Effect of acoustic clutter on prey detection by bats

Bats that capture animal prey from substrates often emit characteristic echolocation calls that are short-duration, frequency-modulated (FM) and broadband(1). Such calls seem to be suited to locating prey in uncluttered habitats, including flying prey, but may be less effective for finding prey among cluttered backgrounds because echoes reflecting from the substrate mask the acoustic signature of prey(2-4). Perhaps these call designs serve primarily for spatial orientation(5-7). Furthermore, it has been unclear whether the acoustic image conveyed by FM echoes enables fine texture discrimination(3,8,9), or whether gleaning bats that forage in echo-cluttering environments must locate prey by using other cues, such as prey-generated sounds(5-7,10-13). Here we show that two species of insectivorous gleaning bats perform badly when compelled to detect silent and immobile prey in clutter, but are very efficient at capturing noisy prey items among highly cluttered backgrounds, and both dead or live prey in uncluttered habitats. These findings suggest that the short, broadband FM echolocation calls associated with gleaning bats are not adapted to detecting prey in clutter.