Flexibility in daily travel routines causes regional variation in bird migration speed
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We used novel Global Positioning System-based satellite telemetry to reconstruct daily time budgets on travelling days of a long-distance migrant, the Osprey Pandion haliaetus, to reveal how landscape affects migratory performance. We compared daily travel routines between the Ospreys’ passage of Europe and the Sahara. In Europe, where feeding habitat is abundant, Ospreys fed both before–after flights and during interruptions, thus, combining migration with foraging. This resulted in a 2.7-h shorter daily flight period in Europe than in the Sahara. A calculated energy budget indicated that a ‘fly-and-forage migration strategy’ is favourable in Europe because associated benefits (energy intake) more than outweigh costs (reduced flight time). The much shorter flight time in Europe was the main explanation why Ospreys covered on average 78 km less distance on a travelling day in Europe than in the Sahara. In addition, there were regional differences in hourly flight speeds that are most probably the result of variation in thermal soaring conditions. We conclude that landscape properties have a profound effect on migration through regional variation in daily routines.
KeywordsFlight speed Habitat use Landscape ecology Satellite tracking Time budget
This research was financed through grants from the Swedish Research Council (to T.A. and to R.K.) and from the Niels Stensen Foundation (to R.K.). We thank René Dekkers and Patrik Olofsson for assistance in the field. We are grateful for support and excellent equipment from Microwave Telemetry Inc. The study was approved by the Ethical Committee in Göteborg (permit to M.H.). We also thank three anonymous reviewers for valuable suggestions and comments.
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