Vocal recognition of former group members, but not unknown kin, in the cooperatively breeding southern pied babbler

Studies of vocal kin recognition in avian species have typically tested responses to vocal signals based upon either familiarity (recognition via ‘learned associations’) or relatedness (recognition of genetic kin) but have rarely simultaneously tested for the effects of both. Here we examined vocal kin recognition in the cooperatively breeding southern pied babbler, Turdoides bicolor, using vocalizations from familiar kin, unfamiliar kin, familiar nonkin and unfamiliar nonkin in a playback experiment. We found limited support for recognition based upon familiarity: individuals appeared to be recognized from a period of prior association and associative learning. Focal birds (dominant females) discriminated familiar birds from unfamiliar birds, but discrimination was evident in only one of three behavioural response measures. Focal birds did not discriminate familiar kin from familiar nonkin, nor did they discriminate unfamiliar kin from unfamiliar nonkin, indicating no support for vocal recognition based on relatedness. The context of the experiment also affected discrimination, with focal birds reacting more strongly to calls from females (potential rivals) than to calls from males. Because familiarity in this species arises from the association of individuals in groups, and most groups comprise close kin, familiarity with group members offers a close proxy for kin recognition. While kin recognition systems based upon familiarity do not allow the identification of unfamiliar kin, the benefits of such recognition may be negligible in cooperatively breeding species that live in kin-based groups.