Sound localization and its relation to vision in large and small New-World bats

Abstract

Passive sound-localization acuity (minimum audible angle) for brief noise bursts was determined behaviorally for two species of New-World bats (Phyllostomidae): Phyllostomus hastatus, a large bat that eats fruit and preys on other vertebrates, and Carollia perspicillata, a small species that eats fruit and nectar. Both use echolocation calls of very low intensity for orientation and obstacle avoidance. The mean minimum audible angle for two P. hastatus was 9 deg, and that for two C. perspicillata was 14.8 deg. This places their passive sound-localization acuity near the mean for mammals. Sound localization varies widely among mammals and the best predictor of a species acuity remains the width of the field of best vision (r=.89, p<.0001). Neither of these bats nor the other three bat species tested so far deviates from the relationship between sound-localization and vision, suggesting that despite their specialization for echolocation, the use of hearing to direct the eyes to the source of a sound still serves as the major source of evolutionary selective pressure for passive sound localization.