Figure 2 | Scientific Reports

Figure 2

From: GPS-telemetry unveils the regular high-elevation crossing of the Himalayas by a migratory raptor: implications for definition of a “Central Asian Flyway”

Figure 2

Main Asian flyways (red lines) used by soaring migrants in Asia during pre- and post-breeding journeys. Traditional flyways-charts (e.g.2,31) depicted two major flyways for Asia: the Eurasian—East African flyway (G) and the East Asian Continental flyway (H). We propose the addition of a composite “Central Asian flyway” (routes A to F) employed by soaring migrants from central Asia to enter or exit their non-breeding quarters in the Indian sub-continent. The passage of soaring migrants is likely to be mainly funnelled through the westernmost (A, B and C) and easternmost (D, E and F) ends of the Himalaya Range. The eastern crossing of the Himalayas has been poorly documented by tracking-studies for soaring migrants and thus three hypothetical nonexclusive routes are shown. The connection between route D and E is supported by satellite-tracking data on a single Steppe Eagle by Batbayar and Lee6. Plotted routes B and C are based on data from this study, while route A is based on tracking data by Juhant & Bildstein10 and Terraube and colleagues40. Based on terminology proposed in Juhant & Bildstein10 and new routes outlined in this study, we define: route A and B as the “Western Circum-Himalayan Corridor”; route C as the “Western Himalayan Corridor”; route D and E as the “Eastern Himalayan Corridor”; and route F as the “Eastern Circum-Himalayan Corridor”. The red dashed line represents a West–East migration corridor reported by several authors for several raptors, especially for the autumn migration (western Himalaya9; eastern Himalaya6,41,42). It may represent the strategic, approaching movement to the Himalaya crossing in the pre-breeding migration, or the post-crossing exploitation of favourable winds in the post-breeding migration. More tracking data from more species will be needed to uncover its function. The blue dashed line in western Mongolia indicates a likely migratory divide: species passing to the west/east of such divide seem to use the western/eastern Himalayan routes, respectively. This divide also seems to hold for other non-soaring taxa, such as ducks and geese (e.g.5,15,16). The passage of species capable of migrating trough more direct flapping flight or through mixed strategies based on both soaring and flapping (e.g. falcons, harriers, Accipiter hawks) may employ a more central, broad-range crossing of the Himalayas (conceptually approximated by continuous blue lines over a portion only of the Himalaya range to avoid map clogging, (e.g.7,15). The thick red arrows at the top of the map (central-northern Russia) represent the theoretical, more northern basin of provenance of migrants travelling through the more southern depicted routes in the outward, post-breeding migration. The map integrates data from the current study, tracking data from other studies (e.g.5,6,7,16,40), re-sightings of ringed birds (e.g.22), observations at watch-sites of concentrated passage by migrants (e.g.8,9,10,41,42) and previous large-scale maps of main flyways for soaring birds2,31. Major routes are shown only up to their main entry-areas into the Indian subcontinent and into Africa. This map was generated with ArcGIS 10.5, using World Imagery by Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN and the GIS User Community (https://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer), and country borders according to Google Earth imagery (Google India).

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