What ears do for bats: a comparative study of pinna sound pressure transformation in Chiroptera.

• Martin K. Obrist, Department of Biology , York University, North York, Ontario, Canada M3J 1P3. present address: Swiss Federal Institute for Forest, Snow and Landscape Research WSL, CH-8903 Birmensdorf, Switzerland
• M. Brock Fenton, Department of Biology , York University, North York, Ontario, Canada M3J 1P3
• Judith L. Eger, Royal Ontario Museum, Department of Mammalogy, 100 Queens Park, Toronto, Ontario, Canada, M5S 2C6
• Peter A. Schlegel, Zoologisches Institut, Luisenstrasse 14, D-80333 München, Germany

Published in

• The Journal of Experimental Biology 180:190-152 (1993)

Abstract

Using a moveable loud speaker and an implanted microphone, we studied thesound pressure transformation of the external ears of 47 species of bats from 13 families. We compared pinna gain, directionality of hearing and interaural intensity differences (IID) in echolocating and non-echolocating bats, in species using different echolocation strategies and in species that depend upon prey-generated sounds to locate their targets.

In the Pteropodidae,two echolocating species had slightly higher directionality than a non-echolocating. The ears of phyllostomid and vespertilionid species showed moderate directionality.

In the Mormoopidae, the ear directionality of Pteronotus parnellii clearly matched the dominant spectral component of its echolocation calls, unlike the situation in three other species.

Species in the Emballonuridae, Molossidae, Rhinopomatidae and two vespertilionids that use narrowband searchphase echolocation calls showed increasingly sharp tuning of the pinna to the main frequency of their signals.

Similar tuning was most evident in Hipposideridae and Rhinolophidae, species specialized for flutter detection via Doppler-shifted echoes of high duty-cycle narrowband signals.

The large pinnae of bats that use prey-generated sounds to find their targets supply high sound pressure gain at lower frequencies. Increasing domination of a narrow spectral band in echolocation is reflected in the passive acoustic properties of the external ears (sharper directionality).

The importance of IIDs for lateralization and horizontal localization are discussed by comparing the behavioral directional performance of bats with the bioacousticalfeatures.