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Avian color patterns are the outcome of a complex evolutionary process and have different resulting adaptive functions. In this study, we assessed the sexual and age variations in plumage coloration of captive varieties of Erythrura gouldiae; a polychromatic and endangered endangered species of Australia. The chest, belly, extended wing (upper-view) and head (side-view) of 135 individuals of 39 varieties of the species were photographed. Photos were taken on a white background with a strip containing the standard pattern of the basic colors, Red -- Green-Blue, to eliminate the effects of varying lighting conditions. Photographs were processed using Adobe Photoshop CS3, and digital values of the intensity of the Red, Green and Blue channel were measured. The mask and wings showed the highest variability, and in these areas, red color was the most variable. Individuals from those varieties derived from ancestral black mask morph, exhibited more variability. Sexual difference patterns were not equal between varieties nor body areas here in sampled. The mask in females of certain varieties was more colorful than in males, and the blue channel intensity on the chest, belly and wing reached higher values in females. In general, colors intensity of the chest, belly and wing increase with the age, unlike the mask which faded away. [ABSTRACT FROM AUTHOR]

Plumage coloration has long been studied as a sexually selected character. The tawny-bellied seedeater, Sporophila hypoxantha, is a sexually dichromatic species, with adult males the more colorful sex and juvenile males indistinguishable from females. We did choice experiments to evaluate female preferences for males that differ in age or plumage coloration. Females were evaluated in three experiments: (1) choice between males with similar breast brightness that differed in age, (2) choice between males of 2 years of age that differed in breast brightness, and (3) choice between males of 3 or more years of age that differed in breast brightness. We also repeated the latter experiment with estradiol-treated females. We did not find a clear female preference for brighter or older males, as females spent the same proportion of time with males of similar breast brightness that differed in age or with males of similar age that differed in breast brightness. Our results do not support the hypothesis that breast brightness is a cue used by female tawny-bellied seedeaters at the time of choosing males. We propose that, in this species, male plumage coloration might play a role in intrasexual competition. [ABSTRACT FROM AUTHOR]

In numerous avian species, males and females display ornaments that could act as signals in interactions with conspecifics. Much of the research on these ornaments has focused on mutual mate choice and intrasexual competition between males. However, few studies have examined female and male ornamentation simultaneously in the context of intrasexual competition and the acquisition of breeding resources. I examined whether plumage coloration of male and female Prothonotary Warblers (Protonotaria citrea) was related to the quality of their nest site by placing nest boxes in preferred locations over deep water and at less preferred sites over land. Age and body size were not related to the ability of males or females to obtain a nest site over deep water. Males that werebrighter yellow and more pure yellow obtained boxes over deep water, and older females that were more pure yellow did as well. However, in an analysis that included young and old females, I found no relationship between plumage coloration and nest-box quality. These results indicate that coloration could be a signal of competitive ability, particularly in males. [ABSTRACT FROM AUTHOR]

Ovaries from Rhode Island Red donors were transplanted orthotopically into White Leghorn recipients. At maturation, recipients were mated with Rhode Island Red roosters to test the origin of their ovaries, using plumage coloration as a marker. A chick with chimeric plumage coloration was produced, in dicating mechanisms that produce follicles with both donor and recipient ovarian contents. This study sug-gests that ovarian transplantation could be useful for in vivo studies of cytological and molecular mechanisms involved in avian folliculogenesis. [ABSTRACT FROM AUTHOR]

Melanin-based coloration is widespread among vertebrates, yet the adaptive significance of such pigments remains elusive, particularly with regard to the link between melanin and immune-mediated maternal effects. The aim of this study was to investigate whether melanin-based coloration could signal the ability of mothers to mount a humoral response and to transfer maternal antibodies ( Ab) to their young. We injected differently coloured (pale and dark) female feral pigeons ( Columba livia) with Chlamydiae (a natural antigen) and Keyhole Limpet Haemocyanin (KLH, an artificial antigen), and found no significant difference in humoral response between differently coloured females. However, darker females transferred more Ab against Chlamydiae into their eggs than paler ones, despite similar circulating levels of Ab. In addition to this, melanin-based coloration showed a high heritability value. This suggests that a genetically based coloured trait might be linked to the ability of females to transfer specific Ab against Chlamydiae (but not against KLH) to their offspring, independent of their ability to produce Ab. This suggests that transmission of maternal Ab is antigen dependent, and that melanin-based coloration might signal female ability to transmit specific Ab against natural pathogens. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Abstract: Androgens play a major role in the regulation of sexual signal expression of male vertebrates. In this study we assessed the prevalent, yet largely untested, assumption that signal honesty is maintained through condition-dependent androgen regulation by experimentally manipulating body condition of male red-backed fairy-wrens (Malurus melanocephalus) through trimming several flight feathers before the prenuptial molt. In their first reproductive season males of this species exhibit androgen-regulated plasticity in plumage coloration, ranging from red/black (high androgens) to brown (low androgens). Red/black plumage is preferred by females and might be constrained by a negative relationship between body condition and androgen levels. We also evaluated whether corticosterone changes to altered conditional state mediate the relationship between condition and androgens. While we predicted that males with trimmed feathers would expend greater energy and thus be in poorer condition at the time of molt, they were counter-intuitively in better condition compared to control birds, likely as a consequence of subtle behavioral changes. These birds in better condition molted a greater proportion of red/black plumage, as predicted, and also molted more heavily. However, experimental and control birds did not differ in their androgen or corticosterone concentrations. Furthermore, analysis of long-term data from the same population revealed no correlation between condition and androgen levels. Collectively, these results challenge the notion that condition-dependent androgen regulation alone is responsible for maintaining the honesty of sexual signals and highlights the necessity of considering alternate explanations. [Copyright &y& Elsevier]

The article discusses the findings of a study to understand the Humphrey and Parkes (H-P) terminology of molting. It explains the evolution of the H-P nomenclature system that was developed in 1959, and the subsequent application of traditional molt and plumage terminology by Hawkins (2011) to present-day breeding of ducks. The researchers infer that Hawkins misinterpreted the evolutionary approach of the H-P system, resulting in inconsistent definition of homologous molts.

Sexual selection drives the evolution of many spectacular animal displays that we see in nature. Yet, how selection combines and elaborates different signal traits remains unclear. Here, we investigate this issue by testing for correlated evolution between head plumage colour and drumming behaviour in woodpeckers. These signals function in the context of mate choice and male-male competition, and they may appear to a receiver as a single multimodal display. We test for such correlations in males of 132 species using phylogenetic linear models, while considering the effect of habitat. We find that the plumage chromatic contrast is positively correlated with the speed of the drum, supporting the idea that species evolving more conspicuous plumage on their head also evolve faster drum displays. By contrast, we do not find evidence of correlated evolution between drum speed and head colour diversity, size of the head's red patch, or extent of the plumage achromatic contrast. Drum length was not correlated with any of the plumage coloration metrics. Lastly, we find no evidence that habitat acts as a strong selective force driving the evolution of head coloration or drumming elaboration. Coevolution between different signal modalities is therefore complex, and probably depends on the display components in question., (© 2022 The Authors.)

Intense red colours in birds are often owing to ketocarotenoids (KCs). In many land birds, KCs are oxidized from dietary yellow precursors, presumably by the avian carotenoid ketolase CYP2J19, the regulation and constraints of which have important implications for condition-dependence and honest signalling of carotenoid colour displays. We investigated hepatic CYP2J19 gene expression in the seasonally and sexually dichromatic southern red bishop ( Euplectes orix ) in relation to season, sex, progression of the prenuptial moult, testis size, body condition, redness and circulating sex steroids. A coloration function of CYP2J19 is supported by a seasonal upregulation prior to and during the carotenoid-depositing stage of the male prenuptial moult. However, CYP2J19 expression was similarly high in females (which do not moult prenuptially), and remained high in males after moult, suggesting additional or alternative roles of hepatic CYP2J19 or its products, such as detoxification or antioxidant functions. In males, the CYP2J19 upregulation preceded and was unrelated to the rise in plasma testosterone, but was correlated with androstenedione, probably of adrenal origin and compatible with luteinizing hormone-induced and (in females) oestrogen-suppressed moult. Finally, contrary to ideas that carotenoid ketolation rate mediates honest signalling of male quality, CYP2J19 expression was not related to plumage redness or male body condition., (© 2022 The Authors.)

Abstract: Molecular phylogenetic analyses have greatly changed Neotropical avian systematics in the past couple of decades. These new phylogenies provide the necessary framework to study the ecology and natural history of species in the region in an evolutionary context. This study addresses the systematics of Poospiza, Compsospiza, Hemispingus, Thlypopsis, and eight monotypic genera, which form a strongly supported and novel clade within the tanagers. We find Poospiza, Hemispingus, and Thlypopsis to be polyphyletic, confirm or reject relationships proposed based on morphology and life history, and describe novel relationships among these and the monotypic genera. The diversity of plumage, habitat, and geography throughout the clade allows us to test hypotheses of plumage evolution in relation to light environment. We find that overall plumage brightness best fits a model that includes selective regimes based on open versus closed habitats and foraging strata, while plumage measures describing color diversity and chroma best fit a model that only includes selective regimes based on open and closed habitats. [Copyright &y& Elsevier]

Carotenoid pigments were extracted from 29 feather patches from 25 species of cotingas (Cotingidae) representing all lineages of the family with carotenoid plumage coloration. Using high-performance liquid chromatography (HPLC), mass spectrometry, chemical analysis, and H-NMR, 16 different carotenoid molecules were documented in the plumages of the cotinga family. These included common dietary xanthophylls (lutein and zeaxanthin), canary xanthophylls A and B, four well known and broadly distributed avian ketocarotenoids (canthaxanthin, astaxanthin, α-doradexanthin, and adonixanthin), rhodoxanthin, and seven 4-methoxy-ketocarotenoids. Methoxy-ketocarotenoids were found in 12 species within seven cotinga genera, including a new, previously undescribed molecule isolated from the Andean Cock-of-the-Rock Rupicola peruviana, 3′-hydroxy-3-methoxy-β,β-carotene-4-one, which we name rupicolin. The diversity of cotinga plumage carotenoid pigments is hypothesized to be derived via four metabolic pathways from lutein, zeaxanthin, β-cryptoxanthin, and β-carotene. All metabolic transformations within the four pathways can be described by six or seven different enzymatic reactions. Three of these reactions are shared among three precursor pathways and are responsible for eight different metabolically derived carotenoid molecules. The function of cotinga plumage carotenoid diversity was analyzed with reflectance spectrophotometry of plumage patches and a tetrahedral model of avian color visual perception. The evolutionary history of the origin of this diversity is analyzed phylogenetically. The color space analyses document that the evolutionarily derived metabolic modifications of dietary xanthophylls have resulted in the creation of distinctive orange-red and purple visual colors. [ABSTRACT FROM AUTHOR]

Trade-offs in resource allocation have been widely stated as the means by which the honesty of ornamental traits is maintained, but an alternative to this resource trade-off hypothesis is that production of ornamentation is linked to the biochemical efficiency of vital cellular processes. Carotenoids are antioxidants, potentially tying carotenoid-based coloration to the oxidative state of an organism, and some carotenoids are also precursors for vitamin A, which regulates numerous cellular processes. We present a biochemical model for regulation of ornamental coloration based on interdependencies of carotenoid and retinoid biochemistry. We propose that vitamin A regulatory mechanisms, redox systems, and carotenoid pigmentation pathways link carotenoid coloration to oxidative state and to a host of important aspects of performance, such as immune function. The activity of b-carotene ketolase, which catalyzes the oxidation of yellow carotenoids into red carotenoids, is responsive to the states of vitamin A pools and redox systems such that coloration is a direct reflection of the physiological state of an animal. According to the vitamin A-redox hypothesis, feather coloration is associated with a range of performance measures because performance emerges from functionality of the same basic cellular processes that regulate pigmentation. We present the vitamin A-redox hypothesis as a testable alternative hypothesis to the resource trade-off hypothesis for the maintenance of honesty of carotenoid pigmentation. [ABSTRACT FROM AUTHOR]

It is generally assumed that animal energy expenditure is limited by energy acquisition., In a series of publications, Speakman, Król and colleagues argue that the capacity to dissipate metabolic heat may also limit maximum rates of energy expenditure in endotherms (heat dissipation limit theory - HDL theory)., The implications of the HDL theory for the evolution of avian functional traits are substantial and open fascinating research perspectives., Notably, the HDL theory leads us to (i) link elevated bird body temperatures with their capacity to achieve higher rates of heat loss and of energy expenditure, (ii) reconsider the evolution of avian plumage patterns and speculate upon the capacity of white birds to achieve higher field metabolic rates than darker relatives, (iii) hypothesize that the avian brood patch also functions as a thermal window allowing birds to shed excess heat and (iv) revise our current view of the adaptive significance of limited plumage thermal insulation in great cormorants., Such features have important implications for the capacity of birds to cope with global warming and for the design of mechanistic models of animal energetics aiming at predicting their responses to changing environmental conditions. [ABSTRACT FROM AUTHOR]

The presence of sexual differences in plumage coloration (sexual dichromatism) is frequent in birds. However, in many cases, humans cannot detect colour differences that are discernible to birds and it is therefore necessary to employ objective methods that contemplate the characteristics of the avian visual system for the study of plumage coloration. An understudied property of feather coloration is the occurrence of fluorescence, which has been described almost exclusively in parrots from the Eastern Hemisphere using non-objective methods and has been attributed to yellow pigments that are only present in psittacids. In this study, we explore fluorescence and sexual dichromatism through objective and quantitative methods in the plumage of a Neotropical species, the blue-winged parrotlet Forpus xanthopterygius. We measured plumage reflectance and fluorescence emission on museum skins using spectrophotometry and spectrofluorometry, respectively. The reflectance analysis revealed the presence of ultraviolet sexual dichromatism that adds to the differences in the visible range of wavelengths that are detectable by humans. The spectrofluorometric analysis showed that fluorescence is indeed present in this species, both in green plumage patches, where fluorescent pigments are presumably located, and in the blue rump of males, where colour is considered to be purely structurally based. The sexes differed in the intensity and wavelength of their fluorescence emission, representing the first finding of fluorescence sexual dichromatism in birds. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Many animals consume colorful foods, because bright coloration either enhances conspicuousness of food items or signals nutritional rewards. A comparatively under-studied aspect of food color preferences is the role of the background environment in shaping food detectability and choices. Previous work with house finches (Carpodacus mexicanus), for example, showed that individuals preferred red and green food items and avoided yellow ones. However, this study of desert, ground-feeding birds was done with seeds presented against an artificial white background that is unlikely to reflect natural conditions. Therefore, we performed a similar experiment, but quantified selection of colorful foods using a different visual environment that better mimicked natural conditions. We mixed dark, inedible distractor pellets (i.e., analogous to natural desert sand and rocks) with sunflower kernels that were colored red, green, yellow, or orange to test for differences in foraging patterns by sex, age, and expression of male plumage coloration in non-molting house finches. This food presentation resulted in yellow seeds having a significantly greater chromatic, but not achromatic, contrast with the background than red or green seeds. Under these conditions, all birds consumed yellow, and to a lesser extent red, seeds most often, and both adult males and females had a strong preference for yellow kernels; adult males also tended to prefer green kernels, but females tended not to prefer green kernels. Juveniles showed no significant preferences for any seed color, and adult male plumage coloration was not related to seed color preference. Therefore, in contrast to studies using different foraging environments, house finches tended to prefer yellow seeds, supporting models that suggest that visual background and contrast may be more important than color per se in visually mediated foraging decisions of birds. Moreover, the fact that adult males and females differed in food color preference has not been reported previously in songbirds. [ABSTRACT FROM AUTHOR]

The information content of signals such as animal coloration depends on the extent to which variation reflects underlying biological processes. Although animal coloration has received considerable attention, little work has addressed the quantitative genetics of color variation in natural populations. We investigated the quantitative genetics of a carotenoid-based color patch, the ventral plumage of mature great tits (Parus major), in a wild population. Carotenoid-based colors are often suggested to reflect environmental variation in carotenoid availability, but numerous mechanisms could also lead to genetic variation in coloration. Analyses of individuals of known origin showed that, although plumage chromaticity (i.e., color) was moderately heritable, there was no significant heritability to achromaticity (i.e., brightness). We detected multiple long-lasting effects of natal environment, with hatching date and brood size both negatively related to plumage chromaticity at maturity. Our reflectance measures contrasted in their spatiotemporal sensitivity, with plumage chromaticity exhibiting significant spatial variation and achromatic variation exhibiting marked annual variation. Hence, color variation in this species reflects both genetic and environmental influences on different scales. Our analyses demonstrate the context dependence of components of color variation and suggest that color patches may convey multiple aspects of individual state. [ABSTRACT FROM AUTHOR]

The article presents a study on the relation of multiple melanin-based plumage traits of male and female American robins in their mating patterns, individual quality, and breeding performance. The study evaluates the relation of traits including breast plumage, tail-spot size, and damage on American robins' mating patterns. Result shows the relation of birds' breast color and tail-spot damage in assortative social mating. Meanwhile, tail-spot size was not related with social mating patterns.

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. [ABSTRACT FROM PUBLISHER]

The article presents a study which examined the evolutionary changes in the carotenoid-based coloration across the bird species, New World blackbirds (Icteridae). In the study, reflectance spectrometry and ancestral state reconstruction were used to analyze the patterns in the evolution of the red coloration in the bird specie. Based on the results, the red coloration in the bird specie has been gained from a common ancestor that has yellow ornamentation.

When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success in a large colony of American barn swallows ( Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration, are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked. However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males. We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences and sexual selection. [ABSTRACT FROM AUTHOR]

Carotenoids are widely heralded as central to honest signaling due to their dual roles as pigments and antioxidants/immunostimulants. The aim of this study is to test if diet quality and carotenoids alone or in an interaction influence condition, carotenoid availability in plasma and immune responsiveness. Therefore, a diet experiment during the moult of great tits, Parus major, was performed. In a two-way design, we manipulated general quality (digestibility, protein and vitamin content) as well as carotenoid (lutein) content of semi-synthetic diets. Higher quality diet improved individual condition since birds had greater body mass, and to a lesser extent, higher hematocrit. In addition to the expected positive effect of carotenoid supplementation and individual lutein consumption on circulating lutein, there was a positive effect of enhanced diet quality on plasma carotenoid levels. Carotenoid supplementation, but not diet quality, improved the local inflammatory response and maintenance of body mass during a humoral immune reaction. The enhancement of circulating carotenoid levels by improved general quality of the diet or individual condition could provide a testable, mechanistic explanation for the variation in effects of carotenoid supplementation studies. [ABSTRACT FROM AUTHOR]

Eumelanin and pheomelanin are the most common pigments providing color to the integument of vertebrates. While pheomelanogenesis requires high levels of a key intracellular antioxidant (glutathione, GSH), eumelanogenesis is inhibited by GSH. This implies that species that possess the molecular basis to produce large amounts of pheomelanin might be more limited in coping with environmental conditions that generate oxidative stress than species that produce eumelanin. Exposure to ionizing radiation produces free radicals and depletes antioxidant resources. GSH is particularly susceptible to radiation, so that species with large proportions of pheomelanic integument may be limited by the availability of GSH to combat oxidative stress and may thus suffer more from radiation effects. We tested this hypothesis in 97 species of birds censused in areas with varying levels of radioactive contamination around Chernobyl. After controlling for the effects of carotenoid-based color, body mass and similarity among taxa due to common phylogenetic descent, the proportion of pheomelanic plumage was strongly negatively related to the slope estimates of the relationship between abundance and radiation levels, while no effect of eumelanic color proportion was found. This represents the first report of an effect of the expression of melanin-based coloration on the capacity to resist the effects of ionizing radiation. Population declines were also stronger in species that exhibit carotenoid-based coloration and have large body mass. The magnitude of population declines had a relatively high phylogenetic signal, indicating that certain groups of birds, especially non-corvid passeriforms, are particularly susceptible to suffer from the effects of radioactive contamination due to phylogenetic inertia. [ABSTRACT FROM AUTHOR]

Plumage coloration plays an important role in visual communication by signaling aspects of individual quality. It has been proposed that the need for preserving plumage condition and hence signaling content may have promoted a novel signaling mechanism: cosmetic coloration. Here, we investigated whether preen waxes may act as cosmetics by affecting feathers' ornamental coloration in male house finches (Carpodacus mexicanus). We (1) blocked the access to uropygial gland of a group of males and compared their coloration with a control group and (2) applied preen wax extracted from live individuals to museum skins and measured color before and after wax application. We found that red feathers of control males were more colorful than those of experimental males and that applying waxes to museum skins' red feathers increased their color saturation. Our results provide evidence that preen waxes act as cosmetics by enhancing plumage ornamentation, thus revealing the existence of novel mechanisms operating in signaling coloration. Although preen waxes per se would not constitute a signal, selection for signal efficacy might favor individuals that are able to increase signal intensity beyond the optimum necessary for plumage maintenance. Our results support the hypothesis that preen waxes reinforce the honesty of signals, which may be particularly useful in a social context where interactions between individuals are mediated by the intensity of the signals. [ABSTRACT FROM PUBLISHER]

Carotenoid and melanin pigments in the plumage of birds are hypothesized to be sensitive to oxidative stress. We manipulated oxidative status of captive greenfinches (Carduelis chloris L.) by the administration of buthionine sulfoximine (BSO), a selective inhibitor of the synthesis of glutathione (GSH), an intracellular antioxidant. Half of the birds in the treated group, as well as in the control group, also received dietary carotenoid (lutein) supplementation. BSO treatment reduced erythrocyte GSH levels and caused oxidative damage as indicated by the increased concentration of plasma malondialdehyde (MDA), an end product of lipid peroxidation. BSO treatment also reduced the brightness (i.e. increased blackness) of the tips of tail feathers grown during the experiment. These results show that a low systemic GSH level is required for development of eumelanin plumage coloration and that such a low GSH level is also potentially dangerous for the organism. Carotenoid supplementation increased plasma carotenoid levels and chroma of the yellow parts of the feathers grown during the experiment. However, carotenoid supplementation did not reduce plasma MDA levels. Manipulation of GSH did not affect plasma carotenoids or carotenoid-based plumage coloration. These findings argue against the antioxidant function of lutein in vivo and carotenoid signaling of antioxidant status. [ABSTRACT FROM AUTHOR]

A growing body of evidence shows that female birds use male plumage coloration as an important criterion in mate choice. In the field, however, males with brighter coloration may both compete better for high-quality territories and be the object of female choice. Positive associations between territory quality, male–male competitive ability and female preferences can make it difficult to determine whether females actively choose the most ornamented males. Male eastern bluebirds, Sialia sialis, display brilliant ultraviolet (UV)-blue plumage coloration on their heads, backs, wings and tails and chestnut coloration on their breasts, which is positively correlated with condition, reproductive effort and reproductive success. We tested the hypothesis that female bluebirds prefer males that display brighter and more chromatic coloration by experimentally widowing males in the field and allowing replacement females to choose partners. We controlled for the influence of territory quality on female choice by widowing dyads of males with adjacent territories. We found no evidence that UV-blue or chestnut plumage coloration, body size or body condition predicted the male with which a female would pair. We found no support for the hypothesis that the coloration of male eastern bluebirds functions as a criterion in female mate choice. [Copyright &y& Elsevier]

The article presents a study which examines nest-size variation in a Great Tit Parus major population in relation to breeding factors and parental carotenoid-based plumage characteristics. It is observed that sexual signalling via carotenoid-based plumage coloration is known to occur in this species and that it is only the females are the one building nest. The researchers found out that plumage chroma of female and male Great Tits was positively related to nest size, suggesting greater female investment in nest building when mated to males in good condition.

Elaborate secondary sexual traits, such as plumage ornaments, are important signals in reproductive communication and so it is important to maintain them in good condition. Time and energy spent in their maintenance reinforce the honesty of the ornamental traits. Variation in plumage visual properties as a function of maintenance has until now received little attention. Here, we used a combination of spectroradiometric measurements of plumage coloration, a physiological model of bird vision and behavioural observations to investigate how grooming behaviours affect plumage coloration in experimentally soiled male domestic canaries. Although showing a similar total amount of grooming, dirty males showed more feather ruffling and less preening than control males, suggesting that removal of dirt does not require an increase in grooming activity and that ruffling is likely to be more efficient for removing dirt. Grooming activities were not correlated with changes in plumage reflectance, probably because the same grooming behaviour is more efficient at removing feather dirt when performed by some individuals than by others. Dirty males were distinguishable in coloration up to 2.5h after soiling. Shoulders and throat were the dirtiest of all body parts and took males more time to clean. Taken together, these results suggest that females are able to assess visually the difference between potential partners differing in their soiling level. If grooming activity is costly, females could base their choice on the coloration of plumage areas more susceptible to soiling and difficult to clean. [Copyright &y& Elsevier]

The article focuses on a study which examined the whole chemical pathway of carotenoids in a bid to understand its role as mediators of trade-offs in avian ecology. Data were gathered from matured leaves of birch and oak trees during a time when leaf eating caterpillars are abundant. High performance liquid chromatography (HPLC) was used to analyse these leaves. Particular focus is given to vegetation cover in Great Tit populations. Results of the study showed that leaves collected from urban areas had significantly lower total carotenoid concentration than rural leaves. In addition, lower absolute concentration of lutein was seen in urban leaves. The study also found that there was more cover in Great Tit populations in urban areas.

Animals may assess the quality of other individuals by using information that different ornaments may provide. The European Roller ( Coracias garrulus) is a socially monogamous species in which males and females display highly conspicuous plumage colouration. According to the mutual selection hypothesis, we predicted that, in this species, plumage coloration could signal individual quality in both sexes because both female and male rollers invest a considerable amount of time caring for their offspring. We used spectrophotometric measurements to investigate the information content of multiple plumage colour traits. We found that the roller is actually a sexually dimorphic and dichromatic species. Different plumage colours from different origins were correlated within individual. Head and back brightness correlated with body condition in both sexes, and in males, head brightness correlated with the number of fledglings in successful nests, while head green-yellow saturation correlated with parental provisioning. Meanwhile, in females, back brightness was related to the number of fledglings in successful nests and to parental provisioning rate. In addition, there was a positive assortative mating in relation to weight, body condition, head green-yellow saturation and back brightness. Finally, we found a positive correlation between parent and offspring coloration. Altogether, these results suggest that multiple colour traits may act as quality indicators in the roller and that they may be used by the two sexes to assess potential mate quality. [ABSTRACT FROM AUTHOR]

Carotenoid-based plumage coloration has been shown to be dependent both on pigment content and feather structure. Against this background, we predict a relationship between feather pigment content and plumage hue. Furthermore, given the susceptibility of chroma to developmental perturbation of feather structure, we predict body condition to be related to chroma. We tested these predictions in the great tit, Parus major. Carotenoid content in yellow breast feathers was analysed by high-performance liquid chromatography (HPLC). Lutein was the main carotenoid contained in great tit feathers, followed by zeaxanthin. The hue of the feathers was accurately predicted from their lutein concentration, and chroma was predicted from the body condition value. Our data suggest that plumage coloration in the great tit could independently provide information on the ability of the signaller to collect carotenoids (via hue) and body condition (via chroma). Published results both from the great tit and other species support this view. [ABSTRACT FROM AUTHOR]

Many birds undergo seasonal changes in plumage coloration by prebreeding moult, abrasion of cryptic feather tips, or both. Seasonal dichromatism is thought to result from optimizing coloration to the conflicting demands of different life-cycle periods, sexual selection for conspicuousness being substantial during the mating season, whereas selection for camouflage and for social signals may act in all seasons. Furthermore, energetic and time demands may constrain the extent of moult, thereby limiting colour change. We investigated the relative importance of several factors in shaping this variation in a songbird clade using phylogenetic comparative methods. We found that prebreeding moult relates most strongly to breeding onset and winter diet, demonstrating that both time and food availability constrain feather replacement. Feather abrasion was best predicted by winter flocking behaviour, and secondarily by open habitats, implying that exposure to predators and the simultaneous need for social signalling may favour the expression of partially obscured ornaments in the non-breeding season. The combined occurrence of prebreeding moult and feather abrasion was associated with the polygynous mating system, suggesting that species under strong sexual selection may employ both strategies of colour change to ensure the full expression of breeding coloration. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 711–721. [ABSTRACT FROM AUTHOR]

Abstract: Red hues are a challenge in studies on the evolution of bird coloration, as multiple pigments such as carotenoids, pheomelanin, psittacofulvins, porphyrins, turacin, haemoglobin and even exogenous iron-oxides, may confer red colors. Determining the pigment type is paramount and here we investigate the differences in spectrum reflectance for six pigments resulting in red colorations in feathers of different species, with a focus on discriminating among melanins and carotenoids. Pigment chemical identification was obtained from the literature or using High Performance Liquid Chromatography (HPLC) in our laboratory. We have also derived discriminant formulas for identification of the major known types of pigments based on parameters of the reflectance curves obtained with a portable spectrometer. Our results indicate that the reflectance patterns of coloration perceived as red patches widely differ. The distinction between carotenoid- and melanin-based reflectance curves is relatively straightforward: sigmoid versus straight slope. The spectral reflectance curves of feathers containing red psittacofulvins are sigmoid, whereas iron oxide and porphyrin-containing feathers recall pheomelanins in rendering a straight slope. In the case of turacin-based coloration, the spectral shape is unique. For the pigments with enough number of species sampled (i.e., carotenoids, melanins and psittacofulvins) the differences in reflectance shape are important enough to allow separation of carotenoid and melanin derived colorations based on reflectance curves alone. [Copyright &y& Elsevier]

Only during the past decade have vision-system-neutral methods become common practice in studies of animal color signals. Consequently, much of the current knowledge on sexual selection is based directly or indirectly on human vision, which may or may not emphasize spectral information in a signal differently from the intended receiver. In an attempt to quantify this discrepancy, we used retinal models to test whether human and bird vision rank plumage colors similarly. Of 67 species, human and bird models disagreed in 26 as to which pair of patches in the plumage provides the strongest color contrast or which male in a random pair is the more colorful. These results were only partly attributable to human UV blindness. Despite confirming a strong correlation between avian and human color discrimination, we conclude that a significant proportion of the information in avian visual signals may be lost in translation. [ABSTRACT FROM AUTHOR]

Males of many species can breed in distinct alternative phenotypes; for example, in many birds some males breed in dull plumage while others breed in bright plumage. Because females often appear to prefer brighter males, it is unclear why some males breed in dull plumage. Males in dull plumage might enjoy enhanced within-pair reproductive success if they can gain access to better breeding territories, or they might have relatively high extrapair reproductive success if they are better able to intrude on the territories of other males. To test these possibilities, we examined the reproductive consequences of plumage color in the red-backed fairy-wren (Malurus melanocephalus), a species in which males can breed in either bright plumage or dull plumage or serve as nonbreeding auxiliaries. Male plumage color was distributed bimodally and was loosely associated with age, such that some males molted into bright plumage a year or more earlier than others. Both male phenotypes were cuckolded at similar rates, but bright males sired significantly more extrapair young than did dull males, and this effect was independent of age. Thus, 1-year-old males who bred in dull plumage had low seasonal reproductive success compared with same-aged males who bred in bright plumage. These results suggest that males may not reap any fitness benefits by breeding in dull coloration, compared with breeding in bright plumage, but rather may be constrained to breed in suboptimal plumage by the timing of plumage acquisition. [ABSTRACT FROM PUBLISHER]

The occurrence of multiple phenotypes within a sex of a single species has long puzzled behavioral ecologists. Male red-backed fairy-wrens Malurus melanocephalus exhibit 3 behaviorally distinct types in their first breeding season: breed in bright nuptial plumage, breed in dull plumage, or remain as an unpaired auxiliary (helper) with dull plumage. The retention of dull plumage by auxiliaries and dull breeders is an example of delayed plumage maturation (DPM), a widespread phenomenon in birds whose costs and benefits are not well understood. At a mechanistic level, DPM might allow dull males either to deceptively mimic females (female mimicry hypothesis) or to honestly signal their subordinate status (status-signaling hypothesis). DPM might function via either mechanism to provide ultimate benefits relative to developing nuptial plumage by increasing reproductive success, survival, or both. In this study, we tested the hypothesis that DPM is related to increased male survival in the red-backed fairy-wren via either female mimicry or status signaling. Aviary-based experiments revealed that dull males were perceived as male, which is consistent with the status-signaling hypothesis but contradicts the female mimicry hypothesis. Further aviary and field-based experiments also revealed that dull males were socially subordinate to bright males and received less aggression than bright males, further evidence for status signaling. However, male survival was not related to plumage coloration or breeding status. These findings indicate that male plumage coloration signals social status but that dull plumage does not afford a net survival advantage, perhaps because plumage color is a conditional strategy. [ABSTRACT FROM PUBLISHER]

In many birds, carotenoids have dual functions as irreversible plumage pigments and as physiologically essential vitamins and antioxidants. They must be obtained through the diet and may therefore be a limiting resource, a constraint that is likely to vary with factors such as sex, habitat, and time of year. In the present study, we investigated signs of carotenoid limitation in great tits, Parus major, in relation to sex, season, year, and within an urban versus a rural habitat. The two main carotenoids, lutein and zeaxanthin, were analysed by high-performance liquid chromatography in the plasma and in the yellow carotenoid-based breast feathers. We found that plasma carotenoid concentrations were significantly influenced by sex, season, and year, but not by urban versus rural habitat. At moult, plasma concentration was positively correlated with feather pigmentation, independent of body condition and sex. During the breeding season, however, circulating carotenoid concentrations were negatively related to the feather pigmentation (i.e. from previous autumn moult). We suggest that great tits are carotenoid deprived before leaf emergence, and that carotenoid utilization and limitations are sex-specific, but that there are neither any obvious honesty-maintaining costs of pigmentation, nor any fitness consequences of the colour variation. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92, 521–527. [ABSTRACT FROM AUTHOR]

Status signals are traits that advertise an individual’s competitive abilities to conspecifics during aggressive disputes. Most studies of status signals in birds have focussed on melanin-based plumage signals, but recent research shows that carotenoid-based signals may also play a role in aggressive signaling. We assessed the relative importance of melanin- and carotenoid-based plumage patches as agonistic signals in a small passerine, the golden whistler ( Pachycephala pectoralis). Display signals in male golden whistlers include an unpigmented white throat patch, a carotenoid-based yellow breast and nape band, and a melanin-based black chin-stripe. We found that only the white throat patch was correlated with contest-related attributes. Males possessing large throat patches defended larger territories and commenced breeding earlier. When caged males with either experimentally reduced, or unmanipulated throat patches were presented to conspecifics, those with experimentally reduced patches attracted less aggression from male subjects. Focal males also responded faster to caged males with throat patches similar in size to their own, suggesting that they may assess relative throat patch size before engaging in aggressive encounters. Females did not discriminate between “reduced” or “control” treatments. Our data strongly suggest that only the unpigmented throat patch functions as a status signal. As this signal is unlikely to have significant development costs, honesty may be maintained through social costs. [ABSTRACT FROM AUTHOR]

The Blue-tailed Bee-eater (Merops philippinus) is a cooperatively breeding and socially monogamous member of the Coraciiformes that displays conspicuous coloration and elongated central rectrices ("streamers"). Humans cannot distinguish males from females; both sexes are brightly colored with a chestnut throat patch, a yellow chin, and green body coloration fading into a turquoise-blue rump and tail. We quantified coloration with ultraviolet- (UV) visible spectrometry and measured morphology to determine the extent of sexual dichromatism and dimorphism. Males displayed more exaggerated coloration, longer tail streamers, and were larger than females. Multiple plumage ornaments (measures of plumage coloration an!i streamer length) were positively correlated in both sexes. Males in better body condition expressed darker chestnut throats and more chromatic green body plumage. Females in better body condition, however, exhibited more chromatic blue rumps and yellow chins. This study represents the first objective description of plumage ornamentation in the order Coraciiformes. [ABSTRACT FROM AUTHOR]

Sexual dimorphism, mating system, and parental care are known for only a few species of the large passerine family Furnariidae. We conducted a study of sexual dimorphism in morphology, coloration, and parental roles during incubation and chick-rearing in the Thorn-tailed Rayadito (Aphrastura spinicauda), a characteristic resident ovenbird of the southern temperate rainforests of Chile and Argentina. Through molecular sexing, morphological measurements, and spectrophotometric analysis of body plumage and rectrices of reproductive adults captured on Chitoé Island (southern Chile), we determined that males were between 2% and 10% larger than females in mass, tarsus length, and wing length, while no difference was found for the length of the bill or the two longest central rectrices and their characteristic spines, or in plumage coloration. Heavy males were paired with heavy females and light males with light females. Males and females participated equally in all reproductive activities during the incubation and nestling phases, except removal of nestling feces, in which females were twice as active as males. In a study of habitat use on Navarino Island (extreme southern Chile) we found that the extended graduated tail, with rectrices that end in spines, which gives the species its name, was not used as a support while foraging and could be related to another function such as sexual or social signaling. The absence of sexual dimorphism in plumage and parental roles in rayaditos may be related to the use of the long, graduated tail as a signal of quality by both sexes, although this hypothesis requires confirmation through future mate choice studies. [ABSTRACT FROM AUTHOR]

Although the evolution of genetic color polymorphisms has received much theoretical interest, few empirical studies have investigated the adaptive function of alternative color morphs. Furthermore, most studies have focused almost exclusively on the evolution and adaptive expression of male coloration, leaving the role of conspicuous female coloration largely unknown. Using the color polymorphic Gouldian finch (Erythrura gouldiae), this study experimentally tests the status signaling function of head color (red, yellow, and black) among the 3 female color morphs. In standardized dominance contests between unfamiliar females of different head colors, red-headed females dominated both black- and yellow-headed females. During contests between the morphs, red-headed females passively displaced black- and yellow-headed opponents, whereas interactions between red-headed dyads were particularly aggressive and more frequent than interactions within dyads of the other color morphs. This effect of red dominance further persisted when head color was experimentally altered; red-manipulated females (of the other morphs) dominated both black- and yellow-headed females, whereas blackened red-headed females were dominated by naturally red-headed birds. Together with similar dominance-related differences among male morphs, these results suggest that the 3 color morphs may display alternative strategies in dominance behavior. [ABSTRACT FROM PUBLISHER]

Several experimental studies have shown that female birds use ornamental melanin and carotenoid plumage coloration as criteria in mate choice. Whether females choose mates based on natural variation in structural coloration, however, has not been well established. Male eastern bluebirds ( Sialia sialis) display brilliant ultraviolet (UV)-blue plumage coloration on their head, back, wings, and tail, which is positively correlated with condition, reproductive effort, and reproductive success. We experimentally tested the hypothesis that female eastern bluebirds prefer as mates males that display brighter structural coloration by presenting breeding-condition females with males of variable coloration. We conducted two types of mate-choice experiments. First, females chose between males whose coloration was manipulated within the natural range of variation in the population; feathers were either brightened with violet marker or dulled with black marker. Second, females chose between males with naturally dull or bright plumage coloration. In both manipulated and unmanipulated coloration trials, female choice did not differ significantly from random with respect to structural coloration. We found no support for the hypothesis that the UV–blue coloration of male eastern bluebirds functions as a criterion in female mate choice. [ABSTRACT FROM AUTHOR]

Lek-mating Long-tailed Manakins (Chiroxiphia linearis) exhibit an unusual pattern of delayed plumage maturation. Each year, males progress through a series of predefinitive plumages before attaining definitive plumage in their fifth calendar year. Females also exhibit variation in plumage coloration, with some females displaying male-like plumage characteristics. Using data from mist-net captures in northwest Costa Rica (n = 1,315) and museum specimens from throughout the range of Long-tailed Manakins (n = 585), we documented the plumage sequence progression of males, explored variation in female plumage, and described the timing of molt in this species. Males progressed through a series of age-specific predefinitive plumages, which enabled the accurate aging of predefinitive-plumaged males in the field; this predefinitive plumage sequence is the basis for age-related status-signaling in these males. Females tended to acquire red coloration in the crown as they aged. However, colorful plumage in females may be a byproduct of selection on bright male plumage. Females exhibited an early peak of molt activity from February to April, little molt from May through July, and a second, more pronounced peak of molt activity in October. By contrast, males in older predefinitive-plumage stages and males in definitive plumage exhibited comparable unimodal distributions in molt activity beginning in June and peaking between July and October. Our data are consistent with selective pressure to avoid the costs of molt-breeding overlap in females and older males. Our findings have important implications for social organization and signaling in Long-tailed Manakins, and for the evolution of delayed plumage maturation in birds. [ABSTRACT FROM AUTHOR]