Social entrainment in the old frugivorous bats, Rousettusleschenaulti from the Lonar crater

Onset and end of activity of the old frugivorous bats Rousettus leschenaulti, roosting in a temple ruin of the Lonar crater were observed at 10-day intervals for one year. The old bats emerged about 4 h after and returned about 4 h before the young bats. Onset of activity of the old bats was entrained by the loud vocalization of the early emerging young conspecifics at dusk. The old bats free-ran when the young conspecifics were evicted from the roost but re-entrained when they were re-introduced. Socially isolated old bats in the laboratory also free-ran in the scotophase of LD 12:12 cycles until the onset of activity coincided with lights-off which resulted in a delayed phase shift. After the exposure to light, the sequence of events repeated all over again. Ecological implications of this social entrainment are discussed.