A flock of black-headed gulls are seen in Longwangtan Park of Lhasa, Southwest China’s Tibet autonomous region, Dec 12, 2015. [Photo/Xinhua]

A great crested grebe is seen in Longwangtan Park of Lhasa, Southwest China’s Tibet autonomous region, Dec 12, 2015. [Photo/Xinhua]

A flock of bar-headed geese are seen in Longwangtan Park of Lhasa, Southwest China’s Tibet autonomous region, Dec 12, 2015. [Photo/Xinhua]