Aposematism or startle? Predators learn their responses to the defenses of prey

We used the responses of four trained captive big brown bats (Eptisicus fuscus) to the clicks of arctiid moths to test the hypothesis that predators learn their responses to preys' defensive displays. Bats were trained to fly to a platform where they sometimes received a mealworm reward. On about 5% of the occasions on which bats came within 0.5 m of the platform, they were randomly presented with one of three acoustic stimuli, including recorded clicks of an arctiid moth, synthetic clicks (white noise temporally matched to arctiid clicks), or tape noise. It took less than three trials for the bats to habituate to the arctiid clicks and longer for them to cease responding to the other stimuli. In less than eight pairings of arctiid clicks and a noxious food reward, two of the bats learned to associate moth clicks with a bad taste. Our data support the hypothesis by showing that although unexpected clicks startle inexperienced bats, they may also warn experienced bats of bad-tasting prey.