Collective Predator Perception Advertisement in Fish

The idea that prey might advertise their perception of predators to avoid attacks has received considerable attention in the literature. However, evidence for reduced attack frequencies or attack success in predators as a result of perception advertisement in prey is limited or indirect. Here we present a field study which investigated the benefits of waves produced by fish at the water surface when diving down collectively in response to attacks of avian predators. Instead of merely escaping, fish engaged in surface waves that were highly conspicuous, repetitive and rhythmic involving many thousands of individuals for up to 2 min. Experimentally-induced fish waves doubled the time birds waited until their next attack therefore substantially reducing attack frequency. In one avian predator, capture probability, too, decreased with wave number and birds switched perches in response to wave displays more often than in control treatments suggesting that they directed their attacks elsewhere. Taken together these results support fish waves’ function of perception advertisement. A predator confusion effect is also possible but so far is not known to be associated with waving behaviour especially given that rhythmic waving could make prey more predictable. Collectively produced perception advertisements raise some intriguing questions of how fish synchronise to produce such signals and which pathway has led to their evolution.