the black tern , chlidonias niger , is a small tern generally found in or near inland water in europe and north america .
as its name suggests , it has predominantly dark plumage .
adult  are 25 cm (9.75 in) long , with a wing span 6/1 cm (24 in), and weigh 62 g (2.2 oz) .
they have short dark legs and a short , weak-looking black bill , measuring 2728 mm , nearly as long as the head .
the bill is long , slender , and looks slightly decurved .
they have a dark grey back , with a white forehead , black head , neck (occasionally suffused with gray 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 grayish-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-gray .
the north american race , c .
n .
surinamensis , is distinguishable from the european form in all plumages , and is considered by some to be a separate species .
in flight , the build appears slim .
the wing-beats are full and dynamic , and flight is often erratic as it dives to the surface for food; similar to other tern species .
its call has been described as a high-pitched "kik"; the sound of a large flock has been called "deafening" .
hybridisation between this species and white-winged black tern has been recorded from sweden and the netherlands .
two juvenile birds at chew valley lake , england , in september 1978 and september 1981, were also believed to be hybrids; they showed mixed characters of the two species , specifically a combination of a dark mantle (a feature of white-winged black) with dark patches on the breast-side (a feature of black tern , not shown by white-winted black) .
their breeding habitat is freshwater marshes across most of canada , the northern united states and much of europe and western asia .
they usually nest either on floating material in a marsh or on the ground very close to water , laying 24 eggs .
in england the black tern was abundant in the eastern fens , especially in lincolnshire and cambridgeshire , until the early nineteenth century .
the english naturalist thomas pennant in 1769 referred to "vast flocks" of black terns "whose calls are almost deafening" .
extensive drainage of its breeding grounds wiped out the english population by about 1840. intermittent attempts by the species to recolonise england have proved unsuccessful , with only a handful of english breeding records , and one in ireland , in the second half of the twentieth century .
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 .
