Informative content of melanin‐based plumage colour in adult Eurasian kestrels

Covariation between melanin‐based colorations and other phenotypic attributes has been rarely measured simultaneously in males and females. Such covariations and mechanisms mediating them have crucial importance determining the signalling function of these coloured ornaments in the two sexes. We examined the role of four melanin‐based coloured plumage patches as indicators of quality in both males and females of the sexually dimorphic and dichromatic Eurasian kestrel Falco tinnunculus. Previous kestrel studies have focused on the size of melanin plumage patches in either males or females as indicators of individual quality. Here, we used spectrophotometric measurements of three plumage patches and the size of another plumage patch to investigate the information content of multiple plumage colour traits in male and female kestrels. We found that females with bright plumage in the head and with high UV chroma in black parts of the rump showed good body condition and innate immunity. In addition, laying date was significantly explained by the intensity of the brown in the head of females. Meanwhile, in males we only found that individuals with greyer rumps showed better innate immunity. Altogether, our results indicate that, irrespective of the mechanism promoting covariation between coloration and individual quality, melanin‐based coloration can inform on individual quality in adult kestrels.     

Carotenoid-Based Plumage Coloration Predicts Leukocyte Parameters during the Breeding Season in Northern Cardinals (Cardinalis cardinalis)

Dichromatism in songbirds is often associated with polygyny and dimorphic parental investment, and is thought to arise via sexual selection. Northern cardinals (Cardinalis cardinalis) are not only dichromatic but also monogamous and biparental, suggesting that plumage coloration in this species may serve different functions than in more typical dichromatic species. In order to explore the role of sexual selection in the evolution of plumage coloration in cardinals, we used reflectance spectrophotometry to investigate whether two carotenoid‐based ornaments, the male’s red breast and the female’s underwing coverts, contain information that potential mates or competitors could use to assess condition. We found that whereas coloration was not related to body condition (measured as the residual body mass from a regression of body mass on wing chord), more saturated carotenoid coloration was associated with higher heterophil to lymphocyte ratios in males, and with higher white blood cell counts in females. Thus, in both sexes, carotenoid coloration was positively linked to immune measures normally associated with higher levels of stress and infection. These results do not indicate that carotenoid‐based coloration functions as a signal of low levels of stress or disease in this species. We propose instead that because plumage coloration may be related to competitiveness, the more saturated individuals increase their risk of injury, stress, and infection by engaging in more competitive behavior or by secreting more testosterone, or both. Our finding that carotenoid pigmentation is positively associated in males with the size of the cloacal protuberance, an androgen‐sensitive sex character, supports this hypothesis.     

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.     

The role of melanin- and carotenoid-based plumage coloration in nest defence in the Great Tit

Although plumage coloration is recognized to convey valuable information about the bearer's parental abilities, few studies have explored the relationship between coloration and nest defence. In this study in Great Tit Parus major, we analysed the relationship between nest defence and melanin‐ as well as carotenoid‐based plumage coloration, after controlling for ecological variables known to influence nest defence. A principal components analysis was applied to classify birds according to how vigorously they defended the nest, and the intensity of nest defence was tested against plumage coloration. Males with a large black tie defended their nests more vigorously, but no such effect was found for yellow breast coloration. This suggests that melanin‐based coloration in the Great Tit is associated with aggression, including both dominance‐aggression and nest defence, whereas carotenoid‐based coloration is not. The challenge in future studies will be to demonstrate whether females use this trait as an ornament to assess male quality and whether they trade off between the different ornaments a male may exhibit.     

Plumage coloration and personality in early life: sexual differences in signalling

Several studies have shown that melanin‐based traits play a crucial role in social contexts as they are associated with dominance, personality and social behaviour. However, most of these studies have focused on adults, and the role of these traits in juveniles has rarely been explored. Here, we explore the association between two melanin‐based traits and nestling personality in Common Kestrels Falco tinnunculus. Our results show that female nestlings with blacker plumages displayed bolder personalities, providing evidence of sex‐dependent phenotypic integration of these two traits in males and females. We consider that this differential integration may arise from different selection pressures acting on males and females on plumage coloration during adulthood and that nestling coloration can act as a status signal within the juvenile age‐class.     

Eumelanin levels in rufous feathers explain plasma testosterone levels and survival in swallows

Pigment‐based plumage coloration and its physiological properties have attracted many researchers to explain the evolution of such ornamental traits. These studies, however, assume the functional importance of the predominant pigment while ignoring that of other minor pigments, and few studies have focused on the composition of these pigments. Using the pheomelanin‐based plumage in two swallow species, we studied the allocation of two pigments (the predominant pigment, pheomelanin, and the minor pigment, eumelanin) in relation to physiological properties and viability in populations under a natural and sexual selection. This is indispensable for studying the evolution of pheomelanin‐based plumage coloration. Pheomelanin and eumelanin share the same pathway only during their initial stages of development, which can be a key to unravel the functional importance of pigment allocation and thus of plumage coloration. Using the barn swallow, Hirundo rustica, a migratory species, we found that plasma testosterone levels increased with increasing the proportion of eumelanin pigments compared with pheomelanin pigments, but not with the amount of pheomelanin pigments, during the mating period. In the Pacific swallow Hirundo tahitica, a nonmigratory congener, we found that, during severe winter weathers, survivors had a proportionally smaller amount of eumelanin pigments compared with pheomelanin pigments than that in nonsurvivors, but no detectable difference was found in the pheomelanin pigmentation itself. These results indicated that a minor pigment, eumelanin, matters at least in some physiological measures and viability. Because the major pigment, pheomelanin, has its own physiological properties, a combination of major and minor pigments provides multiple information to the signal receivers, potentially enhancing the signaling function of pheomelanic coloration and its diversification across habitats.     

Evolutionary trade‐off between naturally‐ and sexually‐selected melanin‐based colour traits in worldwide barn owls and allies

Natural selection typically constrains the evolution of sexually‐selected characters. The evolution of naturally‐ and sexually‐selected traits can be intertwined if they share part of their genetic machinery or if sex traits impair foraging success or increase the risk of depredation. The present study investigated phenotypic correlations between naturally‐ and sexually‐selected plumage traits in the Tytonidae (barn owls, grass owls, and masked owls). Phenotypic correlations indicate the extent to which selection on one trait will indirectly influence the evolution of another trait. In this group of birds, the ventral body side varies from white to dark reddish, a naturally‐selected pheomelanin‐based colour trait with important roles in predator–prey interactions. Owls also exhibit eumelanin‐based black spots, for which number and size signal different aspects of individual quality and are used in mate choice. These three plumage traits are strongly heritable and sexually dimorphic, with females being on average darker reddish and more spotted than males. Phenotypic correlations were measured between these three plumage traits in 3958 free‐living barn owls in Switzerland and 10 670 skin specimens from 34 Tyto taxa preserved in museums. Across Tyto taxa, the sexually‐selected plumage spottiness was positively correlated with the naturally‐selected reddish coloration, with redder birds being more heavily spotted. This suggests that they are genetically constrained or that natural and sexual selection are not antagonistically exerted on plumage traits. In a large sample of Swiss nestlings and within 34 Tyto taxa, the three plumage traits were positively correlated. The production of melanin pigments for one plumage trait is therefore not traded off against the production of melanin pigments for another plumage trait. Only in the most heavily‐spotted Tyto taxa do larger‐spotted individuals display fewer spots. This indicates that, at some threshold value, the evolution of many spots constrains the evolution of large spots. These analyses raise the possibility that different combinations of melanin‐based plumage traits may not be selectively equivalent.     

Carry‐over effects of conditions at the wintering grounds on breeding plumage signals in a migratory bird: roles of phenotypic plasticity and selection

To understand the consequences of ever‐changing environment on the dynamics of phenotypic traits, distinguishing between selection processes and individual plasticity is crucial. We examined individual consistency/plasticity in several male secondary sexual traits expressed during the breeding season (white wing and forehead patch size, UV reflectance of white wing patch and dorsal melanin coloration) in a migratory pied flycatcher (Ficedula hypoleuca) population over an 11‐year period. Furthermore, we studied carry‐over effects of three environmental variables (NAO, a climatic index; NDVI, a vegetation index; and rainfall) at the wintering grounds (during prebreeding moult) on the expression of these breeding plumage traits of pied flycatcher males at individual and population levels. Whereas NAO correlates negatively with moisture in West Africa, NDVI correlates positively with primary production. Forehead patch size and melanin coloration were highly consistent within individuals among years, whereas the consistency of the other two traits was moderate. Wing patch size decreased with higher NAO and increased with higher rainfall and NDVI at the individual level. Interestingly, small‐patched males suffered lower survival during high NAO winters than large‐patched males, and vice versa during low NAO winters. These counteracting processes meant that the individual‐level change was masked at the population level where no relationship was found. Our results provide a good example of how variation in the phenotypic composition of a natural population can be a result of both environment‐dependent individual plasticity and short‐term microevolution. Moreover, when plasticity and viability selection operate simultaneously, their impacts on population composition may not be evident.     

Age‐dependent relationships between coloration and reproduction in a species exhibiting delayed plumage maturation in females

Males of many bird species exhibit delayed plumage maturation (DPM), a condition in which young individuals display an immature plumage. Several adaptive hypotheses have been suggested for the signaling utility of DPM in males. Tree swallows Tachycineta bicolor, however, are one of the few bird species to exhibit DPM in females, but not in males. Few studies have focused on the age‐dependent signaling function of female plumage traits due to the uncommon nature of DPM in females. Therefore, we used reflectance spectrometry and scanning electron microscopy of sub‐adult (melanin‐based brown) and adult (iridescent‐blue structural) female tree swallows to characterize plumage coloration. Next, we asked whether variation in plumage coloration in females reflects condition and reproductive performance between and within age classes. We found that older females were in better body condition and laid eggs earlier in the season compared to young females; however, average egg mass and reproductive success (number of offspring fledged and offspring condition) did not differ between age classes. There were significant relationships indicating that young females with more‐ornamented (darker brown melanin) plumage laid smaller eggs, but hatched eggs earlier in the season leading to nestlings in better condition compared to less‐ornamented young females. Older females that were more ornamented (brighter, greater blue chroma, and lower hues in iridescent plumage) laid heavier eggs, but ornamentation was negatively associated with immune function, health, and reproductive success. Together, these data suggest that female ornamentation reflects reproductive performance and that there are complicated relationships between plumage coloration, condition, and reproductive performance that ultimately influence reproductive success.     

Reduced sexual dichromatism,mutual ornamentation,and individual quality in the monogamous Zenaida dove Zenaida aurita

Although variation in plumage coloration is known to occur both between and within sexes, its study remains limited to a few bird families. The Zenaida dove Zenaida aurita is a socially monogamous tropical columbid bird species, characterized by an overall cinnamon‐brownish plumage and structural colorations on the head and neck. The species has been described as sexually dichromatic for plumage, although color differences between males and females are not obvious in the field. We investigated variation in the presumably melanin‐based color of the crown, mantle, breast, and belly, in the iridescent dark‐blue streaks on the head, and in the symmetric iridescent patches on the neck, over the whole spectrum visible to birds. Further, unlike most previous studies, we assessed covariation between plumage color and phenotypic traits in both males and females in relation to the putative signaling function of ornaments. Zenaida doves appeared to be slightly sexually dichromatic for the hue of pigment‐based colored areas, with males being on average more reddish than females. However, this difference was not discernible when considering the avian visual system. Conversely, although the reflectance spectra of iridescent plumage did not significantly differ between sexes in brightness, chroma or spectral position of the peaks, color discrimination analyses showed that individuals should be able to perceive between‐ or within‐sex differences in the color of the iridescent patch. In addition, several color parameters of brown and iridescent feathers were significantly related to territorial status, body condition, wing chord, and, albeit weakly, to individual multilocus heterozygosity. Overall, our results thus suggest that plumage color might be a reliable signal of quality in individuals of both sexes in this species. Further studies are needed to test the potential implication of plumage coloration in mate choice and mating patterns in the Zenaida dove.     

Genetic and environmental components of variation in eumelanin and phaeomelanin sex-traits in the barn owl

Knowledge of the mechanism underlying the expression of melanin-based sex-traits may help us to understand their signalling function. Potential sources of inter-individual variation are the total amount of melanins produced but also how biochemical precursors are allocated into the eumelanin and phaeomelanin pigments responsible for black and reddish-brown colours, respectively. In the barn owl (Tyto alba), a eumelanin trait (referred to as 'plumage spottiness') signals immunocompetence towards an artificially administrated antigen and parasite resistance in females, whereas a phaeomelanin trait ('plumage coloration') signals investment in reproduction in males. This raises the question whether plumage coloration and spottiness are expressed independent of each other. To investigate this question, we have studied the genetics of these two plumage traits. Crossfostering experiments showed that, for each trait, phenotypic variation has a strong genetic component, whereas no environmental component could be detected. Plumage coloration is autosomally inherited, as suggested by the similar paternal-to-maternal contribution to offspring coloration. In contrast, plumage spottiness may be sex-linked inherited (in birds, females are heterogametic). That proposition arises from the observation that sons resembled their mother more than their father and that daughters resembled only their father. Despite plumage coloration and spottiness signalling different qualities, these two traits are not inherited independent of each other, darker birds being spottier. This suggests that the extent to which coloration and spottiness are expressed depends on the total amount of melanin produced (with more melanin leading to a both darker and spottier plumage) rather than on differential allocation of melanin into plumage coloration and spottiness (in such a case, darker birds should have been less spotted). A gene controlling the production of melanin pigments may be located on sex-chromosomes, since the phenotypic correlation between coloration and spottiness was stronger in males than in females.     

The role of pigment based plumage traits in resolving conflicts

The role of melanin ‘badges of status’, in male–male competition has been well‐studied, in contrast, carotenoid based plumage has largely been examined in the context of female mate choice. Recent work has shown that carotenoid signals can also function in male–male competition, although the functions of the two types of signals is currently unclear. Here, we examine the relationships between colouration, dominance and aggression in the crimson finch Neochmia phaeton, a species where males have both conspicuous red carotenoid plumage and a black melanin patch. We examined the importance of carotenoid and melanin based signals in three contexts: 1) among free‐living birds interacting at a feeding station: we found that neither colour signal influenced the outcome of interactions; 2) in staged dyadic contest in captivity: we found that coloration from carotenoid pigments was positively related to the probability of winning a contest, while the size of the melanin plumage patch was not related to winning; and 3) in staged dyadic contests where male plumage colour had been masked: we found that the number of interactions required to determine dominance increased. While the underlying natural plumage colour was still important in these contests, birds with more intense carotenoid colouration were now more likely to lose. These results confirm carotenoid‐based signalling in male–male contests. However this signal is used in conjunction with other factors such as self‐assessment and body condition. Contrary to traditional expectations, the black melanin patch was not found to be important in this context.     

Haemosporidian parasites depress breeding success and plumage coloration in female barn swallows Hirundo rustica

Parasites are major effectors of natural selection and also play a role in sexual selection processes. Haemosporidian blood parasites are common in vertebrates and have been shown to vary in their effects depending on both the parasite and host species, on the host trait investigated as well as on host condition and stage of infection. Here we investigated infection of adult barn swallows Hirundo rustica by Plasmodium, Leucocytozoon and Haemoproteus species during the chronic stage of infection and the consequences for host fitness traits. Prevalence was higher than 10% only for Plasmodium. Chronic stage infection by Plasmodium was associated with reduced female breeding success, but did not affect breeding dates. Infection did not affect the expression of male secondary sexual traits (tail length and melanin‐based plumage coloration), but was associated with paler coloration of females. Finally, we found a negative effect of infection by Plasmodium on feather growth rate in older but not in yearling individuals. Because feathers are moulted during wintering in sub‐Saharan Africa where infection of barn swallows by Plasmodium occurs, our results suggest that male secondary sexual traits have little potential to reveal acute‐stage infection whereas plumage coloration of females may advertise their infection status. In addition, these results suggest that infection by Plasmodium can influence the course of plumage moult. Thus, our results add to the observations of negative effects of haemosporidian infection on fitness traits in birds and provides evidence that these effects can vary among traits and in relation to age and sex.     

Selection on a eumelanic ornament is stronger in the tropics than in temperate zones in the worldwide‐distributed barn owl

Spatial variation in the pattern of natural selection can promote local adaptation and genetic differentiation between populations. Because heritable melanin‐based ornaments can signal resistance to environmentally mediated elevation in glucocorticoids, to oxidative stress and parasites, populations may vary in the mean degree of melanic coloration if selection on these phenotypic aspects varies geographically. Within a population of Swiss barn owls (Tyto alba), the size of eumelanic spots is positively associated with survival, immunity and resistance to stress, but it is yet unknown whether Tyto species that face stressful environments evolved towards a darker eumelanic plumage. Because selection regimes vary along environmental gradients, we examined whether melanin‐based traits vary clinally and are expressed to a larger extent in the tropics where parasites are more abundant than in temperate zones. To this end, we considered 39 barn owl species distributed worldwide. Barn owl species living in the tropics displayed larger eumelanic spots than those found in temperate zones. This was, however, verified in the northern hemisphere only. Parasites being particularly abundant in the tropics, they may promote the evolution of darker eumelanic ornaments.     

Variation in melanin pigmentation of a sexually selected plumage trait and its adaptive value in the Common Snipe Gallinago gallinago

There is increasing evidence that melanin‐based plumage coloration correlates with different components of fitness and that it may act as a social or sexual signal of individual quality. We analysed variation in melanin pigmentation in the outermost tail feathers of the Common Snipe Gallinago gallinago. During courtship flights, male Snipe use their outermost tail feathers to generate a drumming sound, which plays a role in territory establishment and mate choice. As the outermost tail feathers are displayed to females during these flights, we predicted that conspicuous variation in their rusty‐brown (pheomelanin‐based) coloration may act as an honest signal of individual quality. To test this prediction, we spectrophotometrically measured brightness (an indicator of total melanin content) and red chroma (an indicator of pheomelanin content) of the outermost tail feathers in 180 juvenile and adult Common Snipe. An age‐related decline in feather brightness was found exclusively in females, suggesting that melanization could have evolved by natural selection to camouflage incubating birds. In both sexes, brightness of the tail feathers was inversely correlated with their structural quality (as measured with mass–length residuals), suggesting that melanization could increase mechanical properties of feathers and, in males, enhance the quality of courtship sonation. Red chroma positively correlated with total plasma protein concentration, supporting our prediction that pheomelanin pigmentation of tail feathers may act as an honest signal of condition. Our study indicated that variation in the melanin‐based coloration of the outermost tail feathers in the Common Snipe could have evolved as a result of several different selection pressures and it emphasizes the complexity of the processes that underlie the evolution of melanin‐based plumage coloration in birds.     

Winter Plumage Coloration in Male American Goldfinches: Do Reduced Ornaments Serve Signaling Functions in the Non‐Breeding Season?

The signaling role of sexual ornaments that are displayed during the mating season is well known for many species, but dimorphisms that occur in the non‐breeding season have received much less attention, particularly when individuals only partially express their breeding condition during reproductively inactive periods. I assessed variation in the expression of colorful breeding and non‐breeding plumages in male American goldfinches (Carduelis tristis), a species in which males molt out of their colorful breeding ornaments in the fall but still display reduced carotenoid‐ and melanin‐based sexual dichromatism during the winter. I found that variability in the saturation of carotenoid‐based plumage pigmentation did not differ significantly between the breeding and non‐breeding seasons. Moreover, the area of melanin coloration in the cap was more variable in winter than when it is fully displayed during breeding. I also detected a significant positive correlation between the extent of melanin coloration during the winter and the saturation of non‐breeding carotenoid‐based plumage. Because of such variation in and correlated expression of these two color ornaments in winter, it is conceivable that male goldfinches display these hints of non‐breeding coloration for use as conspecific social or sexual signals. Natural selection pressures like predation and energetic demands are traditionally thought of as factors that restrict sex ornaments to breeding times alone, but this should not preclude animals from simply reducing their exaggerated features during winter and finding an expression optimum that balances signal costs and value. Such ‘remnant’ winter ornaments might be expected to evolve not only in animals that live in large non‐breeding groups (e.g. status‐signaling systems) but also in those where mates begin associating before breeding onset.     

Uncorrelated evolution between vocal and plumage coloration traits in the trogons: a comparative study

The costs of bird song incurred in a diversity of ways may result in trade‐offs in the production and maintenance of elaborate plumage ornaments. In this paper, we examine evolutionary trade‐offs between acoustic and visual signalling in trogon birds (Trogonidae). Using multiple regressions with phylogenetically independent contrasts, we found that interspecific variation in male plumage coloration was not significantly predicted by song traits (reduced by PCA) or altitude. Although plumage coloration is expected to decrease with increases in song elaboration, both groups of variables were not related. Given that song and plumage coloration traits are likely targets of sexual selection, we also examined their relationships with sexual plumage dimorphism. We found that male carotenoid‐derived coloration was positively related to sexual plumage dimorphism, suggesting that sexual selection on male carotenoid‐derived coloration may be stronger than on melanin‐ or structurally based coloration, or than on acoustic traits. Comparative studies on other bird families accounting for the effects of phylogeny as well as environmental covariates are required to test the generality of our findings in trogons.     

Coloration,Paternity, and Assortative Mating in Western Bluebirds

Coloration in birds can act as an important sexual signal in males, yet in many species, both sexes display bright colors. Social selection may account for this pattern, with more brightly colored individuals pairing together on the best territories. Mutual mate choice may also explain this, as males investing a great deal of parental care in the offspring should be choosy about their social mates. It is less clear whether this pattern of mate choice can apply to extra‐pair partners as well. We examined western bluebirds (Sialia mexicana) to determine whether more colorful individuals tended to pair with one another, both in social pairs and between females and their extra‐pair partners. Both male and female western bluebirds display both UV‐blue structural plumage and a melanin‐based chestnut breast patch, although females are duller than males. Social pairs mated assortatively with regard to UV‐blue brightness, but not chestnut coloration. There was no evidence that extra‐pair partners mated assortatively, but males with brighter UV‐blue coloration had fewer extra‐pair offspring in their nests. Older males were more successful at siring extra‐pair offspring, despite displaying no differences in coloration compared to younger males. Coloration did not play a role in determining extra‐pair male success. These results suggest that coloration plays a role in the formation of social pairs, but not mate choice for extra‐pair partners.     

Dorsal pattern polymorphism in female Iberian wall lizards: differences in morphology,dorsal coloration,immune response,and reproductive investment

Sex‐specific colour polymorphisms have been extensively documented in many different taxa. When polymorphism in colour pattern is restricted to females, the condition is known as female‐limited pattern polymorphism (FPP), which has been less commonly addressed in vertebrates. FPP is present in several lizard species, although most research on lizards has focused on carotenoid‐ and pteridine‐based coloration and not on melanin‐based polymorphisms. In the present study, we focus on Iberian wall lizards, Podarcis hispanicus, where two female melanin‐based dorsal patterns can be clearly distinguished: striped and reticulated‐blotched. We indirectly tested the hypothesis that selection acts differentially among P. hispanicus female morphs to create alternative morph‐specific phenotypic optima at different levels by investigating whether morphs differ in fitness proxies. We specifically examined whether the two female dorsal pattern morphs differed in adult morphology, dorsal coloration, immune response, reproductive investment, and growth. We did not find a relationship between melanin‐based coloration and hatchling growth and immune response, despite a correlation between these traits possibly being expected as a result of pleiotropy in the melanocortin system. However, our results show that female dorsal morphs in P. hispanicus differ in terms of adult morphology, dorsal coloration, and reproductive investment. Reticulated‐blotched P. hispanicus females had deeper heads and longer femora, less melanin, and more brownish coloration, and also had larger and heavier hatchlings than striped females.     

Conditions on the Mexican moulting grounds influence feather colour and carotenoids in Bullock's orioles (Icterus bullockii)

Carotenoid‐based plumage coloration plays a critical role for both inter‐ and intrasexual communication. Habitat and diet during molt can have important consequences for the development of the ornamental signals used in these contexts. When molt occurs away from the breeding grounds (e.g., pre‐alternate molt on the wintering grounds, or stopover molt), discerning the influence of habitat and diet can be particularly important, as these effects may result in important carryover effects that influence territory acquisition or mate choice in subsequent seasons. Several species of songbirds in western North America, including the Bullock's oriole (Icterus bullockii), migrate from the breeding grounds to undergo a complete prebasic (post‐breeding) molt at a stopover site in the region affected by the Mexican monsoon climate pattern. This strategy appears to have evolved several times independently in response to the harsh, food‐limited late‐summer conditions in the arid West, which contrast strongly with the high productivity driven by heavy rains that is characteristic of the Mexican monsoon region. Within this region, individuals may be able to optimize plumage coloration by molting in favourable areas characterized by high resource abundance. We used stable isotope analysis (δ¹³C, δ¹⁵N) to ask whether the diet and molt habitat/location of Bullock's orioles influenced their expression of carotenoid‐based plumage coloration as well as plumage carotenoid content and composition. Bullock's orioles with lower feather δ¹⁵N values acquired more colorful plumage (orange‐shifted hue) but had feathers with lower total carotenoid concentration, lower zeaxanthin concentration, and marginally lower canthaxanthin and lutein concentration. Examining factors occurring throughout the annual cycle are critical for understanding evolutionary and ecological processes. Here, we demonstrate that conditions experienced during a stopover molt, occurring hundreds to thousands of kilometers from the breeding grounds, influence the production of ornamental plumage coloration, which may carryover to influence inter‐ and intrasexual signaling in subsequent seasons.