This study was mainly conducted in the Altun and Kunlun mountain ranges on the edge of the Tibetan Plateau and adjacent areas including parts of the Pamir Plateau and wetlands of the Lop Nur Basin, as these sites have been demonstrated as potential habitats of Black-necked cranes by previous reports (References). The elevation ranges from 3,800–6,900 m and mountains above 5,500 m have permanent snow (Butler et al., 1986; Achuff and Petocz 1988; Bleisch et al. 2009). The climate of the area is continental, dry and cold with average daily temperatures from − 21 to 2.4 oC in winter and − 3.4 to 21 oC in summer. Precipitation is sparse and frequently falls as snow or sleet even in summer. The Altun Nature Reserve, covering an area of 45,000 km2 and characterized by high elevations, low annual precipitation, low nutrient levels and extremely cold weather in the winter (Butler et al., 1986; Achuff and Petocz 1988; Ablimit, 2004, Ma, 2010; Mardan et al., 2013, Mardan et al,. 2021).
We also surveyed the suspected areas within the Pamir Plateau, Tarim River Basin and Bostan Lake which were reported to presumably have crane distributions (Fig. 1, areas with the question marks) ( Chen, 1985; Gao, 1986; Huang et al., 1989; Feng, 1991; Tian, 1999). These reports assumed that there may be ideal habitats for large populations of the species, and that, there were more than 1000 Black-necked cranes in Xinjiang. We assume that this population estimate is too large because it is not justified to extrapolate the density of the main distribution regions to the total area, given that approximately 20% of the total area of Xinjiang is considered to be suitable habitat for Black-necked cranes (Tian, 1999; Ma et al., 2011).
The present study comprises the second nation-wide field survey of wildlife resources of China, which was initiated in 2010 and completed in November 2017. The entire population was counted with direct count method at a total of 25 sampling sites (Fig. 1). Surveys were made in March-April, and October-November to establish the arrival and departure dates of the species. Data was collected on the number of individuals, nests, number of eggs laid, hatching success and survival of fledglings (Oring and Lank 1982). Nikon binoculars and spotting scopes were used to spot the birds. Locations were taken using a Garmin 12 CX GPS. A digital stop watch, a hand tally counter and a still camera were used to record specific events. Direct or visual count method was used to count the birds. Such a method has been widely used for counting aquatic birds (Eltringham and Atkinson 1961; Roux 1973; Zewarts 1976; Alford and Bolen 1977; Amat 1984; Sridharan 1989). Interviews with local wardens and pastoralists, and officials of the administrative were administered to get information on the distribution and conservation status of the cranes. The severities of the potential threats to the cranes at different sites were estimated based on literature reviews, preliminary interviews and field assessment. We analyzed our survey data using SPSS 15.0 (SPSS 2005).