Plumage Ornaments Research Articles

Long-term effects of yolk androgens on phenotype and parental feeding behavior in a wild passerine

Early growth conditions, such as exposure to maternally derived androgens in bird eggs, have been shown to shape offspring in ways that may have important long-term consequences for phenotype and behavior. Using an experimental approach, we studied the long-term effects of yolk androgens on several phenotypic traits and parental behavior in adult and female collared flycatchers (Ficedula albicollis). We elevated yolk androgen levels and monitored the experimental recruits the following breeding seasons. Androgen treatment had a sex-dependent effect on adult body condition, yolk androgen-treated males being heavier than control males when controlling for size, a result which may be caused potentially by selective mortality, physiological differences, or different life-history strategies. Androgen treatment did not however affect the expression of sexually selected plumage ornaments (forehead and wing patch size), UV coloration, or parental feeding rate in either sex. Our results suggest that yolk androgens are unlikely to affect sexual selection via plumage characteristics or contribute to breeding success via altered parental care. Yolk androgens do not seem to act as a means for female collared flycatchers to enhance the attractiveness of their sons. The lower return rate previously observed for androgen-treated male offspring compared to controls may therefore not be due to lower mating or breeding success, but may rather reflect lower survival or higher dispersal propensity of yolk androgen-treated males.

Carotenoid-Based Ornaments of Female and Male American Goldfinches (Spinus tristis) Show Sex-Specific Correlations with Immune Function and Metabolic Rate

Conspicuous ornamentation has been linked to immunological and physiological condition in males of many species. In species where both sexes are ornamented, it is unclear whether the signal content of ornaments differs between males and females. We examined the immunological and physiological correlates of carotenoid-based bill and plumage ornamentation in American goldfinches Spinus tristis, a species in which bright orange bills are sexually monomorphic but yellow plumage is sexually dimorphic during the breeding season. Because bill color is dynamic over short periods while plumage color is static over longer time frames, we tested whether these signals have the potential to provide temporal information about immunity and condition. In both sexes, bill color (but not plumage color) was negatively related to leukocyte differential, a measure of recent stress, while plumage color (but not bill color) was positively related to resting metabolic rate. In females, bill color also positively correlated with immunoglobulin Y, a component of acquired immunity, while plumage color positively predicted natural antibody levels, a component of innate immunity. In males, neither bill color nor plumage color predicted immune function, suggesting that the mechanisms underlying these signals vary with sex. Our results demonstrate that dynamic signals such as bill coloration do not merely reflect the same information provided by static signals but that these two classes of signal provide information about different temporal aspects of phenotypic quality. Furthermore, our results indicate that a signal expressed in both sexes has the potential to provide different information depending on the sex of the bearer.

Structural coloration signals condition, parental investment, and circulating hormone levels in Eastern bluebirds (Sialia sialis)

Many of the brilliant plumage coloration displays of birds function as signals to conspecifics. One species in which the function of plumage ornaments has been assessed is the Eastern bluebird (Sialia sialis). Studies of a population breeding in Alabama (USA) have established that plumage ornaments signal quality, parental investment, and competitive ability in both sexes. Here we tested the additional hypotheses that (1) Eastern bluebird plumage ornamentation signals nest defense behavior in heterospecific competitive interactions and (2) individual variation in plumage ornamentation reflects underlying differences in circulating hormone levels. We also tested the potential for plumage ornaments to signal individual quality and parental investment in a population breeding in Oklahoma (USA). We found that Eastern bluebirds with more ornamented plumage are in better condition, initiate breeding earlier in the season, produce larger clutches, have higher circulating levels of the stress hormone corticosterone, and more ornamented males have lower circulating androgen levels. Plumage coloration was not related to nest defense behavior. Thus, plumage ornamentation may be used by both sexes to assess the physiological condition and parental investment of prospective mates. Experimental manipulations of circulating hormone levels during molt are needed to define the role of hormones in plumage ornamentation.

Winter body condition in relation to age, sex and plumage ornamentation in a migratory songbird

Winter body condition may play important roles in the life history of migratory birds, but it is difficult to estimate. We used the growth rate of winter‐grown tail feathers of Collared Flycatchers Ficedula albicollis as an indicator of winter body condition, comparing this trait between age classes and sexes and relating it to plumage ornamentation (forehead and wing patch sizes). Adults and males were in better nutritional condition during winter, as indicated by their faster tail feather growth rates, than were yearlings and females, respectively, which could indicate differences in individual quality and foraging ability with age, or age‐ and sex‐related winter habitat segregation. However, feather growth rate was related neither to the size of the winter‐grown forehead patch nor to the size of the summer‐grown wing patch, suggesting weak condition‐dependence for the winter‐grown ornament and complex life‐history consequences for the summer‐grown ornament.

Influence of Hatch Order on Begging and Plumage Coloration of Nestling Eastern Bluebirds

Hatching asynchrony in altricial songbirds can influence the morphology and behavior of nestling birds. We compared the position of nestling Eastern Bluebirds (Sialia sialis) in the hatching hierarchy to their (1) position in the egg-laying order, (2) rate of nestling begging, (3) circulating corticosterone, (4) size, and (5) plumage coloration. Most nestlings hatched within 36 hrs of each other, and nestlings hatched in the order in which eggs were laid. Early-hatched nestlings were heavier than late-hatched nestlings for the duration of the growth period and begged less intensely than their late-hatched siblings. There was little evidence of severe effects of hatch order. Hatch order did not influence nestling corticosterone levels nor did we find effects of hatch order on ornamental plumage coloration. Our data suggest no long-term effect of hatching asynchrony on the development of sexually selected plumage coloration.

White Flank Spots Signal Feeding Dominance in Female Diamond Firetails, Stagonopleura guttata

AbstractPlumage colour can be used as an honest signal to convey health and status, which has traditionally been examined in the sexual selection context of choosy females and elaborate males. We use a model avian system to study the role of plumage coloration in a social context such as inter‐ and intrasexual competition over food resources. The diamond firetail (Stagonopleura guttata) is an endemic Australian finch: females have more white flank spots than males, and white spot number was correlated with cell‐mediated immune response in females. We use two experimental designs to test the role of white flank spots for feeding dominance and dominance discrimination in a group‐living bird. The results from two‐choice trials and from single‐arena trials showed that female ornamentation was consistently important in social food contests, and males consistently responded to female spot number. Females with higher spot number fed first, in trials with males and/or females. Also, females preferred to feed next to test birds with low spot number, but males showed no preference for feeding next to birds with few or many spots. Finally, latency to feed was predicted by spot number: both males and females had longer latency to feed if test birds had more spots than the focal birds. We conclude that female, but not male, ornamentation was important for inter‐ and intrasexual food competition. This is one of the very few studies to show that the same plumage ornament can have a different function between the sexes as a signal of social status. Moreover, this study shows that white plumage can be a signal of dominance.

Throat patch size and darkness covaries with testosterone in females of a sex-role reversed species

In male birds, size and blackness of melanin-based ornaments may signal competitive ability and quality. Testosterone is an important physiological mediator of these signals as these ornaments are testosterone dependent. Experimental manipulation of circulating testosterone in females suggests that similar mechanisms are at work in plumage ornaments of females. However, hormone manipulations typically result in testosterone levels that are far higher than physiological concentrations experienced by females. Thus, it remains unclear whether natural variation of testosterone levels would be sufficient to generate variation in female plumage coloration. A signaling value of plumage ornamentation is particularly important in females of sex-role reversed species, in which females are the more competitive sex. We examined the relationship between plumage coloration, body condition, and circulating testosterone in female barred buttonquails (Turnix suscitator), a classically polyandrous species. Even though female testosterone levels were low, they were strongly positively related with body condition and the size and blackness of the melanin throat patch. In males, no such relationships were apparent, suggesting that females may have an enhanced sensitivity for testosterone or its metabolites. These unique results reveal that a hormonal mechanism may be involved in sex-role reversal in this species.

Convergent gains of red carotenoid-based coloration in the New World blackbirds

Many birds have colorful plumage ornaments that utilize carotenoid pigments, and these are often displayed in signaling contexts. Researchers in behavioral ecology have focused on examining carotenoids in general, and red carotenoids in particular, because they may be an honest index of individual condition or quality. However, few studies have examined the evolutionary changes in carotenoid-based coloration across a phylogeny. We used reflectance spectrometry to examine carotenoid-based coloration across the New World blackbirds (Icteridae). We scored discrete character states based on these measurements and mapped them onto the icterid phylogeny. Our results indicate that red coloration has been gained six times in the blackbirds from a common ancestor that exhibited yellow ornamentation. This result was supported by both parsimony and likelihood methods of ancestral state reconstruction and by each of three different scoring methods. Thus, multiple lineages of icterids have convergently evolved red patches from a common ancestor that most likely used yellow. Several other studies have observed repeated gains of red coloration, which suggests that our observations may reflect a directional trend common among avian clades.

Age-related variation in carotenoid-based plumage ornaments of male Red Bishops Euplectes orix

Males in many bird species develop elaborate carotenoid-based plumage ornaments which often play an important role as signals of individual quality in intra- or intersexual selection. However, knowledge of the pattern of age-related variation in plumage traits is crucial to interpret results on associations between plumage signals and reproductive performance. We investigated how age is related to brightness and carotenoid saturation of the orange-red breeding plumage in males of known age in the Red Bishop (Euplectes orix), a polygynous and sexually dimorphic weaverbird species. We found that the relationships of both plumage brightness and carotenoid saturation with age were best explained by a quadratic function, with males in their prime (i.e. 3–5 years old) having a brighter and more carotenoid-saturated plumage than both very young and very old males. The implications of our results for studies in the context of animal signalling are discussed.

The crest of the peafowl: a sexually dimorphic plumage ornament signals condition in both males and females

Both male and female peafowl grow crests on top of their head - iridescent blue in males, dull iridescent green and brown in females - but the potential signal function of this plumage ornament is unknown. In this study, peafowl crests were measured in three feral populations, and morphological variation in this ornament was studied in relation to body condition (body mass in relation to tarsus length) and health (white blood cell concentration and ectoparasite load). Prior to the start of the breeding season, male crests are wider with greater pennaceous area, and are more likely to have all feathers grown out compared with female crests. Only crest length changed with measurement date, increasing over time; in males, crest measurements were not related to the extent of train feather development. Crest morphology is a potential signal of individual health and condition in both sexes, but in different ways. In females, the amount of crest plumage grown out to its full extent was related to body condition at the start of the breeding season, whereas in males, the size and pennaceous area of the ornament were related to ectoparasite load. Observations of within-sex agonistic behaviour suggest a possible role for the crest ornament in status signaling in males, because males that engage in more aggressive interactions tend to have wider crests. There was no evidence for a relation between crest morphology and agonistic behaviour in females.

Intraspecific preen oil odor preferences in dark-eyed juncos (Junco hyemalis)

Most birds possess a uropygial gland that produces a secretion, preen oil, that contains volatile compounds that may transmit information about individual attributes. However, the ability of passerine songbirds to discriminate among the odors of different individuals has not yet been demonstrated. We tested whether dark-eyed juncos (Junco hyemalis) could discriminate among preen oil odors from 1) conspecifics and heterospecifics; 2) male and female conspecifics; 3) conspecifics from same or different population or subspecies; and 4) males with large or small plumage ornaments. Our evidence suggests that juncos can discriminate between the odor of conspecifics and heterospecifics. In 2-way choice tests between conspecific odors, both males and females spent more time with male preen oil. Subjects did not discriminate between odors of individuals from their own population or a different one, and no relationship was found between choice and plumage ornaments. Unexpectedly, females spent more time with the odor of males with smaller body size, regardless of population of origin. This result was especially surprising because an analysis of preen oil volatile compounds revealed that the odors of smaller males were less male-like than the odors of larger males. We conclude that songbirds are able to detect odors from preen oil as shown by their ability to distinguish odors arising from males and females. They may also be able to distinguish among individuals of varying body size. Abstract » Full Text (HTML) Full Text (PDF) Lay Summary

Plasma Antioxidant Capacity and Oxidative Damage in Relation to Male Plumage Ornamental Traits in a Montane Iberian Pied FlycatcherFicedula hypoleucaPopulation

Melanin-based plumage ornaments may express individual quality in the context of social and sexual selection. Oxidative stress and antioxidant defences may be expressed through melanin-based plumage traits. Male Pied Flycatchers Ficedula hypoleuca exhibit eumelanic dorsal plumage and white feather patches on forehead and wing feathers. Although these traits have been related to sexual selection in some populations, no physiological correlate of variation in these characters has been previously shown. Here we test if these plumage traits are related to plasma oxidative stress and antioxidant capacity. We captured males while feeding nestlings in a population breeding at high altitude (1200–1400 m) in central Spain and collected blood samples from brachial veins. Percentage black on dorsal plumage and extension of white on folded wing and forehead were obtained from digital photographs. Plasma samples were analysed in the laboratory to obtain lipid peroxidation as a measure of oxidative damage by quantifying malondialdehydes (MDA), and antioxidant capacity. When controlling for male mass, breeding date and brood size, only forehead patch size was negatively associated with plasma lipid peroxidation levels and positively related to antioxidant capacity. There was no association among different plumage traits. Thus forehead patch size in montane Iberian populations may signal male phenotypic quality through plasma oxidative stress and antioxidant capacity possibly due to altitudinal effects on oxidative stress.

Fecundity selection on ornamental plumage colour differs between ages and sexes and varies over small spatial scales

Avian plumage colours are some of the most conspicuous sexual ornaments, and yet standardized selection gradients for plumage colour have rarely been quantified. We examined patterns of fecundity selection on plumage colour in blue tits (Cyanistes caeruleus L.). When not accounting for environmental heterogeneity, we detected relatively few cases of selection. We found significant disruptive selection on adult male crown colour and yearling female chest colour and marginally nonsignificant positive linear selection on adult female crown colour. We discovered no new significant selection gradients with canonical rotation of the matrix of nonlinear selection. Next, using a long-term data set, we identified territory-level environmental variables that predicted fecundity to determine whether these variables influenced patterns of plumage selection. The first of these variables, the density of oaks within 50 m of the nest, influenced selection gradients only for yearling males. The second variable, an inverse function of nesting density, interacted with a subset of plumage selection gradients for yearling males and adult females, although the strength and direction of selection did not vary predictably with population density across these analyses. Overall, fecundity selection on plumage colour in blue tits appeared rare and inconsistent among sexes and age classes.

DIVERGENT PATTERNS OF AGE-DEPENDENCE IN ORNAMENTAL AND REPRODUCTIVE TRAITS IN THE COLLARED FLYCATCHER

Sexual ornaments are predicted to honestly signal individual condition. We might therefore expect ornament expression to show a senescent decline, in parallel with late-life deterioration of other characters. Conversely, life-history theory predicts the reduced residual reproductive value of older individuals will favor increased investment in sexually attractive traits. Using a 25-year dataset of more than 5000 records of breeding collared flycatchers (Ficedula albicollis) of known age, we quantify cross-sectional patterns of age-dependence in ornamental plumage traits and report long-term declines in expression that mask highly significant positive age-dependency. We partition this population-level age-dependency into its between- and within-individual components and show expression of ornamental white plumage patches exhibits within-individual increases with age in both sexes, consistent with life-history theory. For males, ornament expression also covaries with life span, such that, within a cohort, ornamentation indicates survival. Finally, we compared longitudinal age-dependency of reproductive traits and ornamental traits in both sexes, to assess whether these two trait types exhibit similar age-dependency. These analyses revealed contrasting patterns: reproductive traits showed within-individual declines in late-life females consistent with senescence; ornamental traits showed the opposite pattern in both males and females. Hence, our results for both sexes suggest that age-dependent ornament expression is consistent with life-history models of optimal signaling and, unlike reproductive traits, proof against senescence.

Vocal and Optical Indicators of Individual Quality in a Social Seabird, the Crested Auklet (Aethia cristatella)

Indicators of individual quality in ornamentation or in vocalizations have been reported for different animal species. However, no studies have jointly investigated ornamentation and vocalizations in one species. The crested auklet (Aethia cristatella, Alcidae) is a small colonial seabird of the North Pacific and is unusual for a bird in using optical, vocal, and olfactory signals. We estimated the potential for coding individual quality in vocalizations and plumage ornamentation and the relationship between vocal and optical traits in crested auklets. During the summer seasons of 2008–2009, we recorded 359 trumpet calls from 28 individually marked males and measured indices of body size, condition, and plumage patterns of 58 male and 48 female crested auklets from a breeding colony on Talan Island, Sea of Okhotsk. We found strong interindividual differences in trumpet call characteristics. Furthermore, we found that the maximum fundamental frequency of the loudest notes of the trumpet call is negatively correlated with body condition, and head crest length is positively correlated with body size. However, we found no relationship between vocal and ornamental traits. The results suggest that advertising calls of crested auklets signal caller individuality and quality, but future experimental studies should test whether or not this is indeed case.

Haste Makes Waste: Accelerated Molt Adversely Affects the Expression of Melanin-Based and Depigmented Plumage Ornaments in House Sparrows

BackgroundMany animals display colorful signals in their integument which convey information about the quality of their bearer. Theoretically, these ornaments incur differential production and/or maintenance costs that enforce their honesty. However, the proximate mechanisms of production costs are poorly understood and contentious in cases of non-carotenoid-based plumage ornaments like the melanin-based badge and depigmented white wing-bar in house sparrows Passer domesticus. Costly life-history events are adaptively separated in time, thus, when reproduction is extended, the time available for molt is curtailed and, in turn, molt rate is accelerated.Methodology/Principal FindingsWe experimentally accelerated the molt rate by shortening the photoperiod in order to test whether this environmental constraint is mirrored in the expression of plumage ornaments. Sparrows which had undergone an accelerated molt developed smaller badges and less bright wing-bars compared to conspecifics that molted at a natural rate being held at natural-like photoperiod. There was no difference in the brightness of the badge or the size of the wing-bar.Conclusions/SignificanceThese results indicate that the time available for molt and thus the rate at which molt occurs may constrain the expression of melanin-based and depigmented plumage advertisements. This mechanism may lead to the evolution of honest signaling if the onset of molt is condition-dependent through the timing of and/or trade-off between breeding and molt.

Not as similar as thought: sexual dichromatism in Chimango Caracaras is expressed in the exposed skin but not in the plumage

Many of the mechanisms involved in visual signalling in birds are based on pigment-based plumage ornamentation and colouration rather than the expression of other, non-plumage-based displays. We have analysed the colouration of the tarsi and ceres of free-ranging Chimango Caracaras Milvago chimango, a controversial morphological trait for this species, and examined the proximal causes related to the expression of colour in these featherless body parts. The tarsi–ceres of 81 Chimango Caracaras captured in central Argentina between 2005 and 2008 were either yellow–yellow or bluish–pink coloured. Differences in colour were not linked with plasma carotenoid levels and did not vary seasonally. Rather, expression of the two colours was affected by the gender and age of individuals. Yellow-coloured tarsi and ceres were recorded only in adult males, while the remaining age and gender groups showed pinkish- and bluish-coloured bare parts, which is the suspected neutral developmental stage under low hormonal levels. These results support sexual rather than natural selection forces acting on the expression of yellow colouration in the bare parts of adult males. However, an exaggeration of yellowish colour during mating periods in accordance with an increase of circulating carotenoid levels may be expected due to the sexually-related nature of this trait. This documented partitioning of colour variation among sexes and ages that is unrelated to melanin-dependent plumages is unusual and contrary to the most widely observed types of sexual dichromatism in birds.

How many color metrics do we need? Evaluating how different color-scoring procedures explain carotenoid pigment content in avian bare-part and plumage ornaments

For a variety of technical and conceptual reasons, biologists have come to use several different methods to quantify the colors of animals. However, the relative abilities of these different color-scoring procedures to capture variation in the actual color-generating mechanisms—pigment or structural composition of the integument—have never been tested systematically. Here, we examined which commonly employed color metrics predict carotenoid content of ornaments in three avian species (house finch Carpodacus mexicanus, mallard duck Anas platyrhynchos, and zebra finch Taeniopygia guttata). We used spectrophotometry to measure reflectance spectra from beak and feather tissue, calculated numerous color metrics (e.g., hue, chroma, brightness, principal components, and tetrahedral color space position) from these spectra, and determined carotenoid content at the site of color measurement with high-performance liquid chromatography. We found that several principal component, tristimulus, and avian visual model metrics significantly correlated with carotenoid content of house finch feathers and duck beaks. Carotenoid content of mallard beaks was most closely correlated with brightness and saturation metrics, whereas in house finch feathers, carotenoid concentration was best captured by hue and saturation metrics. According to tristimulus scores and visual models, we found that the ultraviolet portion of the spectrum was not an essential predictor of variation in carotenoid content. Also, visual model chromatic contrasts generally were not significant predictors of carotenoid content, although some achromatic contrasts and tetrahedral color space vector parameters were. Our results indicate that numerous methods, especially tristimulus scores, are suitable for capturing pigment-based color variation in two carotenoid-containing ornaments, and we discuss the merits and shortcomings of these different approaches. In contrast, there were no significant relationships between any color metrics and the carotenoid content of zebra finch beaks, suggesting that other color-generating mechanisms besides carotenoids may contribute to color variability in this species.

Achieving luster: prenuptial molt pattern predicts iridescent structural coloration in Blue-black Grassquits

Colors in feathers are produced by pigment deposition or by nanostructures within barbs or barbules. In the absence of pigments or nanostructures, light is scattered incoherently, producing white coloration. Honest advertisement models predict that ornamental colors evolve if they reliably signal individual properties such as viability, health, or nutritional state. In this study, we tested if (1) iridescent structural and (2) unpigmented plumage coloration signal male quality in the Blue-black Grassquit (Volatinia jacarina). During three reproductive seasons, we captured males and measured morphological variables and nuptial plumage coverage, and collected feathers for spectrometry. We found that saturation of the iridescent coloration was positively related to relative molting speed, indicating that males investing more in prenuptial molt also produced more saturated, UV-shifted plumage. Body condition was not related to brightness or saturation of the iridescent plumage, and no male morphological attributes were associated with the white underwing patch coloration or size. Our results suggest that patterns of molt, and possibly feather growth, may affect the organization of optical nanostructures responsible for iridescent coloration, and that the ontogeny of iridescent plumage ornaments must be taken into account in hypotheses concerning honest advertisement of such signals. Thus, coloration in this species may reliably reflect energy allocation to molting, constituting an honest indicator of male quality, life history decisions, or endocrine state. To our knowledge, this is the first report of natural variation in molting pattern being associated with sexually-selected structural color plumage.

Plumage coloration, ejaculate quality and reproductive phenotype in the red-backed fairy-wren

Understanding how pre- and postcopulatory sexually selected traits covary can provide insight into the evolution of male ornamentation and female mate choice. In this study, we examined ejaculate quality and investment in testicular tissue in relation to plumage colour and social status in the genetically promiscuous red-backed fairy-wren, Malurus melanocephalus. In this species, males exhibit one of three alternative reproductive phenotypes during the breeding season: males can breed in red and black plumage, breed in brown plumage, or act as brown-plumed, nonbreeding auxiliaries. We found that red/ black breeders invested more heavily in spermatogenic tissue, had larger sperm reserves, and tended to have greater numbers of sperm in ejaculate samples, when compared to brown breeders and auxiliaries. Within red/black breeders, plumage redness and saturation (i.e. long wavelength hue and increased red chroma) were negatively correlated with ejaculate sample sperm density. In addition, ejaculate motility appeared to be related to variation in plumage coloration such that, overall, males with less elaborate ornamentation showed greater ejaculate quality. These results suggest that pre- and postcopulatory traits negatively covary in red/black plumed red-backed fairy-wrens and indicate a possible trade-off between investment in plumage ornaments and investment in ejaculates.