Photo taken on April 4, 2020 shows a migrant bird flying over the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows a migrant bird resting in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows a migrant bird in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows a migrant bird flying over the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region. (Xinhua/Lian Zhen)

Photo taken on April 4, 2020 shows migrant birds flying over the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows migrant birds flying over the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region. (Photos: Xinhua)

Photo taken on April 4, 2020 shows a migrant bird flying over the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows migrant birds resting in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows a migrant bird in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows migrant birds in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.

Photo taken on April 4, 2020 shows migrant birds in the Ulansuhai Nur wetland in Bayannur, north China's Inner Mongolia Autonomous Region.