Black-tailed Gulls live on all the coasts and on the islands of Korea. They breed in Japan, south of Maritime Province, Kurils, and on the coast of China. The female sea gull looks like the male one, with length of about 43cm. It builds a nest out of dry grass and feeds on fish, amphibians, mollusks, and insects. The sea gulls flock over schools of fish, which helps fishermen find the schools of fish. A Black-tailed Gull of Nando Island lives on uninhabited islands, and the island is also called Alseom or Gull Island. The edge of the island is composed of vertical rock walls. On top of the island are plants such as Sedum oryzifolium Makino, Artemisia dubia Wall, and Artemisia capillaris Thunb. Approximately 15,000 Black-tailed Gulls breed in May or June and they lay about 2 or 3 eggs and prefer the rock wall rather than the top of the island. Except when they are laid on a steep slope, the eggs are stolen, which becomes a serious problem. Since the breeding ground of Black-tailed Gulls on Nando Island is biologically valuable, it is designated and protected as a Natural Monument.