High frequency of extra-pair paternity in Eastern Kingbirds

Genetic parentage in the socially monogamous and territorial Eastern Kingbi rd (Tyrannus tyrannus) was examined in a central New York population by mul tilocus DNA fingerprinting. Extra-pair young were identified in 60% (12 of 20) of nests. Of the 64 nestlings profiled, 42% were sired by extra-pair ma les, but no cases of conspecific brood parasitism were detected. These resu lts are markedly different from a previous electrophoretic study of the sam e species in a Michigan population, which reported 39% of nestlings were un related to one (typically the mother, quasiparasitism) or both (conspecific brood parasitism) of the putative parents. In the New York population, ext ra-pair paternity was most common among females that returned to breed on a former territory. Among females that were new to a breeding territory, ext rapair paternity increased directly with breeding density: Although the pow er of the tests was low, neither breeding synchrony nor male experience wit h a breeding territory appeared to be associated with the occurrence of ext ra-pair young.