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).