Is it safe? Red-eyed treefrog embryos assessing predation risk use two features of rain vibrations to avoid false alarms

Prey use predator cues to inform defensive decisions. Detecting these cues is often complicated by benign stimuli that resemble and can be mistaken for predators, leading prey to display costly defences incorrectly. One strategy that prey have evolved to reduce these 'false alarms' is to respond only to stimuli with characteristics consistent with predator cues. Decision errors might still be frequent, however, in cases where the probability distributions of benign stimulus properties completely overlap those of predator cues. In such cases, inhibition of defensive responses by characteristic features of benign stimuli could further improve discrimination. Red-eyed treefrog embryos, Agalychnis callidryas, hatch prematurely to escape egg predators. They detect predators using vibrations generated during attacks. However, common benign disturbances such as rainstorms generate vibrations with property probability distributions that largely overlap those of predators. We used vibration playbacks to test the hypotheses that embryos use two features of rainstorm vibrations not shared by predator attacks, characteristic high frequencies and an initial period of intensity buildup, to avoid hatching in response to this benign stimulus. The escape-hatching response to otherwise stimulatory vibrations is reduced in the presence of either feature characteristic of rainstorms. Either A. callidryas embryos use rainstorm features to inform their hatching decision or these features alter their perception of predator cues. Identifying likely sources of potential false alarms and comparing their stimulus characteristics to predator cues and prey decision rules will improve our understanding of both the information processing challenges facing prey and the ways they solve them. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.