Real-time weather analysis reveals the adaptability of direct sea-crossing by raptors

Abstract

Many animals seasonally travel between their breeding and wintering grounds. With their advanced mobility, birds often migrate over thousands of kilometres. Recently, satellite-tracking studies have revealed peculiar migration routes for some avian species at a global scale. However, the adaptability of such migration routes has not been clearly demonstrated. Using satellite-tracking data for 33 individuals, we show that the Japanese population of Oriental honey-buzzards (Pernis ptilorhynchus) directly crosses the 650-km-wide East China Sea during their autumn migration, although they fly a longer route around the sea rather than directly crossing it during their spring migration. By applying aerodynamic theory, we show that the buzzards could cross the sea by soaring and gliding flight. Moreover, using a high-resolution meteorologicalprediction analysis, we demonstrate that the migratory trajectory of the birds strongly depends on the wind direction at their estimated locations. In the area, northeastern tailwinds blow stably only during autumn. Thermals were abundant ca. 500-1,000 m over the East China Sea in autumn, but that was not the case in spring. We suggest that the autumnmigration route across the East China Sea is likely to have evolved in response to the specific weather conditions over the sea. Animations showing movements of Oriental honeybuzzards and temporal change in weather conditions are available at:

Evidence that dorsally mounted satellite transmitters affect migration chronology of Northern Pintails

“…5). We acknowledge that other weather conditions such as wind direction and atmospheric pressure systems can influence timing of avian migration (Yamaguchi et al 2012b;Gill et al 2014). We were unable to assess long-term changes in those conditions, and assume they did not differentially affect ringed and radiomarked pintails.…”

Climate change alters the optimal wind-dependent flight routes of an avian migrant

“…Wind variables were downloaded at the 850 MB pressure level with a 6 h temporal resolution. This pressure level corresponds with the average flight height of the birds [19]. Furthermore, it was the lowest-pressure-level data available from the above-mentioned RCM.…”

“…We focused on this relatively small section of the autumn journey as it is characterized by an approximately 680 km non-stop flight over the East China Sea between southwestern Japan and China, and is very likely to be shaped solely by atmospheric conditions [18,19]. Such independence of biotic interactions (e.g.…”

“…As Oriental honey-buzzards start their migration from the Goto Islands of Japan (figure 1) towards China, they depend highly on thermals and tailwinds to complete the sea crossing [18,19]. Wind conditions over the Goto Islands are expected to remain somewhat suitable by mid-century under both climatic scenarios.…”

Can wheatears weather the Atlantic? Modeling nonstop trans-Atlantic flights of a small migratory songbird

“…Our results therefore reinforce conclusions from earlier studies that wind support is crucial to migration along over-ocean routes (cf. Felicísimo et al 2008, Shamoun-Baranes and van Gasteren 2011, Yamaguchi et al 2012.…”