Characteristics of the visually guided escape response of the Mexican free-tailed bat, Tadarida brasiliensis mexicana

Abstract

The visually guided escape response of wild Mexican free-tailed bats was studied in relation to acoustic and visual cues, time of day, light intensity and age. Adults exhibited a positive response towards light; however, when presented in combination, acoustic cues were preferred over visual cues. Bats displayed a reduced positive light response at times corresponding to their morning return to the cave roost from foraging. Individuals decreased their preference for light as light intensity increased and shifted to a positive dark response when the intensity was raised to levels approximating daytime illumination at the front of the cave. This change in orientation to light may explain why bats disturbed during the day fly toward the cave mouth but then circle back rather than leave the cave. In contrast to adults, very young and non-volant pups oriented toward the dark. This behaviour may serve to facilitate growth by keeping the pups closer to a thermoneutral environment. The transition in response from dark-orienting pups to light-orienting adults occurred at about 7 weeks, the age at which pups become volant.