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Most studies on sexual size dimorphism address proximate and functional questions related to adults, but sexual size dimorphism usually develops during ontogeny and developmental trajectories of sexual size dimorphism are poorly understood. We studied three bird species with variation in adult sexual size dimorphism: black coucals (females 69% heavier than males), white‐browed coucals (females 13% heavier than males) and ruffs (males 70% heavier than females). Using a flexible Bayesian generalized additive model framework (GAMM), we examined when and how sexual size dimorphism developed in body mass, tarsus length and bill length from hatching until fledging. In ruffs, we additionally examined the development of intrasexual size variation among three morphs (Independents, Satellites and Faeders), which creates another level of variation in adult size of males and females. We found that 27–100% of the adult inter‐ and intrasexual size variation developed until fledging although none of the species completed growth during the observational period. In general, the larger sex/morph grew more quickly and reached its maximal absolute growth rate later than the smaller sex/morph. However, when the daily increase in body mass was modelled as a proportion, growth patterns were synchronized between and within sexes. Growth broadly followed sigmoidal asymptotic models, however only with the flexible GAMM approach, residual distributions were homogeneous over the entire observation periods. These results provide a platform for future studies to relate variation in growth to selective pressures and proximate mechanisms in these three species, and they highlight the advantage of using a flexible model approach for examining growth variation during ontogeny.

The environment where an embryo develops can be influenced by components of maternal origin, which can shape offspring phenotypes and therefore maternal fitness. In birds that produce more than one egg per clutch, females differ in the concentration of components they allocate into the yolk along the laying sequence. However, identification of processes that shape female yolk allocation and thus offspring phenotype still remains a major challenge within evolutionary ecology. A way to increase our understanding is by acknowledging that allocation patterns can differ depending on the level of analysis, such as the populationversusthe among-female (within-population) level. We employed mixed models to analyze at both levels the variation in allocation along the laying sequence of four steroid hormones, three antioxidants, and four groups of fatty acids present in the egg yolks of wild great tits (Parus major). We also quantified repeatabilities for each component to study female consistency. At a population level, the concentrations/proportions of five yolk components varied along the laying sequence, implying that the developmental environment is different for offspring developing in firstversuslast eggs. Females varied substantially in the mean allocation of components and in their plasticity along the laying sequence. For most components, these two parameters were negatively correlated. Females were also remarkably repeatable in their allocation. Overall, our data emphasize the need to account for female variation in yolk allocation along the laying sequence at multiple levels, as variation at a population level is underpinned by different individual patterns. Our findings also highlight the importance of considering both levels of analysis in future studies investigating the causes and fitness consequences of yolk compounds. Finally, our results on female repeatability confirm that analyzing one egg per nest is a suitable way to address the consequences of yolk resource deposition for the offspring.

The necessity to do basic research, such as the study of animal behaviour, is often questioned. “What is this good for?” people may ask. Many discoveries of basic research lead to novel and practical applications that could not have been predicted in advance. In fact, every penny spent on basic research generates a multiple of economic value in return. This is the most common answer to justify “blue sky” research. However, basic research has a much more important and fundamental value relating to liberty, equality and human rights.

Managing oxidative stress is an important physiological function for all aerobic organisms, particularly during periods of prolonged high metabolic activity, such as long-distance migration across ecological barriers. However, no previous study has investigated the oxidative status of birds at different stages of migration and whether that oxidative status depends on the condition of the birds. In this study, we compared (1) energy stores and circulating oxidative status measures in (a) two species of Neotropical migrants with differing migration strategies that were sampled at an autumn stopover site before an ecological barrier; and (b) a species of trans-Saharan migrant sampled at a spring stopover site after crossing an ecological barrier; and (2) circulating oxidative measures and indicators of fat metabolism in a trans-Saharan migrant after stopovers of varying duration (0-8 nights), based on recapture records. We found fat stores to be positively correlated with circulating antioxidant capacity in Blackpoll Warblers and Red-eyed Vireos preparing for fall migration on Block Island, USA, but uncorrelated in Garden Warblers on the island of Ponza, Italy, after a spring crossing of the Sahara Desert and Mediterranean Sea. In all circumstances, fat stores were positively correlated with circulating lipid oxidation levels. Among Garden Warblers on the island of Ponza, fat anabolism increased with stopover duration while oxidative damage levels decreased. Our study provides evidence that birds build antioxidant capacity as they build fat stores at stopover sites before long flights, but does not support the idea that antioxidant stores remain elevated in birds with high fuel levels after an ecological barrier. Our results further suggest that lipid oxidation may be an inescapable hazard of using fats as the primary fuel for flight. Yet, we also show that birds on stopover are capable of recovering from the oxidative damage they have accrued during migration, as lipid oxidation levels decrease with time on stopover. Thus, the physiological strategy of migrating songbirds may be to build prophylactic antioxidant capacity in concert with fuel stores at stopover sites before a long-distance flight, and then repair oxidative damage while refueling at stopover sites after long-distance flight.

Why mainly males compete and females take a larger share in parental care remains an exciting question in evolutionary biology. Role-reversed species are of particular interest, because such 'exceptions' help to test the rule. Using mating systems theory as a framework, we compared the reproductive ecology of the two most contrasting coucals with regard to sexual dimorphism and parental care: the black coucal with male-only care and the biparental white-browed coucal. Both species occur in the same lush habitat and face similar ecological conditions, but drastically differ in mating system and sexual dimorphism. Black coucals were migratory and occurred at high breeding densities. With females being obligatory polyandrous and almost twice as heavy as males, black coucals belong to the most extreme vertebrates with reversed sexual dimorphism. Higher variance in reproductive success in fiercely competing females suggests that sexual selection is stronger in females than in males. In contrast, resident white-browed coucals bred at low densities and invariably in pairs. They were almost monomorphic and the variance in reproductive success was similar between the sexes. Black coucals were more likely to lose nests than white-browed coucals, probably facilitating female emancipation of parental care in black coucals. We propose that a combination of high food abundance, high population density, high degree of nest loss and male bias in the adult sex ratio represent ecological conditions that facilitate role reversal and polyandry in coucals and terrestrial vertebrates in general.

Polar environments are characterized by discrete periods of continuous light or darkness during the summer and winter months, respectively. Because the light/dark cycle serves as the primary Zeitgeber to synchronize rhythms of most organisms, its seasonal absence in polar regions poses challenges to the circadian organization of organisms that reside in these environments. Although some species become arrhythmic, others, such as migratory songbirds, are able to maintain an intact diurnal rhythm during polar summer. This suggests that birds may switch to alternative environmental cues, such as daily changes in light intensity and ambient temperature, which may have the potential to reset the biological clock. However, identifying the low-amplitude Zeitgeber that synchronizes rhythms in free-living polar-dwelling animals has been difficult to demonstrate. In this study, we measured behavioral and melatonin profiles of free-living Lapland longspurs (Calcarius lapponicus) near Barrow, Alaska (71°N) during the continuous daylight of summer in the Arctic. Diel cycles in activity and male singing were apparent throughout the polar day with a quiescence period of 4-5 hr starting around 24:00 Alaska Daylight Time. This inactivity corresponded with elevated melatonin profiles. In contrast, territorial aggression of males in response to a conspecific intruder was not dependent upon time-of-day. Diel changes in light intensity and ambient temperature were negatively associated with daily melatonin profiles after taking into account time-of-day effects. These results suggest that photic and thermal cues may act either as alternative Zeitgeber cues, or possibly masking agents. Distinguishing between these two possibilities will require further study.

Summary Many aspects of the social environment affect hypothalamic-pituitary-adrenal (HPA) axis function and increase circulating glucocorticoid concentrations. In this review, we examine the relationships between the social environment and the function of the HPA axis in vertebrates. First, we explore the effects of the social environment on glucocorticoid secretion in territorial (primarily non-social) species, with an emphasis on the effects of variation in population density, as modified by environmental factors such as predation risk and food availability. In general, high population density or frequent territorial intrusions are associated with increased glucocorticoid secretion in a wide range of taxa, including mammals, birds, fish and reptiles, although there is considerable variability across species. Second, we consider the effects of social interactions and dominance rank on glucocorticoid secretion in social species, mostly in birds and mammals. We review studies that have detected an association between social status and glucocorticoid levels – sometimes with higher glucocorticoid levels in low-ranking individuals, and sometimes with higher glucocorticoid levels in dominant individuals. The relationship between dominance and glucocorticoid levels varies among species, populations and years, in a manner that depends on the stability of the social hierarchy, environmental conditions, the type of breeding system, and the manner in which high rank is obtained and maintained. Finally, we discuss the concept of allostasis and consider interactions between social effects and other environmental factors, noting that there is relatively little research on these interactions to date. For both non-social and social species, we identify priorities of future research. These priorities include more complete descriptions of HPA function that move beyond measurements of basal glucocorticoid concentrations (which will generally require field experiments), to studies that examine organizational effects of social stressors, that directly test the relationship between HPA function and fitness, and that examine how glucocorticoid responses affect population dynamics. Although several lines of evidence suggest that glucocorticoid responses can affect the fitness of individuals and therefore can alter the dynamics of populations, the effect of glucocorticoid responses on population dynamics remains essentially unstudied.

Phenotypic flexibility allows animals to adjust their physiology to diverse environmental conditions encountered over the year. Examining how these varying traits covary gives insights into potential constraints or freedoms that may shape evolutionary trajectories. In this study, we examined relationships among haematocrit, baseline corticosterone concentration, constitutive immune function and basal metabolic rate in red knot Calidris canutus islandica individuals subjected to experimentally manipulated temperature treatments over an entire annual cycle. If covariation among traits is constrained, we predict consistent covariation within and among individuals. We further predict consistent correlations between physiological and metabolic traits if constraints underlie species-level patterns found along the slow-fast pace-of-life continuum. We found no consistent correlations among haematocrit, baseline corticosterone concentration, immune function and basal metabolic rate either within or among individuals. This provides no evidence for constraints limiting relationships among these measures of the cardiovascular, endocrine, immune and metabolic systems in individual red knots. Rather, our data suggest that knots are free to adjust individual parts of their physiology independently. This makes good sense if one places the animal within its ecological context where different aspects of the environment might put different pressures on different aspects of physiology.

Summary 1. Methods to measure metabolites of steroid hormones from faeces have become very popular in wildlife conservation and ecology, because they allow gathering physiological data without the necessity to capture the animals. However, this advantage comes at costs that are particularly relevant when studying free-living animals in their natural environments. Previous methodological reviews have stressed the importance of validations to prove that real metabolites of the hormone in question are measured, but the research community has largely ignored further caveats relating to sex, diet, metabolic rate and individual differences in hormone metabolite formation. 2. Often the sexes differ in how they metabolize hormones. As a consequence, one may not be able to compare hormone metabolite concentrations between males and females of one species. 3. Diet can alter the way hormones are metabolized, and different diets can change the amount of faecal bulk. Both phenomena can result in measurement artefacts that may seriously distort the estimation of hormone metabolite concentrations. As a consequence, comparisons of hormone metabolite concentrations, for example, between seasons or populations, may become problematic. 4. Changes in ambient temperature and food availability may trigger large fluctuations in metabolic rate of free-living animals. These fluctuations may then result in major distortions of faecal hormone metabolite concentrations without any change in bioactive hormone levels. 5. Bacteria metabolize hormones in the gut. Individual differences in bacterial composition can cause differences in how hormones are decomposed. Thus, individuals may differ with regard to what kind of hormone metabolites they form and with regard to the relative composition of these hormone metabolites. As only specific metabolites are measured, differences in metabolism may distort the results. 6. In summary, non-invasive hormone research measures various end products of a hormone after its clearance from the circulation and extensive modification by bacteria. Not only does this increase random variance, it may also generate systematic noise, which may seriously distort the signal (i.e. the hormonal status of the individual) in a non-random manner. Thus, we still need to learn much more about whether this widely used technique reliably measures the physiological status of animals in uncontrolled environments.

Past studies have suggested a fundamental difference in testosterone concentrations between tropical and northern latitude male birds, with the convention being that males in the tropics express much lower levels of testosterone. However, recent comparative studies have shown that tropical males with a short and synchronous breeding season (i.e. a breeding season typical of northern species) express maximum testosterone levels similar to those of northern latitude birds. Here, we ask the converse: do northern latitude songbirds that express a defining life-history characteristic typical of the tropics, i.e. year-round territoriality, have an annual testosterone profile similar to that of tropical songbirds? For the few year-round territorial species for which data are available, we found that seasonal testosterone profiles and seasonal maxima in plasma testosterone were similar between males of tropical and non-tropical species. For example, males of both groups expressed seasonal maxima during the period when females were fertile, and testosterone levels at this time were similar. In contrast, this and other studies show that species with seasonal territories typically express maximum testosterone levels earlier in the breeding cycle, when territories are first being established. Taken together, we suggest that specific life-history traits may play a more important role in determining testosterone profiles of tropical and non-tropical birds than breeding latitude and encourage further studies to allow for more formal comparisons.

The immunocompetence handicap hypothesis (ICHH) posits that the hormone testosterone mediates a trade-off between investment in reproduction and immunological condition. In this study, we tested the ICHH in the Red Bishop Euplectes orix, a polygynous weaverbird. Males of this strongly sexually dimorphic species show an elaborate courtship display to attract females and compete aggressively with other males for nesting sites in breeding colonies. We experimentally elevated testosterone levels in breeding male Red Bishops kept in an aviary with a subcutaneous implantation of testosterone-releasing pellets. We then compared behaviour, development of territory size and immunological condition (as assessed through a white blood cell count) of the experimental group with a control group treated with placebos. In addition, we measured the primary and secondary response to phytohaemagglutinin (PHA) to investigate the effect of testosterone on both innate and acquired immunity. Males with elevated levels of testosterone enlarged their territories and conducted more courtship behaviour, while showing a decrease in health, expressed by an increased heterophil/lymphocyte ratio compared with the control group. Males of the control group showed an increase of the secondary response to PHA, as expected under the assumption that repeated exposure to an antigen enhanced the immune response due to acquired immunity. However, males with experimentally increased testosterone levels did not show such an enhanced immune response in the secondary PHA test (although sample size and power of the statistical tests were low), indicating that testosterone treatment might directly or indirectly suppress some component of the acquired immune response.

Most species of birds show bi-parental or female-only care. However, a minority of species is polyandrous and expresses male-only care. So far, such reversals in sex roles have been demonstrated only in precocial bird species, but there was suggestive evidence that such a mating system may occur in one altricial bird species, the black coucal, Centropus grillii. In a field study in Tanzania we investigated whether black coucals are sex-role reversed and polyandrous. We found that males were mated to one female, rarely vocalized and provided all parental care from incubation of eggs to feeding of young. In contrast, female black coucals were about 69% heavier and 39% larger than males and polyandrous. They spent a large proportion of time calling from conspicuous perches, defended breeding territories, did not help in provisioning young and had a higher potential reproductive rate than males. We conclude that the black coucal currently represents the only altricial bird species with sole male parental care and a classical polyandrous mating system. High nest predation pressure and small territory sizes due to high food abundance may have been important factors in the evolution of sex-role reversal and polyandry in this species.

Florida scrub-jays (Aphelocoma coerulescens) in the suburbs breed earlier than jays in native habitat. Amongst the possible factors that influence this advance (e.g., food availability, microclimate, predator regime, etc.), is exposure to artificial lights at night (LAN). LAN could stimulate the reproductive axis of the suburban jays. Alternatively, LAN could inhibit pineal melatonin (MEL), thus removing its inhibitory influence on the reproductive axis. Because Florida scrub-jays are a threatened species, we used western scrub-jays (Aphelocoma californica )t o investigate the effects of LAN upon reproductive hormones and melatonin. Jays were held under conditions inwhichthedark-phaseofthelight:dark cyclewas withoutillumination andthenunder low levels of LAN. Under both conditions, birds were exposed first to short-days (9.5L:14.5D) that were gradually increased to long-days (14.5L:9.5D). At various times, blood samples were collected during the light part of the cycle to measure reproductive hormones (luteinizing hormone, LH; testosterone, T; and estradiol, E2). Similarly, samples to assess melatonin were collected during the dark. In males, LAN caused a depression in LH levels and levels were � 4� greater under long- than short-days. In females, there was no effect of LAN or photoperiod upon LH. LAN resulted in depressed T levels in females, although there was no effect on T in males. E2 levels in both sexes were lower under LAN than under an unlighted dark-phase. Paradoxically, MEL was higher in jays underLAN,andunderlong-days.MELdidnotdiffer bysex.LANdisrupted theextraordinarily strong correlation between T and E2 that existed under unlighted nocturnal conditions. Overall, our findings fail to support the hypothesis that LAN stimulates the reproductive axis. Rather, the data demonstratethatLANtendstoinhibitreproductivehormonesecretion,althoughnotinaconsistent fashion between the sexes. J. Exp. Zool. 319A:527-538, 2013. © 2013 Wiley Periodicals, Inc. How to cite this article: Schoech SJ, Bowman R, Hahn TP, Goymann W, Schwabl I, Bridge ES. 2013. The effects of low levels of light at night upon the endocrine physiology of western scrub- jays (Aphelocoma californica). J. Exp. Zool. 319A:527-538.

Introduction: Two Workshops in Ornithology: A General Introduction: Dedication to Eberhard Gwinner: Ulf Bauchinger and Wolfgang Goymann. . I. Measurement of Hormones from Droppings and Egg Yolk of Birds:. 1. Introduction to the European Science Foundation Technical Meeting: Analysis of Hormones in Droppings and Egg Yolk of Birds: Wolfgang Goymann and Susanne Jenni-Eiermann. 2. Potential Impact of Nutritional Strategy on Noninvasive Measurements of Hormones in Birds: Kirk C. Klasing. 3. Measurement of Corticosterone Metabolites in Birds' Droppings: An Analytical Approach: Erich Mostl, Sophie Rettenbacher, and Rupert Palme. 4. Noninvasive Monitoring of Hormones in Bird Droppings: Physiological Validation, Sampling, Extraction, Sex Differences, and the Influence of Diet on Hormone Metabolite Levels: Wolfgang Goymann. 5. Measuring Fecal Glucocorticoid Metabolites in Mammals and Birds: The Importance of Validation: Chadi Touma and Rupert Palme. 6. Measuring Fecal Steroids: Guidelines for Practical Application: Rupert Palme. 7. A Noninvasive Technique to Evaluate Human-Generated Stress in the Black Grouse: Marjana Baltic, Susanne Jenni-Eiermann, Raphael Arlettaz, and Rupert Palme. 8. Measuring Corticosterone Metabolites in Droppings of Capercaillies (Tetrao urogallus): Dominik Thiel, Susanne Jenni-Eiermann, and Rupert Palme. 9. Noninvasive Measures of Reproductive Function and Disturbance in the Barred Owl, Great Horned Owl, and Northern Spotted Owl: Samuel K. Wasser and Kathleen E. Hunt. 10. Synthesis of Measuring Steroid Metabolites in Goose Feces: Katharina Hirschenhauser, Kurt Kotrschal, and Erich Mostl. 11. Sampling Effort/Frequency Necessary to Infer Individual Acute Stress Responses from Fecal Analysis in Greylag Geese (Anser anser): Isabella B. R. Scheiber, Simona Kralj, and Kurt Kotrschal. 12. Investigating Maternal Hormones in Avian Eggs: Measurement, Manipulation, and Interpretation: Ton G. G. Groothuis and Nikolaus Von Engelhardt. 13. Measuring Steroid Hormones in Avian Eggs: Nikolaus Von Engelhardt and Ton G. G. Groothuis. 14. Corticosterone in Chicken Eggs: S Rettenbacher, E Mostl, R Hackl, and R Palme. 15. Steroids in Allantoic Waste: An Integrated Measure of Steroid Exposure in Ovo: Z Morgan Benowitz-Fredericks, Alexander S. Kitaysky, and John C. Wingfield. . II. Optimality in Bird Migration: Adaptations for Long-Distance Migration in Birds? The Search for Adaptive Syndromes:. 16. Are There Specific Adaptations for Long-Distance Migration in Birds? The Search for Adaptive Syndromes: Outline of the European Science Foundation Workshop: Ulf Bauchinger, Christiaan Both, and Theunis Piersma. 17. Flexible Seasonal Timing and Migratory Behavior: Results from Stonechat Breeding Programs: Barbara Helm, Eberhard Gwinner, and Lisa Trost. 18. Are Long-Distance Migrants Constrained in Their Evolutionary Response to Environmental Change?: Causes of Variation in the Timing of Autumn Migration in a Blackcap (S. atricapilla) and Two Garden Warbler (Sylvia borin) Populations: Francisco Pulido and Michael Widmer. 19. Spatial Behavior of Medium and Long-Distance Migrants at Stopovers Studied by Radio Tracking: Nikita Chernetsov. 20. Ecomorphology of the External Flight Apparatus of Blackcaps (Sylvia atricapilla) with Different Migration Behavior: Wolfgang Fiedler. 21. Melatonin and Nocturnal Migration: Leonida Fusani and Eberhard Gwinner. 22. Phenotypic Flexibility of Skeletal Muscles during Long-Distance Migration of Garden Warblers: Muscle Changes Are Differentially Related to Body Mass: Ulf Bauchinger and Herbert Biebach. 23. Is There a "Migratory Syndrome" Common to All Migrant Birds?: Theunis Piersma, Javier Perez-Tris, Henrik Mouritsen, Ulf Bauchinger, and Franz Bairlein