The black tern (Chlidonias niger) is a small tern with an all-black head and body, contrasting with grey wings, back and tail in spring. Generally found in or near inland water in Europe, Western Asia and North America, the genus name is from Ancient Greek khelidonios, "swallow-like". The sexes appear similar. Vulnerable to loss of marsh habitat, its numbers have decreased in many areas during recent decades. The Black Tern breeds in freshwater marshes across most of Canada, the northern United States and much of Europe and western Asia, in loose colonies and usually forages, roosts, and migrates in flocks of a few to more than 100 birds, occasionally up to tens of thousands.