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Population limitation models of migratory birds have sought to include impacts from events across the full annual cycle. Previous work has shown that events occurring in winter result in some individuals transitioning to the breeding grounds earlier or in better physical condition than others, thereby affecting reproductive success (carry-over effects). However, evidence for carry-over effects from breeding to wintering grounds has been shown less often. We used feather corticosterone (CORTf) levels of the migratory Louisiana Waterthrush Parkesia motacilla as a measure of the physiological state of birds at the time of moult on the breeding territory to investigate whether carry-over effects provide linkages across the annual cycle of this stream-obligate bird. We show that birds arriving on wintering grounds with lower CORTf scores, indicating reduced energetic challenges or stressors at the time of moult, occupied higher quality territories, and that these birds then achieved a better body condition during the overwinter period. Body condition, in turn, was important in determining whether adult birds returned the following winter, with birds in better condition returning at higher rates. Together these data suggest a carry-over effect from the breeding grounds to the wintering grounds that is further extended with respect to annual return rates. Very few other studies have linked conditions during the previous breeding season with latent effects during the subsequent overwintering period or with annual survival. This study shows that the effects of variation in energetic challenges or stressors can potentially carry over from the natal stream and accumulate over more than one life-history period before being manifested in reduced survival. This is of particular relevance to models of population limitation in migratory birds.

Ecologists frequently use physiological tools to understand how organisms cope with their surroundings but rarely at macroecological scales. This study describes spatial variation in corticosterone (CORT) levels in feathers of invasive house sparrows (Passer domesticus) across their range in Mexico and evaluates CORT–climate relationships with a focus on temperature and precipitation. Samples were collected from 49 sites across Mexico. Feather CORT (CORTf) was measured using methanol-based extraction and radioimmunoassay. Relationships between CORTf and spatial and climate variables were examined using simple linear regressions. Ordination was used on climate data, CORTf was plotted against the resulting axes, and univariate regression trees were used to identify important predictors of CORTf. Universal kriging interpolation was used to illustrate spatial variation in CORTf across Mexico. Correlations with ordination axes showed that high CORTf was associated with low precipitation during the rainy season and low dry season temperatures. Specifically, CORTf was negatively related to May precipitation and January and July minimum temperatures, and positively related to April deuterium excess and June minimum temperatures. CORTf was higher in second-year birds compared to after-hatch years and after-second years. House sparrows had higher CORTf levels in the hot, dry, north-central region of Mexico, and CORTf was negatively related to temperature and precipitation. House sparrows molt primarily from August–September but climate conditions throughout the year were important predictors of CORTf, suggesting that conditions outside of molt can carry over to influence energetics during feather growth. These data suggest that dry conditions are challenging for house sparrows in Mexico, supporting previous work showing that precipitation is an important predictor of broad-scale CORT variation. This work highlights the utility of CORTf for evaluating the influence of physiology on current avian range limits; furthermore, these data may allow us to predict future changes in species distributions.

Carotenoids produce many of the red, orange and yellow signal traits of birds, and individuals must trade off utilizing carotenoids for physiological processes versus ornamentation. Proximate mechanisms regulating this trade-off are poorly understood, despite their importance for expression of color signals. Corticosterone (CORT) may play a significant mechanistic role in signal expression because it mobilizes energy substrates and influences foraging behavior. We used a unique feather-based approach to test whether CORT mediates expression of carotenoid-based coloration. First, we investigated relationships between levels of CORT from feathers (CORT(f)) and carotenoid-based plumage signals in common redpolls (Acanthis flammea). Then, we determined how the width of growth bars and probability of having fault bars on feathers varied with CORT(f), specifically whether these metrics reflected developmental costs of elevated CORT ("stress" hypothesis) or represented an individual's quality ("quality" hypothesis). CORT(f) correlated positively with the strength of carotenoid signals, but only in adult males. However, also in adult males, CORT(f) was positively related to width of feather growth bars and negatively with probability of having fault bars, providing support for the quality hypothesis. Overall, CORT(f) was lower in adult males than in females or young males, possibly due to dominance patterns. Our results indicate that CORT may indirectly benefit feather quality, potentially by mediating the expression of carotenoid signals. We place our sex-specific findings into a novel framework that proposes that the influences of CORT in mediating carotenoid-based plumage traits will depend on the extent to which carotenoids are traded off between competing functions.

The study of population regulation is crucial for understanding population dynamics and for conservation. We report on trends in population size and reproduction of Bald Eagles (Haliaeetus leucocephalus) at Besnard Lake, Saskatchewan, Canada, during 1968-2012. We investigated the relative importance of density-dependent (population size) and density-independent (climate) factors in explaining variation in population growth rate and productivity. The number of occupied Bald Eagle territories increased until ca. 1988, but remained stable afterwards, fluctuating around ca. 26 pairs. The number of successful pairs increased until only ca. 1977 and remained relatively stable or slightly declined afterwards (ca. 16 successful breeding pairs per year). We found a strong negative density-dependence in all reproduction parameters (mean productivity, nesting success, mean brood size at fledging). Annual production initially increased in the 1970s, but decreased afterwards, while nesting success decreased throughout the whole study period. We also found a strong density-dependence in population growth rate, indicating that the stabilized population was regulated. It probably reached its carrying capacity in the late 1970s, although population size continued to increase until the late 1980s. Mean brood size at fledging was negatively related to the number of failed nesting pairs. Density alone explained most of the variation in breeding performance, although milder springs were weakly associated with a higher nesting success. Finally, we found evidence for regular fluctuations in mean productivity, and particularly in nesting success, with a 5-yr period. We discuss possible mechanisms behind the observed patterns of density-dependent reproduction and implications for our knowledge of how this eagle population is regulated.

Physiological mechanisms link the environment with population dynamics, and glucocorticoid hormones are of particular interest because they respond adaptively to environmental change and can influence vertebrate reproduction and fitness. We tested a novel approach of synchronizing feather-based measures of corticosterone (the primary avian glucocorticoid; CORTf) and ratios of stable isotopes (SIs) of C (δ13C) and N (δ15N) to provide information about environmental conditions and an integrated physiological response to those conditions over the same period of feather synthesis. Using a fragmented metapopulation of Dupont’s larks Chersophilus duponti, an endangered steppe songbird, we analyzed interrelationships among CORTf, δ13C, δ15N, and the physical environment, including measures of habitat loss and fragmentation. CORTf was not related to any habitat variable measured directly. However, we detected a significant spatial structure to CORTf values and food availability, with greater similarity in both at smaller spatial scales. Using SIs as proxies for the local environment, we found CORTf was negatively related to δ13C. Values of CORTf, δ13C, and the relationship between the two were likely driven by variation in agricultural land use surrounding lark habitat patches. Our feather-based approach revealed that individual physiology was sensitive to environmental conditions (e.g., an interaction of food availability and variation in habitat) at a local scale, but not patch or landscape scales. Combining CORTf and SIs may be a promising tool because it can provide individual-based information about habitat, physiology, and their relationship during the same time period.

Among European breeding birds, those wintering in the Sahel region have undergone a sustained and severe decline. Long-term data show that variation in primary production of the Sahelian staging area significantly affects survival of many species, a relationship probably mediated by trophic resource availability. However, the physiological, hormonal and behavioural responses underlying this relationship remain unexplored. We present a potential explanation for the importance of prevailing conditions during winter to understand the population ecology and current trends of migratory species. We measured corticosterone levels in feathers of Egyptian vultures Neophron percnopterus grown in Africa and Europe, showing how conditions faced by birds during wintering periods result in the release of more corticosterone over time than when those individuals were on their summering grounds. This pattern was concordant with home-range size differences (c. 33 times larger in Africa than in Europe). We suggest that as wintering habitat of Egyptian vultures in the Sahel region has degraded during recent times, food availability has also been reduced. An increase in corticosterone during winter with a consequent increase in locomotor activity, for example, food searching behaviour, may normally be adaptive. However, enlarging home ranges could be futile if conditions are not better in the dispersal area, and costs of the higher corticosterone level, including energy expenditure from enhanced activity, may pose a significant trade-off. These physiological responses may be characteristic of other European trans-Saharan migrant birds that have undergone significant population declines.

Summary. The screaming cowbird Molothrus rufoaxillaris is described as being sexually monochromatic, although it has a rufous axillary patch that shows inter-individual size variation. We investigated potential sex differences in patch size in 82 molecularly-sexed adults. All males exhibited large patches and 23 females had small patches; however, seven females lacked a patch and nine had large patches. Patch size was associated with sex and independent of body condition, location or date of sampling. We discuss several hypotheses that may explain the incidence of this male character in some females.

8 pages, 3 figures, 1 table, Offspring of long-lived species should face costs of parental trade-offs that vary with overall energetic demands encountered by parents during breeding. If sex differences exist in how parents make the trade-off, sex-specific differences may exist in the contribution of each parent to those costs. Adaptations of offspring facing such costs are not well understood, but the hormone corticosterone probably plays a role. We manipulated breeding effort in Cory's shearwaters (Calonectris diomedea) to increase costs to offspring and used an integrated measure of corticosterone from chick feathers to investigate how experimental variation in parental investment influences offspring physiology. Average foraging trip duration and foraging efficiency (FE) of breeding pairs were not related to chick corticosterone, but sex biases in FE were. Adult male investment was more strongly related to chick corticosterone than was female investment. Importantly, we show for the first time suppression of adrenocortical activity in nestling Procellariiform seabirds, and explain how our results indicate an adaptive mechanism invoked by chicks facing increased costs of parental trade-offs, Funding for this work was provided by the Natural Sciences and Engineering Research Council of Canada and the Stuart and Mary Houston Professorship in Ornithology (to G.R.B.), and projects REN2002-01 164 and BOS2000-0569-CO2-01 from the Spanish Government. G.D.F. was supported by a University of Saskatchewan Dean’s Scholarship, a Ruby Larson Scholarship, a Malcolm A. Ramsay Memorial Award, and the Nature Saskatchewan Graduate Student Grant

Despite the fact that the ability of animals to avoid being consumed by predators is influenced by their behaviour, morphology and life history, very few studies have attempted to integrate prey responses across these adaptation types. Here, our goal was to address the link between life-history traits (size and growth trajectory) of tadpoles and behavioural responses to predators. Specifically, we wanted to determine whether information learned about predators was influenced by prey growth trajectory before and after learning. We manipulated the size/growth trajectory of tadpoles by raising them under different temperatures. Tadpoles raised on a slow-growth trajectory (under cold conditions) and taught to recognize a salamander subsequently showed stronger responses after 2 weeks than tadpoles that were raised on a fast-growth trajectory (under warm conditions). When we account for the effect of size (r (2)=0.22) on the responses of prey to predator cues, we find that the growth trajectory pre-learning but not post-learning influences the learned responses of the tadpoles. The differences in responses to predators may reflect differential memory associated with the predator. To our knowledge, this is the first study that has attempted to link life-history traits (size and growth rate) with learning of predators. In order to gain a comprehensive understanding of antipredator responses of prey animals, we call for additional integrative studies that examine prey anti-predator responses across adaptation types.

For a comprehensive understanding of the evolution of animal signals, it is necessary to understand how the performance of visual displays is maximized to get the most possible attention from receivers. We assessed whether the white plumage of Snowy Owls Bubo scandiacus functioned as a social signal and, if so, how coloration and behavioural adaptations enhance signal efficacy. Signalling theory predicts that: (1) the colour properties of plumage should vary across the body, with the brightest parts being those involved in visual display performance; (2) specific displays calling attention to or enhancing detection or conspicuousness to conspecifics should be evident; and (3) location of the signallers should be such that signal efficacy is optimized. All three predictions were supported. The brightest areas of the plumage (particularly the face, throat and upper breast) were always unspotted, and white is particularly effective in open habitats characteristic of this species. The birds displayed a specific posture and orientated toward the sun preferentially on sunny days, and Owls with the whitest (least spotted) plumage displayed more and signalled more frequently from perches on the ground, where albedo from the snow may enhance the visual display. Snowy Owls integrate coloration, behaviour and environment through habitat selection to maximize the efficacy of their visual displays.

In the Athabasca oil sands region of northern Alberta, mining companies are evaluating reclamation using constructed wetlands for integration of tailings. From May to July 2008, reproductive performance of 40 breeding pairs of tree swallows (Tachycineta bicolor), plus growth and survival of nestlings, was measured on three reclaimed wetlands on two oil sands leases. A subset of nestlings was examined for i) feather corticosterone levels, ii) delayed-type hypersensitivity response, and iii) innate immune function. Nestlings on one of two wetlands created with oil sands process affected material (OSPM) were heavier and had greater wing-lengths, and mounted a stronger delayed-type hypersensitivity response compared those on the reference wetland. Corticosterone was significantly higher in male nestlings on one of two OSPM-containing wetland compared to the reference wetland. Body condition of 12-day-old female nestlings was inversely related to feather corticosterone. Under ideal weather conditions, reclaimed wetlands can support healthy populations of aerially-insectivorous birds.

Food-supplementation studies on birds during egg laying have generally manipulated macronutrients and energy. Such studies have shown variable effects on egg size in American Coots (Fulica americana). We determined the relative influences of local environment, food quantity, and food quality on egg size in American Coots by supplementing food and carotenoids at three sites in Saskatchewan. Eggs were collected and analyzed for carotenoid content and stable isotopes (δ15N and δ13C) in the yolk to determine whether variation in the type of food eaten contributes to egg size. We also report on the isotopic analysis of American Coot tissues and their eggs to assess evidence of endogenous versus exogenous protein and lipid allocations to reproduction. We provide isotopic evidence that American Coots used endogenous lipid, but not protein, reserves for egg formation and that egg size is more dependent on exogenous sources of nutrients. Laying sequence was the only variable across nesting locales that h...

4 pages, 1 figure, 1 table.-- PMID: 19351566 [PubMed].-- Printed version published Jul 2009., Porphyrins are a widespread group of pigments in nature, but, contrary to melanins and carotenoids, their occurrence as plumage colorants seems to be anecdotal and their function, if any, is unknown. Using thin-layer chromatography and high pressure liquid chromatography, we have found coproporphyrin III, the same porphyrin type previously reported in owls, in the plumage of nestling black-shouldered kites (Elanus caeruleus). The first plumage grown at the nest in this species includes reddish-brown contour feathers in the upperparts, and particularly in the breast area, which fade during the weeks-long post-fledging period to become either gray or white consistent with the definitive adult plumage. In these reddish feathers, we have also found small amounts of pheomelanins and traces of eumelanin. The contribution of each pigment to the final colour perceived by birds or other animals is unknown. In white and grey feathers of the same species no porphyrin was found, and only traces of eumelanin were detected in the grey ones. The fact that the reddish feathers are only found in the juvenal plumage, when individuals are vulnerable in an open nest, leads us to hypothesize a camouflage role for this ephemeral plumage. As porphyrins are involved, although not exclusively, we can for the first time ascribe them a function in the plumage of birds., JJN and IMG were funded by project CGL2006-07481/BOS of the Spanish Ministry of Science and Education. GRB was funded by the Natural Sciences and Engineering Research Council of Canada and the Stuart and Mary Houston Professorship in Ornithology.

Responses of parent birds to changes in demands by their offspring have typically been investigated by manipulating brood size and testing for altered patterns of provisioning. We applied an alternative method to breeding pairs of American Kestrels (Falco sparverius) by modifying the duration of their nesting periods. Rather than focusing on how hard parents can work on any given day, this novel approach tests how long they can sustain the stress of provisioning and the associated behavioral consequences. We manipulated nesting periods by exchanging nearly fledged young at the age of 20 days with offspring from other nests that were 10 days old. We found that males provisioned their second foster broods at rates similar to those for their original broods. By contrast, females brooded offspring in second foster nests less and also delivered less food to them. As a consequence, male offspring in second nests gained less mass than those in first nests, and nestlings of both sexes had reduced feather...

Intraspecific variation in plumage may have a functional significance in mate choice. As a result, breeding birds are often paired assortatively with respect to colour. However, whether this within-pair correlation is a result of homotypic preference whereby individuals pick a mate that looks like themselves, or directional preference whereby all individuals have the same phenotypic preference, is often unknown. Using data collected between 1989 and 2006, we describe intraspecific variation in the striking white feathers on the leading edge of the wing, lesser coverts and mantle of 144 Spanish imperial eagles (Aquila adalberti), one of the most endangered birds of prey in the world. Females had, on average, more white than males, and pairs mated in a positive assortative fashion. Coloration was not related to age of the bird, food supply (i.e., territory quality) or breeding productivity. Our results are most consistent with the process of homotypic-preference assortative mating, and this may be a result of sexual imprinting, and function as a mechanism to optimize the degree of outbreeding. This pattern of mate selection may explain the rapid evolutionary divergence of A. adalberti from the continental population of imperial eagle A. heliaca., This study was funded by the Dirección General para la Biodiversidad del Ministerio de Medio Ambiente. GRB was supported by a grant from the Natural Sciences and Engineering Research Council of Canada.

It has been suggested that declines in breeding populations of Swainson's hawks (Buteo swainsoni) in California, Oregon, and Nevada may be due to differential mortality of hawks on their wintering grounds. Although massive mortality incidents reported on the wintering grounds partially support this suggestion, there are no data showing differential use of wintering areas by breeding populations of Swainson's hawks. We used stable-hydrogen isotope analysis of feathers to determine whether large flocks of hawks wintering in Argentina consisted of a mixture of individuals from across the North American breeding range or consisted of individuals from discrete breeding populations. We found that flocks of wintering Swainson's hawks consisted of a mixture of individuals. The lack of connectivity between populations of breeding and wintering hawks suggests that high wintering mortality, either natural or human-induced, is unlikely to have direct consequences on a single breeding area in North America. The demographic effects of winter mortality should be 'diluted' across the entire breeding range of Swainson's hawks.

Several species of raptors have two ocelli (eye-like patches) in the back of their head, giving them the appearance of a false face, although this trait has rarely been reported. According to our observations, these markings may be widespread in the family Falconidae, some Accipiter hawks, and some owls (e.g. Glaucidium, and some Athene, Aegolius, and Surnia). In this study, we outline general classes of hypotheses that may account for ocelli on the heads of raptors. The most frequently evoked general hypothesis is that ocelli offer protection against attackers. For example, a predator may abort the effort, be deflected by the ocelli, or be warned that the bearer will retaliate if attacked. We propose two alternatives. Most raptors with ocelli typically include a large proportion of passerine birds in their diets. The false faces may have evolved to aid in the hunting of small birds by actually provoking, or manipulating the nature of, a mobbing response. The benefit of doing so may either be immediate because there are numerous accounts of mobbers being killed, or the benefit may be postponed if the predator is using mobbing as a means of evaluating hunting prospects in a given area. An analysis of the pygmy-owls of the genus Glaucidium indicates that species displaying ocelli in the nape tend to have a high proportion of small birds in their diets and live in open habitats, whereas the opposite is true for species without ocelli. Pygmy-owls with ocelli are also considerably smaller and, collectively, these findings are most consistent with false faces being a conspicuous visual signal to deceive mobbing birds so they can be preyed upon. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 467–477.

In 1998, the Aznalco´ llar mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colonies of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects not seen before the spill, prompting this study. Nestlings with deformed legs had significantly lower plasma phosphorous (P) and higher Ca:P ratios than non-deformed cohorts in the first two years, but in the third year, when more, younger birds were studied, plasma P ranged from much higher to much lower in the affected colony compared with reference birds. Coefficients of variation for phosphorous were 19% and 60%, in reference and contaminated colonies, respectively. Storks from the contaminated colony were unable to control P levels and Ca:P ratios within the narrow limits necessary for normal bone development.

Urban endocrine ecology aims to understand how organisms cope with new sources of stress and maintain allostatic load to thrive in an increasingly urbanized world. Recent research efforts have yielded controversial results based on short-term measures of stress, without exploring its fitness effects. We measured feather corticosterone (CORTf, reflecting the duration and amplitude of glucocorticoid secretion over several weeks) and subsequent annual survival in urban and rural burrowing owls. This species shows high individual consistency in fear of humans (i.e., flight initiation distance, FID), allowing us to hypothesize that individuals distribute among habitats according to their tolerance to human disturbance. FIDs were shorter in urban than in rural birds, but CORTf levels did not differ, nor were correlated to FIDs. Survival was twice as high in urban as in rural birds and links with CORTf varied between habitats: while a quadratic relationship supports stabilizing selection in urban birds, high predation rates may have masked CORTf-survival relationship in rural ones. These results evidence that urban life does not constitute an additional source of stress for urban individuals, as shown by their near identical CORTf values compared with rural conspecifics supporting the non-random distribution of individuals among habitats according to their behavioural phenotypes

Although birds are highly patterned animals, the efficacy and information content of complex colour signalling by combining multiple feathers has rarely been investigated. We examine a melanin-dependent plumage pattern in the red-legged partridge, Alectoris rufa , in a captive breeding facility in Spain. Both males and females are striking in that the majority of the entire side of the body is covered with a bold brown, black and white vertical pattern. During agonistic displays the feathers are aligned in nearly perfect, continuous dorsoventral ‘flank bands’. We report on the unusual morphology and developmental complexity of the pattern, including the number and anatomical location of the display feathers. We investigate whether the area of any of the three colours of individual feathers was a signal of a bird’s quality. Black alone varied significantly with age, sex and mass scaled to body size in both sexes, as well as the heterophil/ lymphocyte ratio of females. Birds in poor condition appear not to be able to pigment the feather completely to its edge. The negative correlation between the black areas of the display feathers of mated pairs and the negative correlation between male ornament size and reproductive success suggest various behavioural associations with colour. Plumage patterns provide many more potential opportunities for signalling an individual’s quality than overall colour alone, and they have the advantage that they can be turned off and on at the appropriate time through behavioural modification.

There is currently a great deal of interest in documenting habitat use of birds in the boreal forest, especially in response to disturbances such as harvesting and forest fires. Studies have shown that some avian species are much more common in recently burned areas, whereas others are absent. Despite this, we know little about the immediate effect of a large forest fire, and its considerable alteration of habitat, on birds during a single breeding season. In 1995, a 72,000-ha forest fire in our study area gave us the opportunity to assess the effects of fire on reproduction of American kestrels (Falco sparverius) in comparison to an adjacent control area. In addition, we also examined territory occupancy by kestrels in the burned and control areas 8 y following the fire. We found no immediate effect of the fire on body condition of adult kestrels, their ability to hatch eggs, or to fledge at least one young. Birds breeding in the area that burned, however, did fledge fewer offspring per nest, and these nestlings had reduced body mass compared to control nests, possibly because of an immediate reduction in available prey following the fire. Nonetheless, given the profound alteration of habitat following the fire, the fact than any birds remained to continue breeding is remarkable. Territory occupancy of the burned area in 2003 was similar to 1995, the year of the fire, but occupancy in the adjacent control area declined during this period. It therefore appears that the control area is becoming a less suitable habitat for kestrels as the forest continues to mature, whereas the burned area is still providing viable habitat for kestrels. We present evidence suggesting that some of the differences in occupancy between the control and burned area may be due to fewer nest predators in the burned area in 2003.

1. Food web interactions in animal communities can be investigated through the measurement of stable isotopes (e.g. δ15N, δ13C). We used this approach in a community of 14 species of seabirds breeding on the Argentinean Patagonian coast. Tissue samples were collected from nestling and adult seabirds, as well as prey, during three consecutive breeding seasons in 28 breeding colonies. 2. Relative to those in other temperate and polar regions, this seabird community showed a high degree of overlap in trophic level (TL) among species (93% of species within a TL range of 0.7) and also a comparatively high mean trophic level (4.1). 3. Relative positions of seabirds in relation to prey suggest that most species feed on pelagic fish and to a lesser extent on invertebrates. Stable isotope values of specialist feeders, Olrolg's (Larus atlanticus) and dolphin gulls (Leucophaeus scoresbii), which were previously assumed to feed mainly on crabs and sea lion excrement, respectively, suggested a broader diet than expected. 4. Based on stable isotope values of individuals, groups of phylogenetically related species generally showed a high degree of overlap within each group. 5. Given the degree of isotope overlap in this species-rich community, coexistence could be interpreted as a consequence of superabundance of food or species diversification in morphology and foraging strategies. The short range of trophic level makes these seabirds vulnerable to the reduction of fish stocks due either to commercial fishing or stochastic fluctuations.

Brood size has the potential to determine the allocation of resources between parents and offspring, as well as influence the relative contributions of each sex to parental effort. However, it is unclear whether brood size is the proximate determinant of parental effort, or conversely whether parental effort is the proximate factor to which brood size is adjusted. If brood size determines parental effort, then theory suggests that parental effort should vary with experimental changes in brood size. In contrast, if parental effort determines brood size, then parental effort is expected to be independent of experimental variation in brood size. To distinguish between these hypotheses, we experimentally reduced brood sizes of American kestrels (Falco sparverius). Our results suggest that male parents responded to brood-size variation and adjusted their provisioning behaviour accordingly. Conversely, female parents did not adjust provisioning in response to brood size, and as a result, offspring in reduced broods received more food on a per-nestling basis. However, condition and survival of offspring were similar in reduced broods and control young, which may have been the result of larger food requirements of small broods, owing to increased thermoregulatory costs compared with control broods. Female parents with reduced broods also did not brood offspring more often, further suggesting that females do not respond to variation in brood size. We conclude that the proximate determinants of parental effort are sex-specific in American kestrels: for males, brood size determines behaviour, whereas for females, behaviour may be a proximate factor determining brood size.

We studied variation in the carotenoid color of flight feathers of hybrid Northern Flickers (Colaptes auratus) and its correlation with reproductive performance and survival. Color scores provided by a digital camera revealed in 218 individuals a continuous spectrum from yellow to red. Males tended to be slightly redder than females. Within individuals, an analysis of color change with age revealed that males, but not females, became redder with age. Except for yearling females, body condition did not improve with age, sug- gesting that color is not linked to body condition measured during incubation. We did not detect any correlations between feather color and measures of reproductive performance, such as clutch size, hatching success, or fledging success, or return rate to the study area. In a hybrid population where intraspecific variation in color is controlled partly by genes, hue or brightness may not be a useful signal of individual quality, contrary to other studies of birds. About 25% of flickers had one or more tail feathers that differed from the rest of the plumage. In each case, the ''odd'' feathers were paler or yellower in color and may have been caused by diet or stress when the feathers were lost and regrown during winter. Such odd colors support the hypothesis that red carot- enoid pigments are costly to maintain under stressful conditions. Received 25 January 2002, accepted 5 August 2002.

For birds with altricial young, the brood-rearing period is one of the most energetically expensive periods in their lives and may be the bottleneck for fitness. Because parents are expected to be prudent in allocating resources between reproduction and self-maintenance, food supply should be an important factor determining reproductive decisions during brood rearing. Parents with abundant food are expected to have enhanced fitness because they are able to reduce their work rates and increase their own survival chances, because their offspring may be of higher quality, or some combination of these. However, few studies have simultaneously documented all of these variables in a single investigation. We performed a food supplementation experiment to test how food supply influenced provisioning decisions by parent American kestrels (Falco sparverius). Female kestrels showed a strong response to extra food and reduced their provisioning rates. As a result, supplemented females had higher return rates than control females, suggesting significant effects of food on female survival. Because females used extra food to increase their fitness, our results suggest that kestrels raising offspring are limited by food. Male kestrels whose nests were supplemented also responded to extra food by reducing provisioning, but to a much lesser extent than their mates. Male parents did not appear to benefit from supplementation, as their return rates were similar to control males. The total amount of food received on a daily basis by nestlings was similar between supplemented and control nests. Supplemented offspring therefore did not fledge in better condition or have higher survival rates than control nestlings; the only significant factor consistently affecting offspring condition and survival was weather.

Summary 1. Measures of the quality of an individual are important in the study of proximate and ultimate factors in biology. Records of developmental history are particularly desirable, as many phenotypical traits are influenced by conditions during growth. Conspicuous irregularities in feathers, known as fault bars, result from a variety of stresses that occur during feather growth. The frequency of fault bars was evaluated on primary and tail feathers (grown 1 year previously) of 1919 adult American kestrels from a breeding population in Canada (1990‐97). 2. Most (91·5%) birds exhibited some fault-barring, although females had significantly more feathers with fault bars than males (17% vs. 14%, respectively). Body size, intensity of haematozoan infections and leucocyte differentials were all unrelated to fault bars; however, birds with many fault bars were in poor body condition during prelaying (males) and incubation (males and females). 3. Individual kestrels tended to be consistent in the number of feathers with fault bars from year to year. 4. The percentage of feathers with fault bars was not associated with the timing of arrival in spring or prey abundance per territory; however, birds of both sexes with many bars were less likely to breed. Birds paired non-randomly, as mates tended to have a similar frequency of fault bars. Males and females with many bars had significantly later clutch initiation dates, but there were no negative consequences regarding clutch size or egg size. 5. Female kestrels with many fault bars had lower survival probabilities. Both sexes were also less likely to be recaptured in years following initial banding if they had many bars, suggesting that they were more likely to emigrate from the study area temporarily. 6. Fault bars on feathers appear to be indicative of an individual’s susceptibility to stress, and are useful in predicting components of fitness. The use of fault bars is a promising tool as they are easy to evaluate and can be assessed on live or dead birds, on moulted feathers and on individuals repeatedly over time.

Natural selection theory suggests that there should be fitness consequences for animals that possess morphological abnormalities such as missing or deformed appendages and other structures. As these characters are expected to be detrimental, morphological abnormalities could be considered “handicaps”. However, little information exists about the nature, prevalence or consequences of naturally occurring handicaps in birds, even though experimental handicapping has been used in some behavioural studies. Here, we document and describe the frequency of natural handicaps in American Kestrels Falco sparverius, and investigate their influence on condition and survival. We considered three different categories of handicap that should negatively impact falcons: missing remiges and rectrices, broken remiges and rectrices, and foot handicaps. Broken feathers, followed by missing feathers, were the most common handicaps detected in kestrels and their prevalence increased throughout the breeding season. Foot handicaps were relatively rare and showed no seasonal trends. There was no effect of any handicap type on body condition or return rates of male kestrels. In contrast, females with either foot handicaps or broken feathers were in significantly poorer condition than control females, and females with broken feathers were less likely than control females to return to the study area in years following initial capture. Given that female kestrels with broken feathers have more fault bars than those without broken feathers, and fault bar formation is related to stresses in a bird's past, we suggest that female kestrels that had broken feathers were of poorer quality than those without broken feathers or those with missing feathers. Females with broken feathers may therefore have been in poorer condition initially than other birds, or if broken feathers are indicative of poor quality, then females with broken feathers may have been less able to cope with the negative impacts of feather loss on flight performance compared to birds with missing feathers.

We used a digital camera to quantify the colour of the tail feathers of 245 northern flickers (Colaptes auratus) in central British Columbia and investigate the frequency of colour morphs in the population of hybrids. The colour values generated by the camera corresponded well to the conventional method of ranking colours by eye, but was advantageous because it provided finer discrimination and a continuous colour variable. Rectrix colour varied in a continuum from the yellow of C. a. auratus to the red of C. a. cafer. By experimentally exposing red and yellow feathers to sunlight we showed that the intermediate orange colours were not a result of secondary fading of the carotenoid pigments. The distribution of colours in the population was bimodal. A paucity of intermediate phenotypes (orange birds) could not be explained by their mortality because return rates of birds to our study area was not associated with colour. New immigrants into the population tended to resemble parental types more often than hybrids. Assortative mating by colour in this population may tend to keep the subspecies separate, contrary to the situation in more southerly areas of the hybrid zone.

The prevalence of elevated exposure to lead was assessed in a migrant population of bald eagles (Haliaeetus leucocephalus) at a waterfowl staging area in the southern portion of the Canadian prairies, from September to November, 1992-1995. Of 103 eagles, 8% exhibited blood lead (PbB) concentrations suggestive of elevated exposure to lead (or = 0.200 microgram ml-1 wet wt.). PbB concentrations in eagles from the study area ranged from0.01 to 0.585 microgram ml-1, while those of nestling eagles from a reference site indicated normal or background exposure (0.01 microgram ml-1). No differences in the prevalence of elevated exposure were detected among genders or age classes (0.5- andor = 1.5-year-old birds) (P0.05). The prevalence of elevated exposure was significantly greater in November than in October (21.7 vs. 3.8%) (all years: chi 2Y = 5.75, P = 0.017). Eagles with shotshell pellets in the digestive tract did not have accompanying high PbB concentrations. The prevalence of elevated lead exposure in this study was low in comparison to other areas in North America. Potential biases in the trapping technique as they relate to interpreting the results are addressed.

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), whi...

In many avian species, older nestlings within a brood may decrease the fitness of younger siblings by aggression or competition. While such a situation suggests a potential parent-offpring conflict, it is often assumed that parents condone sibling aggression because there are few reports of adult birds intervening in fights between their young. However, parent bald eagles (Haliaeetus leucocephalus) interfered in 9% of bouts of sibling aggression using a variety of tactics not previously reported for birds. A review of the literature revealed additional behaviours that may be used to mitigate sibling aggression. We propose that parents may use “general remedial𠇍 behaviours as a long-term strategy to ensure adequate resources to disadvantaged offspring, and “acute responses” involving physical contact, distraction, or deception, to halt particular aggressive acts.

Interest in hematozoan parasites has been considerable in recent years, mostly as a result of Hamilton and Zuk's idea that parasites influence the expression of sexually selected traits. However, little is known about the basic patterns of parasitism and the dynamics of host-parasite relationships. We describe the patterns of blood parasitism in American kestrels (Falco sparverius) sampled throughout the breeding seasons of 1994 and 1995, and investigate the influence of several variables on parasite load. Parasite prevalences in kestrels were high, ranging from 75 to 94% depending on the sex of the birds and stage of the breeding season. Prevalence increased with date, indicating either active parasite transmission or relapses of chronic infections. Parasite intensity also increased with date, but these effects were sex- and year-specific. We detected no sex differences in either prevalence or intensity, but prevalences were higher in young (second calendar year) birds than in older birds. Because this effect was evident early in the breeding season, we suggest that it was due to differential recrudescence of chronic infections between age-classes. Food supply had no effect on parasite load. Among birds that were sampled twice in the same year, parasite status remained relatively constant, although some birds acquired infections while others lost them. Change in intensity between samples was dependent on year; nonetheless, intensities remained relatively stable throughout the breeding season. Kestrels sampled in both years had consistent parasite loads. Parasites were detected in only 3% of kestrel nestlings.

The connection between bald eagles (Haliaeetus leucocephalus) and the consumption of waterfowl, lead shotshell pellet ingestion, and subsequent lead exposure is well documented in the United States and is presumed also to be widespread in Canada. We compared blood lead concentrations in samples from bald eagles ranging in age from 0.5- to 1.5-yr-old at Galloway Bay, Saskatchewan, Canada (n = 97) during October-November, 1992-95 and Hauser Lake, Montana, USA (n = 81) during October-December, 1990-94, within the Great Plains region of North America. Abundant prey are available in the form of hunter-injured waterfowl in Saskatchewan and spawning salmon in Montana; both areas attract large numbers of mid-continent bald eagles during fall migration. Blood lead concentrations suggestive of recent lead exposure (0.201 microgram/ml) were found in 32% and 8% of eagles at Hauser Lake and Galloway Bay, respectively, when samples from each study area were analyzed independently at two laboratories. To determine if this difference was an artifact of interlaboratory variation, we determined a correction factor by reanalyzing 14 Saskatchewan blood samples at each laboratory and predicted blood lead concentrations from Hauser Lake had the samples been analyzed at the Canadian laboratory. Adjusted blood lead concentrations of samples from Hauser Lake indicated that 21% of eagles were recently exposed to lead, a proportion not significantly different from the proportion of the same exposure category at Galloway Bay. Our data do not support the supposition that a large proportion of bald eagles feeding on waterfowl in areas of high hunting pressure will be exposed to lead via consumption of lead shotshell pellets in waterfowl.

1. Sexually selected traits are expected to vary seasonally, with the maximal expression of the character being evident during mate choice; however, the mechanisms controlling or regulating such traits are generally poorly known. 2. Carotenoid pigments responsible for bright red or yellow coloration in the feathers, skin or other integumentary structures of birds are generally believed to vary seasonally because of diet. 3. Variation in carotenoid-dependent skin colour between winter and spring (mating season) was investigated, as was variation in plasma carotenoids across the breeding season in captive American Kestrels, Falco sparverius, fed a uniform diet. 4. Kestrels were more brightly coloured in the mating period than in winter, and plasma carotenoid concentrations declined from the time of mating to the rearing of young. 5. Although carotenoid levels were highly sexually dimorphic during mating and laying, males and both breeding and non-breeding females all had similar levels by the incubation period, and the pattern of variation over time suggests rheostatic regulation. 6. These results suggest kestrels may have the ability to regulate (rather than merely control) their colour physiologically, the variation in colour and carotenoids is consistent with that expected of a sexually selected trait, and the loss of colour after breeding may suggest a trade-off between the show and health functions of carotenoids.

Little is known about the basic biology of Carnus hemapterus (Diptera: Carnidae), a haematophagous parasite of nestling birds. We therefore explored the patterns of C. hemapterus infestations by repeatedly examining American kestrel (Falco sparverius) nestlings from 50 nests in north-central Saskatchewan. Most infestations occurred before chicks were 12 days old and were more frequent early in the breeding season. Nestlings from larger broods had higher prevalences of C. hemapterus, but we did not detect differences in intensity of infestations between broods of different sizes. Within broods up to 5 days old, the heaviest nestlings were preferentially infested by C. hemapterus. Although evidence suggests that ectoparasite infestations are harmful to hosts, we did not detect any mortality attributable to C. hemapterus. Similarly, we did not observe negative effects of C. hemapterus infestations on nestling mass, length of the tenth primary flight feather, haematocrit, or total plasma protein concentration at 24 days old.

International audience; The effects of environmental perturbations or stressors on individual states can be carried over to subsequent life stages and ultimately affect survival and reproduction. The concentration of corticosterone (CORT) in feathers is an integrated measure of hypothalamic-pituitary-adrenal activity during the molting period, providing information on the total baseline and stress-induced CORT secreted during the period of feather growth. Common eiders and greater snow geese replace all flight feathers once a year during the pre-basic molt, which occurs following breeding. Thus, CORT contained in feathers of pre-breeding individuals sampled in spring reflects the total CORT secreted during the previous molting event, which may provide insight into the magnitude or extent of stress experienced during this time period. We used data from multiple recaptures to disentangle the contribution of individual quality vs. external factors (i.e., breeding investment or environmental conditions) on feather CORT in arctic-nesting waterfowl. Our results revealed no repeatability of feather CORT within individuals of either species. In common eiders, feather CORT was not affected by prior reproductive investment, nor by pre-breeding (spring) body condition prior to the molting period. Individual feather CORT greatly varied according to the year, and August-September temperatures explained most of the annual variation in feather CORT. Understanding mechanisms that affect energetic costs and stress responses during molting will require further studies either using long-term data or experiments. Although our study period encompassed only five years, it nonetheless provides evidence that CORT measured in feathers likely reflects responses to environmental conditions experienced by birds during molt, and could be used as a metric to study carry-over effects.

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.

In birds that exhibit sexual size dimorphism, hatching asynchrony, and siblicide, the probability of nestling mortality and the cost of rearing young may vary with different combinations of sex and...

Current avian invasions are often the result of exotic birds accidentally escaping from cages. It has been hypothesised that the higher invasiveness of wild-caught cage-birds compared to captive-bred ones could be related to the loss of ability in captive-bred birds to cope with new environments. The acute stress response plays an important role in how animals cope with challenges because elevated corticosterone (CORT) levels can mediate learning and memory consolidation and help to increase their survival prospects. We experimentally tested whether exotic wild-caught and captive-bred cage-birds differ in their responses to acute stress using a representative sample of parrots. Wild-caught individuals showed longer CORT responses to acute stress than captive-bred ones, both at inter- and intra-specific levels when comparing wild-birds to the first generation born in captivity. Captive-bred birds may have attenuated their CORT responses due to acclimation, while high mortality rates during the international trade of wild-caught birds could have selected those individuals that are better able to cope with stress. We suggest that the longer acute response found in wild-caught parrots could help them to escape from cages and survive when facing challenges in new wild environments, possibly contributing to their higher invasiveness. © 2012 Springer Science+Business Media B.V.

We studied causes and consequences of egg-size variation among clutches of American kestrels (Falco sparverius). Egg. from 275 clutches were measured 1990 to 1992. To test the hypothesis that the size of eggs was contrained by food availability in the pre-laying period, we censused small mammal populations in the three years and performed a food supplementation experiment in 1990 and 1991. Kestrels did not advance the date they laid their first egg but did lay significantly larger eggs in response to extra food. The size of eggs was correlated with small mammal abundance on the territoty, and females in good body condition tended to lay large eggs. Body size did not affect egg size, and there were no relationship between agg size and laying date except in 1900, the poorest food year. Clutches with a large mean egg volume had better hatching success than clutches containing small eggs. We argue that there is a phonetypic component to egg size in kestrels, and that kestrels use egg size to fine-tune reproductive investiment to available resources.

Fluctuating asymmetry, i.e., random, subtle departures from perfect bilateral symmetry, is believed to be a measure of developmental noise. The more physical stress an organism has undergone, the greater the asymmetry. We investigated the degree of fluctuating asymmetry in bones of the American kestrel (Falco sparverius) as a test of the developmental consequences of sexual dimorphism in size. The "cost of rearing" hypothesis predicts that females, because of their larger size, will suffer food shortages more often than males and hence show greater asymmetry. In contrast, the "female dominance" hypothesis predicts that females will be under less developmental stress because their size gives them an advantage when they compete with their brothers for limited food while in the nest. Significant fluctuating asymmetry was detected for all characters of both sexes; however, differences between males and females only approached statistical significance. We suggest that the degree of among-broods variation is so great that the role of gender in influencing developmental stability may be relatively small.

Food supply and hatching asynchrony were manipulated for 90 broods of American kestrels (Falco sparverius) during 1989–1991. We measured the growth and mortality of nestlings within four treatment groups (asynchronous, synchronous, food-supplemented, unsupplemented) to test the brood reduction hypothesis of Lack (1947, 1954). Fledging success did not differ between synchronous and asynchronous broods when food was poor but consistent with the brood reduction hypothesis, nestlings died at a younger age in asynchronous broods. When food was supplemented, mortality did not occur in the synchronous broods but youngest nestlings still died in asynchronous nests despite apparently adequate food for the brood. Oldest nestlings in asynchronous broods fledged with a greater mass than their younger siblings, also consistent with Lack's hypothesis. Average nestling quality in synchronous broods was very dependent on food levels. Synchronous young that were supplemented were, on average, the heaviest of any treatment group but young from unsupplemented synchronous broods were the lightest. Overall, patterns of mortality and growth for kestrels support the brood reduction hypothesis when food is limited, but not when it is abundant. This food-dependent benefit of asynchrony in the nestling period is a prerequisite for facultatively adjusted hatching spans during laying.

Clutches of altricial birds generally hatch over a period of hours or days. Numerous hypotheses have been generated to explain hatching asynchrony, but most experiments have focused on the nestling stage to determine some post—hatch benefit such as increased reproductive success. We concentrated on proximate causes in the prelaying period, which have largely been ignored. In northern Saskatchewan, we censused prey species (small mammals) in early spring and measured the asynchrony of 273 clutches of the American Kestrel (Falco sparverius) over 4 yr. Hatching asynchrony was quantified in two ways: time for all the eggs within a clutch to hatch and mass hierarchies among nestlings. In good food years, the hatchling spans of clutches were more synchronous than in poor years. Similarly, parents on good territories or females in good physical condition had more synchronous broods than parents under food stress. In an experiment, we supplemented food to kestrels during the prelaying period. Parents that were supplemented laid larger eggs and hatched those eggs more synchronously, but control pairs were more successful at raising young to the fledging stage. Synchronous hatching when food is abundant is consistent with the hypothesis of facultative manipulation of hatching spans in relation to nestling food supply, but not with the energy constraint hypothesis.

Declines in Common Loon (Gavia immer) populations associated with increasing human use of lakes have been reported from many areas of North America. In the present report we describe a lake in northern Saskatchewan, Besnard Lake, where there has been a substantial increase in the number of loons, from about 85 in 1976–1979 to about 165 in 1990. A comparison was made with numbers of other birds associated with water. Increases were also seen in American White Pelicans (Pelecanus erythrorhynchos), Osprey (Pandion haliaetus), Great Blue Herons (Ardea herodias), Herring Gulls (Larus argentatus), Ring-billed Gulls (L. delawarensis), and Bonaparte's Gulls (L. Philadelphia). No change was seen in mergansers (Mergus merganser and M. serrator), Bald Eagles (Haliaeetus leucocephalus), or Common Terns (Sterna hirundo). The period 1976–1990 has also seen increased human use on Besnard Lake. The reason for increased loon numbers is uncertain, but could possibly be related to an increase in the numbers of small fish in Besnard Lake as a result of increased fishing pressure disproportionately removing the larger, predatory fish.

Ecologists have frequently used biochemical assays as proxies for processes or phenomena too difficult to explore by traditional means of investigation. Feathers have been subjected to a number of chemical analyses to study such things as their elemental composition, contaminants, and hormones. The reliance on standard methodology of using concentrations to express quantities of chemical substances is seriously problematic because it creates artifacts by ignoring the physiology of feathers. Some elements and compounds are incorporated into the feather as part of the very building blocks of the keratin. However, others that are less functionally important to feathers (but not necessarily to the bird) enter the developing cells in proportion to their abundance in the bloodstream; in other words, feathers are merely receptacles, and deposition of chemicals is time dependent. In the latter case, one that applies to much of the work done on feather chemistry, data expressed as concentrations are meaningless because the varying mass across the feather alters concentrations in a way that has no biological significance. I discuss this problem and various pitfalls in the chemical analysis of feathers, and offer solutions that ultimately will offer a better understanding of the mechanisms influencing feather composition and, thus, the ecological patterns and processes they were meant to study.

Vertebrates commonly use carotenoid-based traits as social signals. These can reliably advertise current nutritional status and health because carotenoids must be acquired through the diet and their allocation to ornaments is traded-off against other self-maintenance needs. We propose that the coloration more generally reveals an individual's ability to cope with stressful conditions. We tested this idea by manipulating the nematode parasite infection in free-living red grouse (Lagopus lagopus scoticus) and examining the effects on body mass, carotenoid-based coloration of a main social signal and the amount of corticosterone deposited in feathers grown during the experiment. We show that parasites increase stress and reduce carotenoid-based coloration, and that the impact of parasites on coloration was associated with changes in corticosterone, more than changes in body mass. Carotenoid-based coloration appears linked to physiological stress and could therefore reveal an individual's ability to cope with stressors., Funding: NERC Advanced Fellowship and ‘Proyecto intramural especial del Ministerio de Educacion y Ciencia’ from Spain to FM; NERC grant (NE ⁄ D000602 ⁄ 1) to SP; NSERC Discovery Grant and Stuart and Mary Houston Professorship in Ornithology to GRB.

Fault bars are translucent areas across feathers grown under stressful conditions. They are ubiquitous across avian species and feather tracts. Because fault bars weaken feather structure and can lead to feather breakage, they may reduce flight performance and lower fitness. Therefore, natural selection might prime mechan- isms aimed at reducing the cost of fault bars, penalizing their occurrence in those feathers more relevant for flight. Here, we tested one prediction of this ‘fault bar allocation hypothesis’: that the prevalence, abundance and risk of damage of fault bars change across the wing feathers of a long-distance migrant, the sandhill crane Grus canadensis as a function of the strength requirements of feathers for flight. We analysed 2411 wing feathers with 4676 fault bars from 39 cranes in active migration. Fault bars did not increase feather damage with feather age. The occurrence of fault bars decreased from proximal to distal wing portions, both in flight feathers and in coverts, according to the presumed greater strength require- ments of external wing feathers during flight. The occurrence of fault bars was variable when producing low feather damage (o2%) but was consistently low for fault bars with a higher damage probability (42–30%). Altogether, our results suggest that fault bars are common on the feathers of birds even after millions of years of evolution because natural selection seems to penalize birds with particu- larly harmful fault bars in certain feathers and of a certain magnitude, but is unable to eliminate less harmful fault bars according to their strength and position

How animals cope with stressors is an important determinant of their well being and fitness. Understanding what environmental perturbations are perceived as stressors, and quantifying how they are responded to, how often they occur and the negative consequences of exposure to glucocorticoids, has been problematic and limited to short-term physiological measures. By contrast, the quantification of corticosterone (CORT) in feathers represents a long-term, integrated measure of hypothalamic–pituitary–adrenal activity. In the present study, we show that by understanding how the hormone is deposited in feathers, in combination with specific sampling protocols, one can identify localised patterns of CORT deposition that reveal different temporal patterns of a bird’s response to stressors. CORT in feathers appears to be stable over time, is resistant to heat exposure and is useful in determining both the overall exposure of the bird to the hormone over days or weeks, as well as identifying discrete, punctuated, stressful events. Variation in feather CORT can also be examined among individuals of a population at one point in time, as well as over years by using museum specimens. The ability to track stress over time allows for new questions to be asked about the health and ecology of birds and their environment.

We examined the frequency of cannibalism of nestling American kestrels (Falco sparverius) in north-central Saskatchewan. We investigated human disturbance and food shortages as possible causes of it. Cannibalism of nestlings by their parents and siblings was confirmed by observation and by the presence of partially eaten carcasses, or inferred from the sudden disappearance of a nestling between frequent nest checks. Cannibalism occurred at 8% of 48 nests in 1988, and 18% of 92 nests in 1989. Not all nestlings that died were cannibalized. Where nestling mortality occurred, carcasses were eaten in at least 20% of nests in 1988, and 63% of nests in 1989. The chicks that were cannibalized died at a significantly younger age than those that died but were not cannibalized. The mass and age of the parent and the laying date were not associated with the occurrence of cannibalism. We found no strong evidence of a causal link between human disturbance and nestling mortality or cannibalism; however, the abundance of small mammal prey was inversely related to the frequency of cannibalism between years, and there were fewer prey and lower prey delivery rates in territories where cannibalism occurred than in territories where nestling mortality did not occur. The fact that some nestlings died but were not eaten suggests that such mortality was unrelated to food shortages. The food advantage of cannibalism may not outweigh potential disadvantages such as disease transmission.

We used instrumental neutron-activation analysis to determine the concentrations of Br, Mn, Cl, Al, and Na in primary feathers 1, 9, and 10 of Spruce Grouse (Dendragapus canadensis) in four jack pine (Pinus banksiana) forests in northern Ontario. Our objective was to see if there were consistent trends in intrapopulation variation of mineral profiles among populations. Except in the case of Na concentration, there were significant sources of variation attributable to age (adult versus chick) and sex in all forests, and there were large differences among study sites. Yearling and adult grouse that recruited to the breeding population differed in the elemental composition of their feathers from long-term residents of the same age. Information on intrapopulation variation, which traditionally has confounded studies of geographic variation, may have useful applications in research and management. If trends are repeatable and predictable, feather profiles may be used to identify the age or sex of a bird and the origin of recruits on a microgeographic scale.