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From local collective behavior to global migratory patterns in white storks

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Science  25 May 2018:
Vol. 360, Issue 6391, pp. 911-914
DOI: 10.1126/science.aap7781

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Follow the leader

What role do social dynamics play in guiding collective migrations? Identifying such dynamics requires following individual animals across long migratory distances. Flack et al. used GPS tags to follow individual juvenile white storks on their southern migration (see the Perspective by Nevitt). Birds generally fell into two categories: leaders and followers. Leaders sought out areas of thermal uplift, flapped less in transit, and flew farther. Followers followed leaders into thermals but had different trajectories, exhibited greater flapping effort, and flew shorter total distances.

Science, this issue p. 911; see also p. 852

Abstract

Soaring migrant birds exploit columns of rising air (thermals) to cover large distances with minimal energy. Using social information while locating thermals may benefit such birds, but examining collective movements in wild migrants has been a major challenge for researchers. We investigated the group movements of a flock of 27 naturally migrating juvenile white storks by using high-resolution GPS and accelerometers. Analyzing individual and group movements on multiple scales revealed that a small number of leaders navigated to and explored thermals, whereas followers benefited from their movements. Despite this benefit, followers often left thermals earlier and at lower height, and consequently they had to flap considerably more. Followers also migrated less far annually than did leaders. We provide insights into the interactions between freely flying social migrants and the costs and benefits of collective movement in natural populations.

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