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

The visually guided escape response of wild Mexican free-tailed bats, Tadarida brasiliensis mexicana, 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 acoustic and visual cues were presented in combination, acoustic cues were preferred. T. b. mexicana show a reduced positive light response at times corresponding to their morning return to the cave roost from foraging. Individuals also decreased their preference for light as light intensity increased, and shifted to a positive dark response when the intensity was raised to levels equivalent to daytime light at the front of the cave. This may explain why roosting bats disturbed during the day fly towards the mouth of the cave but circle back before exiting it In contrast to adults, very young and non-volant pups oriented towards the dark. This behavior would serve to keep pups closer to a thermoneutral environment. The transition in response from dark-orienting pups to light-orienting adults occurred at about seven weeks, the age at which pups become volant. Adults were also found to respond to red, but not far red and infra-red light. Such a behavioral response to red light indicates the need to re-evaluate current lighting methods used in behavioral observation of bats.