When breeding, their plumage, bill, head, and back are black. The wings and tail are various shades of grey. They seldom dive, preferring to pluck their food from the surface. Black terns build their nests upon floating piles of dead vegetation, such as cattails or bur-reeds, floating mats of muck, or similar materials. The nest consists of a small gathering of aquatic vegetation in a cup-like bowl.
Eggs are often only a few centimetres above the water level.
Because of the nest location, wind, heavy rains, waves, or flooding can damage the nest or harm the eggs. Nesting materials often change from one year to the next, which explains why black terns move to different marshes in different years. In 1993, black terns nested on the East Amherst Marsh, but they are nesting on the Amherst Point Marsh this year. This border colony of black terns has changed nesting locations many times since they first nested at Tintamarre in 1967. Black terns have two interesting courtship flights.