Seasonal and regional differences in migration patterns and conservation status of Swan Geese (Anser cygnoides) in the East Asian Flyway
The Swan Goose (Anser cygnoides) breeds across Mongolia and adjacent China and Russia and winters exclusively in China. It is globally threatened, showing long-term major range contractions and declining abundance, linked to habitat loss and degradation. We remain ignorant about the biogeographical subpopulation structure of the species and potential differences in their migration timing, stopovers and schedules, information that could be vital to effective conservation of different elements of the species population, which we address here with results from a telemetry study.
In 2017–2018, we attached GPS/GSM telemetry devices to 238 Swan Geese on moulting sites in three discrete parts of their summering area (Dauria International Protected Area, Central Mongolia and Western Mongolia), generating 104 complete spring and autumn migration episodes to compare migration speed and nature between birds of different summer provenances.
Birds from all three breeding areas used almost completely separate migration routes to winter sympatrically in the Yangtze River floodplain. Although many features of the spring and autumn migrations of the three groups were similar, despite the significantly longer migration routes taken by Western Mongolian tagged birds, birds from Dauria Region arrived significantly later in winter due to prolonged staging in coastal areas and took longer to reach their breeding areas in spring. Among birds of all breeding provenances, spring migration was approximately twice as fast as autumn migration. Areas used by staging Swan Geese (mainly wetlands) in autumn and spring almost never fell within national level protected areas, suggesting major site safeguard is necessary to protect these critical areas.
This study showed the discreteness of migration routes taken by birds of different summer provenances and differences in their migratory patterns, highlighting key staging areas (Yalu River Estuary in China/North Korea for Dauria Region breeding birds, Daihai Lake for Central Mongolian and Ordos Basin for Western Mongolian birds). Based on this new knowledge of the biogeographical subpopulation structure of the Swan Goose, we need to combine data on subpopulation size, their distribution throughout the annual life cycle and conservation status, to develop more effective conservation strategies and measures to reverse population decline throughout the range.