2.1 Study area
This study was conducted in a 5 km reach of the Shangqing River in Jiangxi province (Fig. 1), a tributary of Yangtze River. The site is a major M. squamatus wintering ground, providing foraging habitat for a population of about 50 individuals every year (Wang et al., 2010). The average annual temperature is 16.7 ℃ and the average annual precipitation is 1816 mm. Both sides of the river were covered by forest. There are many gravel bars and islands in this river reach, providing ideal habitats for M. squamatus to forage and roost ((Zeng et al., 2015)). The water depth varies from 0 to 3 meters. Considering the different foraging behaviours, we classified areas with water depth up to 40 cm as shallow and those greater than 40 cm as deep (Fig. 1).