INFORMATION-TRANSFER AT EVENING BAT COLONIES

Four lines of evidence indicate that evening bats, Nycticeius humeralis, at nursery colonies in northern Missouri transfer information by following each other to feeding and roosting sites. (1) Daily estimates of insect density from five automated suction traps showed that common prey in evening bat faecal samples, small beetles and flies, occur in rich patches that persist for several days. Bats apparently respond to prey density and variability because these variables independently predict the number of trips and capture success of foraging bats. (2) Videotape records of the time and weight of bats arriving and departing from a colony indicated that adult females leave within 10s of each other on second and subsequent foraging trips more often than expected within a night. These records also revealed that bats alternate between apparent following and leading over a summer, that unsuccessful foragers follow previously successful foragers within a night, and that the foraging success of putative followers is greater than that of unsuccessful bats which depart solitarily. (3) Radio-tagged bats often returned to foraging sites both within a night and on successive nights. Furthermore, three of 12 radio-tagged bats flew closer to another radio-tagged bat throughout a night than expected if bats foraged independently. (4) Two field experiments in which bats were excluded from their roosts for one night demonstrated that newly volant bats follow adult females to alternate roosts. The possibility that evening bats acquire information passively by monitoring echolocation signals or actively by vocal advertisement is discussed. © 1992.