Fear screams and adaptation to avoid imminent death: effects of genetic variation and predation

Abstract

Fear screams are calls emitted by prey just before or during capture by a predator, and the evolution of such calls has been attributed to the fitness benefits of escape from a predator due to interference by a secondary, kleptoparasitic predator or interference by conspecifics. If fear screams had beneficial effects on individuals carrying the same genes (in terms of learnt avoidance of a predator by related individuals, or predators avoiding future capture attempts of difficult prey), then fear screams should be more prevalent in species with little genetic variation and hence a high degree of shared alleles. In a comparative analysis of 71 species of birds, the proportion of individuals emitting fear screams in different species increased with the degree of genetic similarity among adults in local populations, as reflected by the band-sharing coefficient for neutral minisatellite markers. Furthermore, the proportion of individuals emitting fear screams in different species increased with the degree of preference by a common avian predator, the goshawk Accipiter gentilis, but not by the sparrowhawk Accipiter nisus, showing that individuals belonging to species that suffered disproportionately from predation were more likely to emit fear screams. Finally, the proportion of individuals emitting fear screams in different species increased with the proportion of individuals that were tail-less, thus having successfully escaped a predator. These results suggest that genetic variation has played a role in the evolution of fear screams, and that the frequency of fear screams is related to the risk of predation and the probability of successful escape.