ИСТИНА

Understanding the function of extra-pair paternity (EPP) should be based on three sets of comparisons between features of: 1) cuckolded and extra-pair males; 2) females with and without extra-pair chicks; 3) within-pair and extra-pair chicks. We analysed EPP in Pied Flycatcher (Ficedula hypoleuca) population in Moscow region. Pied Flycatcher males have two peculiarities, which are of a great interest for revealing the adaptive role of EPP, - polymorphism of breeding plumage and combination of monogamy and polygamy. The chicks in 74% of broods were genetic offspring of their social parents. Old females (but not old social males) more often reared extra-pair chicks than the young ones. The colouration of males was not related with the presence of extra-pair chicks in their nests, but the number of extra-pair chicks tended to be higher in broods of pale males. Extra-pair males and cuckolded ones did not differ by age and colouration. Asymptotic body weight of extrapair chicks was higher than that of within-pair chicks. The latter relation and inclination of experienced females to extra-pair copulations give additional arguments in favour of adaptive role of EPP.