Treefrogs adjust their acoustic signals in response to harmonics structure of intruder calls

Spectral properties of animal acoustic signals may help individuals to assess the characteristics of rivals and to adjust their competitive strategies in territorial disputes. Thus, we hypothesize that the distribution of energy across frequency bands in anuran calls determine behavioral responses in male-male competition. Using playback experiments, we investigated the relevance of the harmonic calls in the acoustic communication of the treefrog Dendropsophus minutus. We exposed territorial males to three synthetic acoustic stimuli composed of aggressive notes: (1) standard call (all harmonics and peak frequency corresponding to the second band); (2) inverted-energy call (all harmonics and peak frequency corresponding to the first band); and (3) concentrated-energy call (all energy contained in the second harmonic). Males responded aggressively to all stimuli, mainly by increasing the rate and duration of their aggressive notes. However, when exposed to stimuli with different harmonic ...