Extra-pair paternity in the socially monogamous Sedge Warbler Acrocephalus schoenobaenus as revealed by multilocus DNA fingerprinting

A marked population of Sedge Warblers Acrocephalus schoenobaenus was studied from 1993-95, the reproductive success of pairs was monitored and blood samples collected for DNA profiling. Measures of male physical and behavioural traits were also made, including song repertoire size, the amount of time spent singing and song-flighting, as well as territory quality. Although the Sedge Warbler is generally considered to be monogamous, social polygyny occurred in both 1994 and 1995, giving an overall rate for the two years of 7.7% of males. The overall rate of extra-pair paternity in the population was found to be 8.4% of offspring, with 34.4% of broods containing one or more extra-pair young. No incidences of intra-specific brood parasitism (egg dumping) were identified. Cuckolded males were compared with other males, but no significant differences were identified for any of the physical, behavioural or territorial measures. In particular, there was no evidence that previously detected mate choice cues are related to patterns of paternity within the population, and hence no evidence that such cues indicate genetic benefits to females. It therefore seems likely that repertoire size reflects male phenotypic quality in this species.