During the breeding season, these birds eat insects and freshwater fish such as damselflies and dragonflies, grubs and larvae and other small mollusks. The rest of the year, meals are usually of small marine fish. Some examples are anchovies, silversides and plankton. The average fish taken during breeding season is 2.5 to 3.0 cm and 3 grams. The black terns's courtship ritual is elaborate with much flying.
Males often fly with fish in their mouth to attract females.
They nest in small colonies in upland marshes and sloughs. Their nests can be found on muskrat bouse or floating masses of dead plants, usually over water 4 to 34 inches deep. The typical nest has 3 eggs that are laid from May to early August. Incubation lasts 22 days. The successful hatching rates of nests is very low because of predation and other disturbances.