File photo taken on Nov. 21, 2012 shows birds flying over the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers observe migratory birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Ma Mindian observes migratory birds with a telescope at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 3, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Some members of the ranger team pose for a photo at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers scatter food for birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Zhao Guoping is on duty at a station at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Photo taken on Feb. 3, 2021 shows bar-headed geese at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Zhao Guoping cleans a shelter for sick or injured birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers scatter food for birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Ma Mindian records daily observation results on a booklet at home in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 3, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Photo taken on Feb. 3, 2021 shows black-necked cranes at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

File photo taken on Jan. 2, 2014 shows Ma Mindian (L) and Zang Erjun (passed away in March 2017) scattering corn for birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Photo taken on Feb. 3, 2021 shows black-necked cranes at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Photo taken on Feb. 1, 2021 shows birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers scatter food for birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers patrol at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

File photo taken on Jan. 1, 2013 shows Zang Erjun (passed away in March 2017) scattering food for birds against a blizzard at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)

Rangers observe migratory birds at the Caohai National Nature Reserve in the Yi, Hui and Miao Autonomous County of Weining, southwest China's Guizhou Province, Feb. 2, 2021. Established as a national nature reserve in 1992, Caohai National Nature Reserve covers an area of over 120 square kilometers. During the past years, over 60 people have served as rangers of the reserve, feeding birds, observing bird activities and patrolling in the reserve. Day after day, the torch has been passed from generation to generation among rangers. Thanks to their efforts and support of local authorities, the reserve has become a major winter base for many migratory birds such as black-necked cranes. In recent year, over 100,000 birds have come here to overwinter every year. (Xinhua/Yang Wenbin)