Migration routes of mute swans (Cygnus olor) in East Asia: First description of the Eastern and Western Chinese populations based on satellite tracking

The distribution and migration routes of the most studied swan species, mute swans (Cygnus olor), in East Asia are largely unknown because most of those studies were conducted in Europe and North America. In 2016 and from 2021 to 2022, we deployed satellite tracking devices on 22 and 10 mute swans wintering at the Ili River, Xinjiang of Western China, and summering at Ulansuhai Lake, Inner Mongolia of Eastern China, to determine their migration routes. Eight environmental factors, namely, human population density, the shortest distance to the nearest transportation route, elevation, aspect, slope, air temperature, wind speed and gross primary productivity (GPP), were used to analyse the environmental differences at the stopover sites of swan populations between Eastern and Western China. Ebinur and Ulungur Lakes in Xinjiang of Western China and Kapchagay Reservoir and Sasykkol and Alakol Lakes in Eastern Kazakhstan were the summering sites for the Western Chinese swan population; for the Eastern Chinese swan population, in addition to the Yellow River Delta being identified as a wintering site, the Hongze Lake Region of Jiangsu and Danaoban Lake of Inner Mongolia in China were also identified for the first time as wintering and summering sites, respectively. We also found that human population density and GPP were crucial determinants of stopover duration in the Eastern and Western Chinese swan populations both in spring and in autumn. Our findings provide basic data for future research on mute swans in East Asia and will contribute to conservation action plan development through current conservation status evaluations of important summering, wintering and stopover sites along the migration routes of mute swans.