Echolocating big brown bats shorten interpulse intervals when flying in high-clutter environments

Abstract

Insectivorous big brown bats (Eptesicus fuscus) use frequency-modulated ultrasonic echolocation calls to locate and capture prey, often while navigating through highly cluttered areas of vegetation. To test how their calls change while flying through different clutter densities, a matrix of vertically hanging chain links was constructed in a 4.5-m-wide, 10.5-m-long, and 2.6-m-high flight room. Three different clutter densities (low, medium, and high) were created by varying the number of chains in the matrix (9, 114, and 150, respectively). Four wild-born bats were trained to fly through curved gaps in the chain network. These flights were recorded in the dark with a stereoscopic pair of thermal imaging cameras and a heterodyne bat detector. The bats were flown first through the high-, then the low-, and finally the medium-density configuration over a period of 40 days. Preliminary analysis of the pulse intervals of the bats sounds during flight reveals that the interpulse intervals shorten considerably under high-clutter conditions as compared to medium or low clutter. The data suggest that bats flying through high clutter become limited to shorter interpulse intervals in order to ensonify their immediate environment at the expense of larger-scale navigation. [Work supported by NIH.]