By using a 'black light' and playback of sounds made by foraging insectivorous bats, we examined opportunistic feeding behavior of bats near Camp Verde, Arizona, between 1 and 10 June 1975. Bats were significantly most active during 15-min periods when the light was on and insects were aggregated over it. Bats feeding over the light selectively pursued and captured larger insects, apparently ignoring the smaller ones. Bats did not respond to sounds simulating feeding buzzes of bats, but showed a slight response to the foraging sounds of other bats. Opportunistic feeding by insectivorous bats allows effective exploitation of patchily distributed food resources and can lead to selective feeding when 'hatches' of insects are involved. Opportunistic feeding is not incompatible with selective feeding, and may eventually be established as a strategy common to most insectivorous bats.
