MIGRATIONS OF BEWICK'S SWAN (CYGNUS BEWICKII): NEW DATA ON TAGGING THE MIGRATION ROUTES, STOPOVERS AND WINTERING SITES

摘要

To reveal the origin of the breeding sites of a new, growing, wintering population of Bewick's Swan (Cygnus bewickii) in the delta of Evros River, Greece, in the August of 2015 and 2016 we deployed 14 GPS-GSM 30 g transmitters on adult swans moulting at the Baydaraskaya Bay, Yamal Peninsula, Russia. A total of 11 swans were tracked down to their wintering areas. Three very distinct wintering areas were identified: the Evros Delta (eastern Mediterranean), the Volga Delta, northern Caspian Sea (within both Russia and Kazakhstan), Central Asia (Uzbekistan, Turkmenistan and westernmost China), and Lake Poyang (Yangtze Basin, China). Bewick's Swans from Yamal were thus found wintering in the Evros Delta for the first time. Altogether, three new migration routes were revealed for this species:western (Evros and Volga deltas), central (Uzbekistan, Turkmenistan and westernmost China) and eastern (Lake Poyang). We also investigated the migration track length, the network of stopover sites (14 were identified) and the migration strategy for each of the routes identified. The appearance of new wintering sites (in southeastern Europe and Central Asia) could be related to the remarkable numbers growth of breeding and moulting swans in Yamal along with a strong decrease observed in the population wintering in the North Sea coasts, likely as a result of habitat change. No reliable relation could be established between these two opposite trends.