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The administration of exogenous hormones emerged as an essential tool for field studies in endocrinology. However, working with wild animals remains challenging because under field conditions, not every available method meets the necessary requirements. Achieving a sustained elevation in hormone levels while simultaneously minimising handling time and invasiveness of the procedure is a difficult task in field endocrinology. Facing this challenge, we have investigated the suitability of biocompatible polymeric microparticles, a novel method for drug administration, as a tool to manipulate hormones in small songbirds. We chose the insulin-like growth factor -1 (IGF-1) as the target hormone because it receives great interest from the research community due to its important role in shaping life-history traits. Moreover, its short half-life and hydrophilic properties imply a major challenge in finding a suitable method to achieve a sustained, systemic long-term release. To study the release kinetics, we injected either IGF-1 loaded polylactic-co-glycolic acid (PLGA) microparticles or dispersion medium (control group) in the skin pocket of the interscapular region of captive bearded reedlings (Panurus biarmicus). We collected blood samples for 7 consecutive days plus an additional sampling period after two weeks and complemented these with an in vitro experiment. Our results show that in vitro, PLGA microparticles allowed a stable IGF-1 release for more than 15 days, following a burst release at the beginning of the measurement. In vivo, the initial burst was followed by a drop to still elevated levels in circulating IGF-1 until the effect vanished by 16 days post-treatment. This study is the first to describe PLGA-microparticles as a novel tool for exogenous hormone administration in a small passerine. We suggest that this method is highly suitable to achieve the systemic long-term release of hydrophilic hormones with a short half-life and reduces overall handling time, as it requires only one subcutaneous injection.

Variation in rachis (central shaft) morphology in individual remiges (flight feathers) within and among species reflects adaptations to requirements imposed by aerodynamic forces, but the fine-scale variation of feather morphology across remiges is not well known. Here we describe how the shape of the rachis, expressed by the height/width ratio, changes along the longitudinal and lateral axis of the wing in four bird species with different flight styles: flapping-soaring (white storks), flapping-gliding (common buzzards), passerine-type (house sparrows) and continuous flapping (pygmy cormorants). Overall, in each wing feather, irrespective of species identity, rachis shape changed from circular to rectangular, from the base towards the feather tip. The ratio between the height and width of the calamus was similar across remiges in all species, whereas the ratio at the base, middle and tip of the rachis changed among flight feathers and species. In distal primaries of white storks and common buzzards, the ratio decreased along the feather shaft, indicating a depressed (wider than high) rachis cross section towards the feather tip, whereas the inner primaries and secondaries became compressed (higher than wide). In house sparrows, the rachis was compressed in each of the measurement points, except at the distal segment of the two outermost primary feathers. Finally, in pygmy cormorants, the width exceeds the height at each measurement point, except at the calamus. Our results may reflect the resistance of the rachis to in-plane and out-of-plane aerodynamic forces that vary across remiges and across study species. A link between rachis shape and resistance to bending from aerodynamic forces is further indicated by the change of the second moment of areas along the wing axes.

Moulting is a crucial, yet often overlooked life-history stage in many animals, when they renew their integumental structures. This life-history stage is an energetically demanding somatic growth event that has particular importance in birds because feathers play a crucial role in flight, insulation and communication. Somatic growth processes are regulated by the evolutionarily conserved peptide hormone insulin-like growth factor 1 (IGF-1). However, the role of IGF-1 in feather growth remains unknown. In this study, we captured 41 juvenile free-living bearded reedlings (Panurus biarmicus) that had started their first complete moult and brought them into captivity. Then, we manipulated their circulating IGF-1 levels using poly-(lactic-co-glycolid acid) microparticles (microspheres) that provide a sustained release of IGF-1. The treatment increased IGF-1 levels but did not affect the feather growth rate. However, 2 weeks after the treatment, birds in the increased IGF-1 group were moulting more feathers simultaneously than the controls and were at a more advanced stage of moult. Birds with experimentally increased IGF-1 levels had better quality feathers (measured by a lower number of fault bars) than the controls. These results suggest that an increase in IGF-1 does not speed up feather growth, but may alter moult intensity by initiating the renewal of several feathers simultaneously. This may shorten the overall moulting time but may imply costs in terms of IGF-1-induced oxidative stress.

Reproduction is an energetically demanding life history stage that requires costly physiological and behavioral changes, yet some individuals will invest more into reproduction and breed more successfully than others. To understand variation in reproductive investment, previous studies have evaluated factors during breeding, but conditions outside of this life history stage may also play a role. Using a free-ranging population of black-capped chickadees (Poecile atricapillus), we assessed the repeatability of plastic traits relating to energetic condition (circulating initial corticosterone concentrations and body condition) during the nonbreeding season and evaluated whether these traits predicted reproductive investment in the subsequent breeding season. We found that initial corticosterone concentrations and an index of body condition, but not fat score, were moderately repeatable over a 1-week period in winter. This trait repeatability supports the interpretation that among-individual variation in these phenotypic traits could reflect an intrinsic strategy to cope with challenging conditions across life history stages. We found that females with larger fat reserves during winter laid eggs sooner and tended to spend more time incubating their eggs and feeding their offspring. In contrast, we found that females with higher residual body mass delayed breeding, after controlling for the relationship between fat score and timing of breeding. Additionally, females with higher initial corticosterone in winter laid lighter eggs. Our findings suggest that conditions experienced outside of the breeding season may be important factors explaining variation in reproductive investment.

Whilst the immune system often varies seasonally and exhibits differences between males and females, the general patterns in seasonality and sex differences across taxa have remained controversial. Birds are excellent model organisms to assess these patterns, because the immune system of many species is well characterised. We conducted a meta-analysis using 41 wild bird species from 24 avian families to investigate sex differences and seasonal (breeding/non-breeding) variations in immune status, including white blood cell counts, phytohaemagglutinin (PHA) test, bacteria-killing ability (BKA), haemolysis and haemagglutination assays. We found male-biased macrophage concentration, BKA and haemolysis titers, but only during the breeding season. Sexspecific heterophil concentrations, heterophil/lymphocyte ratios and PHA responses differed between breeding and non-breeding, suggesting larger changes in males than in females. Importantly, sex differences in immune status are stronger during the breeding period than during the non-breeding period. Taken together, our study suggests that both seasonal variation and sex differences in immune system are common in birds, although their associations are more complex than previously thought

Physiological state is an emergent property of the interactions among physiological systems within an intricate network. Understanding the connections within this network is one of the goals in physiological ecology. Here, we studied the relationship between body condition, two neuroendocrine hormones (corticosterone and insulin-like growth factor 1 [IGF-1]) as physiological regulators, and two physiological systems related to resource metabolism (glucose) and oxidative balance (malondialdehyde). We measured these traits under baseline and stress-induced conditions in free-living house sparrows (Passer domesticus). We used path analysis to analyze different scenarios about the structure of the physiological network. Our data were most consistent with a model in which corticosterone was the major regulator under baseline conditions. This model shows that individuals in better condition have lower corticosterone levels; corticosterone and IGF-1 levels are positively associated; and oxidative damage is higher when levels of corticosterone, IGF-1, and glucose are elevated. After exposure to acute stress, these relationships were considerably reorganized. In response to acute stress, birds increased their corticosterone and glucose levels and decreased their IGF-1 levels. However, individuals in better condition increased their corticosterone levels more and better maintained their IGF-1 levels in response to acute stress. The acute stress-induced changes in corticosterone and IGF-1 levels were associated with an increase in glucose levels, which in turn was associated with a decrease in oxidative damage. We urge ecophysiologists to focus more on physiological networks, as the relationships between physiological traits are complex and dynamic during the organismal stress response.

Despite the widely used application of standardized capture-handling protocols to collect blood and assess the physiological stress response, the effect of the actual sampling design (e.g. timing and the number of blood samples) often differs between studies, and the potential implications for the measured physiological endpoints remain understudied. We, therefore, experimentally tested the effects of repeated handling and multiple blood sampling on the stress response in wintering free-living great tits (Parus major). We modified a well-established sampling protocol of avian studies by adding either an additional blood sample or a “sham-manipulation” (i.e. handling associated with the blood sampling procedure without venepuncture), to disentangle the effects of handling stress and blood loss. We combined three different stress metrics along the endocrine-immune interface to investigate the acute short-term stress response: total corticosterone levels (CORT), the heterophil/lymphocyte ratio (H:L), and the Leukocyte Coping Capacity (LCC). Our study provided three key results: i) no relationship between CORT-levels, LCC and H:L, confirming that these three parameters represent different physiological endpoints within the stress response; ii) contrasting dynamics in response to stress by the measured parameters and iii) no difference in stress levels 30 minutes after capture due to one additional blood sampling or handling event. By optimising the sampling design, our results provide implications for animal welfare and planning experimental procedures on stress physiology in passerine species.Summary StatementWhen testing the short-term stress response in free living passerines, both – the scientist and the bird may be better off with a 15-minute stress protocol.

Lifespan evolves as a compromise between antagonistic selection forces. Insulin-like growth factor 1 (IGF-1) is a pleiotropic hormone that regulates several life-history traits. High levels of IGF-1 have been linked to increased mortality, partly by causing oxidative stress. However, these effects have no experimental evidence in wild animals. We implanted microspheres loaded with exogenous IGF-1 into bearded reedlings, a common short-lived Eurasian songbird. The treatment elevated plasma IGF-1 levels for at least 24 h. Oxidative damage to lipids significantly increased the day after the manipulation in treated birds, but returned to baseline levels four days post-treatment. The treatment had no effect on survival over 16 months; however, birds with higher pre-treatment (baseline) IGF-1 levels had better survival prospects. These results suggest that, although high IGF-1 levels may induce oxidative damage, natural variation in this hormone’s level may reflect the outcome of individual optimization.

Avian plumage colors and ornaments are excellent models to study the endocrine mechanisms linking sexually selected traits and individual parameters of quality and condition. Insulin-like growth factor 1 (IGF-1) is an evolutionarily highly conserved peptide hormone. Its regulatory role in cell proliferation and differentiation and its high sensitivity to the nutritional state of individuals suggest it as an interesting candidate, possibly providing a link between body condition and individual capacity to grow elaborated ornamental features. We investigated whether IGF-1 levels during molting correlate with the expression of multiple ornaments in a sexually dichromatic passerine species, the bearded reedling (Panurus biarmicus). We collected blood samples of males and females shortly before the molting completed and measured the size and colors of ornamental traits. Our results indicate that in males, structural plumage colors, the size of the melanin-based ornament (beard), and tail length are independent traits. IGF-1 levels are associated with the length of the tail and the expression of male structural plumage components (UV coloration), but not the melanin-based ornament. In females, plumage color and tail length were independent traits, which were not related to IGF-1 levels. To the best of our knowledge, this study provides the first evidence that IGF-1 could play a role in the development of secondary sexual characters in a bird species.Significance statementIGF-1 is an evolutionarily highly conserved peptide hormone, which recently entered the center stage of research enquiry in evolutionary biology. It is considered as one of the key factors shaping individual life histories, but little is known about its effects on sexually selected traits. We investigated whether IGF-1 levels during molting predict the elaboration of multiple ornamental plumage traits in male and female bearded reedlings (Panurus biarmicus). Our results indicate that higher IGF-1 levels had positive effects on male structural plumage colors and tail feather length. This is the first study, bringing indication for a potential role of IGF-1 in the expression of plumage ornaments in a bird species. Our findings suggest that IGF-1 might serve as an ideal candidate to study the mechanisms linking condition and the capacity to develop sexually selected ornaments.

Life-history theory predicts that, to optimize their fitness, individuals should increase their reproductive effort as their residual reproductive value decreases. Accordingly, several studies have shown that individuals downregulate their glucocorticoid stress response (a proxy of reproductive investment in vertebrates) as they age, and as the subsequent reproductive value decreases. However, and surprisingly, results appear inconsistent, suggesting that the environmental context or the individual state may affect the relationship between age and reproductive effort. Here, we tested for the first time this hypothesis, and more specifically, whether this attenuation of the corticosterone stress response with advancing age depends on the energetic status of individuals. We compared the influence of age on the corticosterone stress response between fasting and non-fasting breeding snow petrels ( Pagodroma nivea ), an extremely long-lived bird. As expected, we found that the corticosterone stress response was attenuated in old petrels, but only when they were not fasting. Interestingly, this pattern was not apparent in fasting petrels, suggesting that old birds downregulate their corticosterone stress response and increase their parental investment only when they are in good body condition. At the ultimate level, old individuals may maintain a strong corticosterone stress response when fasting because the survival costs of increased stress resistance and parental effort might then outweigh their reproductive benefits.

Understanding how vulnerable species are to new stressors, such as anthropogenic changes, is crucial for mitigating their potential negative consequences. Many studies have investigated species sensitivity to human disturbance by focusing on single behavioral or physiological parameters, such as flight initiation distance and glucocorticoid levels. However, little is known about the differential effect that modulating factors might have on behavioral versus physiological stress responses across species. This lack of knowledge make difficult to understand the relationship between both types of reactions, and thus to assess to what extent a behavioral reaction is representative of an internal physiological stress response or vice versa. We collected published data on bird flight initiation distances (FID) and corticosterone (CORT) responses, the two most frequently used indicators of stress reaction. We then investigated how spatio-temporal factors or species-specific characteristics relate to these behavioral and physiological stress responses, and potentially modify the relationship between them. Additionally, we evaluated the strength of the correlation between the two stress responses (behavioral and physiological). Our findings showed that FID and CORT responses were poorly correlated across species, and the lack of correlation was attributable to modulating factors (e.g. latitude and body mass) which influence behavior and physiology differently. These modulating factors, therefore, should be taken into consideration to better interpret FID and CORT responses in the context of species vulnerability to stress.

Avian malaria (caused by Plasmodium spp.) and avian malaria-like infections (caused by Haemoproteus spp.) are widespread and can seriously affect the health of their bird hosts, especially of immunologically naïve individuals. Therefore, these parasites have long been in the focus of bird-parasite studies. However, the species richness and diversity of these protozoan species have only been revealed since the use of molecular techniques. Diversity and prevalence of these parasites among different bird species and even between populations of a species show a large variation. Here, we investigated prevalence of avian malaria and avian malaria-like parasites in two distant populations of a non-migratory wetland specialist passerine, the bearded reedling (Panurus biarmicus). While previous studies have shown that reed-dwelling bird species often carry various blood parasite lineages and the presence of the vectors transmitting Plasmodium and Haemoproteus species has been confirmed from our study sites, prevalence of these parasites was extremely low in our populations. This may either suggest that bearded reedlings may avoid or quickly clear these infections, or these parasites cause high mortality in this species. The remarkably low prevalence of infection in this species is consistent with earlier studies and makes bearded reedlings a possible model organism for investigating the genetic or behavioural adaptations of parasite resistance.

Avian plumage colors and ornaments are ideal models to study the endocrine mechanisms linking sexually selected traits and individual parameters of quality and condition. The insulin-like growth factor 1 (IGF-1), an evolutionarily highly conserved peptide hormone, represents a link between body condition and the individual capacity to grow elaborated ornamental features, due to its regulatory role in cell proliferation and differentiation and its high sensitivity to the nutritional state of individuals. We investigated whether IGF-1 levels during molting affect the expression of multiple ornaments in a sexually dichromatic passerine species, the bearded reedling (Panurus biarmicus). We collected blood samples of males and females shortly before the molting completed and measured the size and colors of ornamental traits. Our results indicate that in males, structural plumage colors, the size of the melanin based ornament (beard) and tail length are independent traits. IGF-1 levels predict the length of the tail and the expression of male structural plumage components (UV-coloration), but not the melanin based ornament. In females plumage color and tail length were independent traits, which were not related to IGF-1 levels. Overall, our results indicate for the first time that IGF-1 could play a role in the development of secondary sexual characters in a passerine species.

International audience; Feather quality is of critical importance to long-distance migratory birds. Here, we report a series of analyses of a unique data set encompassing known-age individuals of the long-distance migratory Sand Martin (Riparia riparia). Sampling over 17 years along the Tisza River, eastern Hungary, has resulted in the recapture of numerous individuals enabling longitudinal and cross-sectional investigation of the role of adaptation to variable environmental conditions on feather morphology. We show that older individuals tend to possess better quality feathers, measured using bending stiffness, feather length and thickness as proxies. Bending stiffness and feather thickness do not change with individual age, in contrast with increases in feather length and declines in daily feather growth versus age of individual alongside moult duration. Individuals who live to older ages tend to have similar, or higher, feather growth rates and better feather quality than individuals captured at younger ages. Thus, on the basis of strong selection against individuals with slow feather growth, as seen in other species of swallows and martins, which causes a delay in moult completion, the results of this analysis highlight the potential cost of producing better quality feathers when this depends on moult duration. Feather length also does change during the lifetime of the individual and thus enabled us to further investigate influence of individual and environmental conditions during the moult. The results of this analysis provide important insights on the adaptive significance of these traits, and the potential use of physical characteristics in unravelling the reasons why long distance migratory bird populations are in global decline.

Social groups often consist of diverse phenotypes, including personality types, and this diversity is known to affect the functioning of the group as a whole. Social selection theory proposes that group composition (i.e. social environment) also influences the performance of individual group members. However, the effect of group behavioural composition on group members remains largely unexplored, and it is still contentious whether individuals benefit more in a social environment with homogeneous or diverse behavioural composition. We experimentally formed groups of house sparrows Passer domesticus with high and low diversity of personality (exploratory behaviour), and found that their physiological state (body condition, physiological stress and oxidative damage) improved with increasing group-level diversity of personality. These findings demonstrate that group personality composition affects the condition of group members and individuals benefit from social heterosis (i.e. associating with a diverse set of behavioural types). This aspect of the social life can play a key role in affiliation rules of social animals and might explain the evolutionary coexistence of different personalities in nature.

Synopsis All organisms must anticipate and balance energetic demands and available resources in order to maximize fitness. As hormones coordinate many interactions between an organism’s internal condition and the external environment, they may be key in mediating the allocation of resources to meet these demands. However, given that individuals differ considerably in how they react to changes in energetic demand, we asked whether variations in endocrine traits also correspond with life history variation. We tested whether natural variation in glucocorticoid hormone levels, oxidative stress measurements, and condition related to reproductive effort in a free-living songbird, the tree swallow, Tachycineta bicolor. We then tested whether any of these traits predicted the probability of a particular individual’s return to the local population in the following two years, an indicator of survival in this philopatric species. We found that males and females with longer telomeres had lighter nestlings. Moreover, individuals with lower plasma antioxidant capacity and higher reactive oxygen metabolites (i.e., greater oxidative stress) were less likely to return to the population. However, none of these traits were related to glucocorticoid levels. Our findings suggest a trade-off between reproduction and survival, with individuals with shorter telomeres having heavier nestlings but potentially paying a cost in terms of higher oxidative stress and lower survival. Interestingly, the evidence of this trade-off was unrelated to natural variation in glucocorticoids.

Begging calls provide a way for parents to gauge offspring state. Although temperature is known to affect call production, previous studies have not examined the influence of ambient temperature at the nest. We recorded ambient temperature and begging calls of 3 day-old tree swallows (Tachycineta bicolor). Our results indicate that typical daily temperature flux can dramatically alter a brood’s begging calls, depending on body size. Broods with small (low body mass) nestlings decreased the rate and length of their calls at colder temperatures, consistent with a biophysical constraint. In contrast, broods with large (high body mass) nestlings increased the rate of their calls at colder temperatures. Parents responded in a context-dependent manner, returning more rapidly after smaller nestlings gave longer begging calls. Our results suggest that the function of offspring begging calls is highly dynamic, with environmental conditions altering the relationship between begging calls and offspring state.

Stress is ubiquitous in the life of animals and a key determinant of their well-being and fitness. By quantifying levels of feather corticosterone in growing feathers (CORTf), we measured integrated stress responses in a monogamous game bird, the red grouse Lagopus lagopus scoticus. We investigated the effects of parasites and social mate choice on female CORTf levels during pairing, and tested the hypothesis that females with more parasites and paired with less attractive males have higher CORTf. We experimentally reduced nematode parasite abundance during pairing in females and investigated the effect of treatment on CORTf, while also considering the social mate’s phenotype (male comb size, as a proxy of sexual attractiveness). The treatment was effective at contrasting parasite loads between control and dosed females, but had no apparent effect on CORTf. In experimental females, reinfection rate after a month positively correlated with CORTf. We found no evidence of assortative mating based on size, condition or ornament size, but females paired with more attractive males (displaying bigger combs) had lower CORTf during pairing. Females for which parasite load was reduced had lower CORTf than control females at all levels of male attractiveness. Social mate choice therefore appears to be an important determinant of female integrated stress responses, which may in turn modulate reinfection rate and parasitism risk. An influence of male attractiveness on female stress may be part of an adaptive response allowing females to adjust reproductive investment to their achieved social mate choice., This work was funded by NERC (NE/D014352/1) and by NSF (IOS-1145625). FM was supported by a distinguish visitor award from the University of Cape Town (2015). LP-R was supported by a postdoctoral contract from MINECO (Severo Ochoa Programme; (SEV-2012-0262). FC and JM-P were supported by a JAE-Doc contract funded by CSIC and ESF. ÁZL was supported by an Eötvös Grant from the Hungarian Scholarship Board and an OTKA grant (K113108).

Biparental care presents an interesting case of cooperation and conflict between unrelated individuals. Several models have been proposed to explain how parents should respond to changes in each other’s parental care to maximize their own fitness, predicting no change, partial compensation, or matching effort as a response. Here, we present an experiment in tree swallows (Tachycineta bicolor) in which we increased the offspring provisioning of females by presenting them, but not their mates, with additional nestling begging calls using automated playbacks. We performed this experiment in two populations differing in future breeding opportunities. We found that in response to a temporary increase in female parental effort, males in the northern population (with lower future breeding opportunities and thus higher brood value) matched the increased effort, whereas males in the southern population did not. We also found that increases in parental care during playbacks were driven by the females (i.e., females initiated the increased effort and their mates followed them) in the northern population but not the southern population. These results support the idea that with incomplete information about the brood value and need, cues or signals from the partner might become important in coordinating parental care. Male tree swallows increase parental effort when their mates need to work harder. Using an automated system, we broadcast playback of hungry nestling calls only when the female parent was visiting the nest. In a population where the value of the current brood was high, males significantly increased their provisioning rate, much more than their partners did. Since only the females could hear the playbacks, and the begging of the nestlings did not change in response to the treatment, we suggest that either the males used their partner’s feeding rate as a cue or the females may have communicated to their mates that they should work harder. These results suggest that cues or signals from the partner may be important in coordinating parental care.

International audience; Stressful developmental conditions can have both short- and long-term effects on animal physiology and behaviour, but studies on this topic are rarely conducted in the wild and, if so, largely focus on only the first few weeks of life. To fill this gap, we tested developmental links between early-life stress and the physiology of wild-caught juveniles later during development. Specifically, we examined potential associations between feather corticosterone levels of hatchling house finches (Haemorhous mexicanus) and several phenotypic and physiological traits measured several months later in juveniles. We assessed four indices of health (oxidative damage to lipids, innate immunity, intestinal parasite infection intensity and plumage colour) and two morphological traits (body mass and tarsus length) in juveniles. Feather corticosterone content was not related to any of the juvenile traits later in development. Our results suggest that physiological variables can change rapidly during ontogeny, such that stress hormone levels in juvenile feathers could be uncoupled from the real stress levels experienced by nestlings. Instead, juvenile physiology might be more dependent on current environmental conditions than on early-life conditions (i.e. environmental matching), and this may limit the effects on fitness of poor early-developmental conditions.

International audience; High levels of environmental contaminants such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and mercury (Hg) have been reported in some Arctic top predators such as seabirds. Chronic exposure to these contaminants might alter the response to environmental changes through interference with the regulation of corticosterone (CORT), a glucocorticoid stress hormone released by the hypothalamo–pituitary–adrenal (HPA) axis. Positive and negative relationships between CORT and environmental contaminants have been reported in polar seabirds. However, patterns appear inconclusive and it is difficult to attribute these relationships to a dysfunction of the HPA axis or to other confounding effects. In order to explore the relationships between the HPA axis activity and contaminants, we tested whether different aspects of the HPA axis of an Arctic seabird, the black-legged kittiwakes Rissa tridactyla, would be related to blood Hg, PCB and OCP concentrations. Male kittiwakes were caught during the incubation period in Svalbard and were subjected to different stress series: (1) a capture-restraint stress protocol, (2) an injection of dexamethasone (DEX) that enabled to test the efficacy of the HPA negative feedback and (3) an injection of adrenocorticotropic hormone (ACTH) that informed on the adrenal responsiveness. The HPA axis activity was unrelated to ∑OCPs and Hg. However, birds with high concentrations of ∑PCBs released more CORT after the ACTH injection. It is suggested that ∑PCBs may increase the number of ACTH-receptors on the adrenals. Additionally, hatching date was delayed in males with higher concentrations of ∑PCBs and ∑OCPs. This study gives new evidence that PCBs and adrenal activity may be related. Thus high PCB burden may make individuals more prone to other stressors such as ongoing climate change.

As species shift their ranges and phenology to cope with climate change, many are left without a ready supply of their preferred food source during critical life stages. Food shortages are often assumed to be driven by reduced total food abundance, but here we propose that climate change may cause short-term food shortages for foraging specialists without affecting overall food availability. We frame this hypothesis around the special case of birds that forage on flying insects for whom effects mediated by their shared food resource have been proposed to cause avian aerial insectivores' decline worldwide. Flying insects are inactive during cold, wet or windy conditions, effectively reducing food availability to zero even if insect abundance remains otherwise unchanged. Using long-term monitoring data from a declining population of tree swallows ( Tachycineta bicolor ), we show that nestlings’ body mass declined substantially from 1977 to 2017. In 2017, nestlings had lower body mass if it rained during the preceding 3 days, though females increased provisioning rates, potentially in an attempt to compensate. Adult body mass, particularly that of the males, has also declined over the long-term study. Mean rainfall during the nestling period has increased by 9.3 ± 0.3 mm decade −1 , potentially explaining declining nestling body mass and population declines. Therefore, we suggest that reduced food availability, distinct from food abundance, may be an important and previously overlooked consequence of climate change, which could be affecting populations of species that specialize on foraging on flying insects.

Innovative behaviors such as exploiting novel food sources can grant significant fitness benefits for animals, yet little is known about the mechanisms driving such phenomena, and the role of physiology is virtually unexplored in wild species. Two hypotheses predict opposing effects of physiological state on innovation success. On one hand, poor physiological condition may promote innovations by forcing individuals with poor competitive abilities to invent alternative solutions. On the other hand, superior physiological condition may ensure greater cognitive capacity and thereby better problem-solving and learning performance. To test these hypotheses, we studied the behavior of wild-caught house sparrows (Passer domesticus) in 4 novel tasks of food acquisition, one of which was presented to the birds in repeated trials, and we investigated the relationships of individual performance with relevant physiological traits. We found that problem-solving performance across the 4 tasks was moderately consistent within individuals. Birds with lower integrated levels of corticosterone, the main avian stress hormone, solved the most difficult task faster and were more efficient learners in the repeated task than birds with higher corticosterone levels. Birds with higher concentration of total glutathione, a key antioxidant, solved 2 relatively easy tasks faster, whereas birds with fewer coccidian parasites tended to solve the difficult task more quickly. Our results, thus, indicate that aspects of physiological state influence problem-solving performance in a context-dependent manner, and these effects on problem-solving capacity, probably including cognitive abilities, are more likely to drive individual innovation success than necessity due to poor condition.

Life history theory predicts that optimal strategies of parental investment will depend on ecological and social factors such as current brood value and offspring need. Parental care strategies are also likely to be mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoid hormones. Here we present an experiment in tree swallows (Tachycineta bicolor), a biparental songbird with wide geographic distribution, asking whether parental care is strategically adjusted in response to signals of offspring need and brood value and whether glucocorticoids are involved in these adjustments. Using an automated playback system, we carried out playbacks of nestling begging calls specifically to females in two populations differing in their brood value: a northern population in Ontario, Canada (relatively high brood value) and a southern population in North Carolina, USA (lower brood value). We quantified female offspring provisioning rates before and during playbacks and plasma corticosterone levels (cort) once during late incubation and once immediately after playbacks. Females in both populations increased feeding rates temporarily during the first two hours of playback but the increase was not sustained for the entire duration of playback (six hours). Cort levels from samples at the end of the playback did not differ between control females and females that received playbacks. However, females that had higher increases in cort between the incubation and nestling period had greater fledging success. These results suggest that females are able to strategically respond to offspring need, although the role of glucocorticoids in this strategic adjustment remains unclear.

Life-history theory predicts that long-lived organisms should reduce parental effort under inclement environmental conditions in order to favour long-term survival. Seabirds are long-lived top predators often exposed to environmental endocrine disrupting chemicals such as mercury (Hg). Hg contaminated birds show disrupted parental behaviour. Avian parental behaviour is governed by two key hormones in birds: corticosterone (CORT, a glucocorticoid hormone) and prolactin (PRL, a pituitary hormone involved in parental care). Any disruption of these hormones may alter the ability of an individual to adjust parental behaviour to environmental conditions. The first aim of this study was to describe the relationships between blood Hg concentrations, plasma PRL and reproductive performance in Arctic black-legged kittiwakes (Rissa tridactyla). We a found negative relationship between plasma initial PRL and blood Hg concentrations in males. Moreover, Hg concentration was negatively related to breeding success in chick-rearing males. Second, to study the effect of a chronic increase of CORT levels on the Hg-PRL relationship, we experimentally increased stress with CORT pellet implantation. We predicted that Hg and CORT would act synergistically on PRL and an increase of CORT concentration would steepen the Hg-PRL relationship. However, adding CORT did not steepen the Hg-PRL relationship. Hatching success was significantly lower in CORT implanted males than in controls, breeding success was not reduced in CORT implanted male kittiwakes with high levels of blood Hg. Our results suggest that Hg may impair reproductive performance through a disruption of PRL secretion. Contrary to our prediction Hg and CORT did not act synergistically, the underlying mechanisms associating CORT and Hg with PRL, might be more complex than a single interaction of two factors. arctic, black-legged kittiwake, breeding success, contaminants, corticosterone, endocrine disruptors, parental investment, parenting hormone This is the peer reviewed version of the following article: [Mercury exposure, stress and prolactin secretion in an Arctic seabird: an experimental study], which has been published in final form at [http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12534/abstract]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Sexually selected traits can signal an individual's ability to contribute offspring care. Differential allocation theory posits that when these same traits also influence brood value, it may be adaptive for partners to adjust care in response to their mates' traits. Evaluating the strength and direction of parental quality signalling and differential allocation is thus essential to understand selection on ornamental traits. We examined relationships between plumage colour and parental care in tree swallows, Tachycineta bicolor, a mutually ornamented species in which plumage colour is related to male and female reproductive performance. Using a model of avian vision to quantify parental colour trait variation, we found that male and female tree swallows that were paired to partners with greener, more saturated plumage colour fed offspring at higher rates. Among tree swallow pairs where both partners were in their second year of breeding or older, individuals with greener, more saturated plumage colour also fed their offspring at higher rates. We show that offspring of males that provisioned more often tended to achieve greater body mass independent of the colour traits of their parents. Our results suggest a role for partner parental care in selection on female ornamentation in this species.

As urbanized areas expand and develop throughout the world, the importance of understanding their effects on wildlife increases. Living in cities may be stressful for animals but may also provide benefits at the same time, and the sum of these effects should manifest in the body condition of individuals. Studies addressing this phenomenon tend to evaluate one or few indices of body condition, each of which may be subject to various confounding effects and seasonal changes. In this study we used multiple approaches to assess the effects of urbanization on adult body condition in house sparrows (Passer domesticus), a passerine undergoing population declines in urban habitats. In line with earlier studies, we found that sparrows in more urbanized habitats have reduced body mass. However, birds had similar scaled mass index (body mass corrected for body size) along the urbanization gradient at all times of the year, contradicting the previous result on type-1 regression residuals. In the non-breeding season, urban and rural birds had similar levels of corticosterone, hematocrit, and heterophil:lymphocyte ratio. In the molting season, hematocrit indicated better condition in rural birds whereas H:L ratio showed the opposite; however, these trends were not consistent between age groups. Two condition-dependent plumage traits, male bib size and wing bar size, showed no systematic variation along the gradient of urbanization. These results suggest that the environmental conditions experienced by adult house sparrows are not more stressful in more urbanized habitats, and they also highlight the importance of considering multiple indices of body condition.

SUMMARY Individuals respond differently to stressors and it has been suggested that stress responses are related to coping styles (consistent individual differences in behavior and physiology). We studied behavioral responses to a novel object and corticosterone response to stress during chick rearing in free-living female house sparrows (Passer domesticus). To prevent mates from influencing each others' behavior, we removed the males temporarily from nests and tested the females the following day either with a novel object placed on the nest box or as control. The two groups differed only in behaviors that were a priori defined as responses to the novel object (latency to first feeding, time spent near the nest, and inspecting the novel object by hovering in front of it) indicating that mate-removal per se had no effect on female behavior. Based on these variables, females' coping behaviors were categorized as ‘bold’, ‘inquisitive’ or ‘shy’ by discriminant analysis. Baseline corticosterone, measured on the day following the novel-object or control test, was not related to any measure of coping. Stress-induced corticosterone, however, was negatively related to number of hoverings in front of the nest (a measure of explorativeness) and accordingly differed between the behavioral coping categories, with ‘inquisitive’ birds having the lowest stress response. We propose that the relationship between physiological stress response and behavioral response to novelty (a component of personality or coping style) may be more complex than previously suggested, and individuals cannot always be unambiguously categorized along a single personality axis.

Kin-selection theory predicts that relatedness may reduce the level of aggression among competing group members, leading to indirect fitness benefits for kin-favoring individuals. To test this hypothesis, we investigated whether relatedness affects aggressive behavior during social activities in captive house sparrow (Passer domesticus) flocks. We found that sparrows did not reduce their aggression towards kin, as neither the frequency nor the intensity of fights differed between close kin and unrelated flock-mates. Fighting success was also unrelated to kinship and the presence of relatives in the flock did not influence the birds’ dominance rank. These results suggest that the pay-offs of reduced aggression towards kin may be low in non-breeding flocks of sparrows, e.g. due to competition among relatives as predicted by a recent refinement of kin-selection theory. Our findings indicate that the significance of kin selection may be restricted in some social systems such as winter aggregations of birds.

Kin selection is often important in the evolution of reproductive behaviour, but we know much less about its significance for nonreproductive social groups. We investigated whether relatedness affects social-foraging behaviour in captive house sparrow, Passer domesticus, flocks, where birds may either search for food or exploit flockmates' food findings by scrounging. In such systems, both increased and decreased frequency of scrounging from relatives can be predicted by kin selection theory, depending on the relative costs and benefits of exploiting close kin. We found that birds used aggressive joining less often and obtained less food by that tactic from their close kin than from unrelated flockmates. In nonaggressive joinings, males also tended to join less often and obtained less food from close kin flockmates than from unrelated birds, whereas an opposite trend was found in females. Close kin males also spent less time feeding together from the same food patch than unrelated males, further suggesting reduced exploitation by male kin. These results suggest that house sparrows are able to recognize their close kin flockmates and reduce aggressive scrounging towards them, and that the sexes may differ in some forms of kin exploitation.

Ho do parents resolve their conflict over parental care? The classical "sealed-bid" model of biparental care suggested that parents use a fixed best effort given the partner's effort. Alternatively, parents may "negotiate" their actual effort until the efforts of both partners settle down to limiting values, but in this case, the resulting efforts will not be the best responses to one another. Consequently, under the best response scenario, the response of 1 parent to the removal of its mate can be predicted from the response to a reduction in its partner's effort, whereas the "negotiation" model predicts that such an extrapolation will underestimate the effort of a parent caring alone. We tested this prediction in free-living house sparrows (Passer domesticus). We experimentally manipulated the males' parental care as follows: males' care in group 1) was reduced by using a capture--handling--release stress protocol, 2) stopped by removing the male, and 3) left as control. In response to these manipulations, control females kept their feeding rate constant, whereas male-stressed-released females showed a moderate increase of feeding rate. When this response was extrapolated to zero male effort, their effort was still significantly lower than the observed effort of male-removed females. These results suggest that females may use the negotiation rule to determine their actual parental effort. Copyright 2009, Oxford University Press.

An important cost of sexual and social colour signals may be increased conspicuousness of the animals to visual predators. Although such predation costs have repeatedly been proposed for various ornaments of birds, especially for melanised and depigmented signals with low presumed production costs, tests of this hypothesis are rare and inconclusive. In this study we investigated whether individual variation in plumage ornamentation was associated with predator-related risk-taking behaviour and short-term survival in free-living House Sparrows Passer domesticus. In a large sample of birds we measured three aspects of coloration used in sexual and social signalling: the size of the melanised black throat patch in males, and the area and conspicuousness of the depigmented wing-bar in both sexes. We measured risk-taking by manipulating the distance of feeders from shelters, and recorded individually ringed birds feeding close to and far from shelter. Sparrows seemed to perceive the farther feeders as more risky, as indicated by the shorter time spent and smaller groups feeding far from rather than close to shelter. However, the use of the more risky (farther) feeders was not related to any of the colour traits we measured, suggesting that Sparrows do not adjust their risk-taking behaviour to their ornamentation. Males (the more ornamented sex) did not take less risk than females. Furthermore, we found no evidence that larger throat patches or more ornamented wing-bars reduced the probability of survival. Our findings were robust and consistent across multiple approaches, even when we controlled for several potential confounding effects. These results do not support the suggestion that melanised and depigmented plumage ornaments have significant predation costs in House Sparrows.

International audience; A crucial problem for every organism is how to allocate energy between competing life-history components. The optimal allocation decision is often state-dependent and mediated by hormones. Here, we investigated how age, a major state variable affects individuals' hormonal response to a standardized stressor: a trait that may reflect allocation between self-maintenance and reproduction. We caught free-living house sparrows and measured their hormonal (corticosterone) response to capture stress in consecutive years. Using a long-term ringing dataset, we determined the age of the birds, and we partitioned the variation into within- and among-individual age components to investigate the effects of plasticity versus selection or gene flow, respectively, on the stress response. We found large among-individual variation in the birds' hormone profiles, but overall, birds responded less strongly to capture stress as they grew older. These results suggest that stress responsiveness is a plastic trait that may vary within individuals in an adaptive manner, and natural selection may act on the reaction norms producing optimal phenotypic response in the actual environment and life-history stage.