The common tern (Latin name: Sterna hirundo) is a typical migratory summer bird. The body is slightly smaller than 35 cm, the top of the head is black throughout the breeding period, the breast is gray, and the tail is deep and fork-shaped. In the non-reproductive period, the upper wings and back are gray, the tail is covered with feathers, the waist and the tail are white, and the forehead is white. When flying, the non-breeding adult and sub-adults are characterized by nearly black horizontal stripes on the front wings, and nearly black outer tail feathers. The upper body of the first winter bird is thick brown with scaly spots on the upper back. The iris is brown; the mouth is black in winter and the base of the mouth is red in summer; the feet are reddish and darker in winter. Mainly distributed in the Arctic and nearby areas, the breeding area is the Arctic and the eastern and central parts of Europe, Asia and North America. Moved from April to May in spring, and moved from September to October in autumn. It has strong mobility and lives through the winter in tropical and subtropical oceans.
