Aerial photo taken on Nov. 21, 2019 shows the scenery of a Yellow River wetland in Zhaodu Town of Dali County, northwest China's Shaanxi Province. (Photos: Xinhua)

An egret is seen at a Yellow River wetland in Zhaodu Town of Dali County, northwest China's Shaanxi Province, Nov. 21, 2019.

An egret flies over a Yellow River wetland in Zhaodu Town of Dali County, northwest China's Shaanxi Province, Nov. 21, 2019.

Wild birds fly over a Yellow River wetland in Fanjia Town of Dali County, northwest China's Shaanxi Province, Nov. 21, 2019.

Egrets are seen at a Yellow River wetland in Fanjia Town of Dali County, northwest China's Shaanxi Province, Nov. 21, 2019.