Intensity Modulation of Advertisement Calls in Bufo woodhousii fowleri

In male Bufo woodhousii fowleri, some advertisement calls are consistently intense from start to finish whereas others become less intense after an initial peak at the beginning of the call. There was higher variation in this intensity modulation, both within-recordings and among individuals in two populations, than in three other call properties: call duration, pulse repetition rate, and dominant frequency. When given a choice between a consistently intense call vs an intensity modulated call in playback experiments, gravid females chose the consistently intense call when both speakers were 6 m from the subject and 12 m away from each other. There was no preference when both speakers were closer to the subject and each other. Thus, females prefer calls with constant intensities more than modulated ones, but their ability to use this vocal property to select mates diminishes when the distances among themselves and calling males are small.