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 by Leucocytozoon cambournaci, no such differences were associated with Plasmodium relictum infections. 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.     

Coloration,Paternity, and Assortative Mating in Western Bluebirds

Coloration in birds can act as an important sexual signal in males, yet in many species, both sexes display bright colors. Social selection may account for this pattern, with more brightly colored individuals pairing together on the best territories. Mutual mate choice may also explain this, as males investing a great deal of parental care in the offspring should be choosy about their social mates. It is less clear whether this pattern of mate choice can apply to extra‐pair partners as well. We examined western bluebirds (Sialia mexicana) to determine whether more colorful individuals tended to pair with one another, both in social pairs and between females and their extra‐pair partners. Both male and female western bluebirds display both UV‐blue structural plumage and a melanin‐based chestnut breast patch, although females are duller than males. Social pairs mated assortatively with regard to UV‐blue brightness, but not chestnut coloration. There was no evidence that extra‐pair partners mated assortatively, but males with brighter UV‐blue coloration had fewer extra‐pair offspring in their nests. Older males were more successful at siring extra‐pair offspring, despite displaying no differences in coloration compared to younger males. Coloration did not play a role in determining extra‐pair male success. These results suggest that coloration plays a role in the formation of social pairs, but not mate choice for extra‐pair partners.     

Pairing success relative to male plumage redness and pigment symmetry in the house finch: temporal and geographic constancy

Male house finches (Carpodacus mexicanus) have carotenoid-based ornamentalplumage coloration. In previous research it was shown that fora single population of house finches in a single year, malesthat paired were on average redder in plumage coloration thanmales that did not pair, and males with redder plumage tendedto nest earlier than males with less red plumage. Here we showthat these patterns continued over 6 years and at two widely separatedlocations. We also tested whether the symmetry of carotenoid-based crownpigmentation differed between paired and unpaired males andfound that paired males have, on average, more perfect symmetryof crown pigmentation than males not paired. These observationssupport the idea that expression of carotenoid-based plumagecoloration by males is a persistent and widespread criterionin female mate choice in the house finch.     

Dietary carotenoids predict plumage coloration in wild house finches

Carotenoid pigments are a widespread source of ornamental coloration in vertebrates and expression of carotenoid-based colour displays has been shown to serve as an important criterion in female mate choice in birds and fishes. Unlike other integumentary pigments, carotenoids cannot be synthesized; they must be ingested. Carotenoid-based coloration is condition-dependent and has been shown to be affected by both parasites and nutritional condition. A controversial hypothesis is that the expression of carotenoid-based coloration in wild vertebrates is also affected by the amount and types of carotenoid pigments that are ingested. We tested this carotenoid-limitation hypothesis by sampling the gut contents of moulting house finches and comparing the concentration of carotenoid pigments in their gut contents with the colour of growing feathers. We found a positive association: males that ingested food with a higher concentration of carotenoid pigments grew brighter ornamental plumage. We also compared the concentration of carotenoids in the gut contents of males from two subspecies of house finches with small and large patches of carotenoid-based coloration. Consistent with the hypothesis that carotenoid access drives the evolution of carotenoid-based colour displays, males from the population with limited ornamentation had much lower concentrations of carotenoids in their gut contents than males from the population with extensive ornamentation. These observations support the idea that carotenoid intake plays a part in determining the plumage brightness of male house finches.     

Do Female Mandrills Prefer Brightly Colored Males?

Although secondary sexual adornments are widespread in male primates, few studies have examined female choice for these characters. Mandrills (Mandrillus sphinx) present an extreme example of sexual dimorphism, with males exhibiting an array of striking adornments. The most dominant adult male in a group exhibits the brightest and most extensive red coloration, while the other males are less brightly colored. I examined whether female mandrills prefer brightly colored males using data on periovulatory sexual behavior during the 1996 mating season for all males 8 years old (n = 5) and all parous females (n = 9) in a semifree-ranging colony at CIRMF, Gabon. Brightness of male coloration is significantly positively correlated with time spent within 2 m of females, female responsibility for proximity, number of sexual presentations received, % approaches accepted by females, and % inspections with which females cooperated. Females also groomed only the brightest male. Behaviors indicating female preference are not correlated significantly with male dominance rank, and partial correlations confirm that the influence of male color on female behavior is stronger than that of male rank. With the influence of male dominance rank controlled, correlation coefficients between female behaviors and male mating success are high and positive. In further support of the hypothesis that females show mate choice for brightly colored males, independent of dominance rank, I report an unusual case wherein the alpha male fell in rank without loss of coloration. He experienced no significant change in female responsibility for proximity, sexual presentations received, or female reaction to approaches or inspections, though he was no longer observed to mate. Accordingly, female mandrills attend to differences in male secondary sexual characters and favor brightly colored males. As brightly colored males are also dominant this reinforces the influence of male-male competition on male reproductive success and may explain the very high reproductive skew in mandrill males and their extraordinary appearance.     

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.     

Ornamental plumage coloration and condition are dependent on age in eastern bluebirds Sialia sialis

Male eastern bluebirds Sialia sialis have striking ultraviolet (UV)-blue coloration on their heads, backs, rumps, wings, and tails and bold chestnut coloration on their breasts. These colored areas are ornaments that correlate with pairing date and reproductive effort, and thus probably influence the choice of mates by females. Such ornaments are expected to increase in color with age and body condition. We investigated the effects of age on body condition and the UV-blue and chestnut coloration of males over four years using both cross-sectional (comparing age classes) and longitudinal analyses (following individuals as they age). We found that both the body condition index and brightness of UV-blue rump coloration increased with age, while UV-blue tail plumage coloration increased between yearling and older males, and the chestnut breast coloration decreased in the oldest age class. The proximate mechanisms whereby individuals reliably signal age via rump brightness and tail coloration are probably different. Contour feathers, including rump feathers, are molted at approximately the same time in all age classes and are likely subject to the same production costs in all age classes. In contrast, the molt schedule of the tail and wing feathers differs between individuals of yearling and older age classes, with yearlings retaining wing and tail feathers for several months longer than adults. The relationship between tail color and age was probably, in part, a consequence of yearlings expressing tails that have increased feather wear and accumulation of dirt. In general, UV-blue coloration increased with age while chestnut plumage decreased with age, indicating that older individuals may tradeoff investing energy in structural and melanin ornaments. By assessing overall plumage coloration, female eastern bluebirds could estimate age class when choosing mates.     

Female pied flycatchers trade between male quality and mating status in mate choice

According to mate choice theory, females should consider both male quality and mating status when choosing a mate. In birds, strong experimental evidence indicates that females prefer males with elaborate traits. No comparable evidence exists to determine whether females take male mating status into account or how they may trade between male quality and male mating status. We studied mate choice of female pied flycatchers (Ficedula hypoleuca) in outdoor aviaries where the effect of territory quality could be eliminated and where we could control which males were mated and which were unmated. We used male plumage colour as our measure of male quality. In the aviaries, focal females could easily compare males and assess their plumage colour and mating status, and resident females were prevented from attacking prospecting females because of separation in different compartments. The study provided evidence for a trade-off in mate choice. Females may compromise by choosing an already mated male if he is more brightly coloured and, presumably, of higher quality than available unmated males. The study did not support the idea that polygyny is based on male deception of females, but the results were consistent with the female aggression hypothesis.     

Female tawny-bellied seedeaters do not prefer more colorful males in choice experiments

Plumage coloration has long been studied as a sexually selected character. The tawny-bellied seedeater, Sporophila hypoxantha, is a sexually dichromatic species, with adult males the more colorful sex and juvenile males indistinguishable from females. We did choice experiments to evaluate female preferences for males that differ in age or plumage coloration. Females were evaluated in three experiments: (1) choice between males with similar breast brightness that differed in age, (2) choice between males of 2 years of age that differed in breast brightness, and (3) choice between males of 3 or more years of age that differed in breast brightness. We also repeated the latter experiment with estradiol-treated females. We did not find a clear female preference for brighter or older males, as females spent the same proportion of time with males of similar breast brightness that differed in age or with males of similar age that differed in breast brightness. Our results do not support the hypothesis that breast brightness is a cue used by female tawny-bellied seedeaters at the time of choosing males. We propose that, in this species, male plumage coloration might play a role in intrasexual competition.     

Carotenoid-based ornamentation and status signaling in the house finch

The status signaling hypothesis (SSH) was devised primarilyto explain the adaptive significance of avian ornamental colorationduring the nonbreeding season. It proposes that conspicuousmale plumage serves as an honest signal of social status withina population of birds. However, to date this hypothesis hasbeen well tested and supported for only one type of plumage coloration, melanin-based coloration. Carotenoid-based pigmentationis known to positively reveal male health and condition duringmolt in a variety of species, but it is poorly understood whetherthis ornament type can also function as a status signal duringthe winter. We tested the SSH in male house finches (Carpodacusmexicanus) by manipulating the carotenoid-based plumage brightnessof first-year males and then pairing unfamiliar birds of differingcoloration 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 predictorof winter dominance; as in other studies with this species,we found only a weak tendency for naturally drab males to dominatenaturally bright males. These results suggest that carotenoid-basedcoloration is not a reliable indicator of social status inmale 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 timeconstraints preclude a second plumage molt or because it aidsin pair formation that begins in late winter.     

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.     

Paternal care as a conditional strategy: distinct reproductive tactics associated with elaboration of plumage ornamentation in the house finch

When individuals in a population differ in physiological conditionand residual reproductive value, selection should favor phenotypicplasticity in reproductive investment such that individualsare able to adopt the reproductive tactic that results in thehighest fitness under given conditions. Here we examined reproductivetactics in relation to the elaboration of condition-dependentsexual ornamentation (carotenoid breast coloration) in a Montanapopulation of the house finches (Carpodacus mexicanus). Malesused distinct reproductive tactics depending on elaborationof their sexual ornamentation. Males with red pigmentation (maximum ornament elaboration) paired with females that nestedearlier, but these males did little provisioning of incubatingfemales and nestlings. In contrast, males with yellow colorationpaired with females that nested later, but these males fedfemale and nestlings more. Consequently, for red males offspringrecruitment was primarily affected by earlier nest initiation, whereas in yellow males it was affected most by male provisioning.In males with intermediate plumage coloration, all measuredcomponents, nest initiation, provisioning of incubating female,and nestling feeding, strongly contributed to offspring recruitment.The fitness consequences of alternative reproductive tacticsof males were influenced by breeding experience and fidelityof their mates. Among first-time breeders, red males achievedthe highest fecundity because of the advantage gained throughearly nesting and pairing with more experienced females andbecause of compensation by their mates for low male provisioningof nestlings. Among experienced breeders, males with intermediateplumage coloration achieved the highest fecundity because ofthe combined benefits of relatively early pairing and high parental care. High variation in sexual ornamentation in a Montana populationof house finches may favor distinct associations of sexualdisplays with a particular set of reproductive behaviors.     

Variation in female guppy preference for male olfactory and visual traits

Animals often use different sensory systems to assess different sexually selected signals from potential mates. However, the relative importance of different signals on mate choice is not well understood in many animal species. In this study, we examined the relative importance of male olfactory and visual cues on female preference in the guppy Poecilia reticulata. We used digitally modified male images to standardize visual stimuli. We found that, regardless of whether females were presented without male visual stimuli or with identical male visual stimuli, they preferred stimuli with the odor of males to those without. However, when females were allowed to choose between dull male visual stimuli with male odor, and brightly colored male visual stimuli without male odor, there was no clear preference for either. Some females preferred the dull male visual stimuli with male odor, whereas some other females preferred the brightly colored male visual stimuli without male odor. These results indicate that the relative importance of olfactory and visual cues in female mate preference varied between individuals.     

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.     

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.     

Structural and melanin coloration indicate parental effort and reproductive success in male eastern bluebirds

Male eastern bluebirds (Sialia sialis) have two types of ornamentalplumage coloration: a brilliant blue-ultraviolet head, back,and wings, and a patch of chestnut breast feathers. The blue-UVcoloration is produced from feather microstructure, whereasthe chestnut coloration is produced by a combination of pheaomelaninand eumelanin pigments deposited in feathers. We tested thehypothesis that plumage coloration reflects male quality ineastern bluebirds, a socially monogamous, sexually dichromaticbird. We investigated whether male ornamentation correlateswith mate quality and parental effort. We quantified three aspectsof male ornament coloration: (1) size of the patch of chestnutbreast feathers, (2) reflectance properties of the chestnutplumage coloration, and (3) reflectance properties of the blue-ultravioletplumage coloration. We found that males with larger breast patchesand brighter plumage provisioned nestlings more often, fledgedheavier offspring, and paired with females that nested earlier.Males with plumage coloration that exhibit more ultraviolethues fledged more offspring. These results suggest that plumagecoloration is a reliable indicator of male mate quality andreproductive success. Both melanin-based and structural-basedplumages appear to be honest signals of male quality and parentalcare that can be assessed by competitors or by potential mates.     

Nonrandom pairing by male barn owls (Tyto alba) with respect to a female plumage trait

In socially monogamous species it is rare for females to bemore intensely colored than males. The barn owl (Tyto alba)is one of the exceptions, as females usually exhibit more andlarger black spots on the plumage. The evolution of sexual dimorphismin plumage traits is commonly assumed to be the result of sexualselection. I therefore examined the prediction that male barnowls do not pair randomly with respect to female plumage spottinessduring a 5-year study in Switzerland. The prediction was supported,as males that changed mates acquired a new female that was similarlyspotted to the previous one, and pairing with respect to plumage spottinesswas positively assortative. Significant repeatability in male pairingwas presumably neither the consequence of sharing the same habitats withfemales displaying a given plumage spottiness nor of morphological characteristicsof the males that could influence mate sampling. A resemblance inplumage spottiness between the mates of sons and of their fathersuggests that repeatability could have resulted from sexualimprinting and/or heritable variance in male preference forspotted females. To test whether males assess female plumagespottiness, I either cut off black spots or small pieces of feathersbut not the spots of already mated females. Males mated to females withreduced plumage spottiness fed their brood at a lower cadencyand achieved a lower reproductive success than other males.This experiment further suggests that female plumage spottinessis a stimulus for males.     

Geographic variation in male ornamentation and female mate preference in the house finch: a comparative test of models of sexual selection

I compared the mate preferences of female house finches (Carpodacusmexicanus) from populations in which males differ in both plumagecoloration and the extent of ventral pigmentation (patch size).Phylogenetic analysis indicated that the small patch of ventralcoloration displayed by males in some populations is derivedfrom a larger-patched ancestral state. Regardless of the appearanceof males in their own populations, however, females from allpopulations showed a preference for the most brightly coloredmales and males with the largest patches. A reduction in patchsize independent of a change in female mate preference is notconsistent with sensory-bias or reproductive isolation modelsof sexual selection or with general predictions of runaway modelsof sexual selection. In contrast, a lack of congruence betweenfemale mate preference and male trait expression is predictedby the honest advertisement model, with house finches respondingto variation in regional and local access to carotenoid plumagepigments.     

Sex-Specific Audience Effect in the Context of Mate Choice in Zebra Finches

Animals observing conspecifics during mate choice can gain additional information about potential mates. However, the presence of an observer, if detected by the observed individuals, can influence the nature of the behavior of the observed individuals, called audience effect. In zebra finches (Taeniopygia guttata castanotis), domesticated males show an audience effect during mate choice. However, whether male and female descendants of the wild form show an audience effect during mate choice is unknown. Therefore, we conducted an experiment where male and female focal birds could choose between two distinctive phenotypes of the opposite sex, an artificially adorned stimulus bird with a red feather on the forehead and an unadorned stimulus bird, two times consecutively, once without an audience and once with an audience bird (same sex as test bird). Males showed an audience effect when an audience male was present and spent more time with adorned and less time with unadorned females compared to when there was no audience present. The change in time spent with the respective stimulus females was positively correlated with the time that the audience male spent in front of its cage close to the focal male. Females showed no change in mate choice when an audience female was present, but their motivation to associate with both stimulus males decreased. In a control for mate-choice consistency there was no audience in either test. Here, both focal females and focal males chose consistently without a change in choosing motivation. Our results showed that there is an audience effect on mate choice in zebra finches and that the response to a same-sex audience was sex-specific.     

The relative role of male vs. female mate choice in maintaining assortative pairing among discrete colour morphs

Mate choice has important evolutionary consequences because it influences assortative mating and the level of genetic variation maintained within populations. In species with genetically determined polymorphisms, nonrandom mate choice may affect the evolutionary stability and maintenance (or loss) of alternative phenotypes. We examined the mating pattern in the colour polymorphic Gouldian finch (Erythrura gouldiae), and the role of mate choice, both female and male, in maintaining the three discrete head colours (black, red and yellow). In both large captive and wild populations, Gouldian finches paired assortatively with respect to head colour. In mate choice trials, females showed a strong preference for mates with the most elaborate sexually dimorphic traits (i.e. more chromatic UV/blue plumage and longer pin-tail feathers), but did not discriminate assortatively. Unexpectedly, however, males were particularly choosy, associating and pairing only with females of their own morph-type. Although female mate choice is generally invoked as the major selective force maintaining conspicuous male colouration in sexually dichromatic species, and is typically thought to drive nonrandom mating, these findings suggest that mutual mate choice and male mate choice in particular, are an important yet neglected component of selection.