Adults are 25 cm (9.8 in) long, with a wingspan 61 cm (24 in), and weigh 62 g (2.2 oz). They have short dark legs and a short, weak-looking black bill, measuring 27 mm (1.1 in), nearly as long as the head. The bill is long, slender, and looks slightly decurved. They have a dark grey back, with a white forewing, black head, neck (occasionally suffused with grey in the adult) and belly, black or blackish-brown cap (which unites in color with the ear coverts, forming an almost complete hood), and a light brownish-grey, 'square' tail. The face is white. There is a big dark triangular patch in front of the eye, and a broadish white collar in juveniles. There are greyish-brown smudges on the ides of the white breast, a downwards extension of the plumage of the upperparts. These marks vary in size and are not conspicuous. In non-breeding plumage, most of the black, apart from the cap, is replaced by grey. The plumage of the upperparts is drab, with pale feather-edgings. The rump is brownish-grey.
Habitat and Distribution
Their breeding habitat is freshwater marshes across most of Canada, the northern United States and much of Europe and western Asia. North American Black terns migrate to the coasts of northern South America, some to the open ocean. Old World birds winter in Africa.
Unlike the `white` Sterna terns, these birds do not dive for fish, but forage on the wing picking up items at or near the water's surface or catching insects in flight. They mainly eat insects and fish as well as amphibians.
They usually nest either on floating material in a marsh or on the ground very close to water, laying 2-4 eggs.