Do female frogs exploit inadvertent social information to locate breeding aggregations?

The advertisement calls of male anurans (frogs and toads) are loud and conspicuous signals, and the sound generated by breeding aggregations of males propagates over long distances. As a by-product of communication within an aggregation, the sounds of a frog chorus constitute a form of inadvertent social information that provides potential long-distance cues about the location and timing of breeding. We investigated whether female American toads (Bufo americanus Holbrook, 1836) and Cope's gray treefrogs (Hyla chrysoscelis Cope, 1880) use the sounds of a chorus to locate breeding aggregations in the absence of other sensory cues. Females of both species approached speakers broadcasting recordings of a chorus made from distances of 0, 20, and 40 m, but not from distances of 80 and 160 m. Female toads also exhibited phonotaxis to a completely artificial chorus sound, but female gray treefrogs did not. We found little evidence to suggest that female American toads and Cope's gray treefrogs differed substantially in their responses to natural chorus sounds despite potential differences in the predictability and duration of breeding seasons in these two species. Our results suggest that the inadvertent social information of a chorus could be used over short distances to locate breeding aggregations.