title: Nonlethal predator effects on the turn-over of wild bird flocks.
abstract: Nonlethal predator effects arise when individuals of a prey species adjust their behaviour due to the presence of predators. Non-lethal predator effects have been shown to affect social group structure and social behaviour as well as individual fitness of the prey. In this experimental study, we used model sparrowhawks to launch attacks on flocks of wild great tits and blue tits whilst monitoring their social dynamics. We show that nonlethal attacks caused instantaneous turn-over and mixing of group composition within foraging flocks. A single experimental 'attack' lasting on average less than three seconds, caused the amount of turn-over expected over three hours (2.0-3.8 hours) of undisturbed foraging. This suggests that nonlethal predator effects can greatly alter group composition within populations, with potential implications for social behaviour by increasing the number of potential interaction partners, as well as longer-term consequences for pair formation and emergent effects determined by social structure such as information and disease transmission. We provide the first evidence, to our knowledge, based on in depth monitoring of a social network to comprehensively support the hypothesis that predators influence the social structure of groups, which offers new perspectives on the key drivers of social behaviour in wild populations.
authors.affiliation: Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, OX1 3PS Oxford, United Kingdom.|Animal Welfare Division, University of Bern, Laenggassstrasse 120, 3012 Bern, Switzerland.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Voelkl
authors.affiliation: Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, OX1 3PS Oxford, United Kingdom.
authors.forename: Josh A
authors.initials: JA
authors.lastname: Firth
authors.affiliation: Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, OX1 3PS Oxford, United Kingdom.
authors.forename: Ben C
authors.initials: BC
authors.lastname: Sheldon
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000502:physiology*; D001717:Birds / Q000502:physiology*; D005843:Geography; D008954:Models, Biological; D011235:Predatory Behavior / Q000502:physiology*; D013997:Time Factors; D006113:United Kingdom