Bats (Tadarida brasiliensis) jam conspecifics in food competition

Abstract

We here describe field experiments testing whether bats adaptively produce sounds to interfere with (“jam”) the echolocation of other bats. Visual observations, low-light videography, and ultrasound recording with microphone arrays allowing reconstruction of bat flight paths were used to document interactions between Mexican free-tailed bats (Tadarida brasiliensis) at two foraging locations in southern Arizona and New Mexico. We tested three sets of predictions based on the jamming hypothesis and two competing hypotheses—cooperative foraging and food patch defense. Bats produced putative jamming calls (termed sinFM calls) that overlapped temporally and spectrally with “feeding buzz” calls made by conspecifics when attacking insects. Bat capture success decreased by 400% when sinFM calls were present compared to when they were absent. Behavioral sequences consisted of two or more bats sequentially making feeding buzzes within a restricted area while another bats made sinFM calls. After making sinFM calls bats frequently turned toward where the other bat made its feeding buzz and then made a buzz of its own. Together, the results support the hypothesis that bats jam conspecifics in extended bouts of food competition. This is the first known case of echolocating animals adaptively jamming conspecifics.