A group of Tibetan wild donkeys are seen in Nagqu, southwest China's Tibet Autonomous Region, Dec. 23, 2019. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Sun Fei)

Two Tibetan wild donkeys run in Nagqu, southwest China's Tibet Autonomous Region, Dec. 22, 2019. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Hou Jie)

A Tibetan wild donkey is seen in Nagqu, southwest China's Tibet Autonomous Region, Dec. 22, 2019. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Sun Fei)

Aerial photo taken on Dec. 23, 2019 shows a group of Tibetan wild donkeys running in Nagqu, southwest China's Tibet Autonomous Region. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Sun Fei)

Aerial photo taken on Dec. 23, 2019 shows a group of Tibetan wild donkeys running in Nagqu, southwest China's Tibet Autonomous Region. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Sun Fei)

Tibetan gazelles graze in Nagqu, southwest China's Tibet Autonomous Region, Dec. 23, 2019. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Hou Jie)

A Tibetan gazelle is seen in Nagqu, southwest China's Tibet Autonomous Region, Dec. 23, 2019. The number of wild animals in Nagqu rises gradually thanks to the improvement of the ecological environment. (Xinhua/Hou Jie)