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.     

Ultraviolet reflectance affects male-male interactions in the blue tit (Parus caeruleus ultramarinus)

Several animal species have been shown to use phenotypic traitsto assess the competitive ability of opponents and adjust theiraggressiveness depending on the likelihood to win the contest.In birds, these phenotypic traits usually involve patches ofcolored feathers. The benefit to harbor honest signals of malequality is the avoidance of wasteful aggressive interactions.Recent work has shown that ultraviolet (UV) plumage reflectanceis an important signal used by females during mate choice. Surprisingly,however, the role of UV signaling on intrasexual selection hasbeen neglected. In the present study, we aimed to test whetherUV reflectance of crown feathers was used as a signal of malecompetitive ability during male-male interactions. Breedingmale blue tits (Parus caeruleus ultramarinus) were exposed duringthe female egg-laying period to blue tit taxidermic mounts witheither control or reduced UV reflectance of crown feathers.In agreement with the prediction that UV reflectance advertisesmale quality, we found that breeding blue tits behaved lessaggressively toward the UV-reduced decoy. To our knowledge,this is the first experimental evidence suggesting a role forUV signaling on intrasexual selection.     

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.     

UV plumage color is an honest signal of quality in male budgerigars

Elaborate and colorful feathers are important traits in female mate choice in birds. Plumage coloration can result from pigments deposited in feathers such as carotenoids and melanins, or can be caused by nano-scale reflective tissues (structurally based coloration), usually producing ultraviolet (UV) coloration. Structural colorations remain the least studied of the three most important feather colorations. Previous studies have found a female preference for UV color in the budgerigar, Melopsittacus undulatus, but it is not clear what information this ornament conveys, nor what is the possible cost associated with its production. We investigated possible correlations between immune response and plumage color of wild-type (green) male budgerigars. In particular we measured the wing web swelling resulting from injection of phytohaemagglutinin (PHA). We did not detect any correlation between the sedimentation rate and morphological and color variables. We found that UV chroma is the best predictor for the cutaneous immune activity. Indeed, male budgerigars with high UV reflectance in the breast feathers showed stronger immune responses. These results are consistent with the idea that UV colors are special signals conveying information about a bird’s condition.     

Reproductive correlates of plumage coloration of female Mountain Bluebirds

Many studies have shown that the plumage coloration of male birds can act as an honest signal of quality, indicating benefits that a female could gain from pairing with a specific male. In some species, females also display ornamental plumage, but less is known about the function and potential adaptive significance of female coloration because most research has focused on male coloration. Male Mountain Bluebirds (Sialia currucoides) display full body, ultraviolet (UV)‐blue plumage, whereas female plumage is more subdued, with blue color focused on the rump, wing, and tail. During the 2011 and 2012 breeding seasons (May–July) near Kamloops, BC, Canada, we examined coloration of the rump and tail of female Mountain Bluebirds to determine if their plumage could act as an indicator of direct reproductive benefits (e.g., enhanced parental care or reproductive success) to potential mates. We found no relationship between female plumage coloration and either provisioning rate or fledging success. However, female coloration varied with age, with after‐second‐year (ASY) females having brighter, more UV‐blue tail feathers than second‐year (SY) females. In addition, ASY females with brighter, more UV‐blue tails had larger clutches. We also observed positive assortative mating by tarsus length. Because previous work with other species suggests that female body size may be a good predictor of breeding success, males could potentially benefit from pairing with larger females. However, reproductive success did not vary with female size in our study. Although our evidence that structural plumage coloration of female Mountain Bluebirds is a signal of direct reproductive benefits for males (e.g., higher reproductive success) is limited, our results (i.e., ASY females with brighter tails than SY females, and ASY females with brighter tails having larger clutches) do suggest the potential for sexual selection to act on female coloration.     

Color expression in experimentally regrown feathers of an overwintering migratory bird: implications for signaling and seasonal interactions

Plumage coloration in birds plays a critical role in communication and can be under selection throughout the annual cycle as a sexual and social signal. However, for migratory birds, little is known about the acquisition and maintenance of colorful plumage during the nonbreeding period. Winter habitat could influence the quality of colorful plumage, ultimately carrying over to influence sexual selection and social interactions during the breeding period. In addition to the annual growth of colorful feathers, feather loss from agonistic interactions or predator avoidance could require birds to replace colorful feathers in winter or experience plumage degradation. We hypothesized that conditions on the wintering grounds of migratory birds influence the quality of colorful plumage. We predicted that the quality of American redstart (Setophaga ruticilla) tail feathers regrown after experimental removal in Jamaica, West Indies, would be positively associated with habitat quality, body condition, and testosterone. Both yearling (SY) and adult (ASY) males regrew feathers with lower red chroma, suggesting reduced carotenoid content. While we did not observe a change in hue in ASY males, SY males shifted from yellow to orange plumage resembling experimentally regrown ASY feathers. We did not observe any effects of habitat, testosterone, or mass change. Our results demonstrate that redstarts are limited in their ability to adequately replace colorful plumage, regardless of habitat, in winter. Thus, feather loss on the nonbreeding grounds can affect social signals, potentially negatively carrying over to the breeding period.     

Ultraviolet reflectance of plumage for parent-offspring communication in the great tit (Parus major)

Ultraviolet (UV) reflectance has been implicated in mate selection.Yet, in some bird species the plumage of young varies in UVreflectance already in the nest and long before mate choiceand sexual selection come into play. Most birds molt the juvenilebody plumage before reaching sexual maturity, and thus, someconspicuous traits of the juvenile body plumage may rather haveevolved by natural selection, possibly via predation or parentalpreference. This second hypothesis is largely untested and predictsa differential allocation of food between fledging and totalindependence, which is a time period of 2–3 weeks whereoffspring mortality is also highest. Here, we test the predictionthat parents use the individual variation in UV reflectanceamong fledglings for differential food allocation. We manipulatedUV reflectance of the plumage of fledgling great tits Parusmajor by treating chest and cheek feathers with a lotion thateither did or did not contain UV blockers and then recordedfood allocation by parents in an outdoor design simulating postfledgingconditions. The visible spectrum was minimally affected by thistreatment. Females were found to feed UV-reflecting offspringpreferentially, whereas males had no preference. It is the firstevidence showing that the UV reflectance of the feathers ofyoung birds has a signaling function in parent–offspringcommunication and suggests that the UV traits evolved via parentalpreference.     

Primary sex ratio adjustment to experimentally reduced male UV attractiveness in blue tits

The study of primary sex ratio adjustment in birds is notoriousfor inconsistency of results among studies. To develop our understandingof avian sex ratio variation, experiments that test a prioripredictions and the replication of previous studies are essential.We tested if female blue tits Parus caeruleus adjust the sexratio of their offspring to the sexual attractiveness of theirmates, as was suggested by a previous benchmark study on thesame species. In 2 years, we reduced the ultraviolet (UV) reflectanceof the crown feathers of males in the period before egg layingto decrease their attractiveness. In contrast to the simpleprediction from sex allocation theory, we found that the overallproportion of male offspring did not differ between broods ofUV-reduced and control-treated males. However, in 1 year, theUV treatment influenced offspring sex ratio depending on thenatural crown UV reflectance of males before the treatment.The last result confirms the pattern found in the previous bluetit study, which suggests that these complex patterns of primarysex ratio variation are repeatable in this bird species, warrantingfurther research into the adaptive value of blue tit sex ratioadjustment to male UV coloration.     

Female plumage coloration is sensitive to the cost of reproduction. An experiment in blue tits

1. A growing number of studies suggest that female ornaments are linked to maternal quality and influence male mate choice. These findings challenge the traditional male-biased view of sexual selection and the hypothesis that female ornaments are the outcome of a genetic correlation with male ornaments. To further test the hypothesis that female traits have a function, it is now essential to investigate their honesty and to determine how signalling and reproduction interact in females. If female traits are honest indicators of quality, then they are likely to have a specific signalling function. 2. We investigated whether carry-over effects of reproduction might ensure the honesty of plumage colour signalling of a bird species with conspicuous UV-blue and yellow coloration, the blue tit Cyanistes caeruleus. Reproductive effort was manipulated by removing clutches, thereby forcing both sexes to reproduce twice and to raise chicks later in the breeding season when food is less abundant. In the year following this manipulation, we investigated the change in plumage in experimental and control males and females. The change was measured in the two putative feather ornaments, the UV-blue cap and the yellow breast, and another feather trait probably less likely to be sexually selected: the wing length. We also tested whether higher-quality females had their coloration less affected by the experiment. 3. We found that control but not manipulated males and females increased their signal towards UV. In addition, in the manipulated group, females that were able to lay more eggs had their UV-blue coloration less affected by the treatment. For yellow coloration, we found that manipulated yearlings but not manipulated adults decreased their yellow chroma in comparison with control. Lastly, our results show that the condition of the manipulated females tended to be positively correlated with yellow chroma. 4. These results show that the trade-offs between reproduction and signalling can ensure the honesty of conspicuous plumage traits in female and male blue tits. In addition, they suggest that female traits have the potential to evolve under sexual selection in this and other bird species.     

The blue tit's song is an inconsistent signal of male condition

Sexually selected traits are often hypothesized to signal malecondition or quality, though empirical evidence is mixed, anda number of alternative models of sexual selection do not requirecondition dependence. We examined the relationship between variousmeasures of condition and dawn songs in male blue tits (Cyanistescaeruleus). We detected 6 largely independent measures of variation(i.e., variables) in these songs. None of these variables wererelated to blue tits' ultraviolet–blue plumage, a demonstratedsexual signal, thus failing to support the redundant signalhypothesis. We found some evidence that the song variables wemeasured signaled male quality. There were correlations betweenbody size and certain song traits, though neither male age normale recapture in the subsequent breeding season (apparent localsurvival) predicted any song variation. We combined our resultswith published effect sizes comparing blue tit song with malequality variables using meta-analysis and found that a few songmeasures are correlates of male quality, though as in our fielddata, neither male age nor survival appeared related to song.Our relatively large sample sizes (>60), combined with ourmeta-analytical integration of 89 effect sizes, make the resultsregarding the signaling value of our measured components ofblue tit song robust. These results demonstrate that 1) onlycertain aspects of signal variation may be condition dependentand 2) even when components of a sexual signal appear correlatedwith condition in some studies, these signal components maybe unrelated or inconsistently related to a variety of conditionindices.     

Seasonal changes in blue tit crown color: do they signal individual quality?

Plumage coloration is generally perceived as a static traitand therefore not a good indicator of current condition. However,changing of feather colors after molt does occur and may haveimportant implications for signal function and sexual selection.We studied longitudinal changes in blue tit (Parus caeruleus)crown ultraviolet (UV)/blue color, a sexually selected trait,by repeatedly measuring the same individuals between early winterand late spring. Whereas crown UV reflectance (UV chroma andhue) decreased dramatically over time, brightness and saturationdid not show consistent patterns of change. The magnitude ofthe decline in coloration exceeded sexual and age dichromatismin hue and UV chroma, respectively. Hence, seasonal color changescould have strong effects on blue tit sexual signaling. Between-individualvariation in the decline in UV coloration was large and relatedto attributes of male, but not female, quality, such as sizeand condition. Thus, conspecifics could potentially gain informationabout male phenotypic quality by assessing color change overthe year. However, the degree of decline in male UV color didnot affect breeding success because neither the number of within-pairnor the number of extrapair offspring produced correlated withchanges in crown color. Seasonal changes in the expression ofplumage coloration are probably widespread, and maintainingplumage coloration could thus constitute an additional honesty-enforcingmechanism after molt is completed.     

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.     

What do we really know about the signalling role of plumage colour in blue tits? A case study of impediments to progress in evolutionary biology

Evolutionary biologists seek to explain the origin and maintenance of phenotypes, and a substantial portion of this research is accomplished by thorough study of individual species. For instance, many researchers study individual species to understand evolution of ornamental traits which appear to be products of sexual selection. I explored our understanding of sexual ornaments in a well‐studied vertebrate species that may serve as a case study for research programs in evolutionary biology. I attempted to located all published papers examining plumage colour and variables related to sexual selection hypotheses in a common European songbird, the blue tit (Cyanistes caeruleus). Researchers have estimated over 1200 statistical relationships with plumage colour of blue tits in 52 studies. However, of the approximately 1000 main‐effect relationships from the 48 studies that are candidates for inclusion in this meta‐analysis, more than 400 were reported without details of strength and direction. Circumstantial evidence suggests that an unknown number of other estimated effects remain unpublished. Missing information is a substantial barrier to interpretation of these papers and to meta‐analytic synthesis. Examination and analysis of funnel plots indicated that unpublished effects may be a biased sample of all effects, especially for comparisons of plumage colour to age and individual quality, and possibly also to measures of mate choice. Further, type I error was likely elevated by the large number of statistical comparisons evaluated, the frequent use of iterative model‐building procedures, and a willingness to interpret a wide variety of results as support for a hypothesis. Type I errors were made more problematic because blue tit plumage researchers only rarely have attempted to replicate important findings in their own work or that of others. Replication is essential to drawing robust scientific conclusions, especially in probabilistic systems with moderate to weak effects or a likelihood of bias. Last, researchers studying blue tit plumage have often developed ad hoc explanations for deviations of results from their predictions. Revising hypotheses in light of data is appropriate, but these revised hypotheses were rarely tested with new data. The only highly robust conclusion supported by meta‐analysis is that male blue tits have plumage that reflects more light in the ultraviolet and yellow wavelengths than the plumage of females. Various other effects, including condition‐dependence of plumage colour expression and a tendency for females to adjust the sex ratio of their offspring in response to male colour, remain uncertain. These obstacles to progress in the blue tit plumage literature are likely common in evolutionary biology, and so I recommend changes to incentive structures which may improve progress towards scientific understanding in this discipline.     

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

The evolution of colorful plumage has been dramatic in lekkingspecies. Several studies show that the size of colorful traitsinfluence female choice in leks; however, relatively littleis known about the specific function of color, in particularits spectral properties, in lekking taxa. To determine the importanceof color in a lekking species, we monitored the mating successof male golden-collared manakins, Manacus vitellinus, and relatedthis to spectral measures of their colorful plumage, as wellas other morphological and behavioral traits shown to be importantin other lekking species. We found that lek centrality, malebody size, and plumage brightness were associated with malemating success. Only plumage brightness, however, entered amultiple regression model, indicating that plumage is the overallbest predictor of mating success. These results provide evidencethat the spectral properties of colorful plumage predict malemating success in a lekking species and provide important insightinto why many lekking birds are dichromatic and elaborate incoloration.     

Multiple sexual ornaments signal heterozygosity in male blue tits

Higher individual genetic quality has been hypothesized to be associated with the expression of conspicuous ornaments. However, the relationship between multicomponent sexual signals and heterozygosity is poorly understood. In this study, we examined whether different ornaments, including song (repertoire size and bout length) and plumage coloration (yellow breast and blue crown), reflect individual genetic diversity in male blue tits (Aves: Cyanistes caeruleus). We estimated genetic diversity using 26 microsatellite markers that were classified as putatively functional (12 loci) and neutral (14 loci). We found that yellow breast carotenoid chroma, blue crown brightness, bout length and body condition were positively associated with heterozygosity at functional loci, but not with genetic diversity estimated at all typed loci or the subset of neutral markers. The lack of strong single‐locus effects and the presence of identity disequilibrium in our population suggest that the observed heterozygosity‐phenotype associations are driven by loci widely distributed across the genome. The predominant role of putatively functional loci evidences that the expression of secondary sexual characters is more tightly reflected by heterozygosity at genomic regions containing coding genes that are being actively expressed, a fact that may make ornamental traits more reliable indicators of the genetic quality of individuals. Overall, this study shows that multiple secondary sexual characters reflect male genetic diversity and lends support to the good‐genes‐as‐heterozygosity hypothesis. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 362–375.     

Is male plumage reflectance correlated with paternal care in bluethroats?

Although it is now well established that the conspicuous maleplumage colors of many birds have been subject to sexual selectionby female choice, it is still debated whether females matewith colorful males to obtain direct or indirect benefits.In species where males provide substantial parental care, femalesmay obtain direct benefits from mating with the males that are best at providing care. The good parent hypothesis suggeststhat male plumage coloration signals a male's ability to provideparental care. Alternatively, the differential-allocation hypothesissuggests that colorful males reduce their care in responseto increased investment by females mated to attractive males.We tested these hypotheses on the bluethroat (Luscinia s. svecica),a socially monogamous, sexually dichromatic bird, in which males have a colorful throat patch consisting of a structurallyderived blue area surrounding a melanin-based chestnut spot.Male plumage coloration was objectively quantified by use ofreflectance spectrometry. We found no evidence of a relationshipbetween male coloration of either the blue patch or the chestnutspot and the level of paternal care. Nor were there any correlationsbetween male coloration and body size or body condition. Thus, our study does not support the hypothesis that male colorationsignals male parental quality (the good parent hypothesis)or the hypothesis that colorful males reduce their care inresponse to increased investment by females (the differential-allocationhypothesis).     

Female coloration indicates female reproductive capacity in blue tits

It is poorly understood whether female morphological and behavioural traits can be used as 'signals'. In particular, experimental tests of the hypothesis that female ornaments reflect quality are scarce. Here, we experimentally examine whether female plumage coloration might signal maternal quality in the blue tit, Cyanistes caeruleus by forcing half of the females breeding in our population to produce a replacement clutch. Using statistical models that controlled for the effects of male coloration, and the effects of age and condition of both parents, we found that carotenoid-based female coloration was positively linked to key proxies of bird lifetime reproductive success: clutch size, fledgling success and recruitment. Importantly, the relationships between maternal yellow carotenoid coloration and both clutch size and recruitment were stronger in the experimental group than in the control group, indicating that breeding females with higher values of yellow coloration were better able to handle the cost of producing a second clutch. Finally, UV-blue female coloration was positively linked to female survival and marginally linked to laying date. Taken together, these results show for the first time in a natural population that female coloration can indicate individual and maternal quality under natural and adverse reproductive conditions. They highlight the potential for the evolution of female ornamental traits through sexual selection.     

Red-winged blackbirds Agelaius phoeniceus use carotenoid and melanin pigments to color their epaulets

Over the past three decades, the red‐winged blackbird Agelaius phoeniceus has served as a model species for studies of sexual selection and the evolution of ornamental traits. Particular attention has been paid to the role of the colorful red‐and‐yellow epaulets that are striking in males but reduced in females and juveniles. It has been assumed that carotenoid pigments bestow the brilliant red and yellow colors on epaulet feathers, but this has never been tested biochemically. Here, we use high‐performance liquid chromatography (HPLC) to describe the pigments present in these colorful feathers. Two red ketocarotenoids (astaxanthin and canthaxanthin) are responsible for the bright red hue of epaulets. Two yellow dietary precursors pigments (lutein and zeaxanthin) are also present in moderately high concentrations in red feathers. After extracting carotenoids, however, red feathers remained deep brown in color. HPLC tests show that melanin pigments (primarily eumelanin) are also found in the red‐pigmented barbules of epaulet feathers, at an approximately equal concentration to carotenoids. This appears to be an uncommon feature of carotenoid‐based ornamental plumage in birds, as was shown by comparable analyses of melanin in the yellow feathers of male American goldfinches Carduelis tristis and the red feathers of northern cardinals Cardinalis cardinalis, in which we detected virtually no melanins. Furthermore, the yellow bordering feathers of male epaulets are devoid of carotenoids (except when tinged with a carotenoid‐derived pink coloration on occasion) and instead are comprised of a high concentration of primarily phaeomelanin pigments. The dual pigment composition of red epaulet feathers and the melanin‐only basis for yellow coloration may have important implications for the honesty‐reinforcing mechanisms underlying ornamental epaulets in red‐winged blackbirds, and shed light on the difficulties researchers have had to date in characterizing the signaling function of this trait. As in several other birds, the melanic nature of feathers may explain why epaulets are used largely to settle aggressive contests rather than to attract mates.     

Mate choice based on static versus dynamic secondary sexual traits in the dark-eyed junco

Some secondary sexual traits (SSTs) such as structural characteristicsare semi-permanent or static, while others, such as courtshipdisplay, are more labile or dynamic. In this paper we reportresults from two experiments designed to test the relative attractivenessto female dark-eyed juncos (Junco hyemalis, Passeriformes, Aves)of a relatively static plumage trait, the amount of white inthe tail, and a relatively dynamic behavioral trait, courtshipintensity. The experiments derived from a study showing that femalejuncos prefer males that court more vigorously. We asked whether femalesalso base their preferences on plumage traits and how they respond whenpresented with a choice between attractive traits that are eitherstatic (plumage) or dynamic (courtship) in nature. In the firstexperiment we presented males to females in paired mate-choicetrials and found that males enhanced with more white in theirtails were more attractive to females than controls with unenhancedtails. Females spent more time with enhanced males and directedmore sexual displays toward them. In the second experiment we testedwhether females preferred males with enhanced tails (a staticSST) or males with enhanced hormone-mediated courtship behavior(a dynamic SST). In this experiment females did not demonstratea consensus preference for either the static or the dynamictrait. Instead, some females preferred the male whose courtshipperformance was enhanced with testosterone, while others preferredthe male with an enhanced tail. We conclude that both kindsof traits are important in junco mate choice, but that somefemales apparently weigh static traits more heavily than dynamicones, while other females use opposite weightings.     

The role of ultraviolet-A reflectance and ultraviolet-A induced fluorescence in the appearance of budgerigar plumage: insights from spectrofluorometry and reflectance spectrophotometry

Fluorescence has so far been found in 52 parrot species when illuminated with ultraviolet-A (UVA) 'black' lamps, and two attempts have been made to determine whether such fluorescence plays any role in sexual signalling. However, the contribution of the reflectance versus fluorescence to the total radiance from feathers, even in the most studied species to date (budgerigars), is unclear. Nor has the plumage of this study species been systematically assessed to determine the distribution of fluorescent patches. We therefore used spectrofluorometry to determine which areas of budgerigars fluoresce and the excitation and emission spectra involved; this is the first time that such a technique has been applied to avian plumage. We found that both the yellow crown and (normally hidden) white downy chest feathers exhibit strong UVA-induced fluorescence, with peak emissions at 527 nm and 436 nm, respectively. Conversely, the bright-green chest and dark-blue tail feathers do not fluoresce. When comparing reflectance spectra (400-700 nm) from the yellow crown using illuminants with a proportion of UVA comparable to daylight, and illuminants with all UVA removed, no measurable difference resulting from fluorescence was found. This suggests that under normal daylight the contribution of fluorescence to radiance is probably trivial. Furthermore, these spectra revealed that males had fluorescent crowns with substantially higher reflectance than those of females, in both the UV waveband and at longer wavelengths. Reflectance spectrophotometry was also performed on a number of live wild-type male budgerigars to investigate the chromatic contrast between the different plumage areas. This showed that many plumage regions are highly UV-reflective. Overall our results suggest that rapid surveys using UVA black lamps may overestimate the contribution of fluorescence to plumage coloration, and that any signalling role of fluorescence emissions, at least from the yellow crown of budgerigars, may not be as important as previously thought.