Song sharing with neighbours and relatives in a cooperatively breeding songbird

Kin recognition is important in allowing cooperative breeders to invest preferentially in helping kin, especially when helping is not restricted to the natal territory. Where spatial cues are not reliable indicators of kinship, animals can use family signatures, which may be learned or genetic. Alternatively, they can use unique signatures that are learned via prior experience in a context that identifies specific individuals as kin. Here we investigate sharing of song types between related and unrelated male western bluebirds, Sialia mexicana, a cooperatively breeding songbird that lives in neighbourhoods composed of a mix of kin and nonkin. Helpers only assist in raising close kin, including parents as well as brothers and grandfathers living on non-natal territories. In a previous study, we demonstrated that western bluebird males are able to recognize related males through their songs. Here we ask whether this kin recognition is based on song sharing within a family or whether western bluebird song sharing is primarily with neighbouring birds regardless of relatedness. The results indicate that western bluebirds often share with related and unrelated neighbours alike, and they rarely share any notes with non-neighbouring birds, whether they are related or unrelated. Although we cannot rule out the possibility of kin signatures that were not measurable using tools currently available for detecting vocal similarity, our findings suggest that kin recognition through song does not rely on note sharing with relatives and that western bluebirds use a more broadly applicable mechanism of vocal kin recognition compared to other cooperative breeders.