An essential stopover on a global flyway
In Anhui province, along the southern bank of the Yangtze River, lies Shengjin Lake, a critical freshwater wetland. This body of water is a designated National Nature Reserve and a Ramsar Wetland of International Importance, recognizing its value to global biodiversity. The lake system is an important stopover and wintering ground for a vast number of migratory waterbirds using the East Asian-Australasian Flyway. Each year, conservation scientists and ornithologists conduct a census to count the visiting bird populations.
The primary focus of the annual count is the Tundra Swan, Cygnus columbianus. Shengjin Lake and the surrounding wetlands of the Yangtze River floodplain host approximately 75% of the East Asian flyway population of these swans during the winter. The annual census, part of the larger Asian Waterbird Census, involves teams from organizations like the Anhui Forestry Department, Anhui University, and Wetlands International. In one census from January 2016, observers counted 24,506 waterbirds from 39 different species. Overall, the number of migratory birds wintering at Shengjin Lake has grown from around 60,000 to approximately 100,000 due to habitat protection efforts.
A climate change barometer
The timing of the swans' arrival is an important data point in the annual census. Studies have shown that migratory birds are arriving at their wintering grounds earlier than they did decades ago, a shift linked to rising global temperatures. At Poyang Lake, another major wetland in the region, birds arrived 10 days earlier than usual during a severe drought year. This phenological shift presents risks; the birds' arrival may no longer synchronize with the peak availability of their food sources, such as the tubers of submerged plants like Vallisneria.
The census also tracks, the census tracks many other significant species. Shengjin Lake is known for being the largest wintering ground for the vulnerable Hooded Crane (Grus monacha), with counts reaching up to 500 individuals. The surveys also record nationally protected species like the Oriental Stork (Ciconia boyciana) and the Eurasian Spoonbill (Platalea leucorodia). Other recorded threatened species include the critically endangered Baer's Pochard (Aythya baeri) and the endangered Swan Goose (Anser cygnoides). In total, 175 bird species have been documented at the reserve.