A Chinese Mergansers, an endangered bird species, is pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)

Chinese Mergansers, an endangered bird species, are pictured in Changbai Mountain National Nature Reserve in northwest China's Jilin Province, July 7, 2020. (Xinhua/Lin Hong)