Population dynamics and habitat use of the Black-necked Crane (Grus nigricollis) in the Yarlung Tsangpo River basin, Tibet, China

Background The Black-necked Crane (Grus nigricollis) is an internationally threatened crane living on the plateau, mainly in winter, in the Yarlung Tsangpo River basin in Tibet, western China. In the past five years, some economic development projects have been conducted in this area, posing potential threats to the wintering populations of the cranes and their habitats. Therefore, the current population dynamics of wintering Black-necked Cranes and habitat suitability in the Yarlung Tsangpo River basin were investigated. Methods Twenty counties were surveyed using the line transect method in December 2017 and January 2018, and we recorded the location, flock size, number of individuals, habitat types and presence of human disturbance in which they occurred. We compared the results from the middle wintering period in this survey with those from 2014. Results The highest number of cranes recorded was 8291, and the results showed that the cranes were mainly distributed in Lhaze, Namling, Samzhubze, and Lhunzub. A total of 577 and 495 flocks were recorded in the early and middle wintering periods, respectively. In the early wintering period, there were significant differences in the number of individuals across the different habitats, with crop stubble land and plowed land representing more than 30% of the total habitat utilization. In the middle wintering period, there were also significant differences in the number of individuals, and the utilization of crop stubble land represented over 60% of the total. Conclusions Wintering Black-necked Cranes mainly fed on spilled grains in stubble habitat after harvest. In the middle wintering period, some of the farmlands were plowed and irrigated, which resulted in food shortages in these areas, and the cranes tended to gather in mixed flocks of large size instead of as a single family. There were still considerable regional wintering populations decreases in Quxu, Nedong, and Sakya in 2018 compared with 2014, and these decreases were mainly due to some recently emerging threats, including farmlands being converted into areas of greenhouse cultivation, highway and railway construction, river dredging, the rapid development of the manufacturing and mining industries, and the lack of protection of important wintering sites.