Intense echolocation calls from two 'whispering' bats, Artibeus jamaicensis and Macrophyllum macrophyllum (Phyllostomidae)

Bats use echolocation to exploit a variety of habitats and food types. Much research has documented how frequency-time features of echolocation calls are adapted to acoustic constraints imposed by habitat and prey but emitted sound intensities have received little attention. Bats from the family of Phyllostomidae have been categorised as low intensity ( whispering) gleaners, assumed to emit echolocation calls with low source levels ( approximately 70dBSPL measured 10cm from the bat's mouth). We used a multi-microphone array to determine intensities emitted from two phyllostomid bats from Panama with entirely different foraging strategies. Macrophyllum macrophyllum hunts insects on the wing and gaffs them with its tail membrane and feet from or above water surfaces whereas Artibeus jamaicensis picks fruit from vegetation with its mouth. Recordings were made from bats foraging on the wing in a flight room. Both species emitted surprisingly intense signals with maximum source levels of 105dBSPLr.m.s. for M. macrophyllum and 110dBSPLr.m.s. for A. jamaicensis, hence much louder than a 'whisper'. M. macrophyllum was consistently loud ( mean source level 101dBSPL) whereas A. jamaicensis showed a much more variable output, including many faint calls and a mean source level of 96dBSPL. Our results support increasing evidence that echolocating bats in general are much louder than previously thought. We discuss the importance of loud calls and large output flexibility for both species in an ecological context.