). Other approximations (Ward-Smith, 1984a,b Rayner, 1979a,b,c, Tucker, 1987) indicate that profile power increases with velocity, resulting in  Ppro = -^Py S C ( )  (7)  3  w  where S and Cry( ro) w  P  a r e  D  pro  2  the wetted surface area of the wings (TO ) and the profile drag  coefficient respectively. The profile drag coefficient is generally estimated to be about 0.02 (Rayner, 1979c). Induced power is the power required to overcome the weight of the bird (drag due to lift). This power requirement decreases with increasing flight velocity, as less energy is required to stay airborne at higher speeds. Induced power can be expressed as  1.2L  4  2  where b is the wingspan (m), 1.2 the aerofoil efficiency factor, and L, the lift, can be determined by  L = [(Mg) + (±A C 2  p  V)}>  (9)  2 2 1  Dipara)  _2  (Pennycuick, 1989), where g is the gravitational constant of 9.81ra,s . The basal metabolic power,  P  me  i,  is given by  0 724  0.23(6.25M - )  P  m e i  =  P  m e t  = 0.23(3.79M - )  (10)  for passerines and  0 723  (11)  for non-passerines (Lasiewski and Dawson, 1967). The term of 0.23 is a conversion efficiency to convert chemical energy to mechanical work (Pennycuick, 1975). The total aerodynamic power requirement,  Ptot  =  Pt t,  l-l(Ppara + Ppro +  0  can be written as  Pind + Pmei)  (12)  The factor of 1.1 accounts for the costs of respiration and circulation (Tucker, 1973; Pennycuick, 1975, 1989). The total power,  Ptot?  is a characteristically U-shaped curve. The minimum point  on this curve is termed the minimum power speed, V . A bird should fly at V if mp  mp  its objective is to stay airborne for as long as possible (least cost per unit time). The maximum range speed, V mr , is given by a tangent to the curve passing through the origin. The maximum range speed is optimal for travelling long distances (least cost per unit distance). 5  Noting that coefficients of drag and lift are a source of uncertainty in the momentum jet theory, Rayner (1979a,b,c) proposed a quasi-steady vortex ring theory as an alternative in describing hovering and forward flight. This method involves the distribution and kinetic energy of vortices left in the wake of the body and wings.  Induced power is defined  as the mean rate of increase of kinetic energy in the wake, and does not involve lift or induced drag coefficients. Profile power is based on parameters of the downstroke (stroke period, downstroke ratio, stroke amplitude, angular position of the wing). Parasite power is estimated using an indicator of size as well as drag coefficients, based on the body angle. Again, the summation of these three aerodynamic power equations gives a U-shaped curve. More recent work on wake vortices includes studies by Spedding et ai. (1984), and Spedding (1987a,b). A theoretical maximum amount of energy can be supplied to the flight muscles (WeisFogh and Alexander, 1977) for sustained flight, and can be expressed as  P The corresponding V  max  = 250(0.17M°- ') 9  max  (13)  can be determined from the power curve, and is thus the maximum  flight speed available to the bird. The stalling speed of a bird, V n, can also be determined. The stalling speed is the eta  velocity at which flow separation occurs on the top surface of the wing, causing a sudden decrease in lift and increase in drag. V t ii can be defined as a  . where C £ (  m a z  V.  tM  a  =(  2 c  M  \  )\  (14)  ) is the maximum lift coefficient.  Plots of power required for flight versus flight velocity based on metabolic studies have tended to be rather flat (Tucker, 1972; Bernstein et al., 1973; Torre-Bueno and Larochelle, 1978; Berger, 1985), although some recent work (Rothe et al., 1987) has resulted  6  in U-shaped power curves. Independent approaches to estimating the mechanical power requirements for flight (momentum jet, vortex theories) have resulted in U-shaped curves, and are based on sound aerodynamic principles. The relationship between muscle efficiency andflightvelocity has not been studied. This is unfortunate because it may provide insights on the difference between mechanical and metabolic power necessary for flight.  B. HISTORY OF F L I G H T SPEED R E C O R D S  Birdflightvelocities have been measured for many years and the speeds at which birds fly has interested many biologists. Speeds have been recorded using various methods, many of which are inaccurate and unreliable. Early attempts at estimating flight speeds produced -1  some results that are difficult to believe, such as a 200mph (90m,s ) record for a swift (Chaetura) by Stuart-Baker (in Meinertzhagen, 1955). Early collections offlightrecords (e.g. Cooke, 1933; Cottam et al, 1942; and Meinertzhagen, 1955) include observations made by automobile speedometers, theodolites, airspeed indicators of airplanes, homing experiments, trains, kites, stopwatches, rangefinders, and estimations from ships and mailboats. Most measurements were made without reference to wind speed and direction or to environmental conditions, although in some cases (Broun and Goodwin, 1943), wind speeds and directions were measured withflightspeeds, but the records remained merely as published lists. As well, many records were obtained by "chasing"a bird with a vehicle, which resulted in an estimation of a maximum flight speed, not of normal routineflightactivity. Flight speed records obtained using such methods are generally unreliable estimates and the sample number is usually low, because of the time required to measure the speeds. The use of stopwatches over a known distance, however, is still a common method (e.g. Bryant and Turner, 1982; Gill, 1985; McLaughlin and Montgomerie, 1985; Tatner and Bryant, 1986). Many studies have been conducted using wind tunnels to evaluate birdflightand its costs (Pennycuick, 1968a,b; Tucker, 1968, 1972; Bernstein et al., 1973; Torre-Bueno and Larochelle, 1978). Flight in wind tunnels may involve air turbulences and distortions due 7  to interference with tunnel walls, redistribution of a bird's shape and weight while wearing a respiratory mask, and also lacks natural wind currents and any environmental cues a bird would normally experience. The flight pattern of a pigeon in a wind tunnel, for example, varies from that of a free flying bird (Butler et al, 1977). The duration of wing flapping periods in free-ranging pigeon flights was found to be longer than in wind tunnel flights. As well, take-off and landing kinematics differed between wind tunnel and free-ranging flights. Although wind tunnel studies may establish a range of velocities at which a particular bird willfly(for example, Torre-Bueno and Larochelle, 1978), they do not necessarily reflect naturalflightvelocities. Lanyon (1962) introduced the Doppler radar unit into thefield,which has been used extensively (Schnell, 1965, 1974; Schnell and Hellack, 1978, 1979). Schnell's equipment consisted of afive-partsystem, including a transmitter, transmitting antenna, a mixer to compare reflected and transmitted waves, and a receiver. This radar unit was calibrated to 2 miles per hour intervals. Recording flight velocities via Doppler radar is a rapid way to collect a large sample size (Blake et ai., 1989). Schnell (1965) notes that he recorded more flight speeds in two summers than the total number that had previously been recorded in the literature. Rayner (1985b) also suggests that Doppler radar is probably the best method to obtainflightspeed records. As well as recording accurate speeds of birdsflyingparallel to the unit, doppler radar records speeds at angles ±20° to the gun that are not significantly different from the true speeds found when the angle is corrected for (Schnell, 1965; Blake et ai., 1989). A more portable doppler radar unit, such as the modified radar handgun used by Blake et ai. (1989) is easier and more convenient to use than Schnell's unit, because it can be easily aimed at a particular bird rather than waiting for one toflyin parallel to it. As well, at angles greater than or equal to 30° , objects of the size of birds are not detected by the radar handgun, and thus almost all speeds recorded can be assumed to be not significantly different from the bird's true speed.  8  C. F L I G H T  STRATEGIES  The characteristic predicted "optimal" speeds from the power curve, V should be considered optimal only under certain conditions. V  mp  mp  and V  mT  is optimal when a bird  wants to travel for the longest amount of time on a given amount of fuel. Flight at this speed would be expected when time is not a constraint or, for example, while searching for food when the food supply is low or uncertain (Rayner, 1985b; Pennycuick, 1975). Swifts in their roosting flights at night are thought toflyat V  mp  (Pennycuick, 1987). V  mr  should  be chosen when there is an advantage to travelling the greatest distance with a set amount of fuel. For example, birdsflyingback and forth to a foraging area shouldflyat V mr , as should birds on migration (Pennycuick, 1975; Rayner, 1985b). Under other circumstances, different speeds may be considered more favourable. Norberg (1981) proposed that flight speeds of parents feeding young should be greater than Vmr in order to bring the most food to the young. Female Lapland longspurs (Calcarius lapponicus) feeding young, however, did notflyfaster than V  mr  (McLaughlin  and Montgomerie, 1985). McLaughlin and Mongomerie suggest that brood size may be a factor in determining air speed. For instance, when brood size is less than a maximum number, there may not be any advantage toflyingabove V . mr  Another reason for flying at velocities other than the characteristic speeds was proposed by Gill (1985). Gill found that Long-tailed Hermit hummingbirds (Phaethornis -1  syperciliosus)flyat an average speed of 11.6m.s between foraging sites, a value significantly greater than the V  mr  -1  value of 7.5m^ . He attributes this higher than expected  flight velocity to a gain in time savings, thereby allowing more visits toflowers(a greater energy gain) or more time for lekking activities (a reproductive gain). As well, Gill (1985) notes that there is competition forflowersso there is an advantage to arriving first. The optimum speed for travel may be that velocity which a bird can maintain the longest, and which was found to be the minimum power speed for the bat Pteropus poliocephalusflyingin a wind tunnel (Carpenter, 1985). Carpenter stated that it should  9  not be assumed than an animal's flight speed is limited only by available fuel or that a bird will fly at its least costly velocity. He proposed that if birds didflyat V  mp  it may be  because that is simply the least strenuous speed. Theflightof most Pro cell ariiformes consists of bothflappingand gliding phases, and is termedflap-gliding.Pennycuick (1987), in recent comparisons offlightbetween northern and southern seabirds, suggested that theflappingspeed offlap-glidingbirds should be reasonably efficient and close to the best gliding speed. Pennycuick determined that the averageflappingorflap-glidingvelocity of the birds recorded lay between V  and V m r ,  mp  and did not significantly optimize either speed. Kestrels (Falco tinnunculus) trained toflyin a corridor were found toflynear maximum range speed when the birds were not loaded, while when loaded with an extra 0.6iV of body weight, their flight speeds decreased to nearly the predicted minimum power speed (Videler et ai., 1988a,b). The approximately 10% decrease of flight speed with an increase in load is contrary to predictions of greater V  mp  and V  mr  with increasing mass. Videler et  ai. (1988a,b) suggest that the birds appear to change theirflightstrategy fromflyingat V  mr  to Vmp, as well as altering their wingbeat kinematics, when their load is increased. Otherflightstudies in wind tunnels (e.g. Torre-Bueno and Larochelle, 1978; Rothe  and Nachtigall, 1985) result in birdsflyingat speeds that may not necessarily be equivalent to ones chosen in the field under natural conditions. White ibises (Eudocimus albus) were found toflyat speeds above the V  mp  values but  far below V m r on their way to and from foraging sites. These observations were made with an ornithodolite system during the early breeding season, before the eggs were hatched (Pennycuick and de Santo, 1989). Blake et ai. (1989) found that barn swallows (Hirundo rustica)flewat speeds greater than V . Recorded flight speeds were divided into two groups based on flight behaviour. mr  The first group flew close to the ground (< 0.5m above ground level) and in a straight _1  line, and had a mean velocity of 8.6m6 . Theflightof the second group was > 0.5m above ground level and not as straight as the first group, and had a meanflightvelocity 10  of 6.8ms~ . 1  V (A.2ms~ ) l  mp  The means of both groups were significantly higher than the predicted and V ( 5 . 6 r a . s ) . -1  mr  The development of a biomechanical model such as the one described for flight is useful in that its predictions can be tested ecologically and may provide helpful insights into the considerations and constraints of specific ecological situations. the consequences of flying at velocities other than V  m r  In particular,  , for example, will have certain  implications for adult birds depending on their circumstances and reason for the flight. In view of the variety of results from the above mentioned studies, it appears that bird flight velocities vary in their relation to predicted velocities. The circumstances of each study, however, also vary, and most describe separate situations.  THIS S T U D Y  Most studies of bird flight speeds have been performed using only a single species with small samples, and each study carried out under different conditions.  As well,  theories leading to calculations of the minimum power and maximum range speeds may vary between studies, as will the technique of measuring the flight speed. Therefore, in terms of determining flight speeds, it would be useful if a large sample size of flight speed recordings could be collected for a range of species using only one reliable and accurate recording technique, and these speeds compared with predicted optimal speeds that were all similarily calculated. As well, the flight speeds should be collected under similar circumstances, in order to test for a particular result and compare between species and possibly within species. The above proposals are the objective of this thesis. The following two chapters describe studies of Doppler radar flight speed recordings of seven species of birds ranging in size from 20<J to 1.0kg. The flight velocities were measured during the breeding season for all birds, and under similar conditions - little or no wind, a clearflightpath, and a knowledge of the purpose of the flight. All measurements were taken using the same equipment. Chapter Two includes flight speeds recorded for all of the study species. Wing and body dimensions were either determined in the field or  11  taken from museum specimens or literature sources. These were used to calculate power curves for each species in order to compare observed and predicted speeds. Chapter Three concentrates on two of the species, for which a more detailed analysis was done. Feeding rates and adult flight speeds in relation to the age and number of nestling were recorded. Power curves were constructed for some individual birds to compare observed and predicted speeds. Nestling energy requirements were estimated and the resulting energy delivery rate compared to actual velocities.  12  CHAPTER  TWO  O B S E R V E D VERSUS P R E D I C T E D F L I G H T SPEEDS  2.1 I N T R O D U C T I O N In order to make comparisons between observed flight speeds and predicted speeds for a number of species, a specific condition was chosen to be constant for each study site, that theflightspeeds recorded would be obtained from birdsflyingto or from a foraging site while raising nestlings. Velocities were recorded with a hand held Doppler radar gun (Blake et al, 1989). In five of the seven species, large sample sizes (ranging from 100 to over 300 speeds per species) were obtained, while the other two samples were of 41 and 64 records respectively. The birds studied represent seven different Familiesfromfour Orders: Passeriformes, Apodiformes, Charadriiformes, and Podicipediformes. Particular species were chosen based mainly on their morphology, to ensure that a range of wing and body dimensions were included. Choice was limited, however, by the availability, accessibility and suitability of the species for radar recordings. The study species included: Tree Swallow (Tachycineta bicolor), Mountain Bluebird (Sialia currucoides), European Starling (Sturnus vulgaris), White-throated Swift (Aeronautes saxatalis), Black Tern (Chlidonias nigra),  Pigeon Guillemot (Cepphus columba), and Red-necked Grebe (Podiceps grisegena). The Tree Swallow and the White-throated Swift are both aerial insectivores. The swallow forages preferably over water and nests in holes in trees, while the swift forages over varied types of mountainous terrain and builds nests in cliff and canyon crevices. The Mountain Bluebird is also an insectivore but catches prey found on the ground. It often hovers above the ground, presumably looking for prey items, before dropping to the ground or continuing itsflight.It can be found mainly in open rangelands and meadows, where it nests in tree cavities or nestboxes. The Black Tern, which is found nesting in marshes and lakes, feeds on insects that it catches whileflying,but it also preys on smallfish.The Pigeon Guillemot and Red-necked Grebe also eatfish,which they catch by diving under 13  the water. Their habitats, however, are quite different. The guillemot is found nesting in rock cliffs of coastal islands and is thus a marine bird. The grebe breeds mainly on shallow lakes and inland marshes. The European Starling is a widespread species common in many habitats. It is chiefly a ground forager on insects but also eats some small fruits, and nests in tree cavities, cliffs, or buildings. It was possible to obtain morphological measurements for some of the species in the field, while other measurements were taken from museum specimens or literature sources. Using these dimensions, aerodynamic power required for flight versus flight velocity could be plotted for each species, as outlined in the general introduction. Flight speeds that had been collected could then be compared statistically to the calculated V  mp  14  and  V . mr  2.2 M A T E R I A L S A N D  METHODS  Calibration of the radar gun and measurement details of flight velocity, wind velocity, morphology, and the study species and locations are outlined below. Most flights were recorded of birds returning to the nest after foraging. If the foraging site could be seen or if the birds were known to be on their way to a foraging site (i.e. they returned a short while later with prey) outgoing flight speeds from the nest were also included. In most cases, the nesting site was known, and if not, food was observed being carried in the bill.  1. Study Species  Flight speeds were recorded for the following seven species: a. Tree Swallow (Tachycineta bicolor), Family: Hirundinidae, Order: Passeriformes b. Mountain Bluebird (Sialia currucoides), Family: Turdidae, Order: Passeriformes c. European Starling (Sturnus vulgaris), Family: Sturnidae, Order: Passeriformes d. White-throated Swift (Aeronautes saxaialis), Family: Apodidae, Order: Apodiformes e. Black Tern (Chlidonias nigra), Family: Laridae, Order: Charadriiformes f. Pigeon Guillemot  (Cepphu3  columba), Family: Alcidae, Order: Charadriiformes  g. Red-necked Grebe (Podiceps grisegena), Family: Podicipedidae, Order: Podicipedi formes 2. Study Locations  The study locations (all in British Columbia, Figure 1), their grid reference and altitude above sea level are given below: a. The Cotton Ranch near Riske Creek (51° 58'JV,122° 31 'W, 1158m). 15  b. Doc English Bluff - Ecological Reserve No.101 (51° 57'N, 122° 16'W, 610m). c. Williams Lake - Scout Island Nature Centre (52° 07'JV, 122° 07W, 590m). d. Mandarte Island (48° 38'JV,125° 17'W, lm).  e. Creston Valley Wildlife Management Area, Creston (49° 06'A*, 116° 31'W, 593m). 3. M e a s u r e m e n t of F l i g h t Velocity-  Flight velocities were measured using a hand-held Doppler K15 radar gun (Blake et al, 1989). The radar gun is able to detect small objects and the digital readout display -1  -1  was modified to read to 0.1ms , with a range of 3 to 30 ma .  The gun was calibrated  with respect to a stopwatch (LCD Professional Quartz, accurate to ±0.05.$) and known distances using automobiles, motorcycles, and bicycles.  Calibrations were performed with a moving target at 0° , 10° , 20° , and 30° relat to the long axis of the radar gun. Radar speeds were corrected using the cosine correction factor (Operators Manual for Stationary Radar). Table 1 shows the results of the two sample t-test and a linear regression comparing the calculated stopwatch speed with the  radar speed at each angle. For 0° , 10° , and 20° there was no significant difference betwe calculated stopwatch speeds and recorded radar speeds. Values at 30° were significantly different. Thus, radar speeds recorded in the range of ±20° would not be significantly different from those recorded at 0° . In most cases, it was possible to point the radar gun directly (±10° ) into the birdflightpath. It was noted during the calibration that at angles of 30° and greater, recordings from bicycles were not detected. This suggests that birds in this range would also be undetected and this was confirmed in thefieldmeasurements. 4. F l i g h t S p e e d Recordings for E a c h Species  a. Tree Swallow (Tachycineta bicolor),&nd Mountain Bluebird (Sialia currucoides) Both of these species nested in nestboxes on the Cotton Ranch near Riske Creek, B.C.. The nextboxes were mounted on fenceposts along the fencelines which separate the 16  F I G U R E 1. Map of Study Locations  The five locations - Williams Lake, Riske Creek, Ecological Reserve No.101, Mandarte Island, and the Creston Valley Wildlife Management Area - where bird flight speeds were taken are plotted, as well as two reference points - Prince George and Vancouver.  17  18  T A B L E I. R A D A R  CALIBRATION  H : Radar speed = Stopwatch speed 0  Angle  Two Sample T-Test a  =  .05, n  -  25  Linear Regression  Radar vs. Stopwatch 2  0°  p = 0.8480  r = 94.45%  10°  p = 0.9828  r = 88.58%  20°  p = 0.9189  r = 97.93%  30°  p = 0.0065  r = 95.06%  19  2  2  2  fields. Much of the terrain was flat and treeless so the activities of the birds were easily observed from a distance. Nesting records were kept for 16 bluebird nests and 13 swallow nests. Flight speed records were attempted for most nesting pairs initially, but many of the bluebirds appeared upset at the disturbance and either abandoned the nest temporarily until I left or visited the nest very infrequently and cautiously. At five bluebird nests, however, my presence caused little or no disturbance and the parents freelyflewto and from the nest. Mountain Bluebirdflightspeeds were thus based on ten individuals - five females and five males, with a total of 263flightspeeds. Flight speed records for the Tree Swallows also represent five females and five males, totalling 313 recordings. The radar gun was positioned, in each case, far enough away from the nest so as not to distress the parents, yet close enough to detect the majority of incoming and outgoing flights. This distance was approximately 5 — 10m from the nest, depending on the birds. Since the radar gun was usually capable of displaying two or three readouts before the bird was out of range, it could be determined if the bird was accelerating or decelerating. Flights where readouts varied by more than 10% were disregarded. Flight speeds were recorded on a daily basis between May 25 and June 17, 1988 for the Mountain Bluebirds and from June 12 to June 18, 1988 for the Tree Swallows. No measurements were taken on days when the wind speed was measured to be greater than 0.5m5  - 1  .  In order to decrease the variability inflightspeed recordings between birds due  to the time of day, recordings were collected as close as possible to the same time period each day at each nest. Thus, although the timing of theflightrecordings will vary between nests, it is fairly constant within each nest. Recordings and observations were made usually for one hour per nest each day for the bluebirds and one half hour per nest each day for the swallows. b. White-throated Swift (Aeronautes saxatalis) Flight speed records for this species were obtained on June 12, June 14, and June 17, 1988 at Doc English Bluff - a cliff overlooking the Fraser River. Velocities were determined for approximately 15 individuals, with a total of 104 speeds. Flight velocities 20  were recorded for wind velocities for up to 0.5ms , and during stronger winds, flight 1  velocity measurements were not taken. c. European Starling (Sturnus vulgaris) European Starling flight velocities were recorded on three consecutive days (June 911, 1988) atfivedifferent nests at the Scout Island Nature Centre in Williams Lake. The nests were located in holes in trees, and all flight records represent only flights of parents returning to the nest. The total number of speeds measured was 163, from ten individuals. Male and female velocities were not analysed separately. d. Pigeon Guillemot (Cepphus columba) Measurements of this species, totalling 230 flight speeds of approximately 80 individuals, were obtained on Mandarte Island over a two-day period (June 21 and June 22, 1988). Velocities were recorded from the shore as the birds left and returned to the rock cliffs in which they nest. Although the Pigeon Guillemot may fly near enough to the water surface to be considered as using the ground effect, the velocities measured were of birds out of the ground effect. In some cases, velocities were recorded of birds just beginning to ascend to the cliffs or near the end of their descent from the cliffs. Because no eggs or young were actually observed in the visible rock crevices, and it was early in the season, the birds may not have begun to feed their young. Thus, theflightsobserved may. have been just feedingflightsfor the parents thenselves. Male and femaleflightspeeds were not analysed separately. e. Red-necked Grebe (Podiceps grisegena) Flight velocities for the Red-necked grebe were obtained as the birdsflewover a dyke between a lake and marshy area, at the Creston Valley Wildlife Management Area near Creston (June 25 and June 26, 1988). The birds were observed on their return flight from foraging as theyflewalong the lake, and smallfishcould be seen between their bills.  21  In total, 64 speeds were collected, and again, male and female speeds were not analysed separately. f. Black Tern (Chlidonias  nigra)  The 41flightvelocities obtained for the Black Tern were recorded by Clive Welham of Simon Fraser University on July 2, July 11, and July 17, 1988. Speeds were measured at the Creston Valley Wildlife Management Area, while birds wereflyingto and from a specific known foraging site. 5. Measurement of W i n d Velocity -1  An anemometer (Anemo, West Germany), accurate to ±0.5m.s , was used to measure wind velocity. Flight speeds were recorded mainly on days when the measured wind velocity -1  was less than 0.5m* . The anemometer was positioned as close as possible to the height of theflightspeed path, which was usually only 1 — 3m above the recording position. 6. Morphological Measurements  Morphological measurements (Table II) obtained include those required to construct aerodynamic power versusflightvelocity curves (body mass, M, wingspan, b, wing area,  Sw , body diameter, d) as well as measurements for comparative purposes (aspect ratio, AR  2  (= b 1Sw ), wingloading, Q (= M/Sw )).  Values for some species were determined  from measurements of the actual study specimens in the field while others were taken from specimens in the Burke Museum at the University of Washington and the Vertebrate Museum at the University of British Columbia. Literature sources (Poole, 1938; Savile, 1957; Bartholomew et al., 1957; Hartman, 1961; Drent, 1965; Bedard, 1969; Dunning, 1984; Rayner, 1985b) were also used. Field measurements of mass (M) were determined using a 50g spring balance. Wing span (b) and body diameter (d) were measured with a lm measuring tape. Tracings of wings were made, which were later digitized to determine wing area. Figure 2 shows wing tracings drawn to scale and the aspect ratios of each of the seven study spcies. 22  T A B L E II. M O R P H O L O G I C A L M E A S U R E M E N T S  Species  Tree Swallow  Mass (kg),n  b (m),n  .020,82"6 .020, l C .017,5  S 2 (m ),n  Q (N •m~ ),n  w  2  6  .0125, cl d .012,10'  c  .298,10 >°"  AR b /S 2  n  15.8,1* 13.9,5> c  7A >  d  c  d  a  Mountain  .028,16  Bluebird  .0285, l l  c  c  c  .309,12 -°"  .0163,12 >°  17.2, l l ^  5.9  c i d  White-throated .0325,20° e  Swift  .0305,19  Black Tern  .065,36° / .060 C .053,5 .0799,915° .0847,1942° 6 .084,3 .08 -.09,11*  European StarHng  .076*  Pigeon Guillemot  .487,5° .483,6''  c a  C  c  .326,3'  .0089,3 '°"  11.9 -°"  .557' C .535,5 '°  .035' C .0275,5 '°"  43.4,3  .344,4°" .389*  .019,3* .0176,4°" .021*  .508,12°"  .0343,12°"  128.7-''°'  .725,5°"  .0598,5  8.9'  16.8' 19.1,5> c  10A >  d  c  d  b  36.6*  6.7°" 7.2* 7.5°"  .450,53J  Red-necked Grebe  1.023,6°  d  167.8°'°"  8.8°"  SOURCES: a. Dunning, 1984 e. Bartholomew, 1957 b. Poole, 1938 /. Savile, 1957 c. Field Measurements, 1989 g. Hartman, 1961 d. Burke Museum, 1989 23  h. Rayner, 1985 i. Bedard, 1969 j. Drent, 1965  F I G U R E 2. W i n g Shapes a n d A s p e c t R a t i o s  Wing outlines traced from actual wings and drawn to scale for the seven study species are shown. As well, aspect ratios (Aft= b /S ) are listed for each species for comparative purposes. 2  w  24  \ ^  „  ^R^d-nec^  £1=8.8  ^  25  7. Power Curve Input Values  Table III gives the input values necessary for the plotting of aerodynamic power versus velocity for each each species. Values were also used from Table II. Field morphology measurements obtained from this study and museum specimen measurements were preferred over literature values. Cr)( ), pro  an  Cr){ a)i par  A, p  d  Pmet  were determined as described in  the general introduction for each species. The air density, p, was determined based on the altitude at each of the study locations. A range of values for the European Starling was used because of the variance in reported morphological measurements.  26  T A B L E III. P O W E R  Species  CURVE INPUT  CD(pro)  VALUES  A  P  Pmet  p  (kgm- )  (m )  3  (W)  2  4  Tree Swallow  0.02  0.40  1.11  7.069 x 10~  Mountain Bluebird  0.02  0.40  1.11  8.867 x 10~  White-throated Swift  0.02  0.40  1.16  8.023 x 10~  European Starling  0.02  0.40  1.16  1.459 x 10" 3 1.558 x 10~  Black Tern  0.02  0.40  1.16  1.148 x 10~  Pigeon Guillemot  0.02  0.35  1.23  4.774 x IO"  Red-necked Grebe  0.02  0.30  1.16 .  8,254 x IO"  27  4  4  3  0.075 0.109 0-071 0.222 0.239  3  0.104  3  3  0.489 0.886  2.3 R E S U L T S  The results offlightspeed measurements are presented in Table IV. The total number offlightspeeds recorded is 1178, and distributions of the data for each species are shown a  in Figure 3. The column showing the results of a x fit to normal distribution (Table 2  IV) shows that, for five of the seven species, theflightspeeds recorded were not normally distributed, indicating that nonparametric statistics should be employed in any further analyses. However, parametric statistics, especially the t-test, are generally quite robust, particularly when using large and/or equal sample sizes (e.g. see Zar, 1984). In addition, the power of the t-test is actually greater when the populations have leptokurtic distributions. When using the Mann-Whitney-U test, for example, any comparison samples larger than ni = 20 and rii = 40 have a critical U value determined by the t-test critical t at *a,(i),oo (Zar, 1984). Since the data sets that are not normally distributed are leptokurtic,  and because the sample sizes are relatively large, parametric statistics are employed. Based on measurements from Tables II and III, plots of aerodynamic power required for flight versus flight velocity were constructed for each species (Figures 4 - 10). The minimum power speed, V  mp  and the maximum range speed, V , are defined on each mr  curve, and represent the predicted optimal flight speeds based on the minimum cost of flight per unit time or minimum cost offlightper unit distance respectively. The slowest velocity on the curve represents Va ta u- The mean of the actualflightspeeds recorded with the radar gun V0 bs , is also shown on each species' power curve, as well as the maximum power,  Pmaxi  available to the birds for flight. For the European Starling, because of the  wide range of masses reported, two power curves were constructed based on minimum and maximum values of mass, with their corresponding maximum range speed, minimum power speed, maximum power and maximum velocity defined. Boxplots outline the distribution of speeds for each species. Table V expresses numerically Vo6« V m p , and Vmr, and compares the observed speeds 5  with V  mp  and V r separately using a One-Sample T-test. Two sets of morphological m  measurements were used as power curve inputs for the European Starling, represented by 28  T A B L E IV. R E S U L T S O F F L I G H T S P E E D Species  n  Mean ± s.e. ms -1  MEASUREMENTS  Range ms~ 1  x Fit to normal distribution 2  Tree Swallow  313  6.6 ± 0.03  4.8 - 9.0  p = 0.003  Mountain Bluebird  263  8.4 ± 0.04  6.2 - 11.9  p < 0.001  White-throated Swift  104  10.1 ± 0.1  7.1-16.5  p = 0.06  European Starling  163  9.8 ±0:04  8.8 - 10.9  p = 0.015  Black Tern .  41  7.1 ± 0.1  5.1 - 9.5  p = 0.02  Pigeon Guillemot  230  10.5 ± 0.08  8.3- 14.2  p < 0.001  Red-necked Grebe  64  10.7 ± 0.09  8.9 - 12.2  p = 0.72  29  F I G U R E 3. Flight Speed Frequency Histograms  Frequency histograms for each species are plotted. Summary statistics and information on each distribution can be found in Table V.  30  s•  8 -  5  6  7  6  9  7  10  Tree Swallow V(m/s)  8  9  10  11  12  8  10  12  14  16  18  White-throated Swift V(m/s)  Mountain Bluebird V(m/s)  a-  7  8  9  Black Tern V(m/s)  9  10  11  12  13  Pigeon Guillemot V(m/s)  14  cr 9  10  11  12  Red-necked Grebe v(m/s)  9.0  9.5  10.0  .10.5  11.0  European Starling V(m/s)  8 -  Ml  8.5  13  11.5  F I G U R E 4. Tree Swallow Power Curve -1 Power (W) required for flight is plotted against flight velocity (ms ) for the Tree Swallow. The minimum power speed, Vmp , maximum range speed, V , and the observed speed, Vob, are shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. P m a x -1 is the maximum power available to the flight muscles at 250Wfc<7 , and Vmax the corresponding maximum flight speed possible. mT  F I G U R E 5. Mountain Bluebird Power Curve -1 Power (W) required for flight is plotted against flight velocity ( m s ) for the Mountain Bluebird. The minimum power speed, Vmp , maximum range speed, V m r , and the observed speed, VD b, are shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. Pmax is the maximum power available to the flight muscles at 250Wfc<7 , and Vmaz the corresponding maximum flight speed possible. -1  F I G U R E 6. White-throated Swift Power Curve -1 Power ..(W) required forflightis plotted againstflightvelocity ( m s ) for the White-throated Swift. The minimum power speed, Vmp , maximum range speed, V^r, and the observed speed, Vob, are shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. Pmax is the maximum power available to theflightmuscles at 2bOWkg~ , and Vmax the corresponding maximum flight speed possible. l  F I G U R E 7. European Starling Power Curve -1 Power (W) required forflightis plotted againstflightvelocity ( m s ) for the European Starling. The minimum power speed, V , maximum range speed, V , and the observed speed, Vob, are,shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. A second power curve is plotted using greater morphological values, resulting 1in, Vm p and V i. Pmax and Pmax' are the maximum power available to theflightmuscles at 250Wifc<7~ for the ranges in mass used, and Vmax and Vma x' the corresponding maximumflightspeeds possible. mp  mr  mr  F I G U R E 8. Black Tern Power Curve -1 Power (W) required forflightis plotted againstflightvelocity ( m s ) for the Black Tern. The rrunimum power speed, V^p, maximum range speed, V , and the observed speed, Vob, are shown, as is a boxplot of the flight speed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. Pmax is the -1 maximum power available to theflightmuscles at 250Wfc</ , and Vmax the corresponding maximum flight speed possible. mr  F I G U R E 9. Pigeon Guillemot Power Curve -1 Power (W) required forflightis plotted againstflightvelocity ( m s ) for the Pigeon Guillemot. The rrunimum power speed, V , maximum range speed, V mr , and the observed speed, Vob, are shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. Pmax is the maximum power available to theflightmuscles at 2 5 0 W f c t j , and Vmax the corresponding maximum flight speed possible. mp  -1  F I G R U E 10. Red-necked Grebe Power Curve -1 Power (W) required forflightis plotted againstflightvelocity ( m s ) for the Red-necked Grebe. The minimum power speed, Vmp , maximum range speed, Vmr , and the observed speed, Vob, are shown, as is a boxplot of theflightspeed distribution. The box covers the upper and lower quartiles, with the central line as the median. The horizontal lines show the range of the data, with extreme values plotted as points. PmaT is the maximum power available to the flight muscles at 2bQWkg~ , and V the corresponding maximum flight speed possible. 1  max  32  Tree Swallow Power Curve  0  2  4  6  V, m/s  8  10  12  Mountain Bluebird Power Curve  White-throated Swift Power Curve  European Starling Power Curve  0  2  4  6  8  V, m/s  10  12  14  16  Red-necked Grebe Power Curve  V, m/s  masses of 0.076kg and 0.084kg with their corresponding wing spans and wing areas. Two values, then, for each of V  mp  and V  mr  are reported. At the significance level of 0.05, all  of the observed speeds were significantly different from both V  and V . For the Tree  mp  mr  Swallow, Mountain Bluebird, White-throated Swift, and Black Tern, V b»  w a s  0  V  mp  greater than  and V m r , while V b for the Pigeon Guillemot was situated between the two predicted 0  a  optimal speeds. V bs for the Red-necked Grebe was less than  V . mp  0  To test the robustness of the power curve and thus the results of comparisons between observed and predicted speeds, the drag coefficients reduced until the null hypothesis H  D  : V0be = V  mr  Cr)( ara) P  and Cr)( ) pro  was not rejected (Table VI). The second  column of Table VI describes the proportion of the original estimate of for V bs to be insignificantly different from 0  a 99% reduction in  V  mr  P  Crj( ra) pa  required  for each species. In most cases, as well as  it was also necessary to reduce  Cr)( ara)i  were each  Cr)( )pro  The third column  represents the values of Cr)( ro) needed to meet the above requirements. An increase in P  either drag coefficient would reduce the values of V  mp  and V , and thus result in even mr  greater discrepancies between observed and predicted speeds. The night speed data were collected at different nesting sites if possible, or, alternatively, on different days using the same group of individuals. Data for Mountain Bluebirds, Tree Swallows and European Starlings were collected at five separate nests for each species, with each nest representing speeds from both the male and female. For the Black Terns, White-throated Swifts, Red-necked Grebes, and Pigeon Guillemots, flight velocities were measured bn different days for the same group of birds. Table VII describes the sample size of each group, the mean, standard error, and range of speeds. The last column indicates the results of a one factor analysis of variance or a t-test performed for each species between the groupings of data. There was no difference between speed recording groups for the Mountain Bluebirds, European Starlings, Black Terns, and the Red-necked Grebes. Tree Swallows, White-throated Swifts and Pigeon Guillemots were significantly different with respect to their data groupings. Table VIII describes the results of a Tukey test performed for the species which showed differences between groups.  40  T A B L E V. COMPARISON OF O B S E R V E D A N D P R E D I C T E D SPEEDS Species  Vmp  V bs 0  Vmr  H:  V x  H  0  ma  0  :  (ms- )  (ms* )  (ms )  (ms )  Vobs  Tree Swallow  6.6  3.6  5.6  13.7  p <  0.001  p <  0.001  Mountain Bluebird  8.4  4.2  6.3  11.3  p <  0.001  p <  0.001  White-throated Swift 10.1  4.7  6.7  13.4  p <  0.001  P <  0.001  European Starling  9.8 9.8  5.5 6.1  7.9 8.6  13.7 14.2  p <  0.001 0.001  p <  p <  p <  0.001 0.001  Black Tern  7.1  3.9  5.6  12.1  p <  0.001  p <  0.001  Pigeon Guillemot  10.5  9.5  12.8  18.2  p <  0.001  p < 0.001*  10.9  14.6  20.5  P = 0.03** p < 0.001*  1  Red-necked Grebe 10.7  1  -1  * V Vrr 'obs <' m i **  obs  V bs 0  Vn. ' mp  41  -1  =  Vp m  T A B L E VI. V A L U E S OF C AND C R E Q U I R E D T O A C C E P T T H E N U L L HYPOTHESIS D(para)  H0  D(pro)  : Vob8 = Vmr ,  a =  0.05  Species  ^D(para)  Tree Swallow  0.0lCr)( ara)  +  0.85Cr)( o)  0.30C.D pro)  Mountain Bluebird  O.OlCD(para)  + 0.55C (pr )  0.05Cr)( )  White-throated Swift  O.OlCu(paro)  +  O.OlCD(pro)  European Starling  O-OlCD(para)  + 0.75CD(pro)  p  pr  D  O  0A4C  D{pro)  0.10Cr)(para)  Black Tern  0.01C (para) D  (  pro  0.08Cr>(pro) 0.30Cr)(prpo)  + 0.68C£j(pro)  42  0.27Cr)(pro)  +  0.50Cx>(para)  T A B L E VII. S U M M A R Y STATISTICS F O R M E A S U R E M E N T G R O U P S A N D ONE-WAY A N O V A B E T W E E N G R O U P S  Ho : No difference between groups or nests Group  n  Range  Number of Nestlings  V bs ± s.e.  6,1 4 4 4 4  8.3 ± 0.1 8.5 ±0.09 8.3 ±0.06 8.5 ±0.1 8.4 ±0.1  6.9—9.7 7.5-10.9 6.7-9.2 7.2 - 10.1 6.2-11.9  p = 0.1980  6.7 ±0.06 6.6 ±0.07 . 6.6 ±0.07 6.6 ±0.07 6.4 ±0.07  5.6-9.0 5.3 - 7.9 5.5-8.0 4.8 - 7.3 5.8 - 8.0  p = 0.0179  0  ANOVA  ms  -1  Bluebird nests  1 2 3 4 5  38 57 78 24 66  Swallow nests  1 2 3 4 5 '  95 49 70 49 50  6 5 6 5 5  Starling nests  1 2 3 4 5  30 30 32 35 36  9.8 ± 0.09 9.7 ±0.09 9.9 ±0.08 9.9 ±0.09 9.9 ± 0.07  8.8-10.9 9.0-10.7 8.9 - 10.8 9.0-10.9 8.9-10.8  P ;= 0.3346  17 12 12  7.0 ± 0.2 7.2 ± 0.2 7.1 ±0.3  5.1 - 7.9 6.3-9.1 5.1 - 9.5  P = 0.7776  11.3 ±0.2 9.3 ±0.3 9.9 ±0.1  8.5 - 16.5 7.1 - 11.5 8.5-11.5  p<  10.7 ±0.1 10.6 ±0.2  8.9 - 12.2 9.0 - 12.0  9.8 ±0.2 9.8 ±0.2 10.7 ±0.1 10.6 ±0.2  8.7-12.2 8.8-12.7 9.0-13.5 8.3-14.2  Tern groups  1 2 3  Swift groups  1 2 3  23 17 64  0.001  Grebe groups  1 2  43 21  p = 0.5969  Guillemot groups  1 2 3 4  24 25 108 73  43  p<  0.001  T A B L E VIII. T U K E Y T E S T R E S U L T S F O R T R E E SWALLOW, WHITE-THROATED SWIFT PIGEON GUILLEMOT . Species  Homogeneous Groups  Tree Swallow Nest Nest Nest Nest Nest  1 2 3 4 5  * * * * * * * *  White-throated Swift Group 1 Group 2 Group 3  * * *  Pigeon Guillemot Group Group Group Group  1 2 3 4  * * * *  44  For the Mountain Bluebird and Tree Swallow, a two-factor analysis of variance was performed to determine whether the sexes flew at different speeds or whether incoming and outgoing foraging flights were different. Table IX shows that there is no significant difference in speeds using either condition for each of the two species. A Mann-Whitney test was employed to detect a possible difference in flight speeds in Black Terns leaving the nest and returning to the nest, but no difference was found (Table X). Since there may have been some variance in flight speeds depending on the time of day of the recording, in cases where measurements were made on more than two or three consecutive days, the time periods of the recordings were kept as constant as possible for each nest. Thus, for the Mountain Bluebird and Tree Swallow, the exact time in terms of day, hour, and minute is known for each flight speed recorded. The flight speed data are plotted with respect to the time of day for the Mountain Bluebird (Figure 13) and Tree Swallow (Figure 14). A regression through each plot resulted in a slope of 0.014 for the Mountain Bluebird and a slope of 0.018 for the Tree Swallow. Neither slope was significantly different from zero (p > 0.25 for each regression).  45  T A B L E IX. T W O - W A Y A N O V A T E S T R E S U L T S F O R  MOUNTAIN BLUEBIRD, TREE SWALLOW H : No difference between male and female speeds or speeds to or from a foraging site 0  Interaction with flight speed  Mountain Bluebird  Tree Swallow  1. male vs. female  p = 0.40  p = 0.19  2. to vs. from site  p = 0.15  p = 0.40  2-factor interaction  l.vs 2.  p=  0.07  46  p=  0.52  TABLE X. MANN-WHITNEY TEST RESULT FOR BLACK TERN H :: No 0  Leaving nest Returning  difference in flight speeds leavingor returning to the nest  n  V f)B  Mann-Whitney  12 29  6.9 7.2  p = 0.8139  0  47  F I G U R E 11. Flight Speed Versus Time of Recording For The Mountain Bluebird  Each recorded flight speed is plotted with respect to the time of the recording in hours. Plotted here are flight speeds from all Mountain Bluebird nests.  F I G U R E 12. Flight Speed Versus Time of Recording For The Tree Swallow  Each recorded flight speed is plotted with respect to the time of the recording in hours. Plotted here are flight speeds from all Tree Swallow nests.  48  CvJ  _  C/3  to  • •:  "D CD CD CL CO  • • *.  sz &  00  CD  i  •  •  .  -  8  10  • • • : • • : *• * • *• • • •.•• * •• 1:• • s s :• s •• • •• •• ••• •• •• •• • • •• • • • • • • • • • • • 111 • t. • • •:: • • •• • •. • •111 ••• • •• • • • • • ••-• • • • • • •• • •  • •  8  :  12  14  • s•  16  T i m e of R e c o r d i n g ( h o u r of t h e d a y )  18  20  22  tt  I  J  I  I  6  8  10  12  14  Time of Recording (hour of the day)  -  16  2.4 D I S C U S S I O N  Results of comparisons of observed velocities with predicted minimum power and maximum range speeds indicate that in five of seven species the observed velocity is significantly greater than both V  mp  and V  mr  (Table V, Figures 4 - 10). For the Pigeon  Guillemot, however, the observed speed lies between the minimum power and maximum range speeds while  Vb 0  s  for the Red-necked Grebe is actually less than the theoretical V . mp  All speeds, with the exception of a few by the Mountain Bluebird, are within the maximum sustainable velocity predicted using 250Wkg~ of flight muscle (Weis-Fogh and Alexander, 1  1977). In order to change the results of comparisons between V  mr  and Voog for the Tree  Swallow, Mountain Bluebird, White-throated Swift, European Starling, and Black Tern, vastly different values for the drag coefficients Cr)(  an pa  ra)  VI). To shift the power curve such that the value of V  mr  d CD(PTO) were necessary (Table would not be significantly different  from Vobs, for the White-throated Swift, for example, values of 0.004 for Cr)(  an par  a)  d 0.009  for Cr){ ) would have to be used, instead of the originally estimated values of 0.4 and 0.02 pro  respectively. Even the smallest deviation from original estimates, which occurred in the cases of the Tree Swallow and the greater set of values for the European Starling, involves using only 30% of the original value for Cr)( ). pro  The above comparisons suggest, then,  that the power curve constructed for each species and the statistical comparisons made between predicted and observed velocities are quite robust. The Pigeon Guillemot and the Red-necked Grebe were not included in this sensitivity analysis because their mean observed flight speeds were already significantly less than V mr  Altering  a n (  Cr)( a) par  l  r  Cr)( ) f° these two species would bascially shift the power curve such that V bs would pro  0  be situated in varying positions between V  mp  The x fitt° 2  a  and V m r .  normal distribution for each species (Table IV) indicates that only  the White-throated Swift and Red-necked Grebe have normally distributed speeds. The other distributions (Figure 3) indicate a clumping around the mean, and can be described as leptokurtic. This indicates that there was a stronger preference for certain velocities 51  near the mean than is predicted for a normal distribution. If a particular flight speed was important to maximize efficiency under certain conditions, then such a distribution would be expected. Table XII lists previously recorded speeds from other sources for the study species. Measurements made using techniques other than doppler radar cannot realistically be considered comparable. Radar measurements noted by Rayner (1985b) for the starling of 9 — 1 0 m s are similar to the mean found in this study. Schnell and Hellack (1979) reported -1  a mean of 10.7ms  -1  for starlings (n = 8). Schnell and Hellack (1979) also recorded 33  flight speeds for the Black Tern in windless conditions with a mean of 7.9ms , close to -1  the 7.1ms  -1  mean determined in this study. Although the above mentioned speeds are  similar to ones found in this study, the context of the flight behaviour is not given. Flight speeds for each species were measured either at separate nests over a given period or with groups of birds over a given period. Table VII shows that between Bluebird nests, Starling nests, Tern groups and Grebe groups there were no bird flight speed differences. There were, however, differences in flight speeds between Swallow nests, Swift groups, and Guillemot groups. The sources of the differences are shown in Table VIII. Differences between nest one and five for the Tree Swallow may just be due to individual variation of the adults, since all other conditions were similar for all nests. Data for the White-throated Swift were collected on three separate days, represented by Groups 1, 2, and 3. All were measured using the same group of individuals in the early evening of each day, but neither number of young or nestling age could be determined. Even if the speeds had been divided into two groups, with groups 2 and 3 separated from group 1, the results of comparisong with V  mr  would be the same, since the predicted V  was only 6.7ms . -1  mr  Flight speeds of the Pigeon Guillemot were collected over a two day period, in the morning and afternoon of each day. Groups 1 and 2 represent speeds for the afternoon flights while Groups 3 and 4 are speeds of morning flights. There was no difference in flight speed for either male or female Mountain Bluebirds or Tree Swallows or between birds leaving and returning to the nest (Table IX, Figures 11,  52  T A B L E XI. PREVIOUSLY R E C O R D E D F L I G H T SPEEDS Species  n  Flight Velocity  Method  Source  (ms- ) 1  Tree Swallow  1  11.2  speedometer  Meinertzhagen,1955  Mountain Bluebird  1  8.0  speedometer  Cottam et aZ.,1942  Sialia sp.  2 4  7.6 5.8-11.6  speedometer speedometer  Cooke,1933 Meinertzhagen,1955  9.0 - 10.0 8.0-18,0  doppler radar wind tunnel doppler radar speedometer speedometer theodolite stopwatch  7 4 7  10.7 11.6-14.3 10.3-14.3 20.1-21.7 19.2-21.9 20.6 18.3-21.5 > 20.1 21.5-22.5 12.5-24.6 11.2 - 13.6  Rayner,1985 Torre-Bueno and Larochelle,1978 Schnell and Hellack,1979 Meinertzhagen,1955  2 1 33  9.4,10.3 4.5 7.9  speedometer speedometer doppler radar  European Starling 8 3 17 22 13 3 3  Black Tern  53  speedometer speedometer stopwatch speedometer  " "  " " Cottam et al, 1942 Cottam et al.,1942 Schnell and Hellack,1979  12). Black Terns leaving and returning to the nest also showed no significant difference in flight speed, although the sample size for leaving the nest was small (n = 12). Since the actual time in terms of day, hour, and minute was recorded for most bluebird and swallow flight measurements, a plot of flight speed versus the time (in hours) was done to check for any variation offlightspeed with time of recording (Figures 11, 12). There appears to be no variation in flight speed with time of day, indicating that for the Mountain Bluebird and the Tree Swallow, the mean speeds of the 8 . 4 m s  -1  and 6 . 6 m s respectively -1  are representative of theflightspeed at the times of the day under observation.  54  CHAPTER THREE DETAILED OBSERVATIONS OF TWO  SPECIES  3.1 I N T R O D U C T I O N  , Many mathematical models have been constructed to explain or describe the foraging behaviours and strategies of animals. A review of optimal foraging by Pyke et al. (1977) classified four main categories of optimal foraging theory - optimal diet choices, optimal patch choices, optimal time durations in particular patches, and optimal patterns and speeds of movements. Stephens and Krebs (1986) detailed extensively the construction and testing of optimal foraging models. Pyke (1981) stated that at least five suggested optimality criteria have been used to predict travel speeds of animals.  These include  maximizing net rate of energy gain, maximizing the ratio of net rate of energy gain to the rate of energy expenditure (growth efficiency), maximizing the ratio of growth efficiency to the rate of energy expended, maximizing distance travelled per unit energy expended (minimizing energy expended per unit distance), and minimizing metabolic rate during travel (maximimzing travel time per unit energy expended). Norberg (1981) developed a model to predict the optimal flight speed of the adult bird when feeding its young. Flights are assumed to be only between foraging sites and the nest, with no foraging during travel. He proposed that adult birds feeding their young should actually fly faster than the maximum range speed, in order to spend more time foraging and thus bring more food to the nest. It may be argued that as a bird flies faster to its foraging site, the time spent in the air will diminish, and thus travelling flight will make up proportionately less time of the total foraging trip (and perhaps become less important as a result). However, because of the U shape of the power curve, a bird should always fly at the smallest ratio of P/V to minimize the cost per unit distance, and thus the flight speed is independent of time spent foraging.  55  The optimal speed, V  op  predicted by Norberg lies between the maximum range  t,  velocity and the maximum speed physiologically possible by the bird. Norberg assumed that the rate of net energy gain will remain constant for a given food availability and independent of flight speed, and also that the amount of food carried on each trip does not change significantly. The derivation of Norberg's model involves two strategies. A bird can eitherflyat a particular speed, termed V o , or it can increase its speed by Sv to V + 8v. If V is assumed 0  0  to be V m r , then decreasing V by 8v will not be a realistic option, since not only will the 0  bird be flying at a slower velocity and have less time for foraging, but it will also require more energy per unit distance flown. If T is the total time spent in bothflyingto and from the foraging site plus the actual time spent foraging, then  T  where t i a  r  = tair  is the time spent airborne and  + If or  (15)  the time spent foraging.  tf  or  In strategy one, it is assumed that the power needed toflyat V is P0, and that the 0  net rate of energy gain during foraging is  P inga  The difference in energy gained from  foraging and energy expended inflightcan be expressed as  A E \  — Pgaintfor  Pairtair  Since  where D is the distanceflownand V theflightspeed, and 0  56  (16)  substitutions can be made to give  AE,  = P (T  -  gain  - P ^ 'o  (19)  0  * 0  In the second strategy, the chosen flight speed is V + 6v, with a corresponding P + 8p 0  0  required to fly.at that speed. The difference between energy gained during foraging and that spent flying at V + 8v is Q  AE -P aintfor-(Po+8p)tair 2  Substituting T — t i a  r  for t / ' a n d o r  A B 2  =  P  B a j  (20)  g  ^  v  „  ( r  6 v  for < > results i n aj  __£_  )  _  (  P „+  M  (  _ £ _  )  ( 2 1 )  In comparing the two strategies, if flying at V + 8v is a better choice than V , then AEi 0  0  should be less than AE . 2  • M - f f l ^ M - ^ l - I M ^ ] '  (22)  This simplifies to  P + 8p_P 0  1  1__  1  which is the expression i n Norberg (1981). If this inequality holds true, then parents feeding their young should fly at V + 8v (= V t). 0  op  57  For the Mountain Bluebird and the Tree Swallow, information on time spent foraging by the adults, number of visits to the nests, number of nestlings, the masses of the nestlings (only for the bluebird), as well as flight speeds to foraging sites were collected. Power curves for eight individual female adults were constructed such that the female's flight speeds could be compared to her own predicted V p and 7 . m  m r  Possible values of  P in ga  were determined by setting V b to V t and compared to the energy requirements of the 0  8  op  young.  58  3.2 M A T E R I A L S A N D  METHODS  Detailed observations during the nesting period were obtained for the Tree Swallow (Tachycineta bicolor)  and the Mountain Bluebird (Sialia currucoid.es), from May 25 to  June 17, 1988 and July 3 to July 17j 1988. Brood size, nestling mass, time budgets, and input values for power curves were determined as described below.  1. Brood Size and Mass of Nestlings  Nestling age was determined by observing dates of hatching. Nests were checked each day until all eggs had hatched or were cold to the touch. Each nest box had a removable roof, which could easily be taken off to examine the nest. Thereafter, nests were checked after each session of flight speed recordings and observations, to confirm brood size or record any deaths or disappearances of the young. The nestboxes were placed in pairs along fencelines. Each pair was approximately 30 — 50m away from the next pair. Within a pair of boxes the distance between the two was 1 or 2m, and in some cases both boxes were on the same fence post. In most instances, one of the two nestboxes was occupied by a Mountain Bluebird pair and the other by a Tree Swallow pair. Since it was not certain what the effect of handling the nestlings would be on the parents or the nestlings, the masses of the Mountain Bluebird nestlings were measured using the young from the second brood (July 3 - July 17, 1988). Approximately half of the bluebird pairs had second broods, so nestling masses and brood sizes were recorded for five nests. Only clutch sizes were recorded with respect to the Tree Swallow young for theirfirstbrood, and no second Tree Swallow broods were found.  2. Time Budgets  During the half hour or hour time period per day in which flight speeds were being obtained for each bird, time and details of activities (number of visits to the nest, time spent foraging) were also noted. Observations were recorded on paper and time noted 59  from a running stopwatch. In addition, one bluebird nest was observed for a full day. Since hovering played an important role in the foraging activities of the bluebirds, hovering durations were timed with a stopwatch when possible. Details of consecutive hoverings were also noted on some occasions. Total observation time was 49.2/i for Mountain Bluebirds and 15.6/i for Tree Swallows.  3. I n d i v i d u a l P o w e r C u r v e s  In some cases, flight velocities were collected from birds for which body mass, wingspan, and body diameter had been measured. This was so for five female bluebirds and three female swallows. For these birds, separate curves of aerodynamic power for flight versusflightvelocity were plotted and thus actual measuredflightvelocities for each bird could be compared to predicted optimal flight speeds based on it own dimensions. Table XII shows the input values necessary for the construction of power curves of the five female Mountain Bluebirds and three female Tree Swallows. Table III gives the remaining needed input values which are basically constant within a particular species.  60  T A B L E XII. INDIVIDUAL F E M A L E P O W E R C U R V E INPUT VALUES *  Bird  Mass (kg)  b(m)  S (m )  Bluebird 1  0.031  0.30  0.0161  7-1  Bluebird 2  0.030  0.30  0.0166  9.6 '  Bluebird 3  0.029"  0.31  0.0146  7.1  Bluebird 4  0.030  0.32  0.0167  7.1  Bluebird 5  0.031  0.30  0.0150  9.6  Swallow 2  0.018  0.28  0.0123  7.1  Swallow 4  0.020  0.31  0.0117  7.1  Swallow 5  0.018  0.29  0.0115  7.1  * Remaining input values obtained from Table III.  61  2  w  A (m  2  p  x 10 ) 4  3.3 R E S U L T S  Table XIII summarizes observations made at five Mountain Bluebird nests and five Tree Swallow nests. Details of observations for individual nests are given in the appendix (Tables A l - A10). The average number of visits to the nest per hour by both Mountain Bluebird parents was 11 (Table XIII), ranging from 3.2 to 28.6 visits per hour. For each parent, then, the average number of visits to the nest per hour was 5.5. Power (1980) found that the average number of visits to the nest per hour by Mountain Bluebirds was 6.1 for males and 7.1 for females, with no significant difference between the two. He noted that, over the nestling period, the parents shared equally in feeding equally in feeding the young. The total number of observations was 240 and there was also a wide range of values from 0 visits per hour to 29.5 visits per hour (Table 6, Power, 1980). Power did not state the number of nestlings per nest for those particular observations, while in the present study four of the five nests contained four young. The other nest originally consisted of six young but after three days only one nestling remained alive. There was no apparent difference in frequency of nest visits by the parents of this nest when compared to the other four nests. Of the 118 bluebird foraging trips for which I recorded both the time of departure and return to the nest, the average time for one foraging trip was 2.2 minutes (Table XIII). A few observations (14 visits over 30 minutes) by Grass (197.0) indicated similar results, with average foraging times of 2.6 minutes per trip for a male (5 visits over 30 minutes) and 3.2 for a female (9 visits during 30 minutes). The time for a foraging trip included the time spent feeding the young as well as obtaining more food and returning, so may account for the slightly longer trip duration than I recorded. The mean of 165 recorded visits to the nest by the Tree Swallow in this, study was 15.5, with a wide range from 6.7 to 56.5. The number of visits per hour per nestling also varied greatly, from 1.3 - 9.4, with a mean of 2.8.  62  T A B L E XIII. S U M M A R Y OF N E S T VISITS F O R T H E M O U N T A I N B L U E B I R D A N D T R E E SWALLOW n  Mean ±s.d.  Median  Range  11.0 ± 6.2  9.2  2.8-28.0  3.2 ± 1.8  2.8  0.7-7.2  2.2 ± 1.0  2.0  1.0-5.0  15.5 ± 12.3  11.4  6.7-56.5  2.8 ± 2.0  2.1  1.3-9.4  1.8 ± 0.8  2.0  1.0-4.0  Mountain Bluebird #Visits/hr  390 visits  Visits/hr nestling Time/trip (min)  118 trips  Total time foraging (min/hr)  24.2  Tree Swallow # Visits/hr  165 visits  Visits/hr nestling Time/trip (min)  54 trips  Total time foraging (min/hr)  27.9  63  A plot of the age of young versus the number of visits per hour per nestling for all nests (Figure 13) has a significant slope of 0.13 (Table XIV). However, in comparing results for individual nests (Figure 14), there is no distinct trend common to all nests. Nests one and three show increased feeding rates as the nestlings mature, while nests two, four and five indicate a diminishing feeding rate with increasing nestling age. The number of feedings per hour per nestling determined by Power (1966) range from 0.7 to 3.8, while in the present study, the range was 0.7 to 7.2 feedings per hour per nestling. The greater number of feedings per nestlings in the current study may be due to a smaller brood size (an average of 4 young compared to 5 and 6 young in Power (Table 4, 1966)). Flight speeds of adult bluebirdsflyingon foraging trips did not change with increasing age of the young (Figure 15). The slope of the regression is 0.012 and is not significant (Table XIV). The trends observed for each nest separately can be seen in Figure 16. The results of tests for significant differences inflightspeeds between recording days within each nest are displayed in Table XV. For the Mountain Bluebird, nests one, three, and five showed a significant difference in flight speeds between recording days, while flight speeds recorded on different days for nests two and four were found not to be significantly different. Aerodynamic power versus flight velocity was plotted forfiveindividual female Mountain Bluebirds, since morphological measurements as well asflightspeeds were obtained from them. Table XVI indicates the results of comparisons of observedflightspeeds for each female with predicted V  mp  and V  mr  values from the females' individual power curves.  In each case, the observedflightspeeds were significantly greater than the predicted V and  mp  V mr . The mass of the nestlings each day was determined for the second brood of Mountain  Bluebirds, at five separate nests, totalling 20 nestlings. Growth of the young is shown in Figure 17. Fitting a nonlinear regression to the plot results in a logistic growth curve, the equation of which is also defined. This growth curve is similar to one constructed using nestling data from Power (1966). 64  F I G U R E 13. Age of Young Versus Feeding Rate For A l l Bluebird Nests  The number of feedings per hour per nestling are plotted against the age of the bluebird young. The numbers beside each point indicate from which nest the observation was made (e.g. 1 = Bluebird Nest One). The results of a regression through this plot are shown in Table XIV. F I G U R E 14. Age of Young Versus Feeding Rate For Individual Bluebird Nests  The number of feeding visits made to the nest each hour per nestling is plotted against the age of the young in days for each nest.  65  00  ?  5  CD  LO  3 3  CO  4 3  2 CM  t  h  0  5  10  4  3  15  A g e of Y o u n g (days)  20  25  Bluebird Nest One  15  Bluebird Nest Two  20  5  10 Age of Young (days)  Bluebird Nest Four  Bluebird Nest Five  14  16  10  12  14  16  18  20  15  Age of Young (days)  A g e of Y o u n g (days)  Bluebird Nest Three  20  Age of Young (days)  5  10 Age of Young (days)  22  24  26  15  20  T A B L E XIV. REGRESSIONS OF N E S T L I N G A G E VERSUS A D U L T F L I G H T S P E E D A N D VISITS T O T H E N E S T (FOR A L L B L U E B I R D NESTS) Regression  Slope (b)  Intercept  r  2  H :b = 0 0  Nestling age vs. Visits/hr/nestling  0.13  1.46  10.75%  p = 0.0445  Nestling age vs. Adult flight speed  0.012  8.20  0.41%  p = 0.3581  68  F I G U R E 15. Age of Young Versus Adult Flight Speeds For A l l Bluebird Nests 1  Flight speeds (rar ) from all nests are plotted against the age of the bluebird young (days). Each point represents the mean of observed speeds for a particular day from one nest, with the standard errors also shown. The results of a regression through this plot are shown in Table XIV. F I G U R E 16. Age of Young Versus Adult Flight Speed For Individual Bluebird Nests  Flight speeds (ms ) from each nest are plotted against the age of the bluebird young (days). Each point represents the mean observed speed for each day, and the standard errors are also plotted. -1  69  02,  Adult Flight S p e e d (m/s) 6  cn  >  CQ CD  o  <  — K  O .c =3 CQ  "2 &i CO  cn  ro o  cn  7  8  9  10  11  Bluebird Nest One  10  15  Bluebird Nest Three  Bluebird Nest Two  20  25  10  10  15  Age of Young (days)  Age of Young (days)  Bluebird Nest Four  Bluebird Nest Five  Age of Young (days)  I II  J 10  12  14  16  Age ol Young (days)  18  14  16  18  . Age ol Young (days)  20  L . 22  24  1  T A B L E X V . ONE-WAY A N O V A T E S T R E S U L T S F O R D I F F E R E N C E S B E T W E E N FLIGHT SPEED RECORDING DAYS  H : No difference in flight speeds between recording days Q  Nest  Recordings  n  Number of Recording Days  ANOVA  Bluebird  1 2 3 4 5  38 57 78 24 66  6 8 10 4 8  P P V V P  0.0174 0.7886 0.0011 0.0946 0.0013  95 49 70 49 50  7 5 6 5 5  P P p p p  0.1817 0.0457 0.0507 0.0837 0.9429  30 30 32 35 36  3 3 3 3 3  p p p p p  0.1175 0.3604 0.1547 0.5649 0.4262  Tree Swallow  1 2 3 4 5 Starling  1 2 3 4 5  72  T A B L E X V I . COMPARISONS OF O B S E R V E D SPEEDS W I T H P R E D I C T E D SPEEDS F O R INDIVIDUAL F E M A L E BIRDS Bird  n  Vo6s  H :  Vmp ms  Vmr ms~  V bs  1  -1  0  0  =  V  mp  Vobs ~  V  Bluebirdl  17  8.1 .  4.6  6.7  p<  0.001  Bluebird2  19  .8.5  4.4  6.4  p<  0.001  p < 0.001  Bluebird3  50  8.3  4.4  6.6  p<  0.001  p < 0.001  Bluebird4  12  8.5  4.3  6.4  p<  0.001  p<  0.001  Bluebird5  42  8.3  4.5  6.6  p  p<  0.001  Swallow2*  9  6.7  3.8  5.8  P <  0.001  p < 0.001  Swallow4*  21  6.6  3.8  5.9  p<  0.001  p<  Swallow5*  23  6.4  3.8  5.8  p<  0.001  < 0.001  P  P  mr  < 0.001  0.001  < 0.001  * Sex of the Tree Swallow was not determined for all flights. Only flight speeds known to be by females are noted here.  73  F I G U R E 17. Mountain Bluebird Growth Curve  The mass of the bluebird nestlings (g) is plotted against their age (days). Each point represents the average nestling mass for a particular day. Standard errors for each point are also plotted. The fitted line represents a logistic growth curve, and the equation of the line is _ 32.075 ~ 1 + 14.24e-- * 446  74  3.4 D I S C U S S I O N  To determine the optimal speed,  V t, op  at which to bring food to the nest, as predicted  by Norberg (1981), the net rate of energy gain during foraging,  P in, ga  must first be known.  The model assumes that the adult bird balances its own energy budget and the net rate of energy gain thus does not include the adults' cost of foraging or maintenance. If the foraging rate and value of prey items are known, alternative method to determine  can easily be calculated. An  P in ga  is to view the net energy gained during foraging  P in ga  as that taken to the nest (the gross energy required for the nestlings) plus the amount of energy for travelling flight. This can be viewed by rearranging equation 16, to give  (OA\  p _ A2Jq + Pgirtgir •i gain — , t for  where AEi can be considered the amount of energy brought to the nest. If the observedflightspeeds of the birds studied corresponded to the V  opt  as predicted  by Norberg (i.e. they wereflyingat the optimal speed to deliver a given amount of energy to the young), then  P i ga  n  could be determined by simply finding a new tangent to the  curve at V008 for each species. This is done by setting instead of V  mr  Vb 0  s  as the smallest ratio of  P/V,  The vertical dotted line in Figure 18 shows the position of V ba for the  .  0  Mountain Bluebird while the slanted dotted line represents the tangent to this point. The Y^intercept of this line indicates the value of P  i,  ga  this method,  P i ga  n  n  if V b is considered to be Vopt- Using 0  8  for the Mountain Bluebird is shown to be 0.48W (Figure 18) and 0.12W  for the Tree Swallow (Figure 19). To decide if the above values of P  ga  in  were sufficient to support the nestlings plus the  costs offlight,nestling energy requirements were first determined, as outlined below. Only a percentage of the gross energy intake (the energy that is consumed by the young birds) is eventually used for the maintenance and growth of the nestling. The rest is lost as wastes or expended during assimilation. Outlines of the distribution of the gross  76  F I G U R E 18. Determination of P the Mountain Bluebird  g a i n  for  Power for flight (W) versus flight velocity (ms ) is plotted, for the Mountain Bluebird. V , V , and V he are defined, as is P ax- The sloped dotted line represents the tangent to V008, and thus the Y-intercept indicates P in if Voba is taken to be V t. -1  mp  mr  0  m  ga  F I G U R E 19. Determination of P the Tree Swallow  op  g a i n  for  Power forflight(W) versusflightvelocity (ms ) is plotted, for the Tree Swallow. V , Vmr, and V bs are plotted, as is P xThe sloped dotted line represents the tangent to Voba, and thus the Y-intercept indicates P i ifY bs is taken to be V t. -1  mp  0  ma  ga  n  77  0  op  energy can be found in Ricklefs (1974), King and Farner(1961) and O'Connor (1984). Following O'Connor (1984), the portion of the Gross Energy Intake (GEI) that is actually metabolized by the bird each day is termed the Daily Energy Budget (DEB). The DEB is the sum of Existence Metabolism (EM) and Productive Energy (PE). EM is the rate of energy used to maintain a constant mass, while PE is the energy available for activities such as growth. Ricklefs (1974) states that biosynthetic work (growth or PE) can be estimated if growth rate, energy density and the net efficiency of synthesis for the nestling are all known. Since masses for the second brood of Mountain Bluebird nestlings were recorded each day, starting at the age of two days, the growth rate in terms of increased mass per day is known. A logistic growth curve fitted to the nestling mass measurements is shown in Figure 28. The form of the growth curve is  Y  = T  T  ^  (  2  5  )  where a, /3, and 7 are coefficients, and Y and X are coordinates of a point on the curve. Energy density can be expressed as  D = 4.1868(a + bW) where D is the energy density (kJg  -1  ),  W  (26)  is the percent of adult body mass, and a and b  are coefficients (Ricklefs, 1974). Since energy density has been determined for only a few species, the average values of a and b for seven passerine species (Ricklefs, 1974 Table 24) were used to describe the nestling Mountain Bluebird relationship. This procedure was also followed by Walsberg (1978). Energy densities were thus estimated for each nestling mass. Net efficiency of synthesis was estimated as 75% (Ricklefs, 1974). The energy required for growth, then can be expressed as  80  PE =  D x growth rate 0.75  (27)  where PE is expressed in kjd Existence metabolism can be approximated as the adult's mass-specific metabolic rate (Walsberg, 1978, Ricklefs, 1974). Table XVII lists the estimates of EM, PE, DEB, and GEI for the bluebird nestlings at each mass. The efficiency of assimilation determines the additional energy (resulting in the GEI) required to maintain the daily energy budget (O'Connor, 1984). Assimilation efficiencies range from 60 - 80% (Table 6.1, O'Connor, 1984). Ricklefs (1974) notes that assimilation efficiencies for insect diets ranges from 70 — 80%. A value of 70% assimilation efficiency is used in this study. The gross energy intake, then, is approximated by summing the energy requirements for nestling growth and maintenance and dividing by the assimilation efficiency. This gross energy intake must also take into account the number of nestlings and the amount of time available spent foraging by the adults (Table XIII).  PEjkJd- ) 1  Gross energy required per nestling =  +  b~7ro  The energy requirement will be expressed as kJd , -1  EM(kJd~ ) l  (28)  but the unit of day must be the  amount of the day available for foraging, not the 24-hour day, because the parents will have to supply the required energy in a limited time. For the Mountain Bluebird, the time available for foraging is approximately 16 hours per day at the study site (personal observation). Some error in the energy calculations may be due to the fact that the nestling masses and thus the growth rate were determined for the second brood of nestlings while flight speed measurements were recorded while the adults were raising thefirstbrood. Growth rates are known in some cases to be slightly different between first and second broods 81  (Ricklefs, 1968). However, the second broods all contained four nestlings each, which was the case for four of five of the first broods, so energy demands on the parents were thought to be similar. A growth curve was plotted using Mountain Bluebird nestling masses of first and second broods obtained by Power (1966) and the coefficients of the logistic growth curve equation were similar when compared to the coefficients determined from this study (coefficients of a,  and 7 from Power's data were 24.87, 13.44, and —0.44, while from  the present study they were 32.06, 14.24, and —0.45 respectively). The coefficient /3 is a constant proportional to the overall growth rate and may be used as a comparison between and within species. The minimum energy required during the nestling period by the nestlings will be at the age of one day. Since measurements of mass were not started until the young were two days old, thefirstgrowth rate cannot be obtained until day three, when the increase in mass from day two to day three can be determined. Thus, day three is considered here as the minimum known energy requirement to be brought to the nest. Values of the gross energy intake (GEI) for one nestling at each mass are listed in Table XVII. Since four of thefivenests studied consisted of four young, and assuming that each parent fed the young equally, GEI is considered for one adult bluebird to be the rate of energy delivered for two nestlings. The minimum GEI required when two young are three days old is 0.89 Watts. The maximum GEI occurs when two young are fifteen days old (GEI= 3.8W). An average GEI over the nestling period is 2.33W\ Walsberg (1983) has determined a general expression for average and peak energy expenditure of nestlings based on a regression of data from ten species. Average energy expenditure per nestling is written as  ln(E#) = Jnl4.05 + 0.440ZnM  (29)  where M is the adult body mass (in g) and Efj is the average energy expenditure per nestling (kJdr ). Peak energy expenditure is 1  82  ln(E ) = lnl3.4Q + Q.52BlnM  (30)  N  where EN is the peak energy expenditure per nestling (kJd~ ). l  E  N  and  EN  are energy  for growth and maintenance of the young only and must also be corrected to gross energy intake. Table XIX shows similar results of the Walsberg (1983) equations and for peak and average energy expenditures per nestling determined by following O'Connor (1984) and Ricklefs (1974), for the Mountain Bluebird and Tree Swallow. Nestling energy requirements for the Tree Swallow (Table XVIII) were calculated in the same manner as for the Mountain Bluebird nestlings. Nestling masses from Paynter (1954) were used since swallow nestlings in this study were not weighed. The estimate of gross energy requirements brought by the parents was based on 2.5 nestlings for each parent since three of the five nests consisted of five young. The other two nests were each of six young so would be underestimated. The minimum nestling energy requirement for one nestling was determined to be 0.19W. These nestling energy estimates may not be very accurate because nestling masses were used of nestlings from a different study and study location, and also because the calculations themselves are only a rough approximation of nestling energy requirements. Comparisons of the peak and average nestling energy expenditures with those calculated using Walsberg's equations, however, indicate similar results (Table XIX). Upon comparing the values of P  determined when V b» is assigned as  %  ga  n  0  V  opt  with the  estimated nestling energy requirements, it appears that V0D8 is not a good approximation to  V . opt  For the Mountain Bluebird, P  in  ga  determined from Figure 18 was found to be  0.48W, while the minimum nestling requirement for two nestlings at the age of three days was estimated as 0.89 W.  P in, ga  then, clearly does not cover the cost of feeding  two young, even at three days old. It would also not cover the cost of the travelling flight, as indicated in equation 16. The difference between energy required by the nestlings and energy apparently delivered may be partially explained by the observation that the  83  T A B L E XVII. M O U N T A I N B L U E B I R D NESTLING ENERGY REQUIREMENTS Age (days)  Percent of E M Adult Mass (kJd' ) (%)  3 4  21.1 28.8 41.4 50.5 67.7 74.7 83.5 88.4 96.5 102.0 106.0 106.0 114.0 115.0 109.0 109.0  5 6 7 8 9 10 11 12 13 14 15 16 17 18  1  8.65 11.82 17.01 20.76 27.82 30.71 34.31 36.33 39.64 41.75 43.68 43.39 47.00 47.13 44.69 44.98  PE (kJd' )  DEB (kJd' )  GEI (W) (1 nestling)  9.23 13.05 24.38 19.17 41.75 17.97 23.90 14.74 23.98 16.20 14.39 -2.2 28.97 1.17 -19.15 2.25  17.87 24.87 41.39 39.93 69.57 48.68 58.21 51.07 63.62 57.95 58.07 41.19 75.97 48.31 25.54 47.23  0.443 0.6118 1.027 0.9903 1.725 1.207 1.444 0.802 1.578 1.437 1.440 1.022 1.884 1.198 0.6334 1.171  1  84  1  T A B L E XVIII. T R E E S W A L L O W NESTLING ENERGY REQUIREMENTS Age  Percent of E M  (days)  A d u l t Mass  (Md ) -1  PE (kJd' ) 1  DEB (kJd- ) 1  (%)  GEI (W) (1 n e s t l i n g )  2  11.3  3.58  4.05  7.63  0.189  3  17.6  5.58  6.53  12.11  0.300  4  26.0  8.27  9.71  17.98  0.4459  5  38.5  12.24  16.44  28.68  0.711  6  45.6  14.50  10.01  24.51  0.6078  7  64.6  20.54  31.58  52.12  1.293  8  82.1  26.10  33.16  59.26  1.470  9  93.6  29.76  14.64  44.40  1.101  10  100.7  32.02  10.82  42.83  1.062  11  105.8  33.64  -2.10  31.54  0.782  12 13  104.9  33.36  -1.00  32.36  0.803  104.4  33.19  3.18  36.37  0.902  14  105.9  33.67  1.11  34.77  0.862  15  106.4  33.83  -3.10  30.72  0.762  16 17  105.0  33.38  104.2  -1.65 -8.42  31.73 24.70  0.787 0.6127  18  100.4  33.13 31.92  -2.67  29.25  0.725  19  99.1  31.51  -4.02  27.48  0.682  20  97.2  30.90  -6.70  24.20  0.600  85  T A B L E XIX. C O M P A R I S O N S O F N E S T L I N G E N E R G Y E X P E N D I T U R E S FOR ONE NESTLING Peak Nestling Expenditure kJd1  Average Nestling Expenditure kJd' 1  Mountain Bluebird Estimated Walsberg (1983)  108.5 112.2  67.0 87.6  84.7 85.4  44.6 48.9  Tree Swallow Estimated Walsberg (1983)  86  adults sometimes caught prey items within a few metres of the nest, thus increasing energy delivery to the young. Similar conclusions can be reached when comparing nestling energy requirements. The value of P  ga  in  when  Pgain  V bs 0  with the Tree Swallow  is considered to be V  opt  is  0.12W, while the minimum requirement for 2.5 nestlings is 0A7W, at the age of two days. Again, this does not take into account theflightcosts. The results indicate that adultflightspeeds do not vary with increasing age and size of the young for the Mountain Bluebird and the Tree Swallow. A fairly constant velocity is used throughout the nestling period for the Mountain Bluebird. The number of visits to each nestling per hour does increase slightly and significantly with the age of the nestlings, but the r value is only 11%, meaning that only 11% of the variation in feedings can be 2  explained by the variation in nestling age. As seen in Figures 14, there was no general trend common to all nests with increasing nestling age. Since neither visiting frequency nor flight velocity of the bluebird parents increased with nestling age, in order to bring sufficient energy supplies to the young the parents must either spend more hours of the day foraging or make up for this discrepancy in periods of the day that were not under observation. Since each nest was usually observed for only one hour per day, the whole daily activity schedule was not fully known. One bluebird nest, however, was observed for a whole day but cannot be used in comparisons with nestling ages. It is possible that the parents increase their feeding rates during other periods of the day. This is supported by the fact that the feeding rate was quite variable, ranging from 0.7 — 7.2 feedings per hour per nestling. That feeding rates were increased during other parts of the day is also probably true for the Tree Swallow, which also had a variable feeding rate (1.3 — 9.4 visits/hr nestling). Flight speeds of the Tree Swallow were taken starting when the young were one or two days old and continued only until they were six or seven days old. Since only thefirstweek of the nestling period was observed, it is possible that theflightspeed of the adults may have increased when the young became older, with greater energy demands. The observed  87  -1  speed (V bs = 6.6m,s ) seemed to be fairly constant over the first week. Table XV shows 0  that only at nest two was there any difference in flight speeds between any of the recording days. -1  It seems clear that theflightvelocity remained constant at close to 8.4ms for the -1  Mountain Bluebird and 6.6ms  for the Tree Swallow. There were differences within  different nests between recording days for nests two and four but these were both due to only one recording day being different from the rest (Table XV). Female bluebirds and swallows definitely flew at speeds greater than the maximum range speed predicted from their own individual power curves (Table XVI) and the mean velocity of all birds probably did not correspond to V  opt  as predicted by Norberg (1981).  88  C H A P T E R FOUR G E N E R A L DISCUSSION A N D CONCLUSIONS  4.1 G E N E R A L  DISCUSSION  Morphological designs, especially wing dimensions, are important in determining and limiting bird flight speeds. More specialized birds are adapted to using their particular environment, and their body design in relation to flight behaviours and performance is also specialized (Rayner, 1985b). This leads to a rigidity of design "optimality" for a particular habitat and lifestyle. The effect of wing dimensions on flight can be characterized by the wing loading (weight per unit wing area) and the aspect ratio (wing span squared over the wing area). Birds that have a high wing loading tend to be fast fliers, and also have a high stalling speed, Vataiii to avoid. High aspect ratio wings can also contribute to high speed flight (for example ducks, geese, grebes, and some shorebirds), although, when combined with low wing loadings as in swifts, swallows, and terns, for example, minimum power and maximum range speeds are reduced because of diminished induced power requirements for flight. Such birds can afford toflyat slower velocities, although a disadvantage to this is that their speed at which the cost of transport is minimimized is relatively low. The Tree Swallow, White-throated Swift, and Black Tern, all aerial insectivores, were found in this study toflyfaster than V . The Black Tern has a high aspect ratio (10.4) and mr  -2  a low wing loading (19.1 JVm ), which suggests that its power requirements, and thus V , mr  would have been relatively lower than for the other species. However, the Tree Swallow, which has an approximately average aspect ratio (7.4) and low wing loading (13.9Nm~ ) 2  also flew faster than V , as did the swift (with AR = 11.9 and Q = 34.7Nm~ ). Figure 2  mr  2 shows that although the aspect ratios of these three species differ, the general shape of the wing is similar.  89  The starling and the bluebird were found to have similar aspect ratios (6.7 and 5.9 respectively) with similar wing shapes (Figure 2) but the starling had a higher wing loading 2  (Q = 36.6iVm~ compared to Q — \1.2Nm~  2  for the bluebird). The difference in Q is due  almost completely to the difference in mass between the two species, since the wing areas are quite similar (Table II). Both species fly faster than V mr , although their foraging styles are quite different - the starling forages mainly from ground level, while the bluebird often detects prey by hovering above the ground and thus may potentially spend more energy in flight during foraging. It is clear, therefore, that the above five species flew speeds greater than the maximum range speed, V  mr  when the adult birds were flying to and from a foraging site while rearing  their young. The relation of V bs to V 0  mr  appeared to be independent of aspect ratios and  wing loadings as well as the habitat (open rangelands, marshes, mountainous terrain) and foraging style (ground foragers, aerial foragers, and even the case of the Black Tern which sometimes catches fish). The Pigeon Guillemot and Red-necked Grebe both fly at speeds significantly less than Vmr, and in the case of the grebe, less than V  mp  as well. Both species have similar aspect  ratios (8.8 for the grebe and 7.5 for the guillemot - Figure 1) and high wing loadings compared to the preceding five species (Table II). This would suggest that they should be fast fliers, at least flying at V , but this was not confirmed in the results. mr  A possible explanation of the speeds observed for the Pigeon Guillemot is that the birds were not actually feeding young. They were observed leaving and returning to particular crevices in the rock cliffs, but no nestlings were observed, and since it was early in their breeding season, it is possible that the speeds recorded represented foraging flights of adults with no.extra demands from young. Even if this were so, V  mr  would still  be the predicted flight speed for foraging flights in order to minimize the trip costs per unit distance travelled. Another possibility is that since this species also uses its wings for under water propulsion, the wings may be also adapted for under water use, and not exclusively for flight.  90  The Red-necked Grebe, however, was observed carryingfishto its young and its mean recorded flight speed was significantly less than even the minimum power speed, V . The mp  range of its speeds shown by the boxplot in Figure 10 indicate that some of the speeds were less than the theoretical V u. Clearly other factors besides bringing the maximum sia  amount of food to the young determine the flight speed for the Red-necked Grebe. In a more detailed study of breeding Mountain Bluebirds and Tree Swallows, an estimate of P i , ga n  the net rate of energy gained during foraging, was determined using  Norberg's (1981) model. P i  was determined by setting V b as the optimal speed, V ,  ga n  0  8  opt  and drawing a tangent to this point (Figures 18,19). This value of P  in  ga  to nestling energy requirements for both species and  P in ga  was then compared  in both cases was' found to be  less than the minimum nestling energy requirements. Since P ain should also include the g  cost of the travelling flight (equation 16), it appears that both the  P in ga  estimated and thus  the observedflightspeed, V i , were much less than those predicted by Norberg (1981). 0  s  It appears, then, that Mountain Bluebirds and Tree Swallows in this studyflewat speeds intermediate between V  mr  and V t. op  Sinceflightspeed of foraging trips did not increase with the age of the young and the feeding rate to each nestling per hour was also independent of nestling age, it is possisble that, in order to meet the increasing energy demands of their young, the adults increased their foraging rate (although probably not theirflightspeed as it appeared to be constant independent of the time of day of the recording - Figures 11, 12) and delivery rate to the young at some other period during the day not under observation.  91  4.2  CONCLUSIONS  1. Five species (Tree Swallow, Mountain Bluebird, European Starling, White-throated Swift, and Black Tern) were found toflyat speeds greater than their maximum range speed, V , whenflyingto and from a foraging site while raising their young. mr  2. The relation of the observedflightvelocity, Voba, to V for the above five species appeared to be independent of morphology, foraging style, and habitat. mr  3. The two species (Pigeon Guillemot and Red-necked Grebe) whichflewslower than V were both larger birds with much higher wing loadings. Flight speed in the Pigeon Guillemot may not have been related to rearing its young since they may not have been hatched at the time of the recordings.  mr  4. Flight speeds of adult Mountain Bluebirds remained fairly constant over the nestling -1 period at 8.4ms , and did not increase with increasing age of the young. For the Mountain Bluebird, the number of visits to the nest per hour per nestling did not increase with the age of the nestling. Flight speeds of adult Tree Swallows also -1 remained constant over the recording period, with V b = 6.6ms . 0  a  5. When Voos was assigned as V t for the Mountain Bluebird and Tree Swallow the corresponding value of P9a,n was less than the minimum nestling energy requirement. This indicates that the two species studied did notflyat the predicted V t, but at an intermediate speed between V and V t. op  op  mr  op  6. In order to meet nestling energy requirements, Mountain Bluebirds and Tree Swallows probably increase their feeding rate at times of the day other than those that were under observation. This idea is supported by the variable feeding rate bf both species (0.7 — 7.2 visits per hour per nestling for the Mountain Bluebird and 1.3 — 9.4 visits per hour per nestling for the Tree Swallow). Flight speeds were probably not increased for the Mountain Bluebird as they appeared to be constant independent of the time of day of the recording. 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OBSERVATIONS FOR BLUEBIRD NEST ONE Date  Nestling  Observation  Age (days)  Duration (min)  Number of Visits to Nest male  female  Feeding  M e a n Flight  Rate *  Speed -1  total  (ms ),n  May 25  3  June 1  10  50  9  7  16  3.2  June 2  11  30  2  0  2  0.7  8.1, 6  June 2  11  2G  4  1  5  1.9  8.1,6  June 5  15  60  2  5  7  7.0  8.2, 5  June 7  17  59  3  2  5  5.1  8.3, 7  June 8  18  57  1  5  6  6.3  8.8, 9  June 9  19  55  2  1  3  3.3  8.0,5  337  23^  21  44  TOTAL * Number visits/hr/nestling  7.8, 6  T A B L E A2. O B S E R V A T I O N S F O R B L U E B I R D N E S T Number of Visits to Nest  TWO  Nestling  Observation  Age  Duration  (days)  (min)  male  female  total  June 4  5  55  5  6  11  3.0  8.4, 5  June 6  7  59  14  7  21  5.3  8.8,13  June 7  8  35  2  ,2  4  1.7  8.4, 4  June 8  9  20  3  1  4  2.3  8.4, 5  June 9  10  27  1  2  3  1.7  8.6,2  June 11  12  42  7  6  13  4.6  8.5, 12  June 12  13  61  8  7  15  3.7  8.6,10  June 14  !5  30  1  1  2  1.0  8.3, 6  335  41  32  73  Date  TOTAL * Number visits/hr/nestling  Feeding  Mean Flight  Rate *  Speed _1  (ms ),n  T A B L E A3. OBSERVATIONS FOR BLUEBIRD NEST T H R E E Mean Flight  Rate *  Speed  Observation  (days)  (min)  male  female  .total  June 5  3  00  3  2  5  1.3  8.9, 2  June 7  5  58  5  3  8  2.1  7.8, 5  June 8  6  58  2  4  6  1.0  8.0, 6  June 11  9  61  6  6  12  3.0  8.1, 13  June 12  10  37  1  2  3  1.2  8.5, 3  June 13  11  62  0  6  6  1.5  8.7, 7  June 14  12  40  3  2  5  1.9  8.4, 9  June 15  13  25  1  5  6  3.6  8.6,10  June 16  14  45  2  5  7  2.3  8.1,9  June 17  15  40  3  0  9  3.4  8.4,14  480  26  41  67  TOTAL * Number visits/hr/nestling  Number of Visits to Nest  Feeding  Nestling Age  Date  Duration  -1  (m.* ),n  T A B L E A 4 . OBSERVATIONS FOR BLUEBIRD NEST F O U R Date  Feeding  Mean Flight  Rate *  Speed  (days)  Observation Number of Visits to Nest Duration (min) male female total  June 2  11  20  1  5  6  4.5  June 2  11  15  2  0  2  2.0  June 5  14  61  1  9  10  2.5  8.6,4  June 6  15  58  4  7  11  2.8  8.7, 11  June 7  16  43  3  2  5  1.7  8.3, 6  197  11  23  34  Nestling Age  TOTAL * Number visits/hr/ncstling  _1  (m« ),n 7.9, 3  T A B L E A5. OBSERVATIONS FOR BLUEBIRD NEST FIVE Date  Nestling Age  Feeding  (days)  Observation Number of Visits to Nest Duration (min) total male female  June 4  13  59  8  8  16  4.1  7.0, 8  June 6  15  58  8  20  28  7.2  . 8.7,16  June 7  16  57  6  21  27  7.1  8.6,13  June 8  17  62  4  4  8  6.5  8.2, 6  June 9  18  43  2  2  4  1.4  8.5, 9  June 10  19  18  2  1  3  2.5  8.6, 3  June 11  20  39  3  4  7  2.7  8.5, 9  June 12  21  38  1  1  2  3.2  8.5, 2  374  34  61  95  TOTAL * Number visits/hr/nestling  Rate *  Mean Flight Speed _1  (trM ),n  T A B L E A 6 . OBSERVATIONS FOR SWALLOW NEST ONE Date  Number of Visits to Nest  Observation Duration (min)  male  female  total  June 12  22  2  1  3  June 14  22  June 15  26  5  9  June 10  30  2  June 17  17  6  June 18  30  TOTAL  157  * Number visits/hr/nestling  Feeding  Mean Flight  Rate *  Speed -1  (ms ),n 1.4  6.9, 1  6.8  6.8, 19  14  5.4  6.5, 24  8  10  3.3  6.5, 18  10  16  9.4  6.9, 10 6.8, 10  58  T A B L E A7. OBSERVATIONS FOR SWALLOW NEST Date  Observation Duration (min)  June 14  28  June 15  44  June 16  45  June 17  40  June 18  30  TOTAL  157  * Number visits/hr/nestling  Number of Visits to Nest male  female  Feeding Rate *  2  M e a n Flight Speed -1  total 5  3  TWO  (m.? ),n 2.1  6.2, 7  1.4  6.5, 9  5  1.3  7.0, 10  8  2.4  6.7, 13 6.6, 10  23  T A B L E A 8 . OBSERVATIONS FOR SWALLOW N E S T T H R E E Date  Observation Duration  Number of Visits to Nest  Feeding Rate *  Mean Flight Speed -1  (min)  male  female  total  June 13  58  3  5  8  1.4  6.4, 8  June 14  47  3  3  6  1.3  6.2,11  June 15  52  4  7  11  2.1  6.6, 15  June 16  51  4  4  8  1.6  6.9, 12  June 17  29  4  4  8  2.8  6.6, 14  June 18  30  TOTAL  267  * Number visits/hr/nestling  (ms ),n  6.7, 10 41  T A B L E A 9 . OBSERVATIONS FOR SWALLOW N E S T F O U R Date  Observation Duration (min)  Feeding  Mean Flight  Rate *  Speed -1 (m.s ),n  5  2.0  6.8, 8  Number of Visits to Nest male  female  total  June 14  30  June 15  30  3  3  6  2.4  6.3, 11  June 16  21  2  3  5  2.9  6.4, 10 -  June 17  29  5  2.1  6.6, 10  June 18  30  TOTAL  140  * Number visits/hr/nestling  6.7, 10 21  T A B L E A10. OBSERVATIONS FOR SWALLOW N E S T FIVE Date  Observation  Number of Visits to Nest  Duration (min)  male  June 14  22  June 15  35  3  June 16  29  June 17  30  June 18  30  TOTAL  146  * Number visits/hr/nestling  female  Feeding  Mean Flight  Rate *  Speed  total  (ms  -1  ),n  5  2.7  6.3, 9  3  6  2.1  6.4, 10  1  4  5  2.1  6.3, 11  2  4  6  2.4  6.5, 10 6.5, 10  22  


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