Localization of prey by the Indian false vampire bat Megaderma lyra

Abstract

Studies on gleaning bats indicate that they do not mainly rely on echolocation to detect and capture prey from surfaces. In the event of not using echolocation, there may be an error in their passive localization of prey compared to the bats which use echolocation. It is to be tested whether the amount of such error is related with the size of the prey in the passive localization employed by gleaning bats. We conducted experiments on the Indian false vampire bat Megaderma lyra in an outdoor enclosure using small, medium and large-sized frogs as prey. M. lyra captured live and freshly killed frogs only when they jumped or when pulled with a long thread on a sandy floor. Bats were more successful in capturing frogs without error (i.e. landing straight on the frog) under the background of fluorescent light than red light. The number of captures of live frogs without error was also significantly higher compared to the captures of freshly killed frogs under both the lights, except with the large-sized frogs. The number of jumps made by the live frogs decreased with their body lengths increased before M. lyra captured them without error. In a few observations, instead of landing straight on the frogs the bats landed on the floor close to the frogs and then captured them in a short jump (i.e. localization made with an error). The distance between the final position of the frogs and the site at which the bats landed on the floor prior to the capture, is considered as the amount of error committed by bats. While the bats localized and captured the frogs with an error, we found a linear decrease of error with an increase in the body length of the frogs. Bats never responded to the movements of tiny live and dead frogs of 0.8-1.3 cm.