Call directionality and its behavioural significance in male northern elephant seals, Mirounga angustirostris

Abstract

Animals often produce sounds that are focused in a particular direction relative to the caller’s orientation. Although many studies have suggested ways in which directional signal design might have behavioural significance among vocally interacting individuals, there are few direct tests using experimental approaches. During the breeding season and while fasting on land, male northern elephant seals produce airborne threat calls during dyadic interactions when competing for mating opportunities. In this study, we investigated the directional cues of these calls and tested hypotheses regarding directional signalling with respect to the behaviour of receivers during vocally mediated male agonistic interactions. We then determined effects of vocal directionality on receiver responses using an acoustic playback approach. We found that male calls had substantial directionality, particularly at higher frequencies (>1000 Hz). Subordinate males responded more strongly by retreating when the caller faced the receiver compared to when the caller was at a right angle or faced away. We also found a significant difference in responses to playback sequences with different call directivity patterns. Males displayed significantly more negative phonotaxis (i.e. moved away) in response to playbacks that simulated a caller oriented towards them compared to when playbacks simulated a caller oriented away from them. These results suggest that the directionality of threat calls provides important information about the auditory scene and spatial orientation of conspecifics and that this trait, along with the receiver’s ability to extract this information, may have evolved as a consequence of its effect on the breeding success and fitness of the individual.