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Skins of 33 passerine birds were examined for ultraviolet (UV) reflectance by means of UV photography. Most of the species studied appear dull to humans, though on the theoretical grounds they might be expected to evolve bright plumage. The qualitative analysis suggested that UV does not increase brightness of most examples of feathers that appear dull in the visible range, though it may add to the conspicuousness of plumage already bright by human standards. Black but shiny or iridescent birds, whose feathers reflect UV, are the possible exception. Though methods used did not allow the quantitative comparison of the strength of this reflectance with that in the visible range, it seems likely that UV may enhance brightness of iridescent feathers of black coloured birds. Moreover, the supplementary examination of some other, randomly selected species, as well as findings by other authors, suggest that in some cases UV may be important in birds' perception of feathers, especially if they are black or white.
Black-billed Magpies possess distinctive patterns of black and white on their flight feathers which have been suggested to be family-specific. Such a phenomenon could potentially provide a simple field-method for recognising related or unrelated offspring. Using a combination of wing plumage patterns and multilocus DNA fingerprinting the relationship between plumage variation and genetic relatedness in the European Black-billed Magpie was investigated. The plumage of nestmates was more similar to each other than to young in other nests. However, extra-pair offspring could not be identified from nestmates through plumage differences. Within brood similarity may be explained by full-siblings sharing plumage characteristics through random inheritance, or through a shared rearing environment. Extra-pair offspring may resemble their half-sibs due to shared maternal plumage characteristics and a common rearing environment.
Intensity of plumage colour may advertise individual condition, health and parasite resistance of birds. Although numerous studies confirmed such function of ornaments in songbirds, still very little is known about signalling properties of colour feathers in woodpeckers. We test whether the size and colour of a red cap displayed by both male and female Middle Spotted Woodpeckers are related to mass and length of tarsus, wing, tail and beak. We found that body mass was correlated with cap width and brightness in woodpeckers of both sexes. At the same time body mass affected reproductive success of individuals. This suggests that both cap width and brightness has the potential to signal individual condition in the studied species.
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