The black tern is agile in the air and has a rather light, erratic-looking flight. While foraging, it typically circles low over land or water with relatively slow, shallow wing beats, and often feeds in flocks, particularly where food is concentrated (3). The black tern feeds predominantly on insects during the breeding season, although it also takes small fish, snails, amphibians, worms and crustaceans. Outside of the breeding season, the diet consists mainly of small marine fish (2) (3) (4) (5). Hunting takes place in flight, the tern either dipping to the water’s surface or the ground to pick up food items, or pursuing insects in the air. This species only rarely dives into water to catch prey (2) (3) (4). Black tern flocks often concentrate in areas where predatory fish or dolphins have driven prey to the water’s surface (2) (3) (5).
The black tern breeds in small colonies, often close to other species, between May and June (2) (3) (5). This species usually nests over shallow water, building a low mound of plant material on top of the water or on a floating mat of vegetation. A shallow scrape on the ground, an old muskrat (Ondatra zibethicus) house, or the old nest of another waterbird may also be used (2) (3) (4) (5). The nest is often flimsy and easily destroyed by wind or by changing water levels (3). Two to three eggs are laid (2), or sometimes up to six, and the eggshells are specially adapted to survive the damp conditions in the nest (3). Both the male and female incubate the eggs, which hatch after around 19 to 23 days (2) (3). The young terns develop rapidly and may leave the nest after just two to three days, although they remain in vegetation nearby (4). The young are able to fly after around 20 to 25 days (2) (3) (4), after which the family moves to an open area of water and defends a feeding territory. The adults continue to feed the young for two weeks or more (3) (4). The black tern leaves for its wintering grounds from July onwards (5), and young birds do not usually return to breed until at least the second year of life (3). The black tern may live for up to 17 years in the wild (2) (3).