A melanin-based trait reflects environmental growth conditions of nestling male Eurasian kestrels

Abstract

Melanin pigments are responsible for most non-structural brown, black and grey colouration in animals. The extent to which melanin-based colouration in birds is genetically or environmentally determined has been subject to controversy. One reason for this it is paucity of empirical data on the role of key environmental factors, such as food availability, on the development of melanin-based traits. We analysed whether brown and grey colouration in rumps of Eurasian kestrels Falco tinnunculus is based on melanin and examined the relationships between high inter- annual variation in main food supply, parental condition and the expression of grey colouration in male nestlings. We also performed a partial cross-fostering experi- ment to allocate randomly nestlings among environments. The proportion of male nestlings with predominantly grey colouration was higher in years with abundant prey (voles). The only variable associated with intra-annual variation of grey col- ouration in male nestlings was body mass of the female rearing them. The colour- ation of nestlings in the cross-foster experiment was correlated with the body mass of their foster mother, but not with that of their genetic mother. Melanin colouration did not correlate with T-cell mediated immune response. These results indicate that this melanin-based trait reflects the environmental conditions in which the nestlings grew up.