Distinct colour morphs in nestling European Bee-eaters Merops apiaster: is there an adaptive value?

摘要

In a few bird species, dimorphism already exists in nestling and juvenile plumage coloration and these colour morphs are often attributable to different sexes. In this study we detected variation in nestling coloration among European Bee-eaters Merops apiaster. We identified two distinct colour morphs, namely nestlings with yellowish-brown and nestlings with green back feathers. By means of genetic methods, we determined nestling sex. It turned out that the back colour is a significant indicator for sex. Male nestlings have yellowish-brown and females green back feathers, but there are exceptions. Population sex ratio was about equal but we found sex-biased variation in several nests. Furthermore, we found evidence that colour is an indicator for condition especially in those individuals where sex and coloration do not match.