Photo taken on Nov. 17, 2018 shows bar-headed geese overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/He Huan)

　　Photo taken on Nov. 17, 2018 shows black-necked cranes overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/Wang Chunliang)

　　Photo taken on Nov. 17, 2018 shows black-necked cranes overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/He Huan)

　　Photo taken on Nov. 17, 2018 shows bar-headed geese overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/Wang Chunliang)

　　Photo taken on Nov. 17, 2018 shows black-necked cranes overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/Wang Chunliang)

　　Photo taken on Nov. 17, 2018 shows black-necked cranes overwintering in the Caohai national nature reserve in Weining County, southwest China's Guizhou Province. The reserve has recently seen an increasing number of migratory birds overwintering in it. (Xinhua/Wang Chunliang)