Recognition of group membership by voice in Mexican jays, Aphelocoma ultramarina

Mexican jays live in stable social groups of 5-25 individuals. Groups show complex social organization, with dominance hierarchies and defence of terr itories against nonmembers. We tested whether Mexican jays displayed vocal recognition of group membership in a population of colour-banded birds in s outheastern Arizona, U.S.A. We conducted playback trials of primary calls r ecorded either from an identified member of the target group or from a memb er of a nearby but noncontiguous group. Calls were played near established feeding stations during regular feeding sessions. The jays responded differ ently to calls from outsiders and insiders, with more calling, faster appro ach latency and more entries into a response circle (i.e. within 5 in of th e speaker) in response to calls from outsiders. Thus, the primary calls of jays are used to recognize group membership. Mechanisms by which this recog nition is mediated are discussed. (C) 2001 The Association for the Study of Animal Behaviour.