Migratory birds rest at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds fly above the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds fly above the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

A migratory bird rests at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds rest at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds rest at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds fly above the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

A migratory bird rests at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

A migratory bird rests at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds fly above the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

Migratory birds rest at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)

A migratory bird rests at the Shenzhen Bay in Shenzhen, south China's Guangdong Province, Dec. 11, 2019. (Xinhua/Mao Siqian)