Analysis of the correlations between environmental factors and rare cranes in the Poyang Lake region of China

Using survey data during 2001-2013 from a total of 38 lakes in the Poyang Lake region of China, we analyzed the inter-annual change in crane populations and the spatial distribution of crane species. Across the study sites, the total crane population was 6400 ± 2620 individuals during the period 2001-2013. Crane populations varied widely across the study sites: the largest crane population was observed on Bang Lake with an annual average of 2373, followed by Qi Lake, Dacha Lake, and Zhu Lake. The four main crane species, which were active on 50-80% of study lakes during the period of investigation, were G. leucogeranus, G. monacha, G. vipio, and G. grus. In particular, G. leucogeranus, G. monacha, and G. vipio were observed mainly in Poyang Lake National Nature Reserve and nearby lakes. G. grus was mostly observed in Poyang County. The largest populations of G. leucogeranus, G. vipio, and G. monacha were observed on Bang Lake, with annual averages of 1229, 985, and 88 birds, respectively. The largest G. grus population was observed on Qi Lake, with an annual average of 756 birds. We found that habitats for G. leucogeranus, G. monacha, and G. vipio were defined by similar environmental factors. In particular, increasing distance from roads had a positive impact on populations of these three species. By contrast, sedimentary total phosphorus content showed negative correlations with populations of all four main crane species, which implied that eutrophication could pose a threat to these rare crane species.