Photo taken by a hidden camera on June 26, 2019 shows common terns flying back to their nest to feed their baby birds at a milu deer conservation area at the Yellow Sea wetland in Yancheng, east China's Jiangsu Province. More than 300 common terns live on an island of the conservation area now. Thanks to the wetland protection by local government in recent years, more types of birds now live on the area. (Xinhua/Wang Yuguo)