Achromatic plumage reflectance predicts reproductive success in male black-capped chickadees

The size of achromatic (black, white, gray) plumage patchesserves as a male status signal in many species of birds, butvariation in the colors of these patches has received littleattention. We assessed the relation between achromatic plumagereflectance, dominance rank, body condition, and reproductivesuccess in male black-capped chickadees, Poecile atricapillus.We measured plumage reflectance for five body regions of 40male chickadees in late winter and monitored these males throughoutthe following breeding season to determine whether they survivedto breed, whether they successfully paired, whether their partnerlaid eggs, and both their apparent and realized reproductivesuccess. As expected from past studies, a male's dominance ranksignificantly predicted whether his partner laid eggs. However,only achromatic plumage reflectance significantly predictedother measures of male reproductive performance. Among maleswho fledged at least one offspring, both the brightness of whiteplumage regions and the UV-chroma of melanin-based plumage regionswere significant predictors of the proportion of within-pairyoung in their nests. When we consider all males we measured,assigning zero values to males who failed to sire any offspring,the UV-chroma of melanin-based plumage regions was a significantpredictor of realized reproductive success. Bib size was alsorelated to male realized reproductive success. Our findingssuggest that individual variation in achromatic plumage mayplay an important role in sexual signaling in chickadees.     

Alula size signals male condition and predicts reproductive performance in an Arctic‐breeding passerine

While studies of achromatic plumage signaling are scarce relative to chromatic ornaments, achromatic ornaments have the potential to act as an efficient form of visual communication due to the highly conspicuous contrast between black and white body regions. Recently, achromatic plumage reflectance has been shown to indicate condition, yet the condition‐dependence of achromatic patch size remains unstudied. Here we show the first evidence that alula size, an achromatic plumage patch, has the potential to signal a male’s condition and predict reproductive performance. In Arctic‐breeding snow buntings Plectrophenax nivalis, the size of the alula simultaneously predicted pre‐breeding physiological health and the number of offspring produced, through an intermediate variable (lay date). Snow buntings appear to pair assortatively; males and females arriving earlier pair together, and changes in body condition over the breeding season are positively related within pairs. We suggest that simple achromatic plumage patches, like alula size, have the potential to act as condition‐dependent signals. Consequently, females may benefit from assessing these signals to reliably evaluate a male’s condition and reproductive potential as a means of maximizing their reproductive success.     

Carotenoid-Based Plumage Coloration Predicts Leukocyte Parameters during the Breeding Season in Northern Cardinals (Cardinalis cardinalis)

Dichromatism in songbirds is often associated with polygyny and dimorphic parental investment, and is thought to arise via sexual selection. Northern cardinals (Cardinalis cardinalis) are not only dichromatic but also monogamous and biparental, suggesting that plumage coloration in this species may serve different functions than in more typical dichromatic species. In order to explore the role of sexual selection in the evolution of plumage coloration in cardinals, we used reflectance spectrophotometry to investigate whether two carotenoid‐based ornaments, the male’s red breast and the female’s underwing coverts, contain information that potential mates or competitors could use to assess condition. We found that whereas coloration was not related to body condition (measured as the residual body mass from a regression of body mass on wing chord), more saturated carotenoid coloration was associated with higher heterophil to lymphocyte ratios in males, and with higher white blood cell counts in females. Thus, in both sexes, carotenoid coloration was positively linked to immune measures normally associated with higher levels of stress and infection. These results do not indicate that carotenoid‐based coloration functions as a signal of low levels of stress or disease in this species. We propose instead that because plumage coloration may be related to competitiveness, the more saturated individuals increase their risk of injury, stress, and infection by engaging in more competitive behavior or by secreting more testosterone, or both. Our finding that carotenoid pigmentation is positively associated in males with the size of the cloacal protuberance, an androgen‐sensitive sex character, supports this hypothesis.     

Colourful male European Serins Serinus serinus are more careful with their plumage

Ornamental traits typically advertise individual condition and can be costly to maintain. Plumage maintenance behaviour can increase plumage quality and positively influence female mate preference. We investigated this prediction by performing female mate‐choice trials and measuring male plumage maintenance behaviour in the European Serin Serinus serinus. More colourful males spent more time in plumage maintenance than less colourful males, but this was not correlated with body condition or ectoparasite load. Females preferred more colourful males, although this was not influenced by male plumage maintenance. Our findings highlight the fact that investment in plumage maintenance depends on individual coloration and this may reinforce the honesty of ornamental plumage and convey positive information for mate choice.     

Achromatic Plumage Reflectance, Social Dominance and Female Mate Preference in Black-Capped Chickadees (Poecile atricapillus)

Individual variation in achromatic plumage reflectance of male Black‐capped Chickadees (Poecile atricapillus) is correlated with social rank and reproductive success, suggesting it may play an important role in sexual signaling. We asked whether female chickadees could assess male quality based on plumage, in the absence of information about relative social dominance. Sexually mature but inexperienced females captured during the pair formation period in late fall and early winter were presented with a choice of two unfamiliar, sexually experienced males in separate compartments of an outdoor mate choice arena. Following each preference trial, we released the males into a single compartment and scored their pairwise dominance interactions. In 10 of 11 trials, females spent significantly more time with the male subsequently identified as dominant, despite not witnessing the males interact. Spectral analysis of male plumage reflectance revealed that UV‐chroma of dark body regions (bib, cap and mantle) was significantly greater in dominant, preferred males and that dominant, preferred males had significantly brighter white cheek patches. There were no differences in vocalization rates of preferred and non‐preferred males. These results show that female chickadees can rapidly assess unfamiliar males based on visual cues, and suggest that variation in achromatic plumage functions in sexual signaling.     

Why some rails have white tails: the evolution of white undertail plumage and anti-predator signaling

Conspicuous plumage patches have evolved in birds as conspecific signals for mate attraction and assessment, intersexual competition or to signal alarm. Signals may alternatively be directed at potential predators to discourage pursuit. Rails (Family Rallidae) are ground-dwelling birds, many of which inhabit wetlands, while others occur in forests and grasslands. They are renown for their secretive nature and the tendency to flick their tails when observed. This behavior is more conspicuous in species with white undertail coverts that contrast sharply with darker body plumage. Using species comparisons and controlling for phylogeny, we investigated four hypotheses for the evolution of white undertail coverts in rails. We found little support for the hypothesis that white tails are sexually selected: white tails were not more common in species with polygamous as opposed to monogamous mating systems, species with sexual dimorphism, nor species that display their tails in courtship. Nor did our results support the hypothesis that white tail plumage evolved for intersexual competition during territorial interactions. Instead, we found that species that flock for at least part of the year and species found in open as opposed to concealing habitats were significantly more likely to have white undertail coverts. Rail species inhabiting concealing habitats are less commonly gregarious and more likely selected for crypsis. Using phylogenetically-controlled statistical inference we found that adaptation to open wetland habitats significantly precedes the evolution of white undertails, whereas gregariousness likely evolved later in some lineages. The inferred order of trait evolution suggests that this plumage characteristic could have been selected primarily for enhancement of an anti-predator signal rather than a social signal for conspecifics.     

Mutual ornamentation and the parental behaviour of male and female Collared Flycatchers Ficedula albicollis during incubation

One of the benefits of mate choice based on sexually selected traits is the greater investment of more ornamented individuals in parental care. The choosy individual can also adjust its parental investment to the sexual signals of its partner. Incubation is an important stage of avian reproduction, but the relationship between behaviour during incubation and mutual ornamentation is unclear. Studying a population of Collared Flycatchers Ficedula albicollis, we monitored the behaviour of both sexes during incubation in relation to their own and their partner's plumage traits, including plumage‐level reflectance attributes and white patch sizes. There was a marginally positive relationship between male feeding rate during incubation and female incubation rate. Female but not male behavioural traits were associated with the laying date of the first egg and clutch size. The behaviour of the two sexes jointly determined the relative hatching speed of clutches and the hatching success of eggs. Females with larger white wing patches spent less time incubating eggs and left the nestbox more frequently. Males with larger white wing patches fed females less frequently, whereas males with brighter white plumage areas visited the nestbox more regularly without feeding. Females tended to leave the nest less often when mated to males with larger wing patches, and females spent less time incubating when males had more UV chromatic plumage. The behaviour of both partners during incubation therefore predicted hatching patterns and was correlated with their own and sometimes with their partner's plumage ornamentation. These results call for further studies of mutual ornamentation and reproductive effort during incubation.     

Multiple Plumage Ornaments as Signals of Intrasexual Communication in Golden‐Winged Warblers

Avian plumage represents some of the greatest diversity in integument coloration of all animals. Plumage signals are diverse in function, including those that allow for assessing potential mates or the mitigation of agonistic interactions between rivals. Many bird species possess multiple ornamental traits that have the potential to serve as multiple or redundant signals. For example, male golden‐winged warblers (Vermivora chrysoptera) have brilliant carotenoid‐based yellow crowns, melanin‐based black throats, and structurally based white patches on their outer tail feathers. Using a correlative approach, we investigated whether plumage ornaments have the potential to reliably signal ability to acquire higher quality territory, aggressive response to simulated territorial intrusions, and reproductive success. We found that both crown chroma and tail brightness were significantly related to habitat quality and aggression; more ornamented birds held territories with higher quality habitat and were less aggressive toward simulated conspecific stimuli. Older birds sang less threatening songs than younger birds and were more likely to sing their mate attraction song type (type 1) rather than songs typically reserved for agonistic interactions (type 2). Finally, despite our previous research demonstrating that habitat strongly predicts reproductive success in this warbler population, we found no evidence of a direct link between ornamentation and reproductive success. Overall, these data suggest that younger males, and those with lower quality ornaments, compensate with more aggressive behaviors. Additional research is needed to investigate the dynamics between behavioral traits and ornaments to better understand complex signaling and how golden wing signals function in conspecific interactions (male–male interactions and mate‐choice).     

Parental care does not vary with age‐dependent plumage in male Saffron Finches Sicalis flaveola

The status signalling hypothesis states that conspicuous male plumage varies among males and serves as an honest signal of male quality and competitive ability. We expected immature‐plumaged males of the Saffron Finch Sicalis flaveola to feed their incubating mates and nestlings and remove faecal sacs at lower rates than those of mature‐plumaged males. We also predicted that females paired with immature‐plumaged males would compensate for their mates’ lower contribution. We found no differences in either feeding rates or sanitation rates between immature‐ and mature‐plumaged males. Similarly, females mated to immature‐ and mature‐plumaged males fed nestlings at equivalent rates. Apparently, male plumage colour and age are not reliable signals of the ability of a male Saffron Finch to provide for his mate and offspring.     

Signals of quality and age: the information content of multiple plumage ornaments in male western bluebirds Sialia mexicana

Male structural plumage coloration and UV signals in particular can provide information on individual quality and influence female choice, while melanin-pigmented plumage is largely considered to be important in intrasexual competition. Many avian species demonstrate both types of plumage ornamentation that may convey different information about the signaller's quality or condition in addition to age. We examine rufous and blue plumage ornamentation across multiple body regions in relation to age, condition and reproductive performance in male western bluebirds Sialia mexicana. We demonstrate a strong positive relationship between head plumage brightness and both male age and the mass of the offspring. Older males are in better condition and display a reduced plumage patch on the back while the size of the rufous breast patch increases with increasing condition but not with age. Spectral characters from the wings and rump were not associated with any of the reproductive parameters measured. In conjunction with published evidence showing that females preferentially accept extrapair copulations from older males, these data suggest a need for experimental manipulation of plumage colour in known-aged birds to understand mate choice in this species.     

Positive assortative pairing by plumage colour in Spanish imperial eagles

Intraspecific variation in plumage may have a functional significance in mate choice. As a result, breeding birds are often paired assortatively with respect to colour. However, whether this within-pair correlation is a result of homotypic preference whereby individuals pick a mate that looks like themselves, or directional preference whereby all individuals have the same phenotypic preference, is often unknown. Using data collected between 1989 and 2006, we describe intraspecific variation in the striking white feathers on the leading edge of the wing, lesser coverts and mantle of 144 Spanish imperial eagles (Aquila adalberti), one of the most endangered birds of prey in the world. Females had, on average, more white than males, and pairs mated in a positive assortative fashion. Coloration was not related to age of the bird, food supply (i.e., territory quality) or breeding productivity. Our results are most consistent with the process of homotypic-preference assortative mating, and this may be a result of sexual imprinting, and function as a mechanism to optimize the degree of outbreeding. This pattern of mate selection may explain the rapid evolutionary divergence of A. adalberti from the continental population of imperial eagle A. heliaca.     

Why do melanin ornaments signal individual quality? Insights from metal element analysis of barn owl feathers

Melanin-based variation in colour patterns is under strong genetic control and not, or weakly, sensitive to the environment and body condition. Current signalling theory predicts that such traits may not signal honestly phenotypic quality because their production does not entail a significant fitness cost. However, recent studies revealed that in several bird species melanin-based traits covary with phenotypic attributes. In a first move to understand whether such covariations have a physiological basis, we quantified concentrations of five chemical elements in two pigmented plumage traits in the barn owl (Tyto alba). This bird shows continuous variation from immaculate to heavily marked with black spots (plumage spottiness) and from dark reddish-brown to white (plumage coloration), two traits that signal various aspects of individual quality. These two traits are sexually dimorphic with females being spottier and darker coloured than males. We found an enhancement in calcium and zinc concentration within black spots compared with the unspotted feather parts. The degree to which birds were spotted was positively correlated with calcium concentration within spots, whereas the unspotted feather parts of darker reddish-brown birds were more concentrated in zinc. This suggests that two different pigments are responsible for plumage spottiness and plumage coloration. We discuss the implications of our results in light of recent experimental field studies showing that female spottiness signals offspring humoral response towards an artificially administrated antigen, parasite resistance and fluctuating asymmetry of wing feathers.An erratum to this article can be found at     

MALE MATE CHOICE AND THE EVOLUTION OF FEMALE PLUMAGE COLORATION IN THE HOUSE FINCH

The house finch (Carpodacus mexicanus) is a sexually dichromatic passerine in which males display colorful plumage and females are generally drab brown. Some females, however, have a subdued version of the same pattern of ornamental coloration seen in males. In previous research, I found that female house finches use male coloration as an important criterion when choosing mates and that the plumage brightness of males is a reliable indicator of male nest attentiveness. Male house finches invest substantially in the care of young and, like females, stand to gain by choosing high-quality mates. I therefore hypothesized that a female's plumage brightness might be correlated with her quality and be the basis for male mate choice. In laboratory mate choice experiments, male house finches showed a significant preference for the most brightly plumaged females presented. Observations of a wild population of house finches, however, suggest that female age is the primary criterion in male choice and that female plumage coloration is a secondary criterion. In addition, yearling females tended to have more brightly colored plumage than older females, and there was no relationship between female plumage coloration and overwinter survival, reproductive success, or condition. These observations fail to support the idea that female plumage coloration is an indicator of individual quality. Male mate choice for brightly plumaged females may have evolved as a correlated response to selection on females to choose brightly colored males.     

The Value of Immaculate Mates: Relationships between Plumage Quality and Breeding Success in Shelducks

Immaculateness, a novel measure of bird plumage quality, defined as the regularity of the borders of a coloured patch of feathers, and the uniformity of the colour within the patch, tends to decline as a result of feather wear and damage. If it declines more quickly amongst birds in poor condition, it has the potential to act as an honest signal of individual quality and therefore be subject to social and sexual selection. We scored plumage immaculateness in shelducks Tadorna tadorna, based on the absence of white feathers in the red-brown chest band and the evenness of the band's border. We monitored body condition and plumage quality in birds at feeding sites in the Severn Estuary (UK) during the early breeding season when females were forming eggs, and later in the season when chicks arrived. Drakes had more immaculate chest bands than ducks. At preferred feeding sites, drakes were more immaculate, and birds of both sexes were in better body condition. Birds with more immaculate plumage tended to mate assortatively at preferred sites and were more likely to produce a brood that survived the journey to the feeding areas. Immaculateness could therefore be an honest signal of parental quality. Although our evidence is only correlational, we suggest that plumage immaculateness indicates the ability to establish and maintain control over the best breeding sites and feeding territories in the face of competition with other shelducks.     

Phenotypic plasticity in breeding plumage signals in both sexes of a migratory bird: responses to breeding conditions

Adaptive phenotypic plasticity may respond to present ambient conditions. Sexual and social signals in both sexes may express phenotype performance. Plumage signals that change discontinuously allow relating discrete variation to previous performance. Both sexes of the pied flycatcher Ficedula hypoleuca present white patches on the wings and on the forehead, which constitute sexual and social signals. Forehead patches are moulted together with body plumage in Africa, while wing patches are partly moulted in Africa and partly in the breeding area soon after breeding. We studied individual inter‐year changes (corrected for regression to the mean) in the size of forehead and wing patches of both sexes in seven years for females or six years for males in two nearby study areas in central Spain. We found that initial signal extent strongly delimits the possible subsequent changes negatively. There is a negative association of male age with forehead patch changes. Cold and rainy springs are associated in females with decreases in both patch areas and vice versa, while no association with climate is observed in male wing patch changes. Cold pre‐breeding conditions predict positive changes in female wing and male forehead patches. Breeding success is positively associated with forehead patch changes in females. Late‐breeding males experience more positive changes in forehead patch size than early‐breeding males. Some of these trends can be explained by variable costs of breeding in certain conditions for subsequent signal production and/or maintenance, while absence of trends in some cases may be explained by sex differences in costs of breeding and interactions with phenotypic quality of breeders.     

Experimental evidence for female choice and energetic costs of male tail elongation in red-collared widowbirds

The black nuptial plumage of the highly polygynous male red‐collared widowbird (Euplectes ardens) comprises a red carotenoid‐based collar patch and a long graduated tail (c. 22 cm). Tail length was the strongest predictor of male mating success in a previous selection analysis, motivating this experimental test of the relative importance of tail plumes in male contest competition and female choice. Males were assigned to either a short (12.5 cm) or control (20 cm) tail manipulation prior to territory establishment. Male contest competition was unaffected by the tail treatments as the shortened‐ and control‐tailed males were equally successful in acquiring territories of similar size and quality. In contrast, however, although the longer‐tailed control males spent less time in flight and courtship displays, they attracted significantly more prospecting and nearly three times as many nesting females to their territories compared to the short‐tailed males. In further support of tail length as the primary mate choice cue, none of the other measured and potential female cues (e.g. body size, collar colorimetrics, territorial behaviours or territory quality) influenced male reproductive success. In addition to potentially increasing detectability (‘signal efficacy’), the long tail is also a likely indicator of male quality (‘signal content’). Despite the higher activities of short‐tailed males, control‐tailed males showed a steeper decline in condition (relative body mass) during the breeding season. Furthermore, both short‐ and control‐tailed residents lost more condition than did the short‐ and control‐treated floaters (males not establishing territories), suggesting an interaction between tail length and the costs of territory acquisition, defence and courtship displays. These results confirm the role of mate choice and honest quality advertising as the main selection pressures behind elongated tails in widowbirds. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 35–43.     

Dressed to impress: breeding plumage as a reliable signal of innate immunity

Animal signals involved in sexual selection are often indicators of individual quality. The assumption that sexual characters such as breeding plumage may indicate immune state has rarely been tested in free‐living migratory birds, particularly in relation to innate immunity. If sexual characters indeed reflect immune condition, then these could be used to evaluate individual quality. Melanin is a common pigment used in animal communication that mitigates the effects of oxidative stress and has positive effects on energy homeostasis, important functions during the strenuous activity of long‐distance flights. However, melanin is also immunosuppressive, and the melanised patches of breeding plumage may to some extent compromise immune responsiveness. We studied melanin‐based secondary sexual characters (SSC) in a long‐distance migratory wader, the black‐tailed godwit Limosa limosa, and found that breeding plumage features of male and female godwits are linked to components of innate immunity. Males with a larger colour extension had higher circulating levels of haptoglobin and hemolysis activity, while they also presented a lower body condition; whereas females presented a negative trend between colour and bar extension and hemolysis activity, and a positive trend for natural antibodies. The association between signal, immune state and physical condition in males suggests a cost for signal production and immune condition during prenuptial migration. Sex differences in how signals relate with immune capacity are a likely consequence of sex‐specific signalling roles and energy demands. Our results indicate that male godwit breeding plumage reflects innate immunity state, and is therefore a likely signal for females to use during mate choice as an honest indicator of male's capacity to allocate energy/resources to both expensive traits during periods of energetic constraint.     

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 coloration can be perceived as a multiple condition‐dependent signal by Great Tits Parus major

The evolution of multiple signals can be explained because they enhance the perception of a general message by recipients. Plumage coloration frequently acts as a condition‐dependent signal, so that species displaying different colour patches have the potential to transmit information on condition through a multiple signalling system. The Great Tit Parus major exhibits plumage colour patches generated by the main types of colour production, some of which, particularly those based on melanins and carotenoids, are known to be related to body condition. However, the colour expressions of all of the different colour types have never been investigated simultaneously to determine whether they function as multiple signals of condition. In addition, visual perception models have never been applied to a multiple signalling system in a wild population of birds. Here I present information that links body condition with the colour expression of almost all of the different plumage patches of male Great Tits captured during the winter. Birds in better condition had greater reflectance values at short wavelengths in all plumage patches, and this was especially so in the white (i.e. structural) colour of the cheeks. Plumage colour characteristics were calculated by means of avian visual models, suggesting that Great Tits have the capacity to perceive information contained in the plumage coloration of conspecifics. These results show that short‐wavelength reflectance has great potential to transmit biologically significant information on the body condition of birds, even in achromatic plumage patches.     

Limited condition dependence of male acoustic signals in the grasshopper Chorthippus biguttulus

In many animal species, male acoustic signals serve to attract a mate and therefore often play a major role for male mating success. Male body condition is likely to be correlated with male acoustic signal traits, which signal male quality and provide choosy females indirect benefits. Environmental factors such as food quantity or quality can influence male body condition and therefore possibly lead to condition-dependent changes in the attractiveness of acoustic signals. Here, we test whether stressing food plants influences acoustic signal traits of males via condition-dependent expression of these traits. We examined four male song characteristics, which are vital for mate choice in females of the grasshopper Chorthippus biguttulus. Only one of the examined acoustic traits, loudness, was significantly altered by changing body condition because of drought- and moisture-related stress of food plants. No condition dependence could be observed for syllable to pause ratio, gap duration within syllables, and onset accentuation. We suggest that food plant stress and therefore food plant quality led to shifts in loudness of male grasshopper songs via body condition changes. The other three examined acoustic traits of males do not reflect male body condition induced by food plant quality.