Large-scale spatial pattern of bird responses to a potential predator suggests that predator-specific mobbing is a plastic trait

Abstract

Mobbing is a prey antipredator behaviour aimed to reduce the risk of predation. The behaviour may be innate and/or learned. Evaluating this behaviour on a large spatial scale can help to explore the mechanisms behind it. Using a playback experiment, I investigated variation in antipredator behaviour in small passerines in response to vocalisation from a potential predator, Eurasian pygmy owl (Glaucidium passerinum), at 105 sites in 35 localities within and outside the owl’s breeding range. While the birds outside the owl’s breeding range did not respond to the owl’s call, they mobbed at about 60% of the sites within the owl’s breeding range. At sites where the birds did not respond to the owl presentation, alarm calls of forest passerines were broadcasted to them. The birds always mobbed in response to the playback of these alarm calls. These results indicate that the birds’ response to the owl call may be a plastic trait induced by learning, while the response to the alarm calls of birds may be innate, as predation pressure in general can be strong enough to cause directional selection on the prey’s response to the alarm signalling of other birds.