Paternity and paternity assurance behaviour in the bluethroat, Luscinia s. svecica

Abstract

Genetic parentage was examined in the territorial and predominantly monogamous bluethroat, by means of multilocus DNA fingerprinting. Thirty-five per cent (11/31) of nests contained one or more offspring sired by extra-pair males, in total 20% (30/150) of all offspring. The frequency of extra-pair paternity was similar in the two study years. All offspring were genetically related to their putative mother, thus no evidence for intraspecific brood parasitism was found. Extra-pair offspring were not randomly distributed, but were clustered in certain broods, in which on average 54% of the young were sired by extra-pair males. Ten copulations were seen, one of which was an extra-pair copulation. Males guarded their mate intensely around the start of egg laying, staying within 1 m of her for more than 60% of the time. The male typically followed the female, and not vice versa. Hence, mate guarding was not a cooperative behaviour of the two sexes. Male singing activity declined gradually during the breeding season without reaching a peak during the females’ fertile period. Male bluethroats thus apparently use mate guarding and not song as their primary paternity guard. For a subset of pairs ( N=8) the observed behaviour could be related to paternity. These data indicated that, during the fertile period, there were more intrusions in territories with extra-pair offspring than in territories with only legitimate offspring. There was also a non-significant tendency for males with full paternity in their nest to mate guard more intensely than males with reduced paternity.