We examined the ability of male green frogs to assess the size of an opponent based on the dominant frequency of their advertisement call, which is negatively correlated with size, using synthetic stimuli to simulate intruders of different sizes. In one field playback experiment, we broadcast a pair of stimuli representing a small and a large male; in a second experiment, we broadcast calls of a medium and a large male. In both experiments, males produced calls with significantly lower dominant frequencies in response to each stimulus. Contrast analyses revealed that males lowered the dominant frequency of their calls more in response to the large-male stimulus than in responses to the small- and medium-male stimuli. In the second experiment, males also responded to the large-male stimulus by calling at higher rates. There were no differences in mean note duration or the number of moves made toward or around the playback speaker in response to any stimulus. Thus, the frequency of an opponent's calls elicits a differential modification of calling behavior, primarily in the form of differential dominant frequency alteration, suggesting that males use dominant frequency to assess the size of opponents during aggressive encounters.
Bibliographical noteFunding Information:
Acknowledgements We thank H.C. Gerhardt, M.F. Given, L.A. Hay, R.D. Howard, P.T. Lopez, and J.J. Schwartz for helpful comments on previous versions of the manuscript. We are grateful to J. Schmid for providing access to the ponds in Eagle Creek Park. J.J. Schwartz generously provided the software and expertise used to synthesize stimulus calls. This research was funded by an NSF Graduate Research Fellowship to M.A.B., a Butler University Research Grant to S.A.P., and a grant from the Butler Summer Institute to P.C.O.
Copyright 2004 Elsevier Science B.V., Amsterdam. All rights reserved.
- Acoustic communication
- Aggressive interactions
- Frequency alteration
- Rana clamitans
- Size assessment