Plumage colour can be used as an honest signal to convey health and status, which has traditionally been examined in the sexual selection context of choosy females and elaborate males. We use a model avian system to study the role of plumage coloration in a social context such as inter- and intrasexual competition over food resources. The diamond firetail (Stagonopleura guttata) is an endemic Australian finch: females have more white flank spots than males, and white spot number was correlated with cell-mediated immune response in females. We use two experimental designs to test the role of white flank spots for feeding dominance and dominance discrimination in a group-living bird. The results from two-choice trials and from single-arena trials showed that female ornamentation was consistently important in social food contests, and males consistently responded to female spot number. Females with higher spot number fed first, in trials with males and/or females. Also, females preferred to feed next to test birds with low spot number, but males showed no preference for feeding next to birds with few or many spots. Finally, latency to feed was predicted by spot number: both males and females had longer latency to feed if test birds had more spots than the focal birds. We conclude that female, but not male, ornamentation was important for inter- and intrasexual food competition. This is one of the very few studies to show that the same plumage ornament can have a different function between the sexes as a signal of social status. Moreover, this study shows that white plumage can be a signal of dominance

Colour variation in birds is often used to signal functional differences between individuals and sexes, though white plumage has usually been disregarded because white feathers were thought to be cheap to produce and hence unreliable signals. Here, we provide evidence for sex-specific morphological and colour differences in the strikingly patterned but apparently monomorphic Diamond Firetail (Stagonopleura guttata). We found that males had longer and darker tails, wider lores and a darker bill, while females had significantly more white flank spots. These gender-specific trait differences could be used to signal individual quality in sexual or social interactions, and hence we examined the correlation between these traits and the cell-mediated immune response (phytohaemagglutinin, PHA test). During both the breeding and non-breeding seasons, we found a positive correlation between PHA response and white flank spot number as well as their ultra-violet reflectance in females, and a negative correlation with white chroma and hue. In males, there was a positive correlation between PHA response and red rump reflectance (hue, red-chroma). There was no association between PHA response and either tail length or lore depth in either sex. These results add to a growing body of evidence that female spot number and white plumage reflectance signal quality

The evolution of female ornaments is poorly understood. Recent evidence suggests not only

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 nanoscale 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.

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