Beaked and Killer Whales Show How Collective Prey Behaviour Foils Acoustic Predators.

Abstract

Animals aggregate to obtain a range of fitness benefits, but a common cost of aggregation is increased detection by predators. Here we show that, in contrast to visual and chemical signallers, aggregated acoustic signallers need not face higher predator encounter rate. This is the case for prey groups that synchronize vocal behaviour but have negligible signal time-overlap in their vocalizations. Beaked whales tagged with sound and movement loggers exemplify this scenario: they precisely synchronize group vocal and diving activity but produce non-overlapping short acoustic cues. They combine this with acoustic hiding when within reach of eavesdropping predators to effectively annul the cost of aggregation for predation risk from their main predator, the killer whale. We generalize this finding in a mathematical model that predicts the key parameters that social vocal prey, which are widespread across taxa and ecosystems, can use to mitigate detection by eavesdropping predators.