Blue,not UV,plumage color is important in satin bowerbird Ptilonorhynchus violaceus display

Several studies have suggested that peak plumage reflectance in birds matches color preferences used in mate choice. We tested this hypothesis in adult satin bowerbird males that have a short‐wavelength saturated blue‐black plumage with a peak reflectance in the UV. We found that the chroma of the blue (405–480 nm), but not the peak reflecting UV (320–400 nm) portion of the male plumage spectrum was significantly correlated with male mating success. A plot of correlation coefficients between male mating success and plumage saturation showed a well‐defined peak in the blue. This suggests that: 1) blue plumage coloration is more important in mate choice than UV or other colors, and 2) that there is a mismatch between the peak reflectance of the plumage of male satin bowerbirds and the range of plumage wavelengths that are correlated with male mating success. This indicates that it is not safe to infer a role of UV or other colors in mate choice simply because of a peak in plumage reflectance.     

Multiple sexual ornaments in satin bowerbirds: ultraviolet plumage and bowers signal different aspects of male quality

Much attention has been devoted to understanding the evolutionof elaborate male ornaments and how they may signal male quality.However, the evolution of multicomponent sexual signals remainspoorly understood, and past research on this type of signalinghas been largely theoretical. Satin bowerbirds, Ptilonorhynchusviolaceus, are polygynous, are sexually dichromatic, and constructsexually selected display structures (bowers): a model systemfor investigating the evolution and signal function of multiplesexual signals. We studied the interrelationship between bowerfeatures, plumage coloration, and indicators of male qualityin this species. To do this, we located the bowers of male satinbowerbirds in rainforest in Queensland, Australia, and quantifiedbower quality. We captured the male bower owners and used reflectancespectrometry to objectively measure the plumage coloration ofseveral body regions. We measured various indicators of malehealth and condition, including the intensity of infection fromectoparasites and blood parasites. Bower quality and male ultravioletplumage coloration were significantly correlated. By using multipleregression analyses, we show that bower quality predicts ectoparasiteload and body size, whereas ultraviolet plumage coloration predictsthe intensity of infection from blood parasites, feather growthrate, and body size. Our findings support the multiple messageshypothesis of multicomponent signals: Female satin bowerbirdsshould assess both male and bower features to choose the highestquality mates.     

Juvenile infection and male display: testing the bright male hypothesis across individual life histories

Current tests of the bright male hypothesis focus on assaysof adult disease resistance and their relation to male traitdevelopment and female choice. We suggest that if parasiteshave significant harmful effects on juvenile stages of a host,then females selecting males that effectively signal juvenileparasite resistance may gain a significant "good genes" benefit.Currently, there is no information on juvenile and adult infectionor resistance in the same male and whether adult male displayssignal juvenile parasite resistance. In the present study, wemeasure infection of the ectoparasitic louse, Myrsidea ptilonorhynchi,in individual male satin bowerbirds (Ptilonorhynchus violaceus)both as juveniles and nine or more years later as adults. Wetest hypotheses that examine the role of juvenile parasite infectionin mediating sexual selection. We found that (1) juvenile infectionis higher than adult infection in the same individuals, (2)adult males able to hold display sites have lower juvenile infection,and (3) juvenile and adult infection in the same individualsare not significantly correlated. In addition, comparisons amonga larger set of individuals from a single year show that bloodand ectoparasite infections are highly correlated, and bothdecrease with male age and are inversely related to male courtshipsuccess. These results, combined with the evidence that femalesmate exclusively with bower-holding males support the hypothesisthat females use adult male display traits to identify maleswith a high level of juvenile disease resistance. We suggestthat effective tests of the bright male hypothesis should include(1) assessment of infection resistance in both subadult andadult life history stages, (2) tests of whether differencesin age-specific resistance are indicated in adult male displays,and (3) tests to determine if females attend to these traitsin mate choice. Although these requirements increase the difficultyof testing the bright male hypothesis, they are necessary fora more accurate assessment of the effects of parasites on maledisplay and female choice.     

Parasites and Bright Male Plumage in the Satin Bowerbird (Ptilonorhynchus violaceus)

Results from our field studies of the satin bowerbird (Ptilonorhynchusviolaceus) suggest that females choose males as mates basedon their level of infection with the ectoparasite (Myrsideaptilonorhynchi: Menoponidae). We evaluated predictions fromthree hypotheses for why this pattern of choice might evolve.The bright male and correlated infection models both suggestthat females choose parasite free males because these malesare more likely to sire parasite resistant offspring. The brightmale hypothesis suggests that females are able to gauge infectionbased on plumage brightness. The correlated infection hypothesisclaims that females assess resistance to endoparasites througha correlated effect on ectoparasites. In the parasite avoidancemodel female choice is shaped by the proximate benefits of avoidinginfection. Six predictions from these models were tested usinginformation on patterns of infection in satin bowerbirds. Ofthese models the parasite avoidance model was best supportedby the available data.     

Structural coloration and sexual selection in the barn swallow Hirundo rustica

Structural coloration has been hypothesized to play a role insexual selection, and we tested whether this was the case ina field study of the barn swallow Hirundo rustica. The dorsaliridescent plumage of barn swallows has a strong reflectancein the ultraviolet (UV) region, with adult males on averagereflecting 8-9% more than adult females, as revealed by a 2-yearstudy in southwestern Spain. The correlation between structural coloration (described by the reflectance in the UV part of thespectrum, UV chroma and blue chroma) and three other secondarysexual characters significantly associated with male matingsuccess (tail length, tail asymmetry, and red facial coloration)was weak and generally nonsignificant. Nor was there a significantrelationship between color parameters and body condition. Wetested for an association between structural coloration of the dorsal plumage and sexual selection in a number of independenttests. Arrival date of males was not significantly relatedto color; there was no significant relationship between colorationand probability of survival or age; mated males did not havestronger reflectance than unmated males; and the duration ofthe premating period was not significantly related to color.Reproductive success was not significantly correlated withplumage coloration in males, nor was the feeding rate of offspringby brightly colored males higher than that of males with lessbright plumage. Given that sample sizes were large, and the power of statistical tests high, we conclude that current sexualselection on the coloration of the dorsal plumage in the barnswallow is, at best, weak.     

Ultra-violet reflectance of male and female red grouse, Lagopus lagopus scoticus, sexual ornaments reflect nematode parasite intensity

In many birds, females prefer males with the biggest or brightest sexual ornaments, which might reflect a higher phenotypic quality, such as fewer parasites. Unlike humans, most birds detect near-ultraviolet (UV) light, and UV signals can play an important role in sexual signalling and mate choice. Using a spectrophotometer, we analysed the colour of red grouse Lagopus lagopus scoticus sexual ornaments (their combs). We first show that combs reflect both in the red (600–700 nm) and UV (300–400 nm) part of the spectrum. Second, we investigated whether comb size and colour, and UV reflectance in particular, reflected an aspect of individual quality: the intensity of infection by a main nematode parasite, the caecal threadworm Trichostrongylus tenuis . We first analysed comb size and colour variation, and parasite intensity variation, in relation to sex and age. Males had bigger and redder combs than females, but UV brightness was greater for female than for male combs. Comb colour also differed between age groups, with young birds of both sexes showing brighter UV than old birds. Young grouse also had fewer T. tenuis worms than old grouse. We further tested whether intensity of infection could be predicted from comb characteristics (size and colour) in male and female red grouse. We found that parasite intensity was not significantly related to comb size or red brightness, but fewer worms were predicted from brighter UV in combs, in both males and females. The results indicate that UV reflectance of combs have a quality revealing function and might play an important role in grouse mate choice: UV brightness of combs could enable both male and female red grouse to assess the parasite loads of a potential mate.     

The Costs of Male Display and Delayed Plumage Maturation in the Satin Bowerbird (Ptilonorhynchus violaceus)

The costs associated with the evolution of male display traits has attracted much attention in regard to the type of traits that evolve and the timing of their expression. We investigate these costs by using testosterone implants to alter the development of male display traits in the satin bowerbird (Ptilonorhynchus violaceus). Testosterone implants advanced the development of adult display traits in males with juvenile plumage. We then measured the costs of early expression of these characters in treated males. Testosterone implants caused young males to (1) become more involved in behavior normally carried out by older males when visiting bowers, (2) build bowers, and (3) molt prematurely into an adult plumage. No difference was observed between the testosterone-treated birds and controls in return rate or condition the year following treatment, suggesting that the physical costs of display are not high. We found that males in adult plumage are tolerated less, and are not displayed to as frequently as juvenile plumage males at the bowers of established bower holders. The causes of delayed plumage maturation are most consistent with the facilitated-learning hypothesis. That is, early development of adult characteristics reduces the opportunity of young males to learn display behavior critical for later reproductive success.     

Sexual dichromatism in the yellow-breasted chat Icteria virens: spectrophotometric analysis and biochemical basis

Sexual dimorphism or dichromatism has long been considered the result of sexual selection. However, for many organisms the degree to which sexual dichromatism occurs has been determined within the confines of human perception. For birds, objective measures of plumage color have revealed previously unappreciated sexual dichromatism for several species. Here we present an unbiased assessment of plumage dichromatism in the yellow-breasted chat Icteria virens . Chats exhibit yellow to orange throat and breast plumage that to the unaided human observer differs only subtly in color. Spectrophotometric analyses revealed that chat throat and breast feathers exhibited reflective curves with two peaks, one in the ultraviolet and one in the yellow end of the spectrum. We found differences in both the shape and magnitude of reflectance curves between males and females. Moreover, for feathers collected from the lower edge and middle of the breast patch, male plumage reflected more light in the ultraviolet and yellow wavelengths compared to females, whereas male throat feathers appeared brighter than those of females only in the ultraviolet. Biochemical analyses indicated that the plumage pigmentation consisted solely of the carotenoid all- trans lutein and we found that males have higher concentrations of plumage carotenoids than females. Feathers that were naturally unpigmented reflected more UV light than yellow feathers, suggesting a potential role of feather microstructure in UV reflectance.     

Supplemental food increases ornamentation of male nestling Eastern Bluebirds

Although the condition‐dependence and signaling function of ornamental plumage coloration among adult males is well studied, less research has focused on the information content of ornamental coloration among juvenile birds. Eastern Bluebird (Sialia sialis) nestlings grow their nuptial plumage while in the nest and dependent on parents for food, making them an ideal species for studying the development and function of elaborate plumage. Previous research suggests that plumage brightness of Eastern Bluebirds functions, in the juvenile stage, in parent–offspring interactions as a sexually selected trait in adults. Using an experimental approach, we tested the effects of supplemental food on the structural plumage coloration (i.e., tips of primary feathers) of Eastern Bluebird nestlings in Watauga County, North Carolina, during the 2011 breeding season. We provided supplemental mealworms daily to breeding pairs from the onset of incubation through the nestling period, and measured plumage brightness, UV chroma, and mass of nestlings (N = 89 males and 71 females). Male nestlings of supplementally fed parents exhibited brighter plumage. The mass and UV chroma of young bluebirds were not significantly affected by food supplementation. However, the relationship between mass and brightness differed between male nestlings in the control and supplementally fed treatments. Males reared in food‐supplemented territories exhibited a positive relationship between color and mass. Nestlings in control territories, however, exhibited a negative relationship between size and brightness, suggesting that reduced food availability results in a tradeoff between allocating resources toward somatic growth and development of bright plumage. Our results suggest that UV‐blue structural plumage in male juvenile Eastern Bluebirds is at least partially condition‐dependent and may help to explain why plumage color can influence social interactions in Eastern Bluebirds.     

Effects of blood parasites on sexual and natural selection in the pied flycather

The occurrence of the blood parasites Haemoproteus and Trypanosoma in the pied flycatcher, Ficedula hypoleuca , was examined to test current hypotheses that parasites reduce the expression of secondary sexual traits, mating success, breeding success, and survival of infected individuals. The results showed that there was no significant relationship between male plumage brightness and Trypanosoma infection, but males infected with Haemoproteus tended to be brighter than uninfected males, partly because first-year males were less often infected than older males. Polygynous males did not have fewer parasites than monogamous males. Females did not choose uninfected males among those they had sampled. Clutch size and laying date were not related to female infection status, and the number and quality of nestlings was not related to parasite infections of either male or female parent. The ability of males to provide parental care was not related to their infection status. The return rate from one breeding season to the next of infected males was not lower than that of uninfected males. The lack of correlations between parasites and male plumage colour and female mate choice apparently do not support the Hamilton-Zuk hypothesis of sexual selection. However, the absence of demonstration of any negative effects of parasites suggests that infection status may not be a direct measure of parasite resistance, or the degree to which the host suffers. Instead, the results support the alternative view that infected individuals have demonstrated their ability to survive and to cope with the parasites, while uninfected individuals are probably not yet tested for their resistance. This points to problems in using parasite prevalences and distributions, at least of some protozoan blood parasites, for tests of Hamilton-Zuk hypothesis, even though this was done in the first test by Hamilton and Zuk and by many later researchers     

Males in seemingly female‐like plumage do not mimic females: UV reflectance reveals temporal cryptic dimorphism in a manakin species exhibiting delayed plumage maturation

Manakins (Pipridae) are neotropical birds that usually exhibit delayed plumage maturation (DPM). Thus, while plumage of most adult male manakins is brightly conspicuous, subadult males and females are basically dull‐olive green. Although sexual dichromatism in some bird species may be evident only through UV reflectance, this phenomenon, known as hidden sexual dichromatism, has not been previously studied in manakins to compare subadult males and females. Within this framework, we carried out spectrophotometric analyses in searching for hidden sexual dichromatism in the white‐bearded manakin Manacus manacus, through comparison of UV spectra in females and subadult males in green plumage. Our results revealed UV reflectance in both sexes in green plumage. Moreover, we found UV spectral differences in homologous color patches between sexes, particularly at belly. Since the observed differences may allow intraspecific sex recognition of individuals in green plumage, our results do not support the female‐mimicry hypothesis to explain delayed plumage maturation in the white‐bearded manakin. Although our findings dismiss the female mimicry hypothesis, we cannot state whether these results support the non‐mutually exclusive cryptic and status signaling hypotheses. We propose then, that dull coloration of subadult males may serve both as a cryptic trait and to limit the energetic costs of acquiring the adult plumage before sexual maturity. Meanwhile, differential UV color traits between sexes in green plumage may allow adult males to avoid unnecessary energy expenditures in courtship displays in the presence of males near leks, and to selectively focus their the courtship displays on females. In accordance with the status signaling hypothesis, subadult males can be recognized both as males and subordinates and consequently may practice courtship displays without suffering aggressions by adult males. Our results highlight the importance to include a wider range of spectrophotometric information analyses for testing hypotheses regarding delayed plumage maturation.     

Juvenile coloration of Florida Scrub-Jays ( Aphelocoma coerulescens ) is sexually dichromatic and correlated with condition

The Florida Scrub-Jay is a monogamous cooperative breeder in which both males and females display extensive structurally based blue plumage. Juveniles of this species exhibit blue tail and wing feathers that they begin growing as nestlings, and some of these feathers are retained throughout their first year. Although the birds appear to be sexually monochromatic, we assessed whether cryptic dichromatism exists in both the magnitude and pattern of coloration in tail feathers of juvenile Florida Scrub-Jays. We then determined whether variation in plumage coloration is associated with nutritional condition during molt. Tails of juvenile male Florida Scrub-Jays exhibit a greater proportion of UV reflectance than those of females. Mass at age 11 days and ptilochronology of the juvenile tail feathers were used as measures of individual nutritional condition during feather growth, and the latter was found to be positively associated with UV chroma. These data demonstrate that Florida Scrub-Jays are sexually dichromatic and suggest that variation in plumage color may be condition dependent, although we cannot rule out alternative explanations. Juvenile plumage coloration, therefore, has the potential to function as a signal of individual quality in both males and females.     

Seasonal changes in a ultraviolet structural colour signal in blue tits, Parus caeruleus

Recent studies of blue tits, Parus caeruleus , have found sexual selection and a viability-indicating function of the structural ultraviolet and blue crown plumage, but the reasons for this signal variation are not understood. Furthermore, studies in England and Sweden have yielded somewhat different results (particularly with regard to the spectral position of the reflectance peak). Here we investigate whether the blue tit UV/blue ornament varies with time of year since such variation might be relevant to the signalling function as well as the apparent difference between populations. From 400 blue tits captured at two different localities in Sweden, we found that objective measures of 'hue' (spectral location), 'chroma' (spectral purity) and 'brightness' (spectral intensity), varied substantially with season. Just after moult (October), crown 'hue' is maximally UV-shifted (359 nm for males and 373 nm for females). Thereafter the peak drifts upwards and by the time of nestling feeding (June) male reflectance peaks at 404 nm and female at 413 nm. This change is probably due to feather wear as well as fat and dirt accumulation, which might constitute an additional male quality cue. Our results suggest that it is important to consider plumage age when exploring variation in structural plumage coloration, and that it can largely explain the difference between the British and Swedish studies. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 237–245.     

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.     

Territorial responses of male blue tits, Cyanistes caeruleus , to UV-manipulated neighbours

Multiple phenotypic traits can affect the outcome of interactions among territorial animals. Individuals may use current and previously acquired information on phenotypic traits to assess the competitive ability of opponents and adjust the strength of their response depending on the threat the opponent poses. In birds, colourful plumage and song are widespread phenotypic traits. Recent work has shown that ultraviolet (UV) plumage reflectance may be used by males in assessing an opponent’s strength and by females in mate choice. In the present study, we investigated whether and how territorial male blue tits, Cyanistes caeruleus, use previously acquired information from UV reflectance of the crown feathers of neighbours to adjust their response to playback of song of these neighbours simulated to intrude their territory. We compared responses to neighbours with those to unfamiliar strangers with unknown plumage features. We found that subject males with UV-enhanced neighbours responded more strongly to these neighbours than to strangers, i.e. showed more flights, used songs without trill and tended to overlap more songs. Subject males with UV-reduced neighbours gave a lower or similar response to neighbours compared to strangers. This indicates that male blue tits combine previously acquired information about an intruder’s plumage with familiarity of its song, and that their response depends on the perceived quality of the neighbour. This study provides evidence that familiarity in combination with multiple signals of quality may influence territorial relations among neighbours.     

The ubiquity of avian ultraviolet plumage reflectance

Although several bird species have been shown to reflect ultraviolet (UV) light from their plumages, the incidence of UV reflectance, and therefore the potential for UV or UV-enhanced signals, across the avian tree of life is not known. In this study, we collected reflectance data from the plumages of 312 bird species representing 142 families. Our results demonstrate that all avian families possess plumages that reflect significant amounts of UV light. The ubiquity of UV reflectance indicates that all studies of avian behaviour, ecology and evolution involving plumage coloration would benefit from consideration of plumage reflectance in the UV portion of the electromagnetic spectrum. Additionally, we demonstrate the existence of cryptic UV plumage patches and cryptic dimorphism among birds.     

Carotenoid-based plumage coloration of male greenfinches reflects health and immunocompetence

Hypotheses of parasite-mediated sexual selection (PMSS) propose that elaborate male ornaments have evolved due to female preferences. Females would benefit from mating with more ornamental males if males' ornamentation signals their health status and ability to provide parasite resistance genes for the offspring. Carotenoid-based plumage coloration of birds has been hypothesised to honestly reflect an individual's health status due to trade-off in allocation of carotenoids between maintenance and signalling functions. The prediction of this hypothesis, namely that individuals with brighter plumage are able to mount stronger immune responses against novel antigens and reveal generally better health state, was tested in captive male greenfinches (Carduelis chloris). Greenfinches with brighter yellow breast feathers showed stronger humoral immune response against novel antigen (SRBC) while no relationship between plumage coloration and an estimate of cell-mediated immune responsiveness (PHA response) was detected. Elaborately ornamental individuals had better general health state as indicated by the negative correlations between plumage brightness and heterophil haemoconcentration. Consistent with the concept of PMSS, these results suggest that carotenoid-based plumage coloration in greenfinches honestly signals immunocompetence and health status.     

Plumage maintenance affects ultraviolet colour and female preference in the budgerigar

Elaborate or colourful feathers are important traits in female-mate choice in birds but little attention has been given to the potential costs of maintaining these traits in good condition via preening behaviour. While preening is known to be an important component of plumage maintenance, it has received little attention with respect to colouration. We investigated whether preening can influence plumage reflectance and whether females show a preference for plumage cleanliness in captive-bred, wild-type budgerigars, Melopsittacus undulatus. To do this, we compared the spectral colour of birds that were allowed to preen their plumage and individuals that were prevented from preening. The plumage of birds that were prevented from preening showed a significant lower reflectance in the UV range (300-400 nm). Subsequently, we measured females’ preferences for preened and unpreened males using a two-choice test. In a second experiment we allowed females to choose between an unpreened male and a male smeared with UV-absorbing chemicals (UV-blocked male). The proportion of time that females stayed near preened males was statistically higher than for unpreened males, but females spent similar amounts of time with unpreened males and UV-blocked males. These results are consistent with the idea that female budgerigars are able to discriminate between preened and unpreened males, and that UV colours, mediated by preening, can convey information about a bird's current condition.     

Individual color variation and male quality in pied flycatchers (Ficedula hypoleuca): a role of ultraviolet reflectance

Bright coloration of males in many animal species has inspiredresearchers for more than a century. In this field study, weinvestigated whether color variation between individuals isrelated to individual quality in pied flycatcher (Ficedulahypoleuca) males in terms of arrival time at the breeding sites.In addition to traditional visual color scoring, plumage color was measured using spectroradiometric measurements between 320and 700 nm. This range includes the near-ultraviolet wavebandfrom 320 to 400 nm. Males that arrived earlier at breedingsites had higher proportional UV reflectance in the crown andmantle. The proportional UV reflectance in the crown and mantlewas not related to traditionally scored general brownness inmales. However, adult males had a higher proportion of ultravioletin the plumage than yearling males or females. These resultssuggest that in pied flycatcher males, the UV reflectance ofplumage may be positively correlated with individual quality.     

Ultraviolet reflection and female mate choice in the pied flycatcher, Ficedula hypoleuca

In pied flycatchers females seem to prefer male territory quality rather than male characteristics, and the results of female mate choice experiments are divergent. In this outdoor aviary study, we examined how altering the ultraviolet reflection of males affects female mate choice behaviour. We chose pairs of males with similar human-visible dorsal colour and morphological traits. We then reduced the proportional ultraviolet reflectance in one male with sunscreen chemicals. The other male was treated with a chemical that slightly increased the ultraviolet reflectance of the plumage. In the experiment females clearly preferred males with slightly increased ultraviolet reflection. Our results indicate that pied flycatcher females use ultraviolet cues for mate choice when the effect of territory quality is controlled for. The results give us new information about a possible mechanism of mate assessment in this species, and indicate the importance of colour cues in avian mate choice behaviour.