Phenotypic variation in nestlings of a bird of prey under contrasting breeding and diet conditions

Environmental conditions often vary in space and time, and this may explain variation in the expression of phenotypic traits related to individual quality, such as ornamental coloration. Furthermore, the direction and strength of the relationship between coloured trait expression and individual quality might vary under contrasting conditions. These issues have been explored in adult birds but much less so in nestlings, which are more likely to experience different selective pressures and different physiological trade‐offs than adults. Here, we empirically investigated the effects of contrasting breeding and diet conditions on the expression of carotenoid‐based colour traits displayed by marsh harrier (Circus aeruginosus) nestlings. We studied the variation in coloration, body condition, and immune responsiveness of nestlings in four populations over a 5‐year period. We characterized spatiotemporal differences in rearing conditions experienced by C. aeruginosus nestlings in terms of breeding (laying date, clutch size, and number of nestlings hatched and fledged) and diet (percentage of mammal in diet and prey diversity) conditions. We found that breeding conditions influenced the co‐variation between coloration and immune responsiveness in female nestlings, and that diet conditions influenced the condition‐dependence of nestling coloration in later‐hatched nestlings. In addition, breeding conditions influenced nestling body condition and immune responsiveness, whereas diet conditions influenced nestling coloration and body condition. Our study highlights that nestling phenotype (levels of signalling, circulating carotenoids, and immunity) varies both spatially and temporally, and that some of this variation is related to differences in breeding and diet conditions. Moreover, under contrasting conditions, the direction of the relationships between nestling carotenoid‐based coloration and nestling quality may also vary. In order to fully understand the evolution and maintenance of colour traits in nestling birds, studies and experiments should ideally be replicated under contrasting rearing conditions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Developmental plasticity varied with sex and position in hatching hierarchy in nestlings of the asynchronous European roller,Coracias garrulus

Allocation rules between ornamental and other functional traits of birds may differ among individuals and vary with environmental conditions. We supplemented roller (Coracias garrulus) nestlings with methionine in a between‐nest design to investigate the way in which the sex and position in the hatching hierarchy affect the allocation of resources among growth, immunity, and plumage coloration. Methionine induces the production of lymphocytes at expense of growth; thus, we used it to manipulate growth and immunity, which are two traits likely to compromise plumage coloration. We predicted that late‐hatched chicks within a brood (juniors) compared to early‐hatched chicks (seniors) should allocate more to traits directly providing fitness than to ornamental traits because juniors are more affected than seniors by sibling competition. The methionine treatment effectively enhanced the production of lymphocytes in experimental broods. This appeared to be at the expense of plumage coloration in junior nestlings because, in supplemented nests, junior males showed a trend to display less greenish bellies than junior males from control nests. However, juniors from supplemented nests maintained wing growth as in control juniors. The plumage coloration of seniors was unaffected by the methionine supplementation, although they paid the costs of lymphocyte production at a level of growth that was reduced compared to senior nestlings in control nests. Hence, sex, and hatching order affected resource allocation among growth, immunity, and plumage coloration of roller nestlings. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 500–511.     

Laying‐sequence variation in yolk carotenoids and egg characteristics in the red‐winged blackbird Agelaius phoeniceus

In many bird species with asynchronous hatching, smaller, later‐hatched nestlings are out‐competed for food by their larger, earlier‐hatched siblings and therefore suffer increased mortality via starvation. It is thought that female birds can either maintain or reduce the survival disadvantage of later‐hatched nestlings by differentially allocating maternal resources across the eggs of a clutch. Carotenoid pigments are an example of resources that female birds allocate differentially when producing a clutch, but laying sequence patterns for these pigments remain poorly studied in North American songbirds. We examined intraclutch variation in yolk carotenoids and egg metrics in 27 full clutches of red‐winged blackbird Agelaius phoeniceus eggs collected from eight wetlands in central Alberta, Canada. We predicted that carotenoids would decrease across the laying sequence, as in this species, later‐hatched, marginal nestlings suffer greater mortality than earlier‐hatched, core nestlings. We found nine carotenoid pigments in red‐winged blackbird egg yolks, including two that have never been described from avian yolks: α‐doradexanthin and adonirubin. As predicted, concentrations and amounts of most carotenoids decreased across the laying sequence, suggesting that female red‐winged blackbirds depleted their carotenoid resources as they laid more eggs. However, egg mass and yolk mass both increased across the laying sequence, suggesting that female red‐winged blackbirds may use other maternal resources to compensate for the size and survival disadvantage experienced by later‐hatched, marginal nestlings.     

Carotenoids in nestling Montagu’s harriers: variations according to age, sex, body condition and evidence for diet-related limitations

Carotenoids are colored pigments forming the basis of many avian social traits. Before their utilization carotenoids must be acquired through diet and mobilized for specific uses. The relationships between carotenoid-based coloration, circulating carotenoids and body condition have been well studied in adult birds, but little is known in nestlings. Here, we investigated variations in carotenoid-based coloration in a raptor nestling, the Montagu’s harrier (Circus pygargus), both in captivity and in natural conditions, and within a vole (poor-carotenoid source and cyclic prey) specialist population. We studied these variations according to nestling age and sex, and possible limitations in carotenoid availability by comparing years of contrasted prey abundance and using carotenoid supplementation experiments. Captive nestlings, fed only with mice, were strongly carotenoid limited. Wild nestlings were also carotenoid limited, especially in a year of high vole abundance. Nestlings were in better condition but less colored during a peak vole abundance year than during a low vole abundance year, when harriers targeted more alternative preys (birds, insects). Thus, variation in vole abundance resulted in a de-coupling of body condition and carotenoid-based coloration in this population. This suggested that the positive relation between the body condition and carotenoid-based traits, typically found in adult birds, could be restricted to adults or nestlings of species that feed on carotenoid-rich food. Our results should stimulate more work on the functions and mechanisms of carotenoid-based traits in nestlings, which deserve more attention and most likely differ from those of adult birds.     

Carotenoid-based coloration, condition, and immune responsiveness in the nestlings of a sexually dimorphic bird of prey

In many birds, nestlings exhibit brightly colored traits that are pigmented by carotenoids. Carotenoids are diet limited and also serve important health-related physiological functions. The proximate mechanisms behind the expression of these carotenoid-pigmented traits are still poorly known, especially in nestlings with sexual size dimorphism. In these nestlings, intrabrood competition levels and growth strategies likely differ between sexes, and this may in turn influence carotenoid allocation rules. We used dietary carotenoid supplementation to test whether wild marsh harrier (Circus aeruginosus) nestlings were carotenoid limited and whether carotenoid allocation strategies varied between sexes, which differ in their size and growth strategies. When supplemented, nestlings used the supplemental carotenoids to increase their coloration independently of their sex. We showed that the condition dependence of the carotenoid level and the response to an immune challenge (phytohemagglutinin test) differed between sexes, possibly because sexual size dimorphism influences growth strategies and/or intrabrood competition levels and access to different types of food. In this species, which often feeds on mammals, a trade-off likely exists between food quantity (energy) and quality (carotenoid content). Finally, carotenoid-based coloration expressed in marsh harrier nestlings appeared to be indicative of immune responsiveness rather than condition, therefore potentially advertising to parents nestling quality or value rather than nutritional need.     

Carotenoids bolster immunity during moult in a wild songbird with sexually selected plumage coloration

Carotenoid‐based colours in animals are valuable models for testing theories of sexual selection and life‐history trade‐offs because the pigments used in coloration are chemically tractable in the diet and in the body, where they serve multiple purposes (e.g. health enhancement, photoprotection). An important assumption underlying the hypothesized signalling value of carotenoid coloration is that there is a trade‐off in carotenoid pigment allocation, such that not all individuals can meet the physiological/morphological demands for carotenoids (i.e. carotenoids are limited) and that only those who have abundant supplies or fewer demands become the most colourful. Studies of carotenoid trade‐offs in colourful animals have been limited largely to domesticated species, which may have undergone artificial selection that changed the historical/natural immunomodulatory roles of carotenoids, to young animals lacking carotenoid‐based signals or to species displaying carotenoid‐based skin and bare parts. We studied the health benefits of carotenoids during moult in house finches (Carpodacus mexicanus), which display sexually selected, carotenoid‐based plumage coloration. We manipulated dietary carotenoid availability during both winter (nonmoult) and autumn (moult) in captive males and females and found that carotenoid‐supplemented birds mounted stronger immune responses (to phytohemagglutinin injection and to a bacterial inoculation in blood) than control birds only during moult. This study provides experimental, seasonal support for a fundamental tenet of Lozano's ‘carotenoid trade‐off’ hypothesis and adds to a growing list of animal species that benefit immunologically from ingesting higher dietary carotenoid levels. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 560–572.     

Phenotypic, genetic, and environmental causes of variation in yellow skin pigmentation and serum carotenoids in Eurasian kestrel nestlings

In the context of sexual selection and parent-offspring communication, carotenoid-based coloration operates as a dynamic condition-dependent signal, as pigments stored in the skin and in the bill can be reallocated to other tissues in accordance with physiological needs. We studied the proximate factors affecting the carotenoid-dependent coloration of the Eurasian kestrel (Falco tinnunculus). Kestrel nestlings show carotenoid-based coloration at the integument level. Adult males and females share similar characteristics, but to a different extent. By cross-fostering nestlings, we evaluated the importance of the “nest of rearing” and the “nest of origin” to determine variation in skin color and blood carotenoids. The nest of rearing accounted for most of the observed variance in skin color, as well as serum carotenoids, while the nest of origin was not causal to the variability of carotenoids in young kestrels. The study indirectly shows that carotenoid-based color expressed by young kestrels is not affected by pre-laying conditions. Furthermore, we found that carotenoid coloration and blood carotenoid concentration were correlated at phenotypic and environmental levels, while the hereditary component of the carotenoid traits was too low to estimate their correlation at the genetic level.     

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)‐mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA‐mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA‐mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA‐mediated immune response than females only in brood‐reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune‐related trade‐offs when brood reduction occurs may differ between male and female nestlings.     

Cross‐fostering reveals that among‐brood differences in ornamental mouth coloration mostly reflect rearing conditions in nestling house sparrows

Dependent offspring use specialized traits to attract parental care. In birds, this includes morphological ornaments (e.g. colourful plumage or mouthparts) that are associated with nestling condition and shape the allocation of parental care. Ornament expression often differs among broods, even after differences in individual condition are accounted for statistically. Understanding how this variation arises is important for understanding the information content of these signals, their functional importance, and their evolution. The present study used a cross‐fostering experiment to assess the relative contributions of parental effects to among‐brood differences in the mouth coloration of nestling house sparrows, specifically the carotenoid‐richness, overall brightness, and ultraviolet (UV) coloration of rictal flanges. The expression of carotenoid‐based coloration was explained by synchronous breeding, nest‐of‐rearing and nest‐of‐origin. Brightness and relative UV intensity, however, were explained only by synchronous breeding, and there was substantial unexplained variation in all three colour parameters. Among‐brood variation in mouth coloration, then, may primarily contain information about the environment in which offspring are reared. At the individual level, ontogenetic changes in the carotenoid‐richness and brightness of flanges positively reflected mass gain (a proxy for food intake). Larger and yellower chicks gained more mass, consistent with parental preferences for these traits. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 169–179.     

Nestling begging intensity and parental effort in relation to prelaying carotenoid availability

Carotenoids are antioxidants playing major roles in physiologicalfunctions at various stages of an animal's life. Female birdsdeposit large amounts of carotenoids into their eggs. Carotenoidsare, however, a limiting resource, and females are expectedto balance carotenoid deposition into the eggs with their utilizationfor themselves. Carotenoid availability is thus likely to determineboth the levels of yolk carotenoids and maternal care duringrearing. Carotenoids have been shown to benefit the embryo andthe growing nestling, and it can be hypothesized that an increasein carotenoid availability during laying leads to higher nestlingcondition and competitive ability. We manipulated carotenoidavailability to great tit pairs prior to and during egg layingand later partially cross-fostered chicks at hatching. Duringthe rearing period, we measured how carotenoid availabilityaffected nestlings begging behavior and male and female feedingeffort. We also manipulated the ectoparasite load, predictingthat carotenoid supplementation would help adults and nestlingto cope with parasites. Nestlings hatched from eggs laid bycarotenoid-supplemented females and raised in small broods beggedmore intensely. Nestlings in small deparasitized broods alsobegged more actively. The feeding effort of control femalesincreased with brood size, whereas the feeding effort of carotenoid-supplementedfemales was high whatever the brood size. Male feeding effortwas unaffected by our treatment. Our results support the hypothesisthat maternally derived carotenoids increase nestling beggingbehavior and hence competitive ability. They further suggestthat carotenoid availability determines the level of parentalinvestment and can mediate trade-offs between life-history traits.     

Carotenoid pigments in male American goldfinches: what is the optimal biochemical strategy for becoming colourful?

Studies of brilliant carotenoid‐based coloration in birds have traditionally centred on the role that these colours play in attracting mates. More recently, biologists have begun to take a biochemical approach to understanding the types of pigments found in feathers and how these relate to the expression of ornamental coloration. Nevertheless, surprisingly few studies have assessed the types and amounts of carotenoids present in the diet or blood of animals in relation to season, sex, condition or sexually attractive colour traits, particularly for wild birds. It is conceivable not only that the total concentration of pigments available is an important predictor of sexual attractiveness and mate quality, but also that specific pigments vary among individuals and play more important physiological and pigmenting roles than others. We investigated the carotenoid content of blood and feathers in wild‐caught, yellow‐pigmented male American goldfinches (Carduelis tristis) throughout the year to determine the optimal biochemical strategy for becoming colourful. We found that birds acquired two main yellow hydroxycarotenoids (lutein and zeaxanthin) from the diet during both moulting and non‐moulting periods. Blood concentrations of both pigments changed significantly over time, with moulting birds accumulating higher levels of both lutein and zeaxanthin, but proportionally more zeaxanthin, than non‐moulting birds. Moulting birds that acquired more lutein and more zeaxanthin in blood deposited a higher concentration of carotenoid pigments (canary xanthophylls A and B) into plumage and acquired more colourful feathers. In sum, these results indicate that (a) the types of dietary carotenoids available across seasons do not change in American goldfinches, (b) seasonal fluctuations in plasma‐carotenoid signatures may result from differences in dietary access or pigment processing, and (c) the best biochemical strategy for becoming a colourful, wild male goldfinch is to accumulate as many dietary/blood pigments as possible during moult. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 273–280.     

Sex and age differences in reflectance and biochemistry of carotenoid‐based colour variation in the great tit Parus major

The plumage coloration in great tits (Parus major) is the subject of much behavioural and ecophysiological research, yet there is a lack of analyses of the natural colour variation and its mechanisms. We used reflectance spectrometry and high‐performance liquid chromatography to explore individual, sexual and age‐related variation in carotenoid coloration and pigmentation, paramount to the often presumed, but rarely substantiated, costs and ‘honesty’ of carotenoid displays. In adults, we found that sex was the strongest predictor of ‘brightness’ (higher in males) and of ‘hue’ (longer wavelength in females). There was no sex difference in ‘carotenoid chroma’ or carotenoid content of feathers which also was unrelated to adult age (1 or 2+ years) and condition. Similar patterns were revealed for nestlings. Regarding the biochemical ‘signal content’, ‘carotenoid chroma’, but not ‘hue’, was significantly related to the carotenoid content (lutein and zeaxanthin) of feathers. These results refute the previously assumed exaggeration of carotenoid pigmentation in male great tits, and question the condition‐dependence of carotenoid coloration in this species. However, the sexual dimorphism in total reflectance or ‘brightness’, most likely due to melanins rather than carotenoids, may have implications for signalling or other adaptive explanations that need to be explored. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 758–765.     

Habitat structure and prey composition generate contrasting effects on carotenoid‐based coloration of great tit Parus major nestlings

Carotenoid‐based coloration of nestling plumage is generally considered a reliable signal of quality and has consistently been related to habitat structure. The main hypothesis proposed to explain this correlation is that high quality habitats contain high quality food, which in return affects the expression of carotenoid‐based plumage. It therefore assumes that, at the population level, the link between habitat structure and food composition is consistent and more relevant than inter‐individual differences in foraging ability or parental investment. In addition, it is assumed by default that food and habitat produce concordant effects on nestling coloration. In this work we evaluated habitat structure and prey composition in addition to several measures of parental investment. We investigated their relative effect on carotenoid‐based plumage coloration (lightness, chroma and hue) of great tit Parus major nestlings. We found a low correlation between carotenoid‐based coloration of nestlings and that of their parents. Nestling coloration, especially lightness and chroma, increased with the intake of more spiders. The time of breeding was positively correlated with lightness and chroma and negatively correlated with hue. Finally, the maturity of oak trees surrounding nest‐boxes correlated negatively with lightness, and the size of all tree species surrounding nest‐boxes correlated positively with hue of chick plumage. Our findings support the view that habitat structure and prey composition may produce divergent effects on feather pigmentation, and that prey proportions and variables related to parental investment should be assessed when considering carotenoid‐based coloration of chicks. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 547–555.     

Carotenoid scarcity, synthetic pteridine pigments and the evolution of sexual coloration in guppies (Poecilia reticulata).

Carotenoid-based sexual coloration is the classic example of an honest signal of mate quality. Animals cannot synthesize carotenoid pigments and ultimately depend on dietary sources. Thus, in carotenoid-poor environments, carotenoid coloration may be a direct indicator of foraging ability and an indirect indicator of health and vigour. Carotenoid coloration may also be affected, more directly, by parasites in some species. Carotenoids are not, however, the only conspicuous pigments available to animals. Pteridine pigments, with similar spectral properties, are displayed in the exoskeletons and wings of insects, the irides of birds and the skins of fishes, lizards and amphibians. Unlike carotenoids, pteridines are synthesized de novo by animals. We report that the orange spots that male guppies (Poecilia reticulata) display to females contain red pteridine pigments (drosopterins) in addition to carotenoids. We also examined the relationship between drosopterin production by males and carotenoid availability in the field. The results contrasted sharply with the hypothesis that males use drosopterins to compensate for carotenoid scarcity: males used more, not less, drosopterins in streams with higher carotenoid availability. The positive association between drosopterin use and carotenoid availability could reflect the costs of drosopterin synthesis or it could be a consequence of females preferring a particular pigment ratio or hue. Male guppies appear to use drosopterin pigments in a manner that dilutes, but does not eliminate, the indicator value of carotenoid coloration.     

Genetics, local environment and health as factors influencing plasma carotenoids in wild American kestrels (Falco sparverius)

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 conspecifics; 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 fledging 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 significant effect of leucocyte differentials on carotenoid concentrations of nestlings. A strong environmental effect on plasma carotenoids was demonstrated by levels of adult kestrels being correlated within mated pairs, and having a significant association with the abundance of voles, the primary prey species, per territory.     

Patterns of serum carotenoid accumulation and skin colour variation in kestrel nestlings in relation to breeding conditions and different terms of carotenoid supplementation

Carotenoids are pigments synthesised by autotrophic organisms. For nestlings of raptorial species, which obtain carotenoids from the consumption of other heterotrophic species, the access to these pigments can be crucial. Carotenoids, indeed, have fundamental health maintenance functions, especially important in developing individuals as nestling kestrels. The aim of this study was to investigate how body carotenoid levels and skin pigmentation vary in kestrel nestlings (Falco tinnunculus) in relation to nesting parameters. Furthermore, we experimentally altered carotenoid availability (short- medium- and long-term) for nestlings and investigated skin and serum variance. The skin colour variance of 151 nestlings was explained by nest of origin, age and by the body condition (body mass corrected by age), older nestlings with higher body condition being redder. No difference in skin colour was detected between sexes. Differences in hue (skin “redness”) between treatments did not emerge during the first week, but did occur 15 days after administration between long-term supplemented and control chicks. In contrast, the serum carotenoid concentration showed a treatment-dependent increase after 5 days from the first carotenoid administration and at least after two supplemented feedings. In general, hue but not serum carotenoids, was correlated with the body condition of nestlings. Based on the increased skin pigmentation of nestling kestrels in the long-term experimental group, we suggest carotenoid availability to be limited for colour expression. The small increase of serum carotenoids due to supplementation is consistent with the hypothesis that there is a physiological constraint on these pigments, as well as an environmental limitation. The presented results are useful for the understanding of carotenoid uptake and accumulation by a wild raptorial species, located at the top of the food web, highlighting that carotenoids are a limited resource for kestrel nestlings.     

Dietary carotenoids change the colour of Southern corroboree frogs

Animal coloration can be the result of many interconnected elements, including the production of colour‐producing molecules de novo, as well as the acquisition of pigments from the diet. When acquired through the diet, carotenoids (a common class of pigments) can influence yellow, orange, and red coloration and enhanced levels of carotenoids can result in brighter coloration and/or changes in hue or saturation. We tested the hypothesis that dietary carotenoid supplementation changes the striking black and yellow coloration of the southern corroboree frog (Pseudophryne corroboree, Amphibia: Anura). Our dietary treatment showed no measurable difference in colour or brightness for black patches in frogs. However, the reflectance of yellow patches of frogs raised on a diet rich in carotenoids was more saturated (higher chroma) and long‐wave shifted in hue (more orange) compared to that of frogs raised without carotenoids. Interestingly, frogs with carotenoid‐poor diets still developed their characteristic yellow and black coloration, suggesting that their yellow colour patches are a product of pteridines manufactured de novo.     

Hatching asynchrony can have long‐term consequences for offspring fitness in zebra finches under captive conditions

Hatching asynchrony can have profound short‐term consequences for offspring, although the long‐term consequences are less well understood. The purpose of this study was to examine the long‐term consequences of hatching asynchrony for offspring fitness in birds. Specifically, we aimed to test the hypothesis that hatching asynchrony increases the sexual attractiveness and fecundity, respectively, of early‐hatched male and female zebra finch, Taeniopygia guttata (Vieillot, 1817) offspring. Mate‐choice trials comparing male nestlings with the same parents, but that were reared in asynchronous or experimentally synchronous broods, revealed no female preference in relation to hatching regime. We did however find strong evidence that, as adults, late‐hatched males were more attractive to females than siblings that had hatched earlier. Meanwhile, we found a weak trend towards early‐hatched females depositing more carotenoids and retinol in the egg yolk than late‐hatched or synchronously hatched females, although there were no differences in terms of clutch characteristics or the deposition of α‐tocopherol or γ‐tocopherol in the egg yolk. Therefore, we found that the beneficial long‐term consequences of hatching asynchrony were sex specific, being accrued by late‐hatched male nestlings and by early‐hatched female nestlings. Consequently, we conclude that the long‐term consequences of hatching asynchrony are more complex than previously realised. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 430–438.     

The effects of hatching asynchrony on growth and mortality patterns in Eurasian Hoopoe Upupa epops nestlings

Growth is a fundamental life history trait in all organisms and is closely related to individual fitness. In altricial birds, growth of many traits is restricted to the short period between hatching and fledging and strongly depends on the amount of food that parents deliver and the extent of hatching asynchrony. However, empirical studies of energy allocation to growth of different body size traits as a function of hatching asynchrony are scarce. We studied growth and mortality of Eurasian Hoopoe Upupa epops, a species with a long breeding season and high brood size variance, whose nestlings show pronounced hatching asynchrony, in order to test how hatching asynchrony affects different growth traits in the context of territory quality, season and brood size. The growth of five body traits (body mass, and lengths of tarsus, third primary, bill and longest crest feather) was investigated to understand how it was affected by brood size, hatching date and order, and territory quality. In total, 241 nestlings from 39 nests were measured every 4 days in 2014 in south‐western Switzerland. Brood size, hatching date and hatching order had the strongest influence on growth trajectories, although tarsus growth was only marginally affected by these variables. Nestlings that hatched earlier than their siblings were heavier and had longer third primaries, bills and crest feathers compared with later‐hatched siblings. In territories of high quality, hatching order differences disappeared for body mass growth, but persisted for lengths of third primary, bill and crest feathers. Brood size was inversely associated with third primary, bill and crest feather lengths, but positively associated with body mass. Nestling mortality was higher in later‐hatched nestlings and in broods that were raised in territories of lower quality. Our study shows that in nestlings, energy was allocated differentially between body traits and this allocation interacted with hatching order and territory quality. Rapid mass gain by nestlings was prioritized in order to increase competitive ability. Our results provide support for the brood reduction hypothesis as an explanation of hatching asynchrony in Hoopoes.     

Brood size manipulations reveal relationships among physiological performance,body condition and plumage colour in Northern Flicker Colaptes auratus nestlings

Visual signals of quality in offspring, such as plumage colour, should honestly advertise need and/or body condition, but links between nutritional status, physiological performance and the expression of colours are complex and poorly understood. We assess how food stress during rearing affected two physiological measures (T‐cell‐mediated immune function and corticosterone level in feathers: CORT_f) and how these two variables were related to carotenoid and melanin coloration in Northern Flicker Colaptes auratus nestlings. We were also interested in how these two physiological measures were influenced by the sex of the nestling. We experimentally manipulated brood size to alter levels of food availability to nestlings during development. We measured carotenoid‐based colour (chroma and brightness) in wing feathers and the size of melanin spots on breast feathers. In agreement with our prediction, nestlings in the reduced brood treatment had better body condition and stronger immune responses than those in the control and brood enlargement treatments. This supports the hypothesis that immune responses are energetically costly. In contrast, CORT_f was not related to nestling body condition or sex and was unaffected by brood size manipulation. Nestlings of both sexes with stronger T‐cell‐mediated immune responses had larger melanin spots but only males with higher immune responses also had brighter flight feathers. Feather brightness decreased with increasing CORT_f levels. Our study is one of the few to examine the relationship between multiple physiological and plumage measures in nestlings and shows that plumage colour and immune function signalled body condition of nestlings, but that feather corticosterone levels did not.