The nesting biology of the Black Tern (Chlidonias niger) was studied in 1984-1986. Black Terns nested in four of five historical breeding areas. Population sizes had decreased in three of those areas. Detailed nesting observations were carried out in Dingman Marsh in 1985 and 1986. The first laid egg weighed the least in a clutch, while the third egg was the longest. Nests averaged 5.2 cm in height and 11.6 cm in width, and were found primarily on mud mounds in shallow water. Nests contained three eggs, but on the average, less than two of those three eggs survived to hatch, and less than one chick survived to fledge. The first egg had the highest survival probability, while the third chick had the lowest. The average growth curve of chicks showed a slight recession in weight. The majority of nests contained eggs that hatched asynchronously.