GREATER SPEAR-NOSED BATS DISCRIMINATE GROUP MATES BY VOCALIZATIONS

Individuals often benefit from identifying their prospective social pa rtners. Some species that live in stable social groups discriminate be tween their group mates and others, basing this distinction on calls t hat differ among individuals. Vocalizations that differ between social groups are much less common, and few studies have demonstrated that a nimals use group-distinctive calls to identify group mates. Female gre ater spear-nosed bats, Phyllostomus hastatus, live in stable groups of unrelated bats and give audible frequency, broadband calls termed scr eech calls when departing from the roost and at foraging sites. Previo us field observations suggested that bats give screech calls to coordi nate movements among group members. Prior acoustic analyses of 12 acou stic variables found group differences but not individual differences. Here, we use the same acoustic variables to compare calls from three cave colonies, and find that calls differ between caves. We also repor t results from field and laboratory playback experiments designed to t est whether bats use acoustic differences to discriminate calls from d ifferent colonies, groups or individuals. Results from field playbacks indicate that response depends on the cave of origin, indicating that bats can discriminate among calls from different caves. This discrimi nation ability may be based, in part, on;whether calls are familiar or unfamiliar to the listening bats. Laboratory playbacks demonstrate th at bats discriminate calls given by their group mates from calls given by other bats from the same cave irrespective of familiarity. However , these experiments provide no evidence that bats discriminate among i ndividuals. Previous field work indicates that females that forage wit h social group mates map benefit from shared information about food or mutual defence of feeding sites. Indicating group membership is essen tial? since these benefits appear to be restricted to group mates. (C) 1998 The Association for the Study of Animal Behaviour.