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The immunocompetence handicap hypothesis posits that androgen-mediated signals honestly indicate the responsiveness of the immune system because of the immunosuppressive effect of androgens. How- ever, androgen levels may also be related to nutritional status, and differences in body condition could be a more parsimonious explanation for variation in the expression of the signal. We maintained captive male red-legged partridges, Alectoris rufa, under regulated food shortage until they reached 85% of their initial body mass. Controls were provided with food ad libitum. After food shortage, experimental birds had lower androgen and higher corticosterone levels than controls. The condition dependence in andro- gen levels suggests that androgen-mediated signals could be indicating general nutritional state rather than immune function specifically. We propose that androgen-dependent signals may act as indicators of body condition or indicators of immune system quality, depending on the nutritional status of the individual., Financial support was provided by the Research Project PAI-02-006 of the Junta de Comunidades de Castilla-La Mancha, and the Natural Sciences and Engineering Research Council of Canada (to G.R.B.), L.P.R. and J.B. were supported by a FPU and a postdoctoral grant, respectively, from the Spanish Ministerio de Educación y Ciencia. J.B. was also supported by the Isabel Maria Lopez Martinez Memorial Scholarship.

Birds deposit the trace element selenium (Se) into their eggs because an adequate supply of this micronutrient is essential for embryonic development. Although there is considerable interest in egg Se with regard to topics as diverse as poultry nutrition and environmental pollution, data on the natural levels of Se in eggs of free-living avian species are currently very limited. To address this lack of information, we measured the yolk Se concentrations in eggs of 14 avian species collected in the wild. The concentrations (ng/g wet yolk) varied from 394 to 2238, with a mean value of 1040. Values (means +/- SD) for eggs from the UK, Canada and New Zealand were, respectively, 522 +/- 192 (3 species), 1194 +/- 584 (8 species) and 1147 +/- 200 (3 species). However, analysis by appropriate statistical models indicates that the effect of phylogenetic relatedeness among these species is so significant that it removes any effect of geographical location. In particular, species belonging to the order Passeriformes displayed significantly higher yolk Se levels than Non-Passeriforme species. In marked contrast to the free-living species, our previously published data indicate that the Se concentration in egg yolk of the domestic chicken is only about 100 ng/g wet yolk when the birds are maintained on a basal commercial diet without supplementary Se. The results reveal an extensive interspecies variation in yolk Se (across a 6-fold range) for eggs collected from the wild. Nevertheless, the Se concentrations in the yolks of all the free-living species were far higher (4-21-fold) than that achieved in the yolk of the domestic chicken consuming a standard basal diet. (c) 2006 Elsevier GrnbH. All rights reserved.

Tree swallows (Tachycineta bicolor) are widely used as indicators of local polychlorinated biphenyl (PCB) contamination in North America. Although determining total PCB residues in tissues is useful in environmental monitoring, analysis of PCB congener profiles may reveal sources of contamination and thus prove to be a more refined tool to track contaminants through the food web. To show how differences in PCB congener patterns in birds can be linked to the PCB patterns in their prey, we evaluated PCB congeners in tissues of tree swallow nestlings and their insect prey using principal component analysis and Euclidean similarities. The PC1 scores for PCB residues in nestlings fell between those of the Hexagenia (Ephemeroptera, mayflies) and Chironomidae (Diptera, midges), the two major prey groups of the nestlings. The congener pattern was not related to the location of nest boxes within the study area. However, Hexagenia insects and the nestlings that consumed them were richer in less chlorinated congeners and had higher PC1 scores than Chironomidae insect. In concordance, congener pattern of nestlings that hatched earlier and consumed more mayflies was more similar than that of other nestling to the pattern of nestings texagenia as calculated by Euclidean similarities. We point to the importance of understanding the seasonal availability of specific types of insect prey and their PCB congener pattern before these data are applied in models of trophic transfer of individual PCB congeners within a food web.

The signaling function of sexually selected traits, such as carotenoid-dependent avian plumage coloration, has received a great deal of recent attention especially with respect to parasitism and immunocompetence. We argue that parasite-mediated models of sexual selection may have an implicit temporal component that many researchers have ignored. For example, previous studies have demonstrated that carotenoid-dependent traits can signal past parasite exposure, current levels of parasitism, or the ability of individuals to manage parasitic infections in the future. We examined repeated measures of carotenoid-dependent skin color and blood parasitism in American kestrels (Falco sparverius) to distinguish whether coloration might signal current parasitism or the potential to deal with infections in the future. We found no evidence that coloration was related to current levels of parasitism in either sex. However, coloration of males significantly predicted their response to parasitism; males with bright orange coloration during prelaying, when mate choice is occurring, were more likely than dull yellow males to reduce their levels of infection by the time incubation began. Coloration during prelaying may advertise a male's health later in the breeding season. For kestrels, the ability to predict future health would be highly beneficial given the male's role in providing food to his mate and offspring. Coloration of females was not a significant predictor of parasitism in the future, and we provide several possible explanations for this result.

Presentamos una revisión de casos descritos de incubación prolongada en diferentes especies de rapaces, tanto diurnas como nocturnas. Siendo un mecanismo para asegurar que los huevos eclosionen, la incubación prolongada también presenta costos potenciales en términos de la reproducción futura relacionados con la posible pérdida de condición durante la incubación, los riesgos de depredación o las posibilidades de volver a criar en la misma temporada reproductiva. Por ello, la incubación prolongada debería observarse más frecuentemente en especies con bajo riesgo de depredación, sin reemplazo de puestas, con poca asincronía en la eclosión y con cuidado parental compartido. Evaluamos estas hipótesis con datos existentes para diferentes especies. La información compilada que presentamos sugiere que la incubación prolongada de huevos que no eclosionan parece ser un hecho habitual, y no se conoce si se trata de un comportamiento adaptativo. Sería necesario disponer de datos cuantitativos sobre la frecuencia de este comportamiento a nivel de especies para poder probar si éste es atribuible a las características individuales de las especies o está relacionado con variables ecológicas.

In 1998, a 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 colony of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects, prompting this study. Ten fledglings with leg deformities from the spill area were compared with 11 normal storks of the same year class from another region far from the spill. However, metals were analyzed as a continuum rather than by site, as reference birds also contained high levels of metals. Gross pathology of the legs was supported by histopathology, which showed that bone remodeling activity was greater in the deformed storks, which also had more irregular subperiosteal bone, and tended to have higher residual islets of cartilage in their metaphyses, which, in turn were related to metal contaminant residues. Both Ca and P in bone were affected independently by metals. Deformed birds had lower serum bone alkaline phosphatase. Bone malformations, measured by leg asymmetry, was only partially explained by bone metals, indicating that a combination of factors was involved with the abnormal development in these young storks.

Point Pelee National Park of Canada in southwestern Ontario, an important migratory route and vital breeding area for many birds, has localized areas of organochlorine (OC) pesticide contamination from agricultural production during the 1950s and 1960s. During 2001 and 2002, we investigated movement of persistent contaminants through the food web with the insectivorous tree swallow (Tachycineta bicolor) as a sentinel. The a priori site classifications, contaminated or reference, were based on soil residues of dichlorodiphenyltrichloroethane (DDT) and its breakdown products (sigmaDDT), dieldrin, and other OC pesticides. In 2001, all nestling tissue samples were pooled by site, and residue levels did not reflect the soil contaminant status. To improve sampling accuracy in 2002, tissue residues were determined from birds in individual nests. This showed OC pesticides to be higher in samples from contaminated sites compared with reference sites (p = 0.031). Polychlorinated biphenyls (PCBs), which were not detected in soil samples, were present in the nestlings and were not related to site of origin (p = 0.422). In 2002, dietary samples were collected from nestlings and identified to taxon, and representative insects collected from nesting sites were analyzed for PCBs and other OCs. Consumption of terrestrial prey was positively correlated with tissue residues of sigmaDDT (p = 0.006), whereas PCBs came from aquatic prey, Hexagenia mayflies (p = 0.003). Dietary details proved valuable in this study of contaminant transfer in insectivorous vertebrates.

1. Birds respond to unpredictable events in the environment by releasing corticosterone, which triggers alternate responses to overcome stressful situations. However, it has been questioned whether altricial nestlings perceive and respond to ecological stressors. Although some studies show adrenal responsiveness in non-precocial species, others report a hyporesponsive period postulated to avoid deleterious effects of corticosterone. 2. To test whether the environmental surroundings of nestlings modulate their stress levels we used a multi-tier comparative approach of plasma corticosterone: (1) within an individual, (2) among nestlings within a brood hierarchy, (3) among broods within a colony and (4) among individuals from different colonies. 3. Nestlings reacted to our protocol by elevating their corticosterone. Baseline levels differed between colonies, and were higher in singleton nestlings compared with two- and three-chick broods, but there were no differences related to within-brood hierarchies, age or condition index. 4. Acute levels were higher in older birds, suggesting a developmental change in adrenal responsiveness. Body condition also explained acute levels but only in singleton nestlings, with higher concentrations in heavier birds. 5. Overall our results indicate that altricial nestlings do respond to a variety of environ- mental stressors, and variation in aspects of environmental quality (e.g. food supply, parental care) may be associated with the differences in stress

We investigated trophic ecology variation among colonies as well as sex- and age-related differences in the diet of the southern giant petrel Macronectes giganteus, a long-lived seabird that is sexually dimorphic in size. We measured stable isotopes (δ13C, δ15N) in blood samples collected during breeding at Bird Island (South Georgia, Antarctica) in 1998 and at 2 colonies in the Argentinean area of Patagonia in 2000 and 2001. Individuals from South Georgia showed lower δ13C and δ15N values than those in Patagonia, as expected from the more pelagic location and the short length of the Antarctic food web. Males and females showed significant differences in the isotopic signatures at both localities. These differences agree with the sexual differences in diet found in previous studies, which showed that both sexes rely mainly on penguin and seal carrion, but females also feed extensively on marine prey, such as fish, squid and crustaceans. However, males from Patagonia showed significantly higher δ15N and δ13C values than females did, and the reverse trend was observed at South Georgia. This opposite trend is probably related to the different trophic level of carrion between locations: whereas penguins and pinnipeds in Patagonia rely mainly on fish and cephalopods, in South Georgia they rely mainly on krill. Stable isotope values of male and female chicks in Patagonia did not differ; both attained high values, similar to adult males and higher than adult females, suggesting that parents do not provision their single offspring differently in relation to sex; however, they seem to provide offspring with a higher proportion of carrion, probably of higher quality, and more abundant food, than they consume themselves. Stable isotopes at South Georgia were not affected by age of adults. We have provided new information on intraspecific segregation in the diet in a seabird species and have also underlined the importance of considering food web structure when studying intraspecific variability in trophic ecology. © Inter-Research 2005.

Point Pelee National Park in southwestern Ontario, Canada--a major migratory route and vital breeding area for many birds--has localized areas of organochlorine (OC) contamination from the 1950s and 1960s. During 2002, we investigated the effect of tissue OC contaminant levels on the physiology and growth of nestling tree swallows (Tachycineta bicolor). Polychlorinated biphenyl (PCB) contamination in the nestlings positively correlated with hepatic ethoxy-, benzyloxy-, and pentoxyresorufin-o-dealkylase enzyme activities and liver size. Despite detectable physiologic changes associated with body burdens of PCBs, reproductive success of breeding pairs was not affected. Hatching date was negatively correlated with PCB levels, alkoxyresorufin-O-dealkylase (alkROD) activities, liver size, and serum protein levels. alkROD activities were largely dependent on hatching date because insect prey contaminated with PCBs were only abundant during a limited period of time during the breeding season.

This study found abnormalities in multiple reproductive stages in captive American kestrels (Falco sparverius) when exposed to polychlorinated biphenyls (PCBs) through dietary and in ovo exposure. American kestrels laid eggs with environmentally relevant total PCB levels (34.1 micrograms/g whole egg wet weight) when consuming PCB-spiked (Aroclor 1248:1254:1260) food (5-7 micrograms/g body weight per day) for 100 d only in 1998. In 1999, the same adults laid eggs with estimated total PCBs of 23 micrograms/g. Effects of maternal (only female exposed) and paternal (only male exposed) in ovo PCB exposure were investigated. Maternal F1 eggs contained predicted total PCB concentrations of 0.34 microgram/g. Specific abnormalities occurred more frequently during dietary F0 exposure, particularly aggressive courtship interactions, clutch abandonment, occurrences of cracked eggs, and developmental effects. Multiple developmental effects were more pronounced during than after dietary PCB exposure of adults, and although these effects were limited, nevertheless they occurred in the F1 maternal and F1 paternal pairs. However, the incidence of multiple deformities throughout the breeding season increased dramatically from 1998 (13%) to 1999 (56%) in F0 PCB-exposed pairs. Developmental abnormalities were unlikely to be attributed to the extrinsic factors of disease, genetics, or nutritional (vitamin D3) deficiencies, but rather to adverse changes in parental behavior and intrinsic factors involving altered genetic material and PCB exposure. Readily cleared PCB congeners may induce specific types of behavioral and developmental abnormalities, but persistent congeners and metabolites are likely producing (1) odd laying patterns, (2) odd laying patterns, (2) developmental effects including embryonic underdevelopment and edema, and (3) increased incidences of multiple deformities within a clutch.

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.

Carotenoids are important dietary constituents in birds. They serve as pigments and play numerous physiological roles in both the laying hen and developing embryo. However, factors determining the absorption of carotenoids and their allocation to different functions are numerous and complex, and causal relationships are generally poorly known. Our objective was to determine the degree to which carotenoid levels in egg yolks and the plasma of hens were influenced by differences in diet and reproductive output in captive red-legged partridges. Ca- rotenoid concentrations were measured by high performance liquid chromatography in two feeds (high and low carotenoid content) and in yolks and plasma of hens near the start and end of laying. Early in the laying season, plasma and yolk ca- rotenoids varied with diet and were correlated with one another. Late in the season, a dietary effect was evident only for yolks, and there was no relationship between plasma and egg levels of individual hens. However, plasma carotenoids at the end of laying were strongly correlated with the number of eggs that had been laid. Dietary availability, although important, could explain some variation in carotenoid levels in plasma and egg yolks only in the context of reproductive history.

Objective: The aim of the study was to assess the use of Non Steroidal Anti-Inflammatory Drugs (NSAIDs) in patients with a history of osteoporotic vertebral fractures. Methods: We investigated 119 patients with postmenopausal osteoporosis complicated by one or more non recent vertebral fractures. Results: More than 60% of the patients took at least one dose of NSAID weekly. The most prescribed NSAID was nimesulide, at a dose with an exclusively antalgic effect. Patients with wedge fracture and those with a documented vertebral fracture in the last 12 months were those taking NSAIDs more frequently. 77% of the patients that used NSAIDs had concomitant features of osteoarthritis, mainly at the spine or at the knee. The use of NSAIDs was negatively related to the use of specific therapy for osteoporosis, particularly for oral daily tablets. Conclusions: This study highlights the significant use of NSAIDs in patients with osteoporotic vertebral fractures and the overlap between osteoporosis, osteoarthritis and related treatments.

We used stable-isotope analysis (SIA) to evaluate sources of variation in the diet of and prey selection by Magellanic penguins Spheniscus magellanicus breeding on the Argentinean Patagonia coast. Our aim was to determine potential sources of variation in diet, focusing mainly on sex and age, although geographic and temporal effects were also taken into account. In addition, we evaluated how prey selection affects offspring quality. We measured stable nitrogen (δ15N) and carbon (δ13C) isotope values in whole blood of chicks (n = 98), yearlings (n = 15) and adults (n = 143) in 9 different breeding colonies during 2 consecutive breeding seasons (1999 and 2000). We also measured stable isotope values in representative prey consumed by this species. Stable nitrogen and carbon isotope values in blood for penguins varied from 17.8 to 20.0‰ and from -18.1 to -14.8‰, respectively. Both colony and season had a significant effect on the 2 isotope signatures. Adult males had higher blood δ15N and δ13C values than females. Age significantly affected both δ15N and δ13C values, with chicks showing the highest and yearlings the lowest δ15N values. Chicks showed lower δ13C values than yearlings and adults. Mean prey δ15N values ranged from 13.6‰ in squid to 18.0‰ in octopus. As anchovy, the main prey consumed by the species in the study area, did not differ from other fish species (hake) in its δ15N value, we used it to represent a fish dietary alternative. Using a 2-source (anchovy and squid) isotopic mixing model, we determined that the mean proportion of anchovy in the diet was 49% for yearlings, 76% for chicks, and 69% and 67% for adult males and females, respectively. Sex and age differences in diet, as revealed by stable isotopes, may be the consequence of individual morphology (sexual size dimorphism) and reproductive constraints imposed by chick development since growing young require more nutritive prey than adults and yearlings. This reasoning would also explain the significant and positive correlation found between proportion of anchovy in the diet and body condition of chicks. Fil: Forero, Manuela G.. Consejo Superior de Investigaciones Científicas. Instituto Mediterráneo de Estudios Avanzados; España Fil: Hobson, Keith A.. Canadian Wildlife Service; Canadá. University of Saskatchewan; Canadá Fil: Bortolotti, Gary R.. University of Saskatchewan; Canadá Fil: Donázar, Jose A.. Consejo Superior de Investigaciones Científicas; España Fil: Bertellotti, Néstor Marcelo. Consejo Superior de Investigaciones Científicas; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Blanco, G.. Instituto de Investigación en Recursas Cinegéticos; España

The bioaccumulation and toxicokinetics of 42 polychlorinated biphenyls (PCBs) was determined in male American kestrels exposed to an Aroclor-contaminated diet for 120 d followed by a 348-d depuration period. The birds were housed under ambient outdoor temperatures to permit normal fluctuations in body weight during the study. Whole body PCB clearance, plasma/fat distribution coefficients, and plasma PCB clearance constants were determined for individual PCBs to calibrate a two-compartment rate constant model in order to describe PCB elimination in the birds. Plasma/fat partition coefficients (K(PF)) averaged 0.0060 +/- 0.0001 for all congeners of study, were not dependent on chemical hydrophobicity, and did not change in summer versus winter sacrificed animals. Plasma clearance constants (k'pc) for PCBs were observed to be dependent on both chlorine substitution patterns and congener hydrophobicity. Polychlorinated biphenyl congeners categorized as readily cleared congeners contained vicinal meta-para hydrogen substituents on at least one phenyl ring, while slowly cleared congeners were chlorine hindered at these positions. A general equation was derived to predict plasma clearance constants for all tri- to octachlorobiphenyls based on the presence of an open meta-para site on one of the phenyl rings and from the n-octanol-water partition coefficient of the chemical. The equation was validated by comparing predicted versus measured relative biomagnification factors of PCBs determined in birds at the end of the dosing period. The two-compartment model calibrated for PCB elimination in American kestrels may be used to describe PCB toxicokinetics in wild birds provided that seasonal fluctuations in the fat content of the modeled population is known.

Plasma proteins, hematocrit, differential blood counts were examined and nutritional condition was estimated for bald eagles (Haliaeetus leucocephalus) trapped (n = 66) during antumn migration, 1994-95 at Galloway Bay (Saskatchewan, Canada), for the purposes of estimating prevalence of exposure to lead. Sex and age differences in hematocrit and plasma proteins were not observed; however, female eagles exhibited larger median absolute heterophil counts than males. Hematologic values were similar to those previously reported from eagles in captivity. Departures from expected hematological values from a healthy population of eagles were not observed in birds with elevated levels of blood lead (or =0.200 microg/ml). Similarly, nutritional condition was not related to blood-lead concentrations. Therefore, it appears that lead exposure in this population was below a threshold required to indicate toxicological alteration in the hematological values and index of nutritional condition that we measured.

While reproduction of wild birds is adversely affected by multiple environmental contaminants, we determined that polychlorinated biphenyls (PCBs) alone alter reproduction. Captive American kestrels (Falco sparverius), fed PCB-spiked (Aroclor 1248:1254:1260) food (7 mg/kg body weight/d) prior to and during the first breeding season only (100 d) laid eggs with environmentally relevant levels of total PCBs (34.0 microg/g whole egg wet wt vs 0 microg/g for controls). Reproduction changed during, not after, PCB exposure in this two-year study. The PCB-exposed pairs laid smaller clutches later in the season and laid more totally infertile clutches. Hatching success was reduced in PCB-exposed pairs, and 50% of PCB nestlings died within 3 d of hatching. Nearly 60% of PCB-exposed pairs with hatchlings failed to produce fledglings. Higher levels of total PCB residues and congeners were associated with later clutch initiation and fewer fertile eggs, hatchlings, and fledglings. We suggest that nonpersistent PCB congeners have a greater influence on reproduction than do persistent congeners.

The salient feature of the fatty acid profile of kestrel eggs collected in the wild was the very high proportion of arachidonic acid (15.2% 0.7% of fatty acid mass, np5) in the phospholipid fraction of the yolk. Kestrels in captivity fed on dayold chickens produced eggs that differed from those of the wild birds in a number of compositional features: the proportion of linoleic acid was increased in all the lipid fractions; the proportion of arachidonic acid was increased in yolk phospholipid and cholesteryl ester; the proportion of a-linolenic acid was decreased in all lipid classes, and that of docosahexaenoic acid was decreased in phospholipid and cholesteryl ester. Partridge eggs from the wild contained linoleic acid as the main polyunsaturate of all the yolk lipid fractions. Captive partridges maintained on a formulated diet very rich in linoleic acid produced eggs with increased levels of linoleic, arachidonic, and n-6 docosapentaenoic acids in the phospholipid fraction; reduced proportions of a-linolenic acid were observed in all lipid classes, and the proportion of docosahexaenoic acid was markedly reduced in the phospholipid fraction. Thus, captive breeding of both the kestrel and the partridge increases the n-6/n-3 polyunsaturate ratio of the yolk lipids.

Antibody-mediated immune function in adult and recently fledged (30 to 33 d old) American kestrels (Falco sparverius) was examined in birds exposed directly, or only in ovo, to polychlorinated biphenyls (PCBs). In 1998, 9 mature male and 9 female kestrels were fed PCBs, whereas 9 females and 10 males served as controls. A mixture of Aroclors 1248:1254:1260 suspended in safflower oil was injected into the kestrels' food items, while in control diets only the same volume of oil was added. The dosage of PCBs was approximately 7 mg/kg kestrel/d, beginning in March 1998 and continuing for 120 d. In 1998, the antibody-mediated immune response was stimulated by immunization and booster vaccinations of the kestrels using a nonpathogenic antigen, dinitrophenol-keyhole limpet hemocyanin (DNP-KLH). In 1999, offspring from three treatment groups based upon maternal exposure to PCBs were similarly tested for their antibody response. None of these mothers was vaccinated with DNP-KLH the previous year. The maternal groups were: (1) exposed to PCBs in 1998 for 120 d, (2) exposed in ovo in 1998 (i.e., mothers were produced by PCB-exposed parents), or (3) unexposed to PCBs. Serum antibody levels were determined using an enzyme-linked immunosorbent assay (ELISA). In 1998, PCB-exposed adult females had a significantly higher antibody response than did controls, whereas adult males exposed to PCBs had significantly suppressed antibody production. For the nestlings produced in 1999, maternal treatment significantly affected antibody response. Generally, the antibody response in the nestlings was much lower than that seen in adult kestrels. Yet both male and female offspring from mothers that had been fed PCBs the previous year had significantly higher postbooster anti-DNP-KLH titers than control and in ovo-exposed maternal groups, thus mimicking the response seen in the adult females the previous year. These sex-specific responses in PCB-exposed birds provide further evidence of the endocrine-disrupting behavior of PCBs. Both suppression and stimulation of the antibody response are undesirable because this indicates that the immune system is not able to respond normally to challenges by infectious or other disease-causing agents.

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.

Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health-related functions. Carotenoid-dependent coloration may have evolved as a signal to conspeci¢cs; however, factors that may limit availability of carotenoids are poorly known. We investigated how the acquisition of carotenoids may be constrained by availability in the environment, diet, genetic make-up and health status of wild American kestrels (Falco sparverius). Plasma concentrations of siblings at the time of £edging showed a high degree of resemblance ; however, a cross- fostering experiment revealed that variance was largely explained by nest of rearing, rather than nest of origin, thus indicating a low genetic component. A multivariate analysis of attributes of nestlings (sex, size, plasma proteins, immune function), parental reproduction (laying date, clutch size) and rearing conditions (brood size, size hierarchy, nestling mortality) showed only a small signi¢cant e¡ect of leuco- cyte di¡erentials on carotenoid concentrations of nestlings. A strong environmental e¡ect on plasma carotenoids was demonstrated by levels of adult kestrels being correlated within mated pairs, and having a signi¢cant association with the abundance of voles, the primary prey species, per territory

Parasites have the potential to decrease reproductive output of hosts by competing for nutrients or forcing hosts to invest in immune function. Conversely, reproductive output may affect parasite loads if hosts allocate resources to reproduction such that allocation to immune function is compromised. Both hypotheses implicitly have a temporal component, so we sampled parasites both before and after egg laying to examine the relationship between reproductive output (indexed using a combined measure of clutch size, egg volume, and initiation date) and blood parasite loads of American kestrels (Falco sparverius). Parasite loads measured prior to egg laying had no adverse effects on subsequent reproductive output. Females that previously had large reproductive outputs subsequently had lower parasite intensities than those whose outputs were smaller, suggesting that females were capable of allocating energy to both forming clutches and reducing parasite loads. Because male kestrels provide most of their mate's energetic needs before, during, and after egg laying, mate choice by females may have consequences for their parasite loads. Females choosing high-quality mates may not only have increased reproductive output, but may also obtain sufficient resources from their mates to enable them to reduce their parasite burdens. Males whose mates had large reproductive outputs were more likely to subsequently be parasitized and have more intense infections. For individual males sampled both before and after egg laying, those whose mates had larger reproductive outputs were also more likely to become parasitized, or remain parasitized, between sampling periods. Increased parasite loads of males may be one mechanism by which the costs of reproduction are paid.

For animals that are sexually dimorphic in size, the larger sex is expected to be more costly to raise to independence. Manipulating offspring sex ratios may thus be one means by which parents can fine-tune their reproductive effort to resource availability. Parents in poor physical condition or during poor food years should produce more of the cheaper (smaller) sex. We examined the sex ratios of 259 broods of American kestrels (Falco sparverius) between 1988 and 1990 in relation to food abundance (small mammals) and various attributes to the parents. The proportion of males at hatching increased as the food supply declined, and both male and female parents in poor physical condition were more likely to have male-biased broods than those in good condition. The mortality of eggs and young did not appear to be responsible for the biased sex ratios. The sex ratio was independent of the laying date; however, it was correlated with female body size. Small females produced more sons, perhaps because small size is more detrimental for females than males.

Bennett, G.F., Squires-Parsons, D., Siikamaki, P., Huhta, E., Allander, K., and Hillstrom, L. 1995. A comparison of the blood parasites of three Fenno-Scandian populations of the Pied Flycatcher Ficedula hypoleuca. J. Avian Biol. 26: 33 38. Bortolotti, G.R., and Gabrielson, J .R. 1995. Fluctuating asymmetry in the skeleton of the American kestrel, Falco sparverius: a test of the consequences of sexual size dimorphism. Can. J. Zool. 73: 141-145. Clarke, G.M. 1994. The genetic basis of developmental stability. I. Relationships between stability, heterozygosity and genomic coadaptation. In Developmental instability: its origins and evolutionary implications. Edited by T. A. Markow. Kluwer Academic Publishers, Dordrecht, the Netherlands. pp. 17 25. Clarke, G.M. 1995. Relationships between developmental stability and fitness: application for conservation biology. Conserv. Biol. 9: 18-24. Leamy, L. 1984. Morphometric studies in inbred and hybrid house mice. V. Directional and fluctuating asymmetry. Am. Nat. 123: 579 593. Leary, R.F., and Allendorf, F. W. 1989. Fluctuating asymmetry as an indicator of stress: implications for conservation biology. Trends Ecol. Evol. 4: 214 -217. Leary , R.F., Allendorf, F. W., and Knudsen, K. L. 1984. Superior developmental stability of heterozygotes at enzyme loci in salmonid fishes. Am. Nat. 124: 540-551. Moller , A. P. 1992. Parasites differentially increase the degree of fluctuating asymmetry in secondary sexual characters. J. Evol. Biol. 5: 691-699. Moiler, A.P. 1994. Sexual selection in the barn swallow (Hirundo rustica). IV. Patterns of fluctuating asymmetry and selection against asymmetry. Evolution, 48: 658 670. Moiler, A.P. 1995. Sexual selection in the barn swallow (Hirundo rustica) . V . Geographic variation in ornament size. J . Evol . Biol. 8: 319. Palmer, A.R., and Strobeck, C. 1986. Fluctuating asymmetry: measurement, analysis, patterns. Annu. Rev. Ecol. Syst. 17: 391 -421. Simmons, L. W., Tornkins, J. L., and Manning, J.T. 1995. Sampling bias and fluctuating asymmetry. Anim. Behav. 49: 1697 1699. Snyder, N.F.R., and Wiley, J. W. 1976. Sexual size dimorphism in hawks and owls of North America. Omithol. Monogr. 20: 1 -96. SoulC, M . E. 1979. Heterozygosity and developmental stability: another look. Evolution, 33: 396 -401. Swaddle, J.P., Witter, M.S., and Cuthill, I.C. 1994. The analysis of fluctuating asymmetry. Anim. Behav. 48: 986 989. Swaddle, J.P., Witter, M.S., and Cuthill, I.C. 1995. Museum studies measure FA. Anim. Behav. 49: 17001701. Van Valen, L. 1962. A study of fluctuating asymmetry. Evolution, 16: 125 142. Witter, M.S., and Swaddle, J.P. 1994. Fluctuating asymmetries, competition and dominance. Proc. R. Soc. Lond. B Biol. Sci. 256: 299 303. Zakharov, V. M. 1992. Population phenogenetics: analysis of developmental stability in natural populations. Acta Zool. Fenn. 191: 7-30.

The development of second-generation nestling American kestrels (Falco sparverius) was altered by in ovo exposure of only one parent to polychlorinated biphenyls (PCBs). Polychlorinated biphenyls appear to alter nestling development through both maternally and paternally mediated effects. In 1998, F0 parent kestrels consumed approximately 5 to 7 microg total PCBs/g bird/d (Aroclors 1248:1254: 1260) for approximately 100 d prior to eggs hatching; these eggs, containing total PCB concentrations of 34.1 microg/g, produced 13 F1 offspring, which were then paired in 1999 with unexposed kestrels to examine developmental effects of maternal or paternal in ovo PCB exposure. Using a toxicokinetics model, eggs from the maternally exposed group had predicted PCB levels of 0.03 to 0.34 microg/g, with enriched higher chlorinated congeners. Polychlorinated biphenyl concentrations in eggs of all generations have recently been found in eggs and nestlings of free-ranging eagles. Consistent with the first generation, maternally exposed F2 females generally were larger, had altered growth rates, and delayed maximal growth and fledging compared with control females. Maternally exposed F2 males were heavier but had shorter bones, grew more quickly and earlier, and fledged 2 d later than control males. In the maternally exposed group, concentrations of plasma triiodothyronine were elevated in F2 females but suppressed in F2 males. Paternally exposed F2 hatchlings of both sexes were comparable in size to controls with the exception of having longer tarsi bones, but subsequently showed slower, delayed growth (both sexes) and fledging (females) and lower thyroxine concentrations (males). The alterations in thyroid hormones in the F2 generation are discussed in light of the enrichment of higher chlorinated PCB congeners and hydroxylated PCB congeners. The developmental changes in the kestrel nestlings are likely a function of several possible mechanisms involving maternal PCB deposition, parental behavior, and neurobehavioral and endocrine-thyroid function in nestlings.

Diseased animals or those in poor condition are known to have reduced hematocrits. Many investigators have assumed that hematocrit levels thus reflect condition and disease status of an animal. This study tested these assumptions by examining the relation between hematocrits of American kestrels (Falco sparverius) during several stages of the breeding season, and condition, prey abundance, and blood parasite load. We also examined the potential effects of a number of intrinsic and extrinsic influences on hematocrit. Hematocrits did not differ between the sexes, or between the pre-laying and incubation periods. Among females, hematocrit did not vary with the date of sampling, breeding chronology, prey abundance, condition, age, or molt, although hematocrit increased with ambient temperature during incubation. Hematocrit of males was not related to breeding chronology, prey abundance, condition, age, or molt. During incubation, male hematocrit increased with the date of sampling and ambient temperature. Hematocrits of both sexes declined with the time of day that the sample was taken, and increased with the level of infection of the blood parasite Haemoproteus. The use of hematocrits to assess the health and condition of clinically normal kestrels is therefore questionable, and given the positive association with parasite loads, may even lead to erroneous conclusions.

1. The peak load and sibling rivalry hypotheses for hatching asynchrony in birds predict that the pattern of parental food provisioning should differ between synchronous and asynchronous broods. Monitoring parental effort is also an important step towards understanding the life history consequences of asynchrony. 2. In 1989-91, we used electronic event recorders at 57 nestboxes to record the number of visits American kestrels (Falco sparverius) made to experimentally synchronous and asynchronous broods during the nestling period. In another experiment, we recorded the prey provisioning by parents to broods supplemented with food. Nestlings were weighed every third day until fledging. 3. In all three years, parents made more visits to synchronous nests than to asynchronous ones

We investigated variation in the number and size of brood patches of female (n = 133) and male (n = 81) American Kestrels Falco sparverius in northcentral Saskatchewan, Canada. We analyzed brood patch size with respect to characteristics of individual birds such as sex, age, size, condition, and clutch volume. All incubating birds developed brood patches but females tended to have larger patches than males. The size of the brood patch was correlated significantly only with the mass of the female. Birds with large eggs or large clutches did not necessarily have large brood patches, and patch size was not associated with laying date or hatching success. In a comparison with other avian taxa, we found kestrels to be unusual in that their three discrete brood patches did not correspond to the modal clutch size of five eggs. Kestrels potentially have difficulty heating all their eggs simultaneously.

Asynchronous hatching within clutches is a pervasive phenomenon in altricial birds and the subject of considerable controversy. Intraspecific variation in the degree of hatching asynchrony is usually assumed to be the product of individual differences in parental incubation behaviour, yet few studies have reported on how variable such behaviour might be or the patterns of hatching within clutches. Wild American Kestrels in northern Saskatchewan started incubating their eggs prior to clutch completion, but the timing of the onset of incubation varied among pairs. There was considerable variation in the number of eggs to hatch per day within clutches. Many patterns of hatching could not be explained by conventional thinking about parental incubation behaviour, for the order in which eggs hatched was often not the order in which the eggs were laid. Small females were more likely to have such irregular hatching patterns and have hatching failures than large females, possibly because of problems in effectively covering all eggs during incubation.

Concentrations of Br, Mn, Na, Al, and Cl were measured in back and tail feathers and concentrations of Mg and Ca were measured in tail feathers of wild and captive Bald Eagles (Haliaeetus leucocephalus) using instrumental neutron activation analysis. Feather chemistry of four eagles sampled over 3 years showed considerable annual variation. The profiles of tail feathers, however, appeared distinct for each individual. The mineral profiles of feathers of wild nestlings were usually significantly variable among years. A sex difference was evident for Cl, and perhaps Br and Na, in back feathers of nestlings. Mn and Al concentrations were significantly influenced by the species of prey on which the eaglets had fed. Variation attributable to sex likely has a physiological basis, while much of annual variation can likely be explained by diet.

Instrumental neutron activation analysis was used to investigate the feather chemistry of wild and captive bald eagles (Haliaeetus leucocephalus). This paper documents variation that may be attributable to method of feather collection, laundering of samples, and precision of the analysis, as well as the variability within and among feathers from different locations on the body of individual birds. For most samples, reliable estimates could be made of the concentrations of bromine, magnesium. manganese, sodium, vanadium, aluminum, chlorine, calcium, and sulphur. Iodine and copper were detected but could not be measured precisely. There were highly significant patterns of variation along the length of a single feather for most chemical elements. The vane and calamus portions of feathers differed in chemical composition and the concentrations of the elements in the two parts were not correlated. Feathers belonging to the same molt but collected several months apart had similar chemical profiles. Variation within an individual feather and among feathers from different parts of the body necessitates rigorous consistency in the method of sampling feathers. Possible explanations for the observed patterns of elemental composition are discussed.

Theoretically, the ratio of male to female offspring should equal the inverse ratio of the cost of their rearing. For birds exhibiting brood reduction, the cost of raising offspring sexually dimorphic in size may not be independent of the sex composition of the brood if males and females are not equally affected by sibling competition or are not equally effective at competing with a sibling of the opposite sex. Parents may thus manipulate the sex ratio of their brood to achieve an optimal combination of the sexes and to maximize their fitness. By examining the effects of sex, growth, and hatching asynchrony on the relative size of sibling bald eagles, I show that the probability of brood reduction is not equal among broods of different sex composition. The hatching sequence of male first and female second was predicted to have the greatest chance of experiencing nestling mortality. This type of brood is rare in bald eagles because there is a sex-dependent hatching sequence whereby the first egg in mixed-s...

Mass and eighth primary growth of nestling Bald Eagles (Haliaeetus leucocephalus) were studied in north central Saskatchewan from 1980 to 1982. There were no significant differences among years for any measure of growth. Clutch size and the relative timing of hatching within each breeding season also had no effect on growth. In broods of two young, second-hatched chicks (C2) grew slower than first-hatched chicks (C1) if the hatching interval between siblings was 2 days rather than 1 day. As both hatching asynchrony and the degree of suppressed growth of C2 were independent of absolute growth rates (and hence presumably food supply), it was unlikely that individual females modified the degree of asynchrony in any adaptive manner. Nestlings raised in an area predicted to have high fish (prey) productivity, given the morphology and chemistry of the lake, grew faster than chicks in an area of lower productivity. Growth rate was significantly correlated with the total mass of prey, but not the number of prey items, delivered to the nests by the parents.

Nestlings of birds that raise only one young (B1 species) grow slower than those of birds that raise more than one young (B2 species). B2 species may be fast growing because sibling competition exerts a strong selective force for rapid growth. Other hypothesis have been proposed to explain the slow growth of B1's. To overcome the problem inherent in previous investigations of comparing species widely divergent in ecology and phylogeny, I analyzed patterns of variation in growth of one group only: eagles of the world. I fitted growth curves to data obtained from the literature for some species, but most eagles were compared using the length of the nestlings period as an indicator of growth rate. I also collected data on the growth of wild Bald Eagle (Haliaeetus leucocephalus) nestlings. I investigated how postnatal growth may be related to brood size, clutch size, nestlings mortality, body size, and prenatal growth. B1 eagles were found to grow slower than B2 eagles. Differences in foraging ecology, diet, and mode of development are unlikely to account for the observed variability in the rate and form of growth. Contrary to the sibling competition hypothesis, growth rate was not correlated with intensity of sibling competition. Eagles that regularly lay two eggs but always lose one chick because of sibling competition (obligate fratricide) grow slower than those species in which such mortality may or may not occur (facultative fratricide). Species characterized by facultative fratricide grow at a rate expected for their adult body size, whereas to B1 species do not. B1 eagles are characterized by growth curves with early inflection points compared to B2 eagles. The shape of the growth curves and slower growth rates of B1 species and contrary to predictions of the sibling competition hypothesis and may instead have resulted from selection to reduce peak energy requirements of the nestlings. I present a model of the effect of hatching interval, species—specific growth rate, and relative growth of siblings, on the probability of fratricide, which suggests that sibling competition is not an important factor in selecting for rapid growth.

This is the first record of nestling bald eagles as hosts of the parasitic blowfly Protocalliphora avium (Diptera: Calliphoridae). The frequency of infestation of the hematophagous larvae was determined by repeatedly examining eaglets over the entire 10- to 12-week nestling period from 1980 to 1982 in north-central Saskatchewan. Seventy-two nestlings were examined a total of 461 times. All nestlings less than 49 days old were parasitized by large numbers of larvae in the aural cavities, on the nape of the neck, and on the top of the head. The frequency of parasitism was high from the time the eaglets hatched until they were 16 days old when it sharply declined. The birds were repeatedly infested, suggesting that P. avium may have been an intermittent feeder. There was no difference between the frequency of infestation in nests containing one or two chicks, nor between the first-hatched and second-hatched eaglet within a brood. Factors associated with the physical and behavioural development of the eaglets, rather than a seasonal effect on the parasites, may account for the decline and cessation of infestation.

[EN]: Most of our understanding of the function of colored traits displayed by birds and the mechanisms that produce or maintain them comes from studies on adults. However, colored traits are often displayed by nestlings from a young age, and these traits may influence parent-offspring interactions or sibling competition. The mechanisms that may mediate the expression of those traits during growth are still fairly unknown in raptors. In this study, we examined a possible mediating effect of corticosterone levels on the expression of carotenoid-pigmented traits in nestlings of Common Buzzards (Buteo buteo), specifically the yellow-orange coloration of their cere and legs. We assayed corticosterone levels deposited in feathers, which can provide a reliable and integrated index of stress responses during growth. Carotenoids can be used to color integuments, or diverted to other physiological processes involved in self-maintenance. We hypothesized that corticosterone levels mediate how carotenoids can be diverted to functions other than coloration. We show that carotenoid and corticosterone levels were positively associated, perhaps because of a higher metabolic activity in more-stressed nestlings. Corticosterone levels were negatively correlated with the coloration of cere and legs in females only. Altogether, our results support the hypothesis that corticosterone may influence how carotenoid pigments are allocated for needs other than coloration, although in a sex-specific manner. We encourage further studies exploring how individuals cope with and respond to stressful conditions, in order to better understand the complex interactions between corticosterone, carotenoids, and coloration during nestling growth. [ES]: La mayoría de nuestro entendimiento de la función de los atributos coloreados desplegados por las aves y los mecanismos que los producen o mantienen vienen de estudios realizados en adultos. Sin embargo, los atributos coloreados son a menudo desplegados por los pichones desde una edad muy temprana, y estos rasgos pueden influenciar en la interacción padres - crías o en la competencia entre hermanos. Los mecanismos que pueden mediar la expresión de estos atributos durante el crecimiento son todavía bastante desconocidos en las rapaces. En este estudio examinamos un posible efecto de mediación de los niveles de corticosterona en la expresión de los atributos pigmentados por carotenoides en pichones de Buteo buteo, específicamente la coloración amarillo-anaranjada de sus ceras y patas. Valoramos los niveles de corticosterona depositados en las plumas, los cuales pueden servir como un ı´ndice confiable e integrado de respuesta al estrés durante el crecimiento. Los carotenoides pueden ser usados para colorear integumentos o desviados hacia otros procesos fisiológicos involucrados en el auto mantenimiento. Hipotetizamos que los niveles de corticosterona influyen en cómo los carotenoides pueden ser desviados hacia otras funciones aparte de la coloración. Demostramos que los niveles de carotenoides y corticosterona estuvieron positivamente asociados, quizá debido a una actividad metabólica mayor en los pichones más estresados. Los niveles de corticosterona estuvieron negativamente correlacionados con la coloración de la cera y las patas, pero sólo en las hembras. En conjunto, nuestros resultados apoyan la hipótesis de que la corticosterona puede influenciar en cómo los pigmentos carotenoides son distribuidos para otras necesidades además de la coloración, aunque de una manera especófica en cada sexo. Alentamos la realización de estudios adicionales que exploren cómo los individuos se enfrentan y responden a situaciones estresantes, de manera de entender mejor las complejas interacciones entre la corticosterona, los carotenoides y la coloración durante el crecimiento de los pichones. We thank the National Birds of Prey Trust for partially financing the study. We also thank CEH-Banchory and L. Pérez-Rodríguez for support of the fieldwork and lab analyses. JM-P was awarded a JAE doc and research fellowship during the writing of this manuscript.

Patterns of size variation between sex and among plumage classes of bald eagles (Haliaeetus leucocephalus) were examined by measuring 10 variables on museum study skins. Using multivariate statis- tical techniques, a field method was devised to correctly identify the sex of 98.1% of bald eagles examined. Plumage maturation in this species and the problems associated with previous descriptions of plumage succession are discussed.