Habitat selection of wintering cranes in typical wetlands in the middle and lower reaches of the Yangtze River over the past 20 years, China.

The wetlands in the middle and lower reaches of the Yangtze River are the main overwintering and perching places for cranes. To examine the habitat selection mechanism of cranes in this area, two natural wetland reserves, Shengjin Lake and Poyang Lake, which are the main habitats of typical cranes, were selected as the study area. Using 20 years of Landsat satellite image data (between 1999 and 2019), the vegetation cover index was calculated from a pixel dichotomy model, and the landscape pattern index was obtained through Fragstats. The entropy method was adopted to determine the weight of the landscape index, and then, the habitat suitability index was calculated. Combined with the number of typical crane populations in the reserve, the selection mechanism of overwintering habitat of cranes was revealed. On the change of land-use type, the crane habitat of Shengjin Lake transferred more to non-crane habitat, and other land types increased, resulting in the decrease of crane habitat area. However, the change of crane habitat in Poyang Lake Reserve was small, so it can accommodate more cranes to overwintering here. In terms of vegetation coverage, most of the vegetation cover areas of Shengjin Lake were woodland near or far from the lake, but the woodland was not the habitat of cranes. Most of the vegetation-covered areas of Poyang Lake are grassland near the lake, which provide rest and foraging places for cranes. In the landscape pattern, the number of landscape patches in Shengjin Lake was large, the degree of landscape fragmentation was higher than that in Poyang Lake, the landscape complexity was higher, and the landscape diversity was simpler. This is not conducive to the maintenance of crane habitat, but also reduces the attractiveness of overwintering cranes, while the landscape suitability of crane habitat in Poyang Lake was higher than that in Shengjin Lake, and cranes were more likely to choose Poyang Lake as their overwintering habitat.