A mixed strategy of counter-singing behavior in male rock hyrax vocal competitions

Abstract

Maynard-Smith’s game-theoretical framework suggests that conflicts should be resolved through an exchange of agonistic displays which can be as effective as physical attack in securing contested resources. Hence, participants use signaling tactics that are governed by game-theoretical competition rules to maximize their benefit from the interaction. In rock hyraxes, males initiate singing in response to conspecific male songs, possibly to self-advertise and to facilitate comparison of performance by receivers. We hypothesized that hyrax counter-singing strategy can be explained by resident-intruder model and its outcome is determined by the identity and ability of the participants. Natural hyrax singing events and playback-induced events were classified according to the participants’ residence status—resident or bachelor (i.e., non-resident). As predicted by the resident-intruder model, resident listeners tended to reply to conspecific males at high rates (≈40 %), while bachelors showed low reply rates (17 %) to resident initiators. Unexpectedly, the lowest-ranking bachelors showed a tendency to reply to the highest-ranking residents. One possible explanation for this counter-intuitive behavior might be that weaker individuals exploit a situation in which it is unremunerated for a stronger opponent to retaliate (i.e., Napoleon strategy) and seize a self-advertisement opportunity in front of a large audience attending to the high-ranking males’ signal. Overall, we show that male hyraxes employ different counter-singing tactics depending on the residence and rank differences between the participants. This choice of competition tactics can be based on opponents’ individual recognition or/and on direct decoding of opponents’ traits encoded in the song.

Significance statement

In nature, conflicts are usually resolved through signaling rather than by actual fighting. Rock hyrax males often participate in vocal competitions, possibly to reduce the need for physical confrontations. During our study on the dynamics of male hyrax vocal competition, we discovered that hyraxes employ mixed counter-singing strategy dependent on the residence status and social rank differences between the participants. A paradoxical “Napoleon-complex” tactic was observed in interactions between males, when low ranking bachelors were found to interact and challenge the highest-ranking residents. On the other hand, residents were found to interact with opponents regardless of residency and/or rank. On top of the cognitive abilities required to individually recognize an opponent and possibly decode its vocal signals, our results suggest that male hyraxes compare own individual traits to those of the opponent in a mutual signal assessment interaction.