In the winters of 1983-1984 and 1984-1985, oil wells were drilled adjacent to a waterbird colony on Pelican Island in Galveston Bay, Texas, USA. Drilling was finished on Feb. 29, 1984, but technical problems prevented cessation in 1985 until June 7, well into the nesting season. The number of breeding wading birds, laughing gulls (Larus atricilla ), and Forster's terns (Sterna forsteri ) decreased in both 1984 and 1985 following the drilling activity. In 1986, after drilling activities had been terminated, most nesting waterbirds increased on Pelican Island. Wading birds were more severely affected by the disturbance than were gulls and terns. Although Laughing Gull numbers decreased, the contribution of the drilling disturbance to this decrease is unknown, Forster's terns relocated their nest sites within the colony site in response to oilwell construction. It is likely that disturbance during the early spring, when birds were selecting nest sites and establishing territories, was responsible for the observed changes in breeding bird use