Abstract
Flapping flight is relatively costly for soaring birds such as raptors. To avoid costly flight, migrating raptors generally avoid flying over water. As a result, all but one of the global raptor migration flyways are largely over land. The East Asian oceanic flyway for raptors is the exception. Raptor species using this flyway migrate by island-hopping, flying over open ocean for distances of up to 300 km between islands. We used satellite telemetry data for grey-faced buzzards Butastur indicus, a species that dominates the southern part of the flyway, to investigate the geographical and atmospheric factors responsible for the suitability of this flyway for raptor migration. Using a combination of least-cost path analysis and a step selection function, we found that the occurrence of numerous islands and also suitable wind support along the oceanic flyway are responsible for route selection in grey-faced buzzards. These results confirm the role of islands, but also wind, in shaping the East Asian oceanic flyway of long-distance raptor migration.
Highlights
Many raptor species accomplish their long-distance migrations predominantly by soaring on thermals and orographic updrafts2018 The Authors
The oceanic flyway comprises numerous islands that, as our results suggest, significantly contribute to its suitability for raptor migration
The role of islands in facilitating raptor watercrossing has been shown for honey buzzards Pernis apivorus migrating over the central Mediterranean
Summary
Many raptor species accomplish their long-distance migrations predominantly by soaring on thermals and orographic updrafts2018 The Authors. [1,2,3] They are generally reluctant to fly over water bodies, where thermals are weak or absent 2 in most latitudinal zones and where powered flight is required [1,2,3,4]. Because of these adaptations [5], raptors migrate along well-established flyways that occur mostly overland and circumnavigate water bodies or converge on narrow land bridges or short water-crossings where overwater flight is inevitable [1,6,7]. The long distances of up to 300 km between the islands, which is more than distances commonly covered by raptors over water along other flyways, indicate that additional factors, such as atmospheric currents, facilitate raptor migration
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