Flying over the open sea is energetically costly for terrestrial birds. Despite this, over-water journeys of many birds, sometimes hundreds of kilometres long, are uncovered by bio-logging technology. To understand how these birds afford their flights over the open sea, we investigated the role of atmospheric conditions, specifically wind and uplift, in subsidizing over-water flight at a global scale. We first established that ΔT, the temperature difference between sea surface and air, is a meaningful proxy for uplift over water. Using this proxy, we showed that the spatio-temporal patterns of sea-crossing in terrestrial migratory birds are associated with favourable uplift conditions. We then analysed route selection over the open sea for five facultative soaring species, representative of all major migratory flyways. The birds maximized wind support when selecting their sea-crossing routes and selected greater uplift when suitable wind support was available. They also preferred routes with low long-term uncertainty in wind conditions. Our findings suggest that, in addition to wind, uplift may play a key role in the energy seascape for bird migration that in turn determines strategies and associated costs for birds crossing ecological barriers such as the open sea.

Individual consistency in migration can shine light on the mechanisms of migration. Most studies have reported that birds are more consistent in the timing than in the routes or stopover sites during migration, but some specialist species showed the opposite patterns, being more consistent in spatial than temporal aspects of migration. One possible explanation for this contrast is that specialists rely on particular food or habitat resources, which restrict the migratory routes they can take, leading to high spatial consistency. If this is the case, the effect of specialist foraging should become apparent only when birds forage, instead of fasting and flying continuously. To test this effect, we analysed individual consistency in migration of the oriental honey buzzard (Pernis ptilorhynchus), a specialist raptor that feeds on honeybees and wasps, using a long-term tracking dataset. As honey buzzards make extended stopovers during which they forage in spring but not in autumn, the spatial consistency should be higher in spring than in autumn. Honey buzzards were highly consistent in both their migratory routes and stopover sites in Southeast Asia, but only during spring migration. Our results highlight an important link between species' migratory consistency and foraging ecology.

The Grey-faced Buzzard (Butastur indicus) is a migratory raptor breeding in Japan. It has a high breeding density in what is known as “Satoyama”, a traditional mosaic landscape of paddy fields, woodland, grassland, and streams. We studied the foraging behavior of five buzzard pairs in Satoyama of Tochigi Prefecture, central Japan, for two years. Seasonal changes in foraging sites and differences in the amount of prey captured at each foraging site were analyzed by Bayesian inference using a Markov Chain Monte Carlo (MCMC) algorithm. The main vegetation types which characterized the foraging areas of the buzzards varied over the course of the breeding season from paddy fields to levees and grass-arable fields, and eventually to wooded areas. Along with this shift, the main prey of the buzzards changed from frogs to insects. In paddy fields, frogs and small mammals were frequently captured. A variety of prey including frogs, small mammals, lizards, snakes, and insects were taken at levees and grass...