David M. Bird

Sexual Dichromatism in Birds Independent of Diet, Parasites and Androgens

Sexual selection may explain why male animals are typically more colourful than females. Females may choose brightly coloured males for mating because colour is a reliable signal of a male’s genetic resistance to parasites, or that he can bear the cost of the immunosuppressant effects of androgens. Bright yellows, oranges and reds are the product of carotenoid pigments, which are known to have significant health benefits. Therefore, bright colours may be indicative of a bird’s quality because it shows access to a superior diet or superior foraging ability. We maintained populations of American kestrels and loggerhead shrikes in captivity that were largely free of parasites and fed a uniform diet. Male kestrels were more brightly coloured than females in the colour of their ceres, lores and legs, and there were pronounced age- and gender-specific patterns to concentrations of carotenoids in their plasma. Even though shrikes do not show any carotenoid-based colouration, the sexes had pronounced differences in plasma carotenoids. Carotenoids in kestrels were unrelated to androgen levels, but the correlation between carotenoids and plasma proteins suggest colour may be a condition-dependent trait. These results suggest that neglected physiological processes may regulate carotenoids, and hence some colour variation need not be explained by parasites, androgens or diet.

Changes in the Growth, but Not the Survival, of American Kestrels (Falco sparverius) Exposed to Environmentally Relevant Polybrominated Diphenyl Ethers

Polybrominated diphenyl ether (PBDEs) concentrations are increasing exponentially in biota. We studied the growth of American kestrel (Falco sparverius) nestlings exposed in ovo and during development to environmentally relevant PBDE congeners and concentrations. Eggs within each clutch, divided between groups by laying sequence, were injected into the air cell at 19 days of incubation with safflower oil or penta-BDE congeners BDE-47, -99, -100, and -153 dissolved in safflower oil (18.7 μg total [Σ] PBDEs/egg), approximating current levels in Great Lakes herring gulls. The measured proportions of BDE congeners found in the dosing oil were 56.4% of BDE-47; 27.2% of BDE-99; 24.8% of BDE-100; and 0.6% of BDE-153. For 29 days, nestlings were orally gavaged daily with the same ΣPBDE mixture (15.6 ± 0.3 ng/g body weight/day). Relative congener abundances in the dosing mixture compared to the carcasses suggest biotransformation of BDE-47; BDE-183 was also detected. PBDE exposure did not affect hatching or fledging success. PBDE-exposed nestlings were larger (weight, bones, feathers) as they gained weight more quickly and ate more food, the latter in association with their ΣPBDE body burdens. BDE-100 was most influential on nestling growth, being positively associated with size, weight gain, and food consumption. Increasing concentrations of BDE-183 and -153 were related to longer bones, and BDE-99 to longer feathers. The larger size of the PBDE-exposed birds may be detrimental to their bone structure and have excessive energetic costs. The repeated relationships with BDE-100 and growth may be important for wild Falconidae, since this is the predominant penta-BDE congener in these raptors.

Corticosterone levels during post-natal development in captive American kestrels (Falco sparverius)

We investigated post-natal development of the adrenocortical stress-response system in captive American kestrels (Falco sparverius) by measurements of baseline and stress-induced levels of corticosterone at ages 10, 16, 22, and 28 days post-hatching. Baseline levels of corticosterone increased significantly during post-natal development and although chicks aged 10- and 16-days old exhibited comparable baseline corticosterone levels, those of 22-day-old chicks were significantly higher and those of 28-day-old chicks close to fledging were higher than all younger groups. Chicks in this study exhibited low levels of stress-induced corticosterone early in development and did not exhibit adult-type stress-induced levels of corticosterone until 22 days of age post-hatching. Finally, although baseline and stress-induced levels of 28-day-old birds were significantly higher than one-year-old adults, there was no relationship between baseline corticosterone concentrations and time to nest departure. The fact that baseline levels of corticosterone are low during early development and then increase during later development may be an adaptation to the negative effects of chronically elevated corticosterone levels and as previously noted in other studies may minimize these negative effects on rapid growth and development in young birds, potentially maximizing normal growth. The ability of even young kestrel chicks to elevate corticosterone levels in response to stress suggests that they may be able to physiologically cope with food shortages associated with unpredictable food resources which wild kestrels often face.

Plasma corticosterone in American kestrel siblings: effects of age, hatching order, and hatching asynchrony.

Although it is well documented that hatching asynchrony in birds can lead to competitive and developmental hierarchies, potentially greatly affecting growth and survival of nestlings, hatching asynchrony may also precipitate modulations in neuroendocrine development or function. Here we examine sibling variation in adrenocortical function in postnatally developing, asynchronously hatching American kestrels (Falco sparverius) by measurements of baseline and stress-induced levels of corticosterone at ages 10, 16, 22, and 28 days posthatching. There was a significant effect of hatching order on both baseline and stress-induced corticosterone levels during development and these effects grew stronger through development. First-hatched chicks exhibited higher baseline levels than later-hatched chicks throughout development and higher stress-induced levels during the latter half of development. Furthermore, there was significant hatching span (difference in days between first- and last-hatched chicks) x hatching order interaction on both baseline and stress-induced corticosterone levels during development. Hatching span was also positively correlated with both measures of corticosterone and body mass in first-hatched chicks, but was negatively correlated with these factors through most of the development in last-hatched chicks. It is known that hatching asynchrony creates mass and size hierarchies within kestrel broods and we suggest that hierarchies in adrenocortical function among siblings may be one physiological mechanism by which these competitive hierarchies are maintained.

DNA fingerprinting reveals a low incidence of extra-pair fertilizations in the lesser kestrel

DNA fingerprinting of socially monogamous, colonially breeding lesser kestrels, Falco naumanni, revealed that three of 87 (3.4%) nestlings were illegitimate, and all three came from a single nest of 26 sampled (3.8%). Extra-pair paternity may have arisen through either extra-pair copulation (EPC) or mate replacement. The maximum level of extra-pair fertilization (EPF) was low (3.4%) compared to that found in other socially monogamous species and was also lower than predicted according to the frequency of EPCs in a previous study (6.7%). Paired females depend strongly on male provisioning throughout the breeding season and may refuse to engage in EPCs to prevent withdrawal of parental investment by their mates. The DNA analysis also indicated that two nestlings in two diVerent nests resulted from intraspecific brood parasitism. The frequency of parasitized broods revealed by DNA fingerprinting (7.4%, N=27) was higher than that inferred from egg-marking during nest inspections (3.8%, N=52). Pair copulation rates are high in the lesser kestrel but occur in a context of low sperm competition (i.e. low frequency of both EPCs and EPFs). Instead of assuring paternity, frequent copulations may function in females to assess their mates condition. Alternatively, copulations may have a pair-bond function or may reduce the availability of an individual to other potential mates. ? 1996 The Association for the Study of Animal Behaviour

Evaluation of an off-the-shelf Unmanned Aircraft System for Surveying Flocks of Geese

Abstract. Small off-the-shelf unmanned aircraft systems (UAS) could prove useful for surveying waterbirds. A low-end model was evaluated for surveying flocks of Canada Geese (Branta canadensis) and Snow Geese (Chen caerulescens) by comparing photographic counts from repeated flybys to repeated visual ground counts. Due to low contrast of Canada Geese with the ground, UAS counts based on confident detections only had a lower mean than ground counts for five out of six flocks (>30% lower for three flocks) and coefficients of variation (CV) ranging from 11–106%, compared to 1–6% for ground counts. Conversely, UAS counts of high-contrast Snow Geese were 60% higher on average and less variable (CV = 1–6%) than ground counts (CV = 11%). In some cases the aircraft likely detected birds that were not seen from the ground due to an obstructed view. Shortcomings of the UAS were mainly related to its unsophisticated imaging system compared to more expensive models. Otherwise, the UAS proved capable of being conveniently transported and deployed over flocks without causing them to flush. Further consideration should be given to off-the-shelf UAS for surveying waterbirds over small areas (<5-km radius) that are difficult to survey from the ground or as an option for performing low-disturbance surveys.

Effects of short-term food deprivation on growth of hand-reared American kestrels

Sudden prey reductions were simulated to examine their impact on growth parameters of nestling American Kestrels (Falco sparverius) hand-reared in captivity. The experimental design consisted of three treatments: (1) 15 nestlings fed ad libitum (control individuals), (2) 15 nestlings that were starved for 24 hr when 7 days old, and for 36 hr when 21 days old, and (3) 15 nestlings that were starved for 36 hr when 14 days old and for 48 hr when 28 days old. Fitting biometrical data to the logistic model (body mass and the length of antebrachium, tarsus and beak) or linear models (length of the ninth primary and the central rectrix), no significant differences were found for the growth parameters of each trait between control and starved birds. This revealed no long-term effects caused by temporary starvation. Although starved individuals suffered a significant weight loss following the periods of food deprivation, they recovered mass in 2-4 days by increasing food ingestion when the ad libitum diet was restored. This flexibility of the growth of mass can be seen as an adaptive mechanism to permit compensation in day to day fluctuations of the food supply. Although American Kestrels show reversed sexual size dimorphism prior to fledging, males and females responded similarly to starvation.

Effects of dietary PCB exposure on adrenocortical function in captive American kestrels (Falco sparverius).

We experimentally examined the effects of dietary exposure to polychlorinated biphenyls (PCBs) on adrenocortical function in American kestrels (Falco sparverius). Nine captive male American kestrels previously exposed to a PCB mixture (Aroclor™1248:1254:1260; 1:1:1) in their diet were subjected to a standardized capture, handling and restraint protocol designed to produce an increase in circulating corticosterone. A similar protocol has been applied to a wide range of avian species and was used here to evaluate the response of PCB-exposed and control kestrels to a defined physical stressor. Both baseline and stress-induced corticosterone levels were significantly lower in PCB-exposed birds when compared with control birds of the same age. PCB-exposed birds exhibited significantly lower corticosterone levels during the corticosterone response when compared with control birds, independent of body condition. Furthermore, baseline corticosterone concentrations exhibited a hormetic response characterized by an inverted U-shaped dose response in relation to total PCB liver burden. These results support several recent studies which report decreased levels of circulating corticosterone in PCB-exposed wild birds. The results presented here provide the first evidence that exposure to an environmentally relevant level of PCBs (approximately 10 mg/kg body weight) can impair the corticosterone stress response in kestrels, potentially increasing the susceptibility of birds to environmental stressors such as severe weather and predatory and human disturbance.

CHANGES IN EGG COMPOSITION OF AMERICAN KESTRELS EXPOSED TO DIETARY POLYCHLORINATED BIPHENYLS

Changes in the quality of eggs of birds exposed to polychlorinated biphenyls (PCBs) have been described, but have never been directly attributed to PCBs. Polychlorinated biphenyl residues in eggs have been associated with reduced reproductive success and embryonic deformities in wild birds. Egg size and composition, specifically the amount of albumen, yolk, and water in an egg, also influence the growth and viability of embryos and hatchlings, and consequently the reproductive success of birds. To deter mine whether PCB exposure of adult birds affected the size and composition of their eggs, 25 pairs of captive American kestrels (Falco sparverius) were fed a mixture of PCB-spiked (1248:1254:1260) food to give an approximate exposure of 7 mg/kg body weight/d, beginning 1 mo prior to pairing, and continuing throughout the courtship, egg-laying, and incubation periods. This dietary level in the adult female kestrels resulted in mean total PCB residues in the eggs of 34.1 microg/g wet weight (geometric mean), which is environmentally relevant. PCB residues in eggs increased with the time of female exposure to the contaminated diet and laying date. Variation in egg size within PCB clutches was significantly greater than within control clutches, although absolute egg mass and volume did not differ markedly by treatment. Only infertile eggs and only one egg per clutch were used for egg composition analysis. Yolks in the PCB-contaminated eggs were heavier, with less wet and dry albumen relative to control eggs. Water content and eggshell thickness were not significantly affected by PCB exposure. These results suggest that eggs from the PCB treatment have relatively more lipid and less protein available for embryonic development. Changes in egg composition were not associated with egg size, lay date, ambient temperature, humidity, or precipitation, which are factors known to affect these variables in bird eggs. The PCB-induced changes in egg composition described here provide insight into possible mechanisms contributing to reduced reproductive performance in wild birds exposed to PCBs.Changes in the quality of eggs of birds exposed to polychlorinated biphenyls (PCBs) have been described, but have never been directly attributed to PCBs. Polychlorinated biphenyl residues in eggs have been associated with reduced reproductive success and embryonic deformities in wild birds. Egg size and composition, specifically the amount of albumen, yolk, and water in an egg, also influence the growth and viability of embryos and hatchlings, and consequently the reproductive success of birds. To deter mine whether PCB exposure of adult birds affected the size and composition of their eggs, 25 pairs of captive American kestrels (Falco sparverius) were fed a mixture of PCB-spiked (1248:1254:1260) food to give an approximate exposure of 7 mg/kg body weight/d, beginning 1 mo prior to pairing, and continuing throughout the courtship, egg-laying, and incubation periods. This dietary level in the adult female kestrels resulted in mean total PCB residues in the eggs of 34.1 µg/g wet weight (geometric mean), which is environmentally relevant. PCB residues in eggs increased with the time of female exposure to the contaminated diet and laying date. Variation in egg size within PCB clutches was significantly greater than within control clutches, although absolute egg mass and volume did not differ markedly by treatment. Only infertile eggs and only one egg per clutch were used for egg composition analysis. Yolks in the PCB-contaminated eggs were heavier, with less wet and dry albumen relative to control eggs. Water content and eggshell thickness were not significantly affected by PCB exposure. These results suggest that eggs from the PCB treatment have relatively more lipid and less protein available for embryonic development. Changes in egg composition were not associated with egg size, lay date, ambient temperature, humidity, or precipitation, which are factors known to affect these variables in bird eggs. The PCB-induced changes in egg composition described here provide insight into possible mechanisms contributing to reduced reproductive performance in wild birds exposed to PCBs.Changes in the quality of eggs of birds exposed to polychlorinated biphenyls (PCBs) have been described, but have never been directly attributed to PCBs. Polychlorinated biphenyl residues in eggs have been associated with reduced reproductive success and embryonic deformities in wild birds. Egg size and composition, specifically the amount of albumen, yolk, and water in an egg, also influence the growth and viability of embryos and hatchlings, and consequently the reproductive success of birds. To deter mine whether PCB exposure of adult birds affected the size and composition of their eggs, 25 pairs of captive American kestrels (Falco sparverius) were fed a mixture of PCB-spiked (1248:1254:1260) food to give an approximate exposure of 7 mg/kg body weight/d, beginning 1 mo prior to pairing, and continuing throughout the courtship, egg-laying, and incubation periods. This dietary level in the adult female kestrels resulted in mean total PCB residues in the eggs of 34.1 µg/g wet weight (geometric mean), which is environmentally relevant. PCB residues in eggs increased with the time of female exposure to the contaminated diet and laying date. Variation in egg size within PCB clutches was significantly greater than within control clutches, although absolute egg mass and volume did not differ markedly by treatment. Only infertile eggs and only one egg per clutch were used for egg composition analysis. Yolks in the PCB-contaminated eggs were heavier, with less wet and dry albumen relative to control eggs. Water content and eggshell thickness were not significantly affected by PCB exposure. These results suggest that eggs from the PCB treatment have relatively more lipid and less protein available for embryonic development. Changes in egg composition were not associated with egg size, lay date, ambient temperature, humidity, or precipitation, which are factors known to affect these variables in bird eggs. The PCB-induced changes in egg composition described here provide insight into possible mechanisms contributing to reduced reproductive performance in wild birds exposed to PCBs.

Multi‐generational effects of polybrominated diphenylethers exposure: Embryonic exposure of male American kestrels (Falco sparverius) to DE‐71 alters reproductive success and behaviors

Polybrominated diphenylethers (PBDEs) are additive flame-retardants that are environmentally persistent and bioaccumulative compounds of particular concern to species at high trophic levels, including predatory birds. The developmental effects of in ovo exposure to male birds at environmentally relevant levels of the PBDE technical mixture, DE-71, on reproductive success and behaviors using captive American kestrels (Falco sparverius) were determined. Males were exposed in ovo by direct maternal transfer to DE-71 and unintentionally to low concentrations of hexabromocyclododecane (HBCD) at three mean +/- standard error DE-71 concentrations of 288.60 +/- 33.35 ng/g wet weight (low-exposure), 1130.59 +/- 95.34 ng/g wet weight (high-exposure), or background levels of 3.01 +/- 0.46 ng/g wet weight (control). One year following exposure, males were paired with unexposed females. Reproductive success was lower in the high exposure pairs: 43% failed to lay eggs while all other pairs laid complete clutches; they also laid smaller clutches and produced smaller eggs with reduced fertility, parameters that were negatively correlated with paternal in ovo concentrations of all PBDEs, as well as individual congeners and HBCD. Throughout courtship, there were fewer copulations by all in ovo exposed males, fewer mate-calls made by high-exposure males, and decreasing trends in pair-bonding and nest-box behaviors across treatments that continued during brood rearing. The reductions in clutch size and fertility were associated with the reduced frequencies of male courtship behaviors, and were associated with increasing concentrations of the PBDE congeners BDE-47, -99, -100, -53, -138, and HBCD. The results of the present study confirm effects noted in the F(0) generation and demonstrate that exposure to DE-71 affects multiple generations of this predatory avian species at environmentally relevant levels of exposure.