SOCIAL CALLS COORDINATE FORAGING IN GREATER SPEAR-NOSED BATS

The function of social calls emitted by foraging bats has received lit tle study. Here we use observations of free-ranging greater spear-nose d bats, Phyllostomus hastatus, and field playbacks to determine whethe r audible, broad-band 'screech' calls attract mates, warn conspecifics or influence access to food. Five lines of evidence suggest that scre ech calls enable adult females from the same roosting group to fly tog ether from the day roost to feeding sites. (1) Seasonal differences in diet influenced the rate of screech calling recorded outside the cave roost, as well as how often bats departed together. Bats called more often and flew in larger groups when feeding on a concentrated resourc e, balsa, Ochroma lagopus, flowers, in winter than on more dispersed C ecropia peltata fruit in spring. (2) Observations of bats flying outsi de the cave, in flyways and at feeding sites indicated that screech ca lls occurred more often when bats flew in groups than alone. (3) Femal es from the same roosting group were netted at the same feeding site, sometimes simultaneously, several kilometres from the cave. (4) Callin g colour-marked adult females outside the cave were joined by a female group member, both on initial departures and on second foraging trips , more often than non-calling bats. (5) Playbacks attracted conspecifi cs at roost and feeding sites. Screech calls appear to function as con tact calls that recruit and coordinate foraging among group members. W e postulate that females benefit from foraging with unrelated roost-ma tes because they can defend feeding sites more effectively. (C) 1998 T he Association for the Study of Animal Behaviour.