Plumage Brightness Research Articles

Age‐related differences in plumage characteristics of male tree swallows Tachycineta bicolor: hue and brightness signal different aspects of individual quality

Age‐related differences in plumage characteristics of birds can be the result of differential survival of more ornamented individuals, within‐individual changes in plumage attributes with age, or a combination of both. In this study, we investigated age‐class related differences in plumage attributes of male tree swallows Tachycineta bicolor by performing both cross‐sectional and longitudinal analyses. Male tree swallows in their first breeding season do not display delayed plumage maturation, and possess, like experienced breeders, metallic green to metallic blue iridescent plumage on their dorsal surface. Our results showed that, at the population level, older males were brighter and reflected light maximally at shorter wavelengths (i.e. were more blue). Differences in plumage brightness were most likely caused by changes within individuals as males increased in brightness between the first time they were captured and the subsequent year. Differences in hue, however, were not due to within‐individual changes, but rather appear to be the result of greener individuals having lower survival and/or nest site fidelity. Indeed, relatively dull, greener birds had a lower probability of being recaptured the subsequent year. In contrast, we found that if birds captured in their first year as breeding adults were relatively bright, hue was not related to the probability of recapture. These results suggest that plumage attributes in male tree swallows have the potential of being honest signals of quality. Furthermore, plumage brightness and plumage hue might signal different aspects of male quality in this species.

Ultraviolet reflectance and female mating preferences in the common kestrel (Falco tinnunculus)

Previous studies revealed the importance of plumage brightness (considering only the visible spectral range) in female mate choice of common kestrels ( Falco tinnunculus L., 1758). Our study focuses on the effect of UV reflectance on female preference; we hypothesize that common kestrel females prefer males with UV-reflecting plumage and refuse, or are not attracted to, males whose plumage UV reflectance is prevented. We tested the preference of 20 captive females who were given a choice between two males, one behind a UV-transmitting (UV+) filter and another one behind a UV-blocking (UV–) filter. Female preference was measured as frequency and duration of visits to either male, specifically by sitting on the perch or hanging on to the partition wall. Females visited the male behind the UV+ filter more often than the male behind the UV– filter, indicating that females prefer males with UV-reflecting plumage than males without UV reflection. UV plumage and skin reflectance could provide females with information regarding current male conditions more so than other colours and other morphological parameters.

Plumage characteristics, reproductive investment and assortative mating in tree swallows Tachycineta bicolor

Elaborate ornamental plumage has been associated with various measures of individual quality in many species of birds. Male plumage characteristics, which have been relatively well studied, have been shown to reflect past reproductive investment, as well as the potential for reproductive investment in the current breeding attempt. In contrast, the signalling functions of female traits remain largely unexplored. In this study, we investigated the relationship between plumage attributes of breeding adult tree swallows and past reproductive investment, current reproductive investment and social mate pairing strategy. Both males and older females possess metallic green to metallic blue iridescent plumage on their dorsal surface, making this a suitable species for this type of investigation. We did not find any effects of past reproductive investment and success on the plumage attributes of returning breeders. In contrast, female plumage hue covaried with fledging success, and female plumage brightness was positively associated with mean clutch egg mass. In addition, we found that social pairs mated assortatively with respect to plumage brightness. We argue that since plumage characteristics vary with age in both male and female tree swallows, plumage attributes in this species are indicative of breeding experience and may be honest signals of quality. Positive assortative pairing could be the result of mutual mate choice or intra-sexual competition for nest sites by both males and females.

Female and male plumage brightness correlate with nesting failure in azure-winged magpies Cyanopica cyanus

Animals may assess the quality of other individuals by using information that is contained in elaborate traits. We investigated the degree of sexual dimorphism in structural blue plumage coloration and the potential signal value of these traits in the azure-winged magpie Cyanopica cyanus. We predicted that in this species blue coloration should signal individual quality in both sexes since both females and males invest significantly in caring for offspring. Males have more saturated UV/blue coloration than females and blueness decreased from moulting to reproduction. Males and females did not mate assortatively for blue coloration although they did in relation to body size and condition. Blue colour did not correlate with adult body size or condition. However, nest predation decreased with female and male brightness. Our results suggest that blue coloration may potentially be used to assess parental qualities by potential mates in both sexes of the azure-winged magpie.

Plumage color and reproduction in the red-backed fairy-wren: Why be a dull breeder?

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.

Changes in breeding status are associated with rapid bill darkening in male red‐backed fairy‐wrens Malurus melanocephalus

In many animals, an individual's social environment and status can change quickly and unpredictably, suggesting an advantage for signals capable of responding to these changes. However, many signaling traits are fixed for relatively long periods. In birds, for example, most plumage‐based signals are constrained by molt and unable to respond to sudden changes in social environment. Soft parts, conversely, are vascularized and may provide an alternative signaling system that can be updated relatively quickly. In this study, the effects of changes in breeding status are documented for a putative plumage‐based signal, plumage brightness, and a putative soft part signal, bill darkness, in the red‐backed fairy‐wren Malurus melanocephalus. Males that switched from unpaired helper to paired breeder within a breeding season developed significantly darker bills within three weeks of the switch relative to males that did not change status. There was no clear corresponding change in plumage brightness, though the data suggests that changes in plumage brightness are at least possible. These results suggest that bill color is a socially mediated trait capable of responding rapidly to changes in breeding status, and it is proposed that the importance of soft parts as labile signals in birds may be currently under‐appreciated.

Plumage brightness and age predict extrapair fertilization success of male tree swallows, Tachycineta bicolor

In socially monogamous passerines, extrapair paternity can increase the variance in male reproductive success. If gaining extrapair fertilizations is linked to specific secondary sexual ornaments, the opportunity for sexual selection is enhanced. Therefore, to understand the evolution of male phenotypic characteristics, it is important to identify traits that predict male extrapair mating success. Tree swallows show among the highest rates of extrapair paternity known to occur in birds, yet it is unclear whether male extrapair mating success is associated with phenotypic traits that honestly advertise individual quality. We compared morphological characteristics and plumage coloration of male tree swallows that sired extrapair offspring with those that sired only within-pair offspring in the same breeding population to identify the characteristics that predict extrapair fertilization success. Males who produced extrapair offspring had brighter plumage, and were more likely to be returning breeders, than males that did not have extrapair young. In paired comparisons, however, there was no difference between extrapair males and the male they cuckolded. These results suggest that female tree swallows may prefer brighter or older individuals as extrapair mates, but also, that older males may invest more energy in pursuing extrapair copulations. Furthermore, since females had extrapair offspring in their nest regardless of their social mate's morphometric or plumage attributes, we suggest that extrapair mating may be a reproductive strategy allowing females to increase the genetic diversity, while maintaining genetic quality, of their offspring.

Serins with intermediate brightness have a higher survival in the wild

More ornamented individuals are supposed to signal their superior quality and health, however the development of larger ornaments or brighter plumages can affect their survival probabilities. The survival of male serins Serinus serinus in relation to the color characteristics of carotenoid-derived breast coloration was analyzed in a six-year capture–recapture study in northeastern Spain. A total of 210 males were individually marked generating 340 captures, between 1997 and 2003. The model with the best fit indicated a quadratic relationship between brightness of carotenoid-derived coloration and survival, independent of time and age of the birds, so that individuals with intermediate plumage brightness survived longer. Hence, results stress that plumage color in male serins is under stabilizing natural selection, with reduced survival both in drabber and brighter individuals. While lower condition of drabber individuals can explain their lower survival, brighter birds can suffer more from predation risk or from a higher investment of resources into mate attraction and/or reproduction.

Serins with intermediate brightness have a higher survival in the wild

More ornamented individuals are supposed to signal their superior quality and health, however the development of larger ornaments or brighter plumages can affect their survival probabilities. The survival of male serins Serinus serinus in relation to the color characteristics of carotenoid‐derived breast coloration was analyzed in a six‐year capture–recapture study in northeastern Spain. A total of 210 males were individually marked generating 340 captures, between 1997 and 2003. The model with the best fit indicated a quadratic relationship between brightness of carotenoid‐derived coloration and survival, independent of time and age of the birds, so that individuals with intermediate plumage brightness survived longer. Hence, results stress that plumage color in male serins is under stabilizing natural selection, with reduced survival both in drabber and brighter individuals. While lower condition of drabber individuals can explain their lower survival, brighter birds can suffer more from predation risk or from a higher investment of resources into mate attraction and/or reproduction.

Maternal immune factors and the evolution of secondary sexual characters

Secondary sexual characters have been hypothesized to reveal the ability of males to resist debilitating parasites. Although such reliable signaling of parasite resistance may be maintained by parasite-host coevolution, maternal effects potentially provide a previously neglected factor that could affect the level of genetic variation in resistance to parasites. That could be the case because maternal effects have an entirely environmental basis, or because they can maintain considerable amounts of genetic variation through epistatic effects, even in the presence of strong directional selection. Maternal effects have been shown to occur as maternal allocation of immune factors to offspring, and such allocation may depend on the mating prospects of sons, causing mothers to differentially allocate maternal effects to eggs in species subject to intense sexual selection. Here we show that a maternal effect through innate antibacterial immune defense, lysozyme, which is transferred from the mother to the egg in birds, is positively associated with the evolution of secondary sexual characters. Previous studies have shown that females differentially allocate lysozyme to their eggs when mated to attractive males, and elevated levels of lysozyme are associated with reduced hatching failure and superior health among neonates and adults. In this study, comparative analyses of lysozyme from eggs of 85 species of birds showed a strong positive relationship between brightness of male plumage and egg lysozyme, even when controlling for potentially confounding variables. These findings suggest that maternal immune factors may play a role in the evolution of secondary sexual characters.

Feeding innovations and parasitism in birds

The rate of behavioural innovation, such as opportunistic feeding innovation, may facilitate adaptation to novel environments. Because parasites may affect how their hosts adopt novel means of resource acquisition, or because opportunistic behaviours may involve the risk of being exposed to a large parasite fauna, we hypothesize an evolutionary link between the rate of feeding innovations and parasitism. We investigated the phylogenetic relationship between relative frequency of feeding innovations (adjusted for research effort and population size) and relative size of immune defense organs (as a relative measure of parasite-mediated selection) and the prevalence of blood parasites in birds. Using generalized least squares models, we found that species with relatively large bursa of Fabricius, thymus, and spleen had higher rates of feeding innovations than species with small immune defense organs. Similarly, there was a positive interspecific association between feeding innovation and haematozoa prevalence. These relationships were not confounded by migration, relative brain size, geographical distribution, and male plumage brightness. Analyses of causality relying on evolutionary modelling of discrete variables and path analysis suggest that increasing rate of feeding innovation may place species under intense selection due to parasitism. Therefore, behavioural adaptation by feeding innovation seems to have consequences for the coevolutionary arm race between parasites and hosts. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 441–455.

An experimental test of female choice relative to male structural coloration in eastern bluebirds

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 estab- lished. Male eastern bluebirds (Sialia sialis )d isplay brilliant ultraviolet (UV)-blue plumage coloration on their head, back, wings, and tail, which is positively correlated with condition, reproductive effort, and reproductive suc- cess. 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.

Carotenoid-based breast plumage colour, body condition and clutch size in red fodies (Foudia madagascariensis)

Carotenoid-based feather colouration is a classic example of a condition-dependent ornamental trait. In some species of birds, red, orange and yellow feather colouration reflects male quality and advertises the carotenoid concentration of feathers. Such colouration is an important aspect of mate selection by females. The red fody (Foudia madagascariensis) is a highly sexually dimorphic species of the family Ploceidae, in which males exhibit extensive carotenoid-based plumage. We investigated associations between body condition, clutch size, first egg date and carotenoid-based red plumage colour of male red fodies. Breast plumage brightness was positively associated with male body condition, suggesting that this component of colour is condition-dependent. Brighter-red males did not breed earlier but were mated to females that laid larger clutches compared to females mated to duller-coloured males. These data suggest that red colour in red fodies has the potential to function as an honest signal of male quality.

Feather mite abundance increases with uropygial gland size and plumage yellowness in Great Tits Parus major

Plumicolous feather mites are ectosymbiotic organisms that live on bird feathers. Despite their abundance and prevalence among birds, the ecology of the interaction between these organisms and their hosts is poorly known. As feather mites feed on oil that birds spread from their uropygial gland, it has been hypothesized, but never tested, that the number of feather mites increases with the size of the uropygial gland of their hosts. In this study the number of feather mites is considered with respect to uropygial gland size in a breeding population of Great Tits Parus major in order to test this hypothesis. As predicted, the number of feather mites correlated positively with the uropygial gland size of their hosts, showing for the first time that uropygial gland size can explain the variance in feather mite load among conspecifics. Previous studies relating feather mite load to plumage colour have suggested that feather mites may be parasitic or neutral. To confirm this, the yellowness of breast feathers was also assessed. However, the results ran in the opposite direction to that expected, showing a positive correlation between mite load and plumage yellowness, which suggests that further work is needed to give clear evidence for a specific nature of feather mites. However, Great Tits with higher mite loads had lower hatching and breeding success, which may support the idea that feather mites are parasites, although this effect must be taken with caution because it was only found in males. Age or sex effects were not found on the number of feather mites, and it is proposed that hormonal levels may not be sufficient to explain the variation in feather mite loads. Interestingly, a positive correlation was detected between uropygial gland size and plumage brightness, which could be a novel factor to take into account in studies of plumage colour.

Predation by sparrowhawks Accipiter nisus on male and female pied flycatchers Ficedula hypoleuca in relation to their breeding behaviour and foraging

Bright plumage, song display, and aggressive resource defence in males may cause higher predation on males than on females during the breeding season. However, in birds, higher predation on females is sometimes observed. Parental investment may be high in females (egg-laying, incubation and feeding of offspring), which might lead to a high risk of predation. We studied predation by sparrowhawks Accipiter nisus in relation to behaviour in pied flycatchers Ficedula hypoleuca where breeding males are more conspicuous than females in plumage and behaviour. Male pied flycatchers generally occupied more exposed perches than females. Females were more mobile and foraged more than males, especially prior to and during incubation. During the incubation and nestling stages, when predation on the sexes could be directly compared, sparrowhawks took about the same number of male and female pied flycatchers. During incubation, however, females spent about 77% of the day in the nest and were 4.7 times more vulnerable than males per unit of time available (i.e. outside the nest). A comparison with the chaffinch Fringilla coelebs, where hawks took more females than males, indicates that timing of breeding, foraging behaviour and parental roles of males and females affect predation risk.

Melanin-Based Black Plumage Coloration is Related to Reproductive Investment in Cardueline Finches

AbstractAvian color ornaments produced by different mechanisms (i.e., melanin, carotenoid, and structural colors) can communicate different sets of information due to differences in their condition or developmental constraints. Although this suggests that different color signals should be analyzed separately, few comparative studies have focused on specific types of coloration. In cardueline finches, interspecific variation in overall plumage brightness (which integrates all types of coloration) was previously shown to be affected by sexual selection and to covary with fecundity and parental care. Using a phylogenetic comparative approach, we extended this line of research and tested whether a specific component of plumage ornamentation, the melanin-based black frontal coloration of finches, showed a similar association with reproductive effort. We found that the extent of male melanization and melanin dichromatism increased in species with reduced clutch sizes, whereas female melanization was negatively correlated with incubation length. These results remained significant when we controlled for the effects of several ecological variables, and were also consistent between two alternative multivariate model-selection approaches. Our results are consistent with the hypothesis that interspecific variation in melanization may be related to fecundity and parental care through trade-offs between investment in sexual signals and parental efforts.

Plumage brightness predicts male mating success in the lekking golden-collared manakin, Manacus vitellinus

The evolution of colorful plumage has been dramatic in lekking species. Several studies show that the size of colorful traits influence female choice in leks; however, relatively little is known about the specific function of color, in particular its spectral properties, in lekking taxa. To determine the importance of color in a lekking species, we monitored the mating success of male golden-collared manakins, Manacus vitellinus, and related this to spectral measures of their colorful plumage, as well as other morphological and behavioral traits shown to be important in other lekking species. We found that lek centrality, male body size, and plumage brightness were associated with male mating success. Only plumage brightness, however, entered a multiple regression model, indicating that plumage is the overall best predictor of mating success. These results provide evidence that the spectral properties of colorful plumage predict male mating success in a lekking species and provide important insight into why many lekking birds are dichromatic and elaborate in coloration. Copyright 2006.

How feather colour reflects its melanin content

Summary Melanin coloration is the most common type of colour in animals. Many species use melanin‐based black, brown, grey or earth‐toned colours as intraspecific signals of quality. Melanin comes in two main forms in vertebrates – eumelanin and phaeomelanin – and these are said to create different colours, with eumelanin giving a darker black, brown or grey appearance and phaeomelanin a lighter reddish or buff hue. However, the few studies that have examined the melanin content of animal colours, namely from bird feathers, have shown that both phaeomelanin and eumelanin are present in nearly all melanized patches. These pigment types also have different synthetic origins and may be differentially costly to display. Thus, to fully understand the costs and benefits of melanic colours, we must first quantitatively determine the relationship between pigment composition and colour characteristics. We studied melanin content and colour variation in the ventral chestnut‐coloured plumage of male and female Barn Swallows (Hirundo rustica erythrogaster) from North America. Total melanin concentration explained significant variation in the hue, saturation and brightness of male breast plumage and female breast plumage. Eumelanin is the predominant type in these feathers, constituting over 75% of total melanins. Eumelanin and phaeomelanin concentration were significantly positively correlated in the feathers of females but not males. In both sexes, levels of both eumelanin and phaeomelanin concentrations were significantly and positively correlated with hue, saturation and brightness. In males but not females, however, the ratio of eumelanin‐to‐phaeomelanin was also an important predictor of colour, with smaller ratios conferring browner hues. Males also deposit more phaeomelanins, but not eumelanins or total melanins, in breast feathers than do females. These results suggest that phaeomelanin plays a unique role in the colouring strategy of male Barn Swallows.

Male eastern bluebirds trade future ornamentation for current reproductive investment

Life-history theory proposes that organisms must trade-off investment in current and future reproduction. Production of ornamental display is an important component of reproductive effort that has rarely been considered in tests of allocation trade-offs. Male eastern bluebirds (Sialia sialis) display brilliant ultraviolet-blue plumage that is correlated with mate acquisition and male competitive ability. To investigate trade-offs between current reproductive effort and the future expression of a sexually selected ornament, we manipulated the parental effort of males by changing their brood sizes. We found that parents provisioned experimentally enlarged broods more often than reduced broods. As predicted by life-history theory, the change in parental effort had a significant effect on the relative plumage ornamentation of males in the subsequent year: males with reduced broods significantly increased in plumage brightness. Moreover, this change in plumage coloration had a direct effect on the timing of breeding in the following season: males that displayed brighter plumage in the year following the manipulation mated with females that initiated egg laying earlier in the season. These data indicate that male bluebirds must trade-off conserving energy for production of future ornamentation versus expending energy for current reproduction.

COMMUNITY RELATIONSHIPS OF AVIAN MALARIA PARASITES IN SOUTHERN MISSOURI

We studied the organization and temporal stability of an assemblage of malaria parasites (generaPlasmodiumandHaemoproteus) and their passerine avian hosts in a forested study area in southern Missouri, USA, over four years. We detected parasite infections by polymerase chain reaction (PCR) of parasite DNA from host blood samples and identified parasite lineages by sequencing a part of the mitochondrial cytochromebgene. We obtained 757 blood samples from 42 host species. Prevalence of malaria parasitism judged by PCR averaged 38.6% and varied in parallel in the three most abundant host species over the four years of the study. Parasite prevalence bore a U‐shaped relationship to host sample size. Prevalence was weakly positively associated with host body mass, but not with foraging stratum, nest height, nest type, plumage brightness, or sexual dichromatism. Over the sample as a whole, parasite prevalence did not vary between males and females or between hatch‐year and older individuals.We differentiated 34 parasite lineages. The number of host species per lineage varied from one to eight and increased with sample size. We recovered up to 14 lineages of parasite from a single host. Three relatively common lineages in the Ozarks were found nowhere else; four others were recovered from other sites in eastern North America; and six additional well‐sampled lineages were distributed in the Greater Antilles among resident island host species. Parasites that are endemic among native species of hosts on the tropical wintering grounds of Ozark birds were recovered from hatch‐year birds in the Ozarks, indicating that transmission takes place on the summer breeding grounds, and consequently, that suitable vectors are present in both the temperate and tropical portions of the parasite lineage distributions.We estimate that the number of parasite lineages within a local area will approximate the number of host species and that our perception of host breadth and parasite diversity will increase for most lineages and hosts with increased sampling. Thus, host–parasite relationships in a local area, including the role of parasites in sexual selection and the evolutionary maintenance of sex, are likely to be complex, with population and evolutionary dynamics involving many actors.