Wind conditions facilitate the seasonal water-crossing behaviour of Oriental Honey-buzzards Pernis ptilorhynchus over the East China Sea

摘要

Migratory raptors rarely fly over stretches of water larger than 25km, although different species undertake water crossings of varying lengths, depending mainly on their wing morphology. Oriental Honey-buzzards fly c. 680km over the East China Sea in autumn from breeding areas in Japan to wintering areas in Southeast Asia, but avoid this long water crossing in spring. We investigated the effects of weather on this exceptional migratory behaviour and its seasonality through a maximum entropy niche modelling approach. We used data collected through satellite tracking of 31 adult birds as presence points and a set of variables related to wind, precipitation and convective condition as environmental predictors. Results of modelling showed very different, almost non-overlapping, areas suitable for migration over the East China Sea region in autumn and spring. Suitable migration routes in autumn mostly occurred over the sea, whereas suitable areas for spring migration mostly occurred over land, suggesting that circumnavigating the East China Sea is preferable in spring. At the regional scale, wind conditions facilitate water-crossing behaviour of Oriental Honey-buzzards in autumn, but not in spring. Specifically, suitable tailwinds over the sea enable water-crossing in autumn, whereas in spring, wind support and convective conditions are best over land. Our modelling did not suggest any importance of convective conditions for autumn migration. However, we expect that at smaller temporal scales, convective conditions would be a considerable facilitator of the water-crossing behaviour in this species.