Welcome home: Brazilian free-tailed bats adjust their echolocation calls to detect cave opening

Abstract

While both bats and dolphins use sonar to navigate their environment, the sensory challenges between the two are not equal since dolphins typically navigate in the open ocean and bats often navigate in cluttered environments. Brazilian free-tailed bats (Tadarida brasiliensis), for example, adjust their frequency modulated (FM) call structure based upon their environment, producing lower-bandwidth calls in open environments, and higher-bandwidth calls in cluttered environments. In this study, we examined how Brazilian free-tailed bats change the bandwidth of calls when locating the cave opening in a flat, non-cluttered environment. We extracted individual echolocation calls from two locations around the cave, one away from the cave opening and one next to edge of the cave opening, with the only distinctive difference in the environment of the locations being the presence of the cave edge. We found higher starting and lower stopping frequencies for the FM calls at the cave edge, resulting in an increased bandwidth. This higher bandwidth suggests the bats may rely on edge detection to locate the cave opening and change the bandwidth of their signals to improve target resolution when returning to the roost.