IMPACT OF PREDATION RISK ON EMERGENCE BY LITTLE BROWN BATS, MYOTIS-LUCIFUGUS (CHIROPTERA, VESPERTILIONIDAE), FROM A MATERNITY COLONY

When bats emerge from their roosts in the evening to forage and drink, it appears as though their departure involves brief periods when many individuals emerge interspersed with periods during which few individ uals emerge. Clustering is seen in many species of animals and probabl y has an anti-predator or information-transfer function. Regardless of its function, clustering in the emergence of bats may intensify as a result of large numbers of individuals trying to pass through a small exit hole in a short period of time. A total of 31 observations of eme rgence were made from May to Aug. 1992 and 1993 at a maternity colony of little brown bats (Myotic lucifugus), in Cypress Hills, Saskatchewa n, Canada. To determine the effects of a predator on clustering in the emergence, a plastic great horned owl (Bubo virginianus) was used as a predator model and mounted close to roost exits on 8 nights. Recorde d calls of a great horned owl were played back towards the roost. The predator model and associated calls did nor affect the number of bats that emerged, the median time of emergence, or the degree of clusterin g in the emergence. There was a significant positive relationship betw een the extent of clustering in the emergence and the number of bats t hat emerged. Emergences of more than 25 bats were clustered. Thus, we found no evidence to support clustering during emergence as being an a nti-predator response. However, clustering may be intensified with inc reased numbers of individuals trying to pass through a narrow space in a short period of time.