Photo taken on Nov. 11, 2020 shows black-headed gulls near the Jijiang Yangtze River Bridge in Jiangjin District of southwest China's Chongqing Municipality. Since November, flocks of black-headed gulls have arrived in Chongqing on the upper reaches of the Yangtze River. Ornithologists said the Chongqing section of China's longest river has seen the largest migratory flock of black-headed gulls in the past decade. The gulls are concentrating at a rare-fish nature reserve on the Yangtze River, a fact that is likely related to the measures including fishing bans to protect the ecology and environment there, said a researcher with the Chongqing Natural History Museum. (Xinhua/Wang Quanchao)