Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)

Wintering whooper swans are seen at the Yellow River in Hualong Hui Autonomous County of Haidong City, northwest China's Qinghai Province, Dec. 23, 2022. (Xinhua/Wu Gang)