Colonially nesting seabirds have recently undergone habitat shifts in much of the Atlantic coast of the United States because of increasing human disturbance and development of barrier island beaches traditionally used as breeding areas (Buckley and Buckley 1975, 1977; Burger 1977, Burger and Lesser 1977, Erwin 1980). Alternative sites now being used include natural marsh islands, dredge deposition sites, and even man-made structures (Erwin 1979). Although the distribution of breeding adults in different habitats has been described, few studies have been made concerning the relative quality of these new habitats for nesting (Burger and Lesser 1979). Before management decisions can be made, it will be necessary to evaluate the productivity of these sites. In 1980, the Migratory Bird and HabitatResearch Laboratory of the U.S. Fish and Wildlife Service began a long term study to evaluate the reproductive success of the Common Tern (Sterna hirundo) and Black Skimmer (Rynchops niger) in differing habitats along the mid-Atlantic coast of the United States. Objectives of the project are (1) to record reproductive attributes such as egg and clutch size, colony phenology, hatching and fledging success, and the factors affecting success, such as weather and predation, and (2) to correlate success with organochlorine residue levels in eggs and eggshell thickness in cooperation with the Environmental Contaminants Evaluation group of the Patuxent Wildlife Research Center. This last objective will form the basis for a later report and will not be discussed here. This paper will consider only the nesting chronology of Common