Female preferences for socially variable call characters in the cricket frog, Acris crepitans

Male cricket frogs produce only one type of call, the advertisement call, which both attracts females and repels rival males. The temporal and spectral structure of this call varies in a graded fashion with social context: males increase the temporal complexity and decrease the dominant frequency of their advertisement calls when interacting with neighbouring males. Previous studies of male behaviour suggested that vocal escalation signals fighting ability or aggressive intent. In this study, we examined an alternative hypothesis for the function of vocal escalation, that it increases a male's relative attractiveness to females when other males are nearby. We tested female cricket frogs for phonotactic preferences with respect to spectral and temporal call characters. Females did not show preferences for call dominant frequency, although they tended to choose calls with dominant frequencies near the population mean over calls with high or low dominant frequencies. Females preferred temporal call characters representative of interacting males to the temporal characters of undisturbed males. Males may use changes in temporal call characters to facultatively increase their relative attractiveness to females in the presence of other males. (C) 2004 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.