Male reed buntings do not adjust parental effort in relation to extrapair paternity

Parental effort is considered to be costly; therefore, males are expected to provide less care to unrelated offspring. Theoretical models suggest that males should either reduce their care to the entire brood or alternatively distinguish between related and unrelated nestlings and direct provisioning to kin when paternity is in doubt. Reed buntings (Emberiza schoeniclus) have been found to have high levels of extrapair paternity (EPP, i.e., offspring of a male other than the male attending the nest; 55% of offspring), and males are therefore under strong selection pressure to adjust their parental effort according to the proportion of EPP in their brood. In this study, we investigated whether male reed buntings exhibit a reduction in paternal care (incubation and provisioning nestlings) in relation to decreased paternity. We also assess whether males bias their provisioning toward kin. We measured incubation time, provisioning rates, and food allocation to individual nestlings using video recordings at the nests. Microsatellite DNA analysis was used to analyze the paternity of offspring. In direct contrast to a previous study on the same species, our results provided no indication that males lowered their effort with decreased paternity. Furthermore, in nests of mixed paternity, males did not bias their provisioning behavior to kin. It remains to be investigated whether the absence of a relationship between paternity and paternal care can be ascribed to absence of reliable paternity cues or whether the benefits of reducing paternal care did not outweigh the costs in our study population. We found no evidence that the level of paternal care affected male survival or offspring mass, suggesting that both the benefits and costs of any reduction in paternal care would have been low.