Ornamental Plumage Coloration Research Articles

Ornamental Plumage Coloration Interacts with Habitat Urbanization to Predict Problem-Solving in the House Finch Haemorhous mexicanus

Urbanization presents wildlife with many novel environmental challenges and opportunities, including navigating new physical structures and exploiting unique food bases. Thus, animal species that persist or thrive in urban environments may have superior cognitive abilities that allow them to navigate and solve anthropogenic problems. Prior studies have shown neural and behavioral differences between animals inhabiting urban and rural environments, but few have tested cognition-related behavioral responses of animals in an urban context. We administered a novel foraging challenge to caged male House Finches Haemorhous mexicanus — a successful urban and native desert species in the southwestern United States — captured from two urban and two rural locations to examine population differences in problem solving. This task involved opening a tin lid that was slid over the bird's normal small food dish and left only slightly ajar (with no food visible). Male House Finches display exaggerated, sexually selected plumage color that is dependent on diet, so we also tested the hypothesis that more colorful males can better solve foraging problems. We found no differences in problem solving success between urban and rural birds. However, among rural birds, we found that redder males were more likely to solve the foraging task than less-red males. Also, birds that lost more mass during the study were more likely to solve the task, but this was only true among less colorful birds. Our results are consistent with the hypothesis that plumage redness reveals foraging skill in House Finches found in their native environment.

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.

The separate effects of egg size and parental quality on the development of ornamental plumage coloration

The fitness‐related consequences of egg size, independent of the influences of parental quality, are poorly understood in altricial birds. Not only can egg size and parental quality influence growth and survival, but each could influence the development of condition‐dependent plumage coloration in offspring. The Eastern Bluebird Sialia sialis is an altricial, multi‐brooded, cavity‐nesting passerine in which juveniles display dichromatic UV‐blue plumage. Previous research suggests that plumage coloration acts as a signal of individual quality among juvenile and adult Eastern Bluebirds. Here, we separate the effects of egg size and parental quality (defined by egg size laid) on nestling growth and plumage ornamentation by exchanging clutches of large eggs with clutches of small eggs. Nestlings were significantly larger immediately post‐hatching when hatched from a large egg, but to maintain a larger size, nestlings needed to have hatched from a large egg and to have been reared by high‐quality parents. Nestlings were brighter when reared by high‐quality parents and this relationship was strongest later in the breeding season. Nestlings exhibited greater UV chroma if hatched early in the season, but UV chroma was not significantly affected by egg size or parental quality. These findings demonstrate varying influences of both egg size and parental quality on offspring growth and plumage ornamentation but suggest that quality of post‐hatching investment is more influential than pre‐hatching investment.

Evidence that fathers, but not mothers, respond to mate and offspring coloration by favouring high-quality offspring

Parents have limited resources and, when simultaneously rearing multiple offspring, are expected to favour particularly valuable offspring. Because offspring characteristics like sex and ornamentation influence future reproductive value, these traits may influence parental favouritism. Parents in high-quality nest environments should prefer sons because sons show greater variability in reproductive potential than daughters. Moreover, when ornamental plumage coloration is condition dependent, parents should favour brighter over duller sons. We tested parental favouritism for fledgling-aged eastern bluebirds, Sialia sialis, a species in which fledglings display condition-dependent UV-blue coloration on their wings and tails. We simultaneously threatened two offspring with mock predators and recorded which offspring the parents defended. In accordance with the predicted value of offspring, fathers protected brighter over duller sons and protected sons over daughters when mated to high-quality mates. Mothers did not discriminate between sons and daughters or between brighter and duller sons. These results suggest that ornamental plumage coloration in juvenile bluebirds functions as a signal in father–offspring interactions. Paternal and maternal responses of eastern bluebirds to offspring characteristics may differ because of differences in parental allocation strategies or because males assess offspring quality based on variation in plumage coloration, a trait that also functions in competitive interactions among adult males.

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.

Parental Effort in Relation to Structural Plumage Coloration in the Mountain Bluebird (Sialia currucoides)

AbstractIndicator models of sexual selection suggest that costly ornaments signal reliable information regarding an individual's quality to potential mates. In species that produce altricial offspring, the amount of parental care provided by both males and females can impact reproductive success. The Good Parent Hypothesis proposes that ornamentation in biparental species can act as an honest signal of parental ability to potential mates. We tested this hypothesis using the mountain bluebird (Sialia currucoides), a sexually dichromatic, socially monogamous species in which both sexes have structurally based ornamental plumage coloration. A male's plumage color predicted neither the rate at which it provisioned nestlings nor brood growth rate. The same was true for females. We also found no indication of assortative mating by color or body condition. Feeding rates within pairs were positively correlated, which we suggest may be due to pairs responding similarly to the perceived needs of nestlings or to local area prey availability. In sum, our results do not support the Good Parent Hypothesis as an explanation for the evolution of ornamental plumage color in mountain bluebirds. We suggest alternative hypotheses for the evolution of ornamental plumage color in this species.

Ornamental plumage coloration and condition are dependent on age in eastern bluebirds Sialia sialis

Male eastern bluebirds Sialia sialis have striking ultraviolet (UV)‐blue coloration on their heads, backs, rumps, wings, and tails and bold chestnut coloration on their breasts. These colored areas are ornaments that correlate with pairing date and reproductive effort, and thus probably influence the choice of mates by females. Such ornaments are expected to increase in color with age and body condition. We investigated the effects of age on body condition and the UV‐blue and chestnut coloration of males over four years using both cross‐sectional (comparing age classes) and longitudinal analyses (following individuals as they age). We found that both the body condition index and brightness of UV‐blue rump coloration increased with age, while UV‐blue tail plumage coloration increased between yearling and older males, and the chestnut breast coloration decreased in the oldest age class. The proximate mechanisms whereby individuals reliably signal age via rump brightness and tail coloration are probably different. Contour feathers, including rump feathers, are molted at approximately the same time in all age classes and are likely subject to the same production costs in all age classes. In contrast, the molt schedule of the tail and wing feathers differs between individuals of yearling and older age classes, with yearlings retaining wing and tail feathers for several months longer than adults. The relationship between tail color and age was probably, in part, a consequence of yearlings expressing tails that have increased feather wear and accumulation of dirt. In general, UV‐blue coloration increased with age while chestnut plumage decreased with age, indicating that older individuals may tradeoff investing energy in structural and melanin ornaments. By assessing overall plumage coloration, female eastern bluebirds could estimate age class when choosing mates.

Structural and melanin coloration indicate parental effort and reproductive success in male eastern bluebirds

Male eastern bluebirds (Sialia sialis) have two types of ornamental plumage coloration: a brilliant blue-ultraviolet head, back, and wings, and a patch of chestnut breast feathers. The blue-UV coloration is produced from feather microstructure, whereas the chestnut coloration is produced by a combination of pheaomelanin and eumelanin pigments deposited in feathers. We tested the hypothesis that plumage coloration reflects male quality in eastern bluebirds, a socially monogamous, sexually dichromatic bird. We investigated whether male ornamentation correlates with mate quality and parental effort. We quantified three aspects of male ornament coloration: (1) size of the patch of chestnut breast feathers, (2) reflectance properties of the chestnut plumage coloration, and (3) reflectance properties of the blue-ultraviolet plumage coloration. We found that males with larger breast patches and brighter plumage provisioned nestlings more often, fledged heavier offspring, and paired with females that nested earlier. Males with plumage coloration that exhibit more ultraviolet hues fledged more offspring. These results suggest that plumage coloration is a reliable indicator of male mate quality and reproductive success. Both melanin-based and structural-based plumages appear to be honest signals of male quality and parental care that can be assessed by competitors or by potential mates.

Plumage colour in nestling blue tits: sexual dichromatism, condition dependence and genetic effects.

Sexual-selection theory assumes that there are costs associated with ornamental plumage coloration. While pigment-based ornaments have repeatedly been shown to be condition dependent, this has been more difficult to demonstrate for structural colours. We present evidence for condition dependence of both types of plumage colour in nestling blue tits (Parus caeruleus). Using reflectance spectrometry, we show that blue tit nestlings are sexually dichromatic, with males having more chromatic (more 'saturated') and ultraviolet (UV)-shifted tail coloration and more chromatic yellow breast coloration. The sexual dimorphism in nestling tail coloration is qualitatively similar to that of chick-feeding adults from the same population. By contrast, the breast plumage of adult birds is not sexually dichromatic in terms of chroma. In nestlings, the chroma of both tail and breast feathers is positively associated with condition (body mass on day 14). The UV/blue hue of the tail feathers is influenced by paternally inherited genes, as indicated by a maternal half-sibling comparison. We conclude that the expression of both carotenoid-based and structural coloration seems to be condition dependent in blue tit nestlings, and that there are additional genetic effects on the hue of the UV/blue tail feathers. The signalling or other functions of sexual dichromatism in nestlings remain obscure. Our study shows that nestling blue tits are suitable model organisms for the study of ontogenetic costs and heritability of both carotenoid-based and structural colour in birds.

Carotenoid Pigments in Male House Finch Plumage in Relation to Age, Subspecies, and Ornamental Coloration

Like males of many bird species, male House Finches (Carpodacus mexicanus) have patches of feathers with ornamental coloration that are due to carotenoid pigments. Within populations, male House Finches vary in expression of ornamental coloration from pale yellow to bright red, which previous research suggested was the result of variation in types and amounts of carotenoid pigments deposited in feathers. Here we used improved analytical techniques to describe types and amounts of carotenoid pigments present in that plumage. We then used those data to make comparisons of carotenoid composition of feathers of male House Finches at three levels: among individual males with different plumage hue and saturation, between age groups of males from the same population, and between males from two subspecies that differ in extent of ventral carotenoid pigmentation (patch size): large-patched C. m. frontalis from coastal California and small-patched C. m. griscomi from Guerrero, Mexico. In all age groups and populations, the ornamental plumage coloration of male House Finches resulted from the same 13 carotenoid pigments, with 3-hydroxy echinenone and lutein being the most abundant carotenoid pigments. The composition of carotenoids in feathers suggested that House Finches are capable of metabolic transformation of dietary forms of carotenoids. The hue of male plumage depended on component carotenoids, their relative concentrations, and total concentration of all carotenoids. Most 4-keto (red) carotenoids were positively correlated with plumage redness, and most yellow carotenoid pigments were negatively associated with plumage redness, although the strength of the relationship for specific carotenoid pigments varied among age groups and subspecies. Using age and subspecies as factors and concentration of each component carotenoid as dependent variables in a MANOVA, we found a distinctive pigment profile for each age group within each subspecies. Among frontalis males, hatch-year birds did not differ from adults in mean plumage hue, but they had a significantly lower proportion of red pigments in their plumage, and significantly lower levels of the red piments adonirubin and astaxanthin, but significantly higher levels of the yellow pigment zeaxanthin, than adult males. Among griscomi males, hatch-year birds differed from adults in plumage hue but not significantly in pigment composition, though in general their feathers had lower concentrations of red pigments and higher concentrations of yellow pigments than adult males. Both adult and hatch-year frontalis males differed from griscomi males in having significantly higher levels of most yellow carotenoid pigments and significantly lower levels of most red carotenoid pigments. Variation in pigment profiles of subspecies and age classes may reflect differences among the groups in carotenoid metabolism, in dietary access to carotenoids, or in exposure to environmental factors, such as parasites, that may affect pigmentation.

Carotenoid Pigments in Male House Finch Plumage in Relation to Age, Subspecies, and Ornamental Coloration

AbstractLike males of many bird species, male House Finches (Carpodacus mexicanus) have patches of feathers with ornamental coloration that are due to carotenoid pigments. Within populations, male House Finches vary in expression of ornamental coloration from pale yellow to bright red, which previous research suggested was the result of variation in types and amounts of carotenoid pigments deposited in feathers. Here we used improved analytical techniques to describe types and amounts of carotenoid pigments present in that plumage. We then used those data to make comparisons of carotenoid composition of feathers of male House Finches at three levels: among individual males with different plumage hue and saturation, between age groups of males from the same population, and between males from two subspecies that differ in extent of ventral carotenoid pigmentation (patch size): large-patched C. m. frontalis from coastal California and small-patched C. m. griscomi from Guerrero, Mexico. In all age groups and populations, the ornamental plumage coloration of male House Finches resulted from the same 13 carotenoid pigments, with 3-hydroxy echinenone and lutein being the most abundant carotenoid pigments. The composition of carotenoids in feathers suggested that House Finches are capable of metabolic transformation of dietary forms of carotenoids. The hue of male plumage depended on component carotenoids, their relative concentrations, and total concentration of all carotenoids. Most 4-keto (red) carotenoids were positively correlated with plumage redness, and most yellow carotenoid pigments were negatively associated with plumage redness, although the strength of the relationship for specific carotenoid pigments varied among age groups and subspecies. Using age and subspecies as factors and concentration of each component carotenoid as dependent variables in a MANOVA, we found a distinctive pigment profile for each age group within each subspecies. Among frontalis males, hatch-year birds did not differ from adults in mean plumage hue, but they had a significantly lower proportion of red pigments in their plumage, and significantly lower levels of the red piments adonirubin and astaxanthin, but significantly higher levels of the yellow pigment zeaxanthin, than adult males. Among griscomi males, hatch-year birds differed from adults in plumage hue but not significantly in pigment composition, though in general their feathers had lower concentrations of red pigments and higher concentrations of yellow pigments than adult males. Both adult and hatch-year frontalis males differed from griscomi males in having significantly higher levels of most yellow carotenoid pigments and significantly lower levels of most red carotenoid pigments. Variation in pigment profiles of subspecies and age classes may reflect differences among the groups in carotenoid metabolism, in dietary access to carotenoids, or in exposure to environmental factors, such as parasites, that may affect pigmentation.

Pairing success relative to male plumage redness and pigment symmetry in the house finch: temporal and geographic constancy

Male house finches (Carpodacus mexicanus) have carotenoid-based ornamental plumage coloration. In previous research it was shown that for a single population of house finches in a single year, males that paired were on average redder in plumage coloration than males that did not pair, and males with redder plumage tended to nest earlier than males with less red plumage. Here we show that these patterns continued over 6 years and at two widely separated locations. We also tested whether the symmetry of carotenoid-based crown pigmentation differed between paired and unpaired males and found that paired males have, on average, more perfect symmetry of crown pigmentation than males not paired. These observations support the idea that expression of carotenoid-based plumage coloration by males is a persistent and widespread criterion in female mate choice in the house finch.

Melanin–based plumage coloration in the house finch is unaffected by coccidial infection

For most species of birds, ornamental plumage coloration may result from two types of pigments: carotenoids and melanins. Despite the fact that melanin pigments can be synthesized by birds from basic, amino acid precursors, while carotenoids cannot be synthesized by birds and must be ingested, melanin-based plumage coloration and carotenoid-based plumage coloration have often been treated as a single trait in investigations of the function and evolution of plumage coloration. Expression of carotenoid-based coloration is known to be dependent on condition, while the effects of individual condition have not been well-tested for expression of melanin-based coloration. In this study, we experimentally tested the effect of coccidial infection of the intestinal tract of male house finches during moult on expression of melanin-based plumage coloration. Coccidial infection had a significant negative effect on carotenoid-based coloration, but it had no significant effect on melanin-based feather coloration. Unlike carotenoid-based coloration, melanin-based coloration may be cheap to produce, and honesty of melanin-based coloration my require social mediation.

Subadult Plumage in the House Finch and Tests of Models for the Evolution of Delayed Plumage Maturation

-In many passerine species males do not attain definitive breeding plumage until after their first potential breeding season. Such delayed plumage maturation has been the subject of numerous studies, most of which have focused on the adaptive value of femalelike plumage for young males in single populations. Thus, although studies of delayed plumage maturation have been presented as tests of evolutionary hypotheses, most have lacked an appropriate comparative perspective. Moreover, most studies of subadult plumage in passerines have been conducted without information on the general function of ornamental plumage in the species being studied. A study of delayed plumage maturation in the House Finch (Carpodacus mexicanus) provided an opportunity to overcome these problems. The function and proximate control of ornamental plumage coloration in House Finches have been studied extensively. In addition, House Finches occupy a wide range across North America with approximately 15 subspecies recognized, and populations vary in expression of delayed plumage maturation. In most populations, including the most familiar subspecies, C. m. frontalis, males acquire definitive basic plumage in their first prebasic molt. In at least three populations, C. m. griscomi of southern Mexico, C. m. amplus of Guadalupe Island, and Great Basin populations of C. m. frontalis, however, males do not acquire definitive plumage until the completion of their second prebasic molt, spending their first potential breeding season in a female-like plumage. Using a composite phylogeny and parsimony analysis, I show that delayed plumage maturation likely was lost in the ancestral House Finch population and was regained independently by the three taxa in which it is now observed. Thus, delayed plumage maturation in the House Finch is a derived trait. In addition, I show that the acquisition of delayed plumage maturation is associated with a reduction in the extent of ornamental plumage (i.e. a reduction in patch size). These observations support the idea that delayed plumage maturation in the House Finch is an adaptation to increased production costs of red ornamental display plumage in some populations. Received 28 November 1995, accepted 25 April 1996. DELAYED PLUMAGE MATURATION describes a developmental pattern generally limited to males, whereby individuals do not acquire definitive breeding plumage until after their first potential breeding season (Rohwer et al. 1980, Rohwer and Butcher 1988). Studies of delayed plumage maturation most frequently concern Temperate Zone passerines that spend only one potential breeding season in a subadult plumage (Rohwer and Butcher 1988, Butcher and Rohwer 1989, Zack and Stutchbury 1992). Despite a substantial literature on delayed plumage maturation (see Zack and Stutchbury 1992), our understanding has advanced relatively little since interest in the topic was first ignited by Rohwer et al. (1980). I believe that the ma1 E-mail: geoffrey.hill@ag.auburn.edu jority of research on delayed plumage maturation in passerines suffers from two fundamental problems: (1) lack of a general understanding of the function of ornamental plumage coloration, and (2) lack of an appropriate comparative approach to testing hypotheses for the evolution of delayed plumage maturation. The first of these problems clearly is a case of putting the cart before the horse. Ornamental plumage coloration, either bright structural coloration, bright carotenoid-based coloration, or highly contrasting melanin-based coloration, is universally assumed to function as a signal in avian communication (Butcher and Rohwer 1989). Signaling generally is believed to occur in the context of either intersexual or intrasexual interactions (Butcher and Rohwer 1989), but predator-prey interactions also have been considered (Gotmark 1992, 1993). An assump-