A flock of swans on the Dongting lake in Hunan province, Mar 1, 2017. Many birds gather together near the Dongting lake district as they prepare to fly north. Each October, a significant number of migratory birds fly from the northern part of China to the Dongting lake to spend the harsh winter. A survey conducted in January this year showed that there were more than 180,000 migratory water birds in the region, which is the highest since 2006.[Photo/Xinhua]