Aggressive contests in house crickets: size, motivation and the information content of aggressive songs

The function of aggressive signals, including both their information content and the circumstances under which they cause resolution or escalation of conflict, continues to be controversial. We studied the information content of aggressive songs in the house cricket, Acheta domesticus, to test their ability to inform opponents about fighting ability and motivation. We show that songs produced by individual males are highly repeatable and contain information about male resource holding potential, the ability of a male to win an aggressive contest. Temporal components of aggressive song were correlated with male body size, and size affected both the intensity and outcome of fights. In contrast, we found no components of song that signal motivation to fight. Although males with restricted access to mates were significantly more aggressive and won fights more often, their songs did not reflect the asymmetry in motivation to fight. We discuss possible reasons for the absence of signals of motivation during animal contests.