TEMPORAL PATTERNS IN REPRODUCTIVE SUCCESS IN THE ENDANGERED ROSEATE TERN (STERNA-DOUGALLII) NESTING ON LONG-ISLAND, NEW-YORK, AND BIRD-ISLAND, MASSACHUSETTS

Roseate Terns (Sterna dougallii) nest in few colonies in the northeast ern United Slates, and the population is listed as endangered. We comp are reproductive success from 1987 through 1990 at Cedar Beach, Long I sland, and in 1980 and 1987 through 1990 at Bird Island, Massachusetts , to examine yearly and seasonal differences. Productivity was highest for terns breeding in the first six days of the egg-laying period and decreased thereafter. Clutch size, hatching success, and productivity declined significantly during the season, with some variations in pat tern among years and between colony sites. Pairs initiating nests afte r 22 June fledged almost no young. Patterns of reproductive success we re more irregular at the smaller colony (Cedar Beach) than the larger colony. Reproductive success was related to age of adults; young birds (two to three years old) had lower clutch sizes, had lower reproducti ve success, and laid later than older birds. The effective reproductiv e population of the colony included primarily birds that bred in the e arly and peak periods; thus, monitoring reproductive success only from early or peak nests overestimates overall reproductive success. Selec tion against even earlier breeding in this species may be due to lower food resources early in the season and higher predation rates on earl y nests.