Swans forage on the lake in Shandianhe wetland in Guyuan County, north China's Hebei Province, April 22, 2018. A large number of swans and other migratory birds gathered in the Shandianhe wetland recently. (Xinhua/Yang Shiyao)

Swans forage on the lake in Shandianhe wetland in Guyuan County, north China's Hebei Province, April 22, 2018. A large number of swans and other migratory birds gathered in the Shandianhe wetland recently. (Xinhua/Yang Shiyao)