Hundreds of whooper swans arrive to nest in Longyang Lake of southwest China's Qinghai every winter, thanks to the improvement of local ecological environment.[Photo/Xinhua]

Hundreds of whooper swans arrive to nest in Longyang Lake of southwest China's Qinghai every winter, thanks to the improvement of local ecological environment.[Photo/Xinhua]

Hundreds of whooper swans arrive to nest in Longyang Lake of southwest China's Qinghai every winter, thanks to the improvement of local ecological environment.[Photo/Xinhua]

Hundreds of whooper swans arrive to nest in Longyang Lake of southwest China's Qinghai every winter, thanks to the improvement of local ecological environment.[Photo/Xinhua]