Plumage Brightness Research Articles

Incorporating Behavior Services into the Avian Practicea

Although people have been sharing their homes and lives with pet parrots for the past 2000 years, only recently have most pet-bird owners started to realize the potential of these amazing creatures. Originally, birds appealed to humans because of their bright plumage and capacity to imitate human speech. Today, parrots are increasingly recognized as complex, intelligent, and highly social animals. Many parrots are hand raised by humans, making them much more integrated into their human flocks. Like any other animal, parrots are susceptible to several behavioral and psychological disorders. With the exception of the domesticated species such as budgerigars (Melopsittacus undulatus), lovebirds (Agapornis species), and cockatiels (Nymphicus hollandicus), most psittacine birds are only one or two generations from the wild state. They still retain many natural behaviors that help them survive and succeed in the wild but can make it difficult for

Carotenoid-based ornamentation and status signaling in the house finch

The status signaling hypothesis (SSH) was devised primarily to explain the adaptive significance of avian ornamental coloration during the nonbreeding season. It proposes that conspicuous male plumage serves as an honest signal of social status within a population of birds. However, to date this hypothesis has been well tested and supported for only one type of plumage coloration, melanin-based coloration. Carotenoid-based pigmentation is known to positively reveal male health and condition during molt in a variety of species, but it is poorly understood whether this ornament type can also function as a status signal during the winter. We tested the SSH in male house finches (Carpodacus mexicanus) by manipulating the carotenoid-based plumage brightness of first-year males and then pairing unfamiliar birds of differing coloration in a series of dominance trials in captivity. Manipulated plumage color was unrelated to win/loss outcome in these trials. Similarly, the natural pigmentation of males was a poor predictor of winter dominance; as in other studies with this species, we found only a weak tendency for naturally drab males to dominate naturally bright males. These results suggest that carotenoid-based coloration is not a reliable indicator of social status in male house finches during the nonbreeding season. In fact, carotenoid-based coloration may function only in mate choice in this species, and it may be retained throughout the year either because time constraints preclude a second plumage molt or because it aids in pair formation that begins in late winter.

Male greenfinches (Carduelis chloris) with brighter ornaments have higher virus infection clearance rate

Hamilton and Zuk proposed that bright plumage in birds indicates genetic resistance to parasites, and that by selecting brighter males as mates, females can increase their offspring’s fitness due to this inherited resistance. The theory predicts a negative relationship between parasite load and plumage brightness in males. We used Sindbis virus clearance rate after an experimental infection to quantify parasite resistance in male greenfinches (Carduelis chloris) and related variation in clearance rate with variation in male plumage brightness. We found that certain aspects of brightness of the male plumage (i.e. tail-patch area) could be used to predict the virus infection clearance rate. Wing brightness was uninformative of virus clearance rate, but revealed age class. We found no clear relationship between antibody production rate and virus clearance rate or total viraemia. However, males with large tail patches tended to have a higher antibody production rate. The results suggest that the size of the male tail patch may function as an indicator of an individual male’s ability to resist parasite infections, thus supporting the Hamilton-Zuk theory for a novel taxon of parasites, a virus.

Testosterone is involved in acquisition and maintenance of sexually selected male plumage in superb fairy-wrens, Malurus cyaneus

Testosterone has been proposed as a physiological link between the level of sexual signalling and male condition. Bright plumage is one of the most noticeable sexual signals and is often used by females as a basis for mate choice. Yet bright male plumage is not necessarily testosterone dependent. We investigated the role of testosterone in the moult into seasonal nuptial plumage in male superb fairy-wrens. Early pre-nuptial moult is under intense intersexual selection and males can acquire the bright plumage any time between autumn and the next spring. Testosterone was always undetectable or very low in males in dull eclipse plumage. During the pre-nuptial moult, both the number of males with detectable testosterone and average testosterone levels increased sharply. High testosterone was more correlated with nuptial plumage than with presence of the cloacal protuberance (indicative of sperm storage). Subcutaneous testosterone implants always induced the pre-nuptial moult within 2–3 weeks after implantation, even well outside the natural time range of moulting. Moreover, removal of the implants before the nuptial plumage was completed, arrested the moult process. The evidence suggests that development of the nuptial plumage is testosterone dependent, although we cannot exclude that testosterone exerts its action after conversion to a metabolite such as oestrogen. Once the nuptial plumage was completed, all males maintained substantially elevated testosterone, sometimes months before the onset of breeding. These high levels could be necessary to maintain the plumage, and/or are involved in courtship displays. The results are discussed with respect to potential costs involved in acquiring and maintaining the nuptial plumage.

Plumage Brightness and Breeding-Season Dominance in the House Finch: A Negatively Correlated Handicap?

Abstract A variety of observations indicate that the carotenoid-based coloration of male House Finches (Carpodacus mexicanus) is an honest signal of quality. Plumage redness in this species positively reveals male nutritional condition, over-winter survival, and nest attentiveness. As a result, in the breeding season, male House Finches with brighter ornamental plumage are preferred by females as social mates over males with drabber plumage. In the nonbreeding season, however, bright red plumage does not seem to confer an advantage in aggressive interactions, as males with drabber plumage tend to dominate males with brighter plumage. We investigated this apparent paradox by conducting a breeding-season dominance experiment using captive males. We paired unfamiliar males of contrasting plumage brightness in a series of dominance trials during the breeding season and found that drabber males were dominant to brighter males in competition for access to food. Furthermore, in two captive flocks of males, plumage brightness was significantly negatively associated with social dominance. Although we have no conclusive evidence to explain why drab male House Finches are dominant to bright males throughout the year, we believe that motivational asymmetry may contribute to the observed negative correlation between signal intensity and signaler quality (“negatively correlated handicap”). Drab males may be more willing to compete for access to food or to females than are bright males because of the nutritional and/or mating disadvantages from which they suffer.

Plumage Brightness and Breeding-Season Dominance in the House Finch: A Negatively Correlated Handicap?

Plumage Brightness and Breeding-Season Dominance in the House Finch: A Negatively Correlated Handicap?

PLUMAGE BRIGHTNESS AND BREEDING-SEASON DOMINANCE IN THE HOUSE FINCH: A NEGATIVELY CORRELATED HANDICAP?

Abstract A variety of observations indicate that the carotenoid-based coloration of male House Finches (Carpodacus mexicanus) is an honest signal of quality. Plumage redness in this species positively reveals male nutritional condition, over-winter survival, and nest attentiveness. As a result, in the breeding season, male House Finches with brighter ornamental plumage are preferred by females as social mates over males with drabber plumage. In the nonbreeding season, however, bright red plumage does not seem to confer an advantage in aggressive interactions, as males with drabber plumage tend to dominate males with brighter plumage. We investigated this apparent paradox by conducting a breeding-season dominance experiment using captive males. We paired unfamiliar males of contrasting plumage brightness in a series of dominance trials during the breeding season and found that drabber males were dominant to brighter males in competition for access to food. Furthermore, in two captive flocks of males, pluma...

Evolutionary exposition from plumage pattern in African Accipiter

Louette, M. 2000. Evolutionary exposition from plumage pattern in African Accipiter. Ostrich 71 (1 & 2): 45–50. Plumage characteristics were superficially taken into account by Wattel (1973) for his division of the genus Accipiter; Savalli (1995) formulated hypotheses to explain plumage colouration evolution in birds in general. I examine here variation of plumage coloration and pattern in the 14 African species of Accipiter, in order to evaluate their phylogenetic and/or functional values. I study isolated populations in this respect: — A.francesae: the derived Comoro Islands taxa are remarkably different from the Madagascar stock in the disappearance of adult sexual dimorphism and by the ‘reversion’ to an ancestral juvenal pattern. — A. tachiro: the derived Pemba Island taxon is more colourful in adult plumage than the Tanzanian savanna-dwelling stock. The Bioko Island taxon derived from Cameroonian forest stock and is only slightly different therefrom. Juvenal plumage is remarkably variable among central African forest races, supposedly because in sympatry with other Accipiter species, the juvenile needs to be recognised by conspecifics. From a general examination of the African species it appears that: — Adults can be dimorphic (cryptic females) or monomorphic (both sexes colourful or both sexes cryptic). Bright adult plumage serves sexual attraction: in dense environment better visibility of bright colour is on balance advantageous over crypsis. — Juvenal plumages are mostly highly cryptic; ventrally, the basal colour occurs in two phases within species and the pattern is variable among species: it can be streaked, barred or spotted. In most African Accipiter certain bright colours present in the adult are announced in the juvenile plumage. It is assumed that the cryptic juvenal plumage serves to minimise harassment by territorial adults, but in some species, the juvenile resembles the adult female, the reason for this mimicry is not yet established. Juvenal and adult plumages being subject to rapid evolutionary change, they seem to be of limited use in phylogeny.

Plumage polymorphism in Terpsiphone and the rule of island drabness

Plompen, W. 2000. Plumage polymorphism in Terpsiphone and the rule of island drabness. Ostrich 71 (1 & 2): 316. Many related bird species differ through their conspicuous plumage coloration characteristics. On islands, birds often have a drabber plumage coloration than their mainland counterpart. This rule is regarded as the main evidence for the species recognition hypothesis, because on islands mostly only one species per genus is present. In the absence of congeners there may be no benefit from a species specific badge, with drabness as a result. However drabness as such is not predicted by this species recognition hypothesis. In fact the only selective pressure caused by a species recognition mechanism, works in sympatry. Therefore on an island with no related species present, the elaborate coloration that originated in the mainland situation, is allowed to evolve in any sense, or may even not evolve at all. Taking this all together, if under the. species recognition hypothesis island taxa may evolve at random with respect to colouration, and island drabness is a well known phenomenon, then an additional mechanism inherent to the island situation is needed, that causes the degradation of any bright plumage colouration. As a consequence, island drabness in itself does not provide any information at all on the original mechanism that caused plumage elaboration on the mainland.

Blood parasites, leucocytes and plumage brightness in the Cirl Bunting,Emberiza cirlus

1.Although a female preference for pairing with brightly plumaged males has been reported in many species, the reasons for this choice are not fully understood.2.Parasites have been proposed as playing an important role in shaping these preferences because, by pairing with brightly coloured individuals, females can obtain parasite‐free and/or more healthy mates.3.In this paper one of the predictions of this hypothesis is tested, namely a higher health level in brightly coloured individuals, by analysing the relationships among blood parasites, leucocyte levels and plumage brightness in the Cirl Bunting,Emberiza cirlus.4.Two species of blood parasites were detected. Whereas a lower body condition was detected in individuals infected byLeucocytozoon cambournaci,no such differences were associated withPlasmodium relictuminfections. Infected individuals showed higher total leucocyte counts than non‐infected individuals.5.Colour intensity of carotenoid derived colorations was negatively correlated to the relative proportion of lymphocytes and positively correlated to the relative presence of heterophils. Furthermore, the size of yellow feathered areas was positively correlated with the absolute number of leucocytes and the relative presence of heterophils. Only some of these relationships were found for non‐carotenoid derived traits.6.These results suggest that male plumage yellow coloration in the Cirl Bunting is a reliable indicator of health status and supports the hypothesis that females obtain more parasite‐free mates if they pair with brightly coloured individuals.

Evolution of Avian Plumage Dichromatism from a Proximate Perspective

abstract: Several studies have indicated that sexual plumage dichromatism is a result of four proximate mechanisms: estrogen, testosterone, luteinizing hormone, and nonhormonal factors. In estrogen‐dependent dichromatism, dull plumage coloration develops in the presence of estrogen, while bright coloration develops in its absence. In testosterone‐dependent and luteinizing hormone–dependent plumage dichromatism, bright plumage develops in the presence of these hormones, while dull plumage develops in their absence. Placing the proximate control of plumage dichromatism in a phylogenetic context suggests that estrogen‐dependent plumage dichromatism, found in the avian orders Struthioniformes, Galliformes, and Anseriformes, is likely to be ancestral in extant birds, while plumage dichromatism dependent on testosterone, luteinizing hormone, or nonhormonal factors is a more derived condition. An examination of the possible pathways leading to estrogen‐dependent plumage dichromatism suggests that the fewest evol...

Relative Effects of Plumage Coloration and Vegetation Density on Nest Success

Many passerine species are highly dichromatic with brightly-colored males and cryptically-colored females. Bright plumage in males is commonly thought to arise as a rcsult of sexual selection by females such that males with bright coloration possess high fitness. However, bright plumage potentially could expose males to increased predation risk. Consistent with this idea, males of many highly dichromatic passerine species do not incubate. I tested whether brightly-colored males avoid incubation to reduce the probability of visual predators locating their nest. This hypothesis predicts greater hatching success for clutches incubated by cryptically-colored individuals than by brightly-colored individuals. The Northern Cardinal (Cardinalis cardinalis) is a common dichromatic species that breeds throughout the eastern U.S. I placed two button-quail (Turnix sp.) eggs in each of 203 simulated cardinal nests. Dull brown cardboard, simulating a female cardinal, was placed over about half of all clutches. Bright red cardboard, simulating a male cardinal, was placed ovcr the other clutches. Nest success was highest for well-concealed nests (87%) and lowest for nests in open habitat (54%). Nests containing red cardboard did not have significantly lower success than nests with brown cardboard, nor did I detect a significant color X vegetation-density interaction. My analysis may have had insufficient power to detect an effect of color on nest success; alternatively, brightly-colored males that do not incubate may achieve benefits unrelated to predation risk.

Condition–dependent variation in the blue–ultraviolet coloration of a structurally based plumage ornament

After years of investigation into the function of sexually dimorphic ornamental traits, researchers are beginning to understand how bright plumage colour in birds acts as an intraspecific signal. This work has focused primarily on pigment-based ornaments because they are highly variable in patch size, hue and brightness for some species. In contrast, structurally based ornaments have been little studied, in part because they do not appear to be as variable as pigment-based ornaments. We investigated a structurally based plumage ornament in a wild population of blue grosbeaks (Guiraca caerulea), a sexually dimorphic passerine. We report plumage variation that extends into the ultraviolet region of the spectrum. The pattern of covariation between four out of five elements of plumage variation suggests that structurally based ornamentation is pushed towards extreme expression of the trait as predicted by the sexual selection theory. The 'bluest' birds have the highest percentage of blue feathers on the body. These ornamental feathers reflect light maximally at the shortest wavelengths (ultraviolet), with the greatest intensity and the greatest contrast. Age may have some effect on expression of blueness. In addition, plumage variables are correlated with growth bars in tail feathers (a record of nutritional condition during moult in a non-ornamental trait). This suggests that the ornament is partially condition dependent. Thus, blue plumage in male grosbeaks may serve as an honest indicator of age and quality.

The overlooked signaling component of nonsignaling behavior

The handicap principle (Zahavi, 1975, 1987; Zahavi and Zahavi, 1997) is now widely used to explain the evolution of conspicuous signals such as tail ornaments, courtship displays, and nestling begging (Godfray, 1991; Grafen, 1990a,b; Johnston, 1997; Maynard Smith and Harper, 1995). The essence of the model is that signals must be costly to be honest. Females have evolved preferences for males with longer tails or brighter plumage, for example, because only males of high quality can survive and perform with handicapping ornaments. Despite the general acceptance that the handicap principle explains extravagant morphological and behavioral signals, the model’s mechanism has not been broadly applied to explain a host of other behaviors. Here we suggest that the selection on animal behavior to be performed differently when observed by other animals can lead to significant quantitative changes in behavior. Although such changes in the level or intensity of a behavior may not justify calling the behavior a signal, they can evolve as signaling components to behaviors whose primary function is not signaling (i.e., they can shift the level of the behavior from its nonsignaling optimum). We call this idea the overlooked signaling component of behavior. We explore this issue using three examples: (1) prey fleeing a predator; (2) human behavior in the presence of others; and (3) parental care behavior. We then apply the overlooked signaling component to reexamine Zahavi’s (1977, 1995) suggestion that altruism is a signal of social prestige. Whereas Zahavi presents his ‘‘prestige hypothesis’’ as an alternative to kin selection, we show how both theories can work together. We suggest that helping behavior among kin, which increases inclusive fitness, may also eventually evolve into signals of individual quality, condition or need. We conclude by suggesting ways to test for signaling components of animal behaviors.

Testis size variation in the greenfinch Carduelis chloris : relevance for some recent models of sexual selection

Interspecific evidence that testis size responds to selection caused by sperm competition has been obtained from many taxa. However, little is known about the sources of intraspecific variation in testis size, although such variation may have functional significance. Variation in testis size and asymmetry was studied within and between eight geographically separated (and genetically differentiated) populations of greenfinches Carduelis chloris. The relationships between testis size and plumage brightness (degree of yellowness) and the prevalence of haematozoan infections were also investigated in three of these populations, as they related to the predictions of the immunocompetence handicap hypothesis, and Moller's hypothesis relating directional testis asymmetry to phenotypic quality. There were large differences between populations in testis size, with males from northern populations having larger testes than those from southern populations. Within populations, large testes were associated with larger body size and greater age. When the influence of these factors was removed statistically, males with large testes were more likely to be infected with haematozoan parasites, and had brighter yellow plumage. No evidence was found that directional asymmetry in testis size was related to either of these measures of phenotypic quality. These results are consistent with the hypothesis that males with large testes, while signalling higher phenotypic quality as revealed by increased plumage brightness, also pay a cost in terms of reduced immunocompetence, revealed by the increased probability of infection in these males. That these patterns were similar in three different populations adds further strength to these conclusions. Our results suggest that studying the sources of variation in testis size among individuals can reveal interesting processes in sexual selection.

Plumage brightness in relation to haematozoan infections in the greenfinch Carduelis chloris: Bright males are a good bet

Variation in plumage brightness (yellowness) and prevalence and intensity of haematozoan infections in greenfinches Carduelis chloris L. were studied in three populations, widely separated in geographic location from Spain to Finland. Sexual dichromatism (SD) in coloration was marked, males being yellower than females. Although older birds were generally yellower than younger birds, the degree of SD in coloration increased with age, perhaps due to delayed plumage maturation in males. The prevalence of haematozoan infections was unrelated to any measure of male plumage coloration, but the intensity of haematozoan infections was strongly negatively related to male plumage brightness, and this pattern was similar in all three populations. Hence, male plumage brightness reveals information about the extent to which males are parasitized. This result is in accordance with the Hamilton-Zuk hypothesis, which suggests that bright male plumage has evolved to indicate heritable resistance to parasites. The fact that lightly-infected males had brighter plumage than non-infected and heavily infected ones may suggest that non-infected males were a mixture of both susceptible and resistant individuals, whereas lightly infected individuals might have been effectively immune to parasites. Our data provide a clear example of the negative association between plumage brightness and blood parasite loads in birds, and suggest that male plumage yellowness in the greenfinch can function as an indicator of male quality.

The evolution of bill coloration and plumage dimorphism supports the transference hypothesis in dabbling ducks

Bright coloration in male birds is typically thought to be driven by sexual selection (female choice or male–male competition). Bird species often vary in the intensity of bright coloration, but few studies have addressed this cross-species variation. Potentially this variation could result from either variation in female preferences or in the relative costs of male traits. Species of dabbling ducks vary in the presence of bright male plumage and bill coloration. I tested the transference hypothesis for ornament evolution in dabbling ducks using a phylogenetic study of character evolution. The transference hypothesis makes three predictions: (1) a costly male ornamental trait is the ancestral condition, (2) a less costly male ornamental trait is the derived condition, and (3) gains in the less costly trait are associated with losses or absence of the more costly male trait. All three of these predictions were satisfied in this study of the evolution of plumage dimorphism and bright bill coloration in the dabbling ducks, given that bright plumage coloration is more costly than bright bill coloration.

Host immune function and sexual selection in birds

AbstractParasites have been hypothesized to affect sexual selection of their hosts, if secondary sexual characters reliably signal absence of infectious parasites, superior parenting ability caused by the absence of parasites, or heritable resistance to parasites, for which there is some intraspecific and interspecific evidence. Measures of immune defence of hosts provide reliable information on the current infection status of individuals of the chosen sex, usually males, and correlations between immune defence and development of secondary sexual characters thus provide a novel critical test of parasite‐mediated sexual selection. In a comparative study of birds, sexually dichromatic species had higher immune defences, measured in terms of leukocyte concentration and the size of spleen and bursa of Fabricius, respectively, than closely related, monochromatic species. Male plumage brightness was consistently negatively related to the size of the spleen in males of sexually dichromatic species, but not in males of monochromatic species. Hence, the brightest males, which frequently are preferred as mates by choosy females, had low levels of immune defence, suggesting that such males were healthy. This provides evidence for a general role of parasites in sexual selection among their bird hosts.

Sex, size, and plumage redness predict house finch survival in an epidemic

Mycoplasma gallisepticum is a well-known disease of poultry but until 1994 had not been observed in passerine birds. From 1994 to 1996, tens of millions of house finches (Carpodacus mexicanus) are believed to have died in an epidemic of mycoplasmal conjunctivitis, similar to 'pinkeye' in humans. The outbreak of Mycoplasma gallisepticum affected finches of both sexes but disproportionately killed males, shifting the sex ratio from male-biased to female-biased. This differential male mortality is consistent with a cost of testosterone, which is a key prediction of the immunocompetence handicap hypothesis. Males and females that survived the epidemic weighed significantly less and had significantly shorter wing chords, tarsi, and bills than did individuals before the epidemic. Male survivors also had significantly redder plumage than males that did not survive, supporting the idea that plumage brightness serves as an indicator of condition, as proposed by the honest advertisement model of sexual selection.

Moult speed predicts pairing success in male harlequin ducks

The bright plumage of male ducks in sexually dichromatic species is thought to have evolved through intense sexual selection. This study examined the relationship between the timing and speed of moult into this bright plumage and subsequent mating success of male harlequin ducks,Histrionicus histrionicus. Males that moulted relatively slowly had a lower chance of establishing a pair bond than others. The timing of moult was unrelated to whether a male obtained a mate. Moult speed and timing were not correlated within individual males, but were significantly repeatable in individual males over 2 years. Moult speed probably reflects the condition of males, whereas timing of moult is more likely to be related to the distance to an individual's breeding area, which determines the timing of arrival to the moulting grounds. In waterfowl species that have been studied, males usually form dominance hierarchies before pairing and females tend to choose dominant males. We suggest that male harlequin ducks that moult slowly are poor-quality individuals, which are relegated to subordinate status and are unlikely to attract a mate the following autumn.