title: Matching times of leading and following suggest cooperation through direct reciprocity during V-formation flight in ibis.
abstract: One conspicuous feature of several larger bird species is their annual migration in V-shaped or echelon formation. When birds are flying in these formations, energy savings can be achieved by using the aerodynamic up-wash produced by the preceding bird. As the leading bird in a formation cannot profit from this up-wash, a social dilemma arises around the question of who is going to fly in front? To investigate how this dilemma is solved, we studied the flight behavior of a flock of juvenile Northern bald ibis (Geronticus eremita) during a human-guided autumn migration. We could show that the amount of time a bird is leading a formation is strongly correlated with the time it can itself profit from flying in the wake of another bird. On the dyadic level, birds match the time they spend in the wake of each other by frequent pairwise switches of the leading position. Taken together, these results suggest that bald ibis cooperate by directly taking turns in leading a formation. On the proximate level, we propose that it is mainly the high number of iterations and the immediacy of reciprocation opportunities that favor direct reciprocation. Finally, we found evidence that the animals' propensity to reciprocate in leading has a substantial influence on the size and cohesion of the flight formations.
authors: Edward Grey Institute, Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom; Institute for Ecology and Evolution, University of Bern, 3032 Hinkterkappelen, Switzerland; Institute for Theoretical Biology, Humboldt University at Berlin, 10115 Berlin, Germany; bernhard.voelkl@zoo.ox.ac.uk.
authors: Bernhard
authors: B
authors: Voelkl
authors: Structure & Motion Laboratory, Royal Veterinary College, University of London, Herts AL9 7TA, United Kingdom;
authors: Steven J
authors: SJ
authors: Portugal
authors: Waldrappteam, 6162 Mutters, Austria; and Ornithology Section, Bavarian Zoological State Collection, 81247 Munich, Germany.
authors: Markus
authors: M
authors: Unsöld
authors: Structure & Motion Laboratory, Royal Veterinary College, University of London, Herts AL9 7TA, United Kingdom;
authors: James R
authors: JR
authors: Usherwood
authors: Structure & Motion Laboratory, Royal Veterinary College, University of London, Herts AL9 7TA, United Kingdom;
authors: Alan M
authors: AM
authors: Wilson
authors: Institute for Theoretical Biology, Humboldt University at Berlin, 10115 Berlin, Germany; Waldrappteam, 6162 Mutters, Austria; and.
authors: Johannes
authors: J
authors: Fritz
mesh_terms: D025041:Animal Migration; D000818:Animals; D001717:Birds / Q000502:physiology*; D005426:Flight, Animal
keywords: cooperation; formation flight; reciprocity; social dilemma
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