Territorial male bullfrogs (Rana catesbeiana) do not assess fighting ability based on size-related variation in acoustic signals

Some animals use communication signals to assess their opponent'ssize and fighting ability during aggressive conflicts. Malefrogs assess their opponent's size based on the fundamentalfrequency (pitch) of advertisement calls, which is negativelycorrelated with body size, an important determinant of fightingability in frogs. I conducted a field playback experiment to investigate whether territorial male bullfrogs assess the sizeof opponents based solely on size-related variation in fundamentalfrequency. I repeatedly broadcast synthetic bullfrog advertisementcalls to three groups of males. Playback stimuli simulateda large male (n = 24), a small male (n = 24), or an acousticallysize-matched male (n = 34). Neither the simulated size of theopponent, the subject's own size, nor the degree of size asymmetrybetween the subject and simulated intruder had significanteffects on the magnitude of responses during the playback testor on the rate of habituation that occurred with repeated stimulation.Post-hoc analyses of effect sizes and statistical power indicatedthat the effects in this study were quite small compared toprevious studies in other frogs. More important, power analysesindicated that this study had high power (1 - ß >0.90) to detect the magnitude of effect sizes observed in previous studies. Thus, territorial male bullfrogs do not appear to assessan opponent's fighting ability based solely on the fundamentalfrequency of acoustic signals. These results contrast starklywith theoretical predictions and previous empirical work withfrogs.