Photo taken on Dec. 13, 2018 shows migrant birds at Duchang wetland of Poyang Lake, east China's Jiangxi Province. The Poyang Lake, China's largest freshwater lake, saw a flock of migratory birds overwintering. (Xinhua/Fu Jianbin)

Photo taken on Dec. 13, 2018 shows migrant birds at Duchang wetland of Poyang Lake, east China's Jiangxi Province. The Poyang Lake, China's largest freshwater lake, saw a flock of migratory birds overwintering. (Xinhua/Fu Jianbin)

Photo taken on Dec. 13, 2018 shows migrant birds at Duchang wetland of Poyang Lake, east China's Jiangxi Province. The Poyang Lake, China's largest freshwater lake, saw a flock of migratory birds overwintering. (Xinhua/Fu Jianbin)

Photo taken on Dec. 13, 2018 shows migrant birds at Duchang wetland of Poyang Lake, east China's Jiangxi Province. The Poyang Lake, China's largest freshwater lake, saw a flock of migratory birds overwintering. (Xinhua/Fu Jianbin)