NESTING BIOLOGY OF BLACK SKIMMERS, LARGE-BILLED TERNS, AND YELLOW-BILLED TERNS IN AMAZONIAN BRAZIL

Nests of Black Skimmers (Rynchops niger) (n = 37), Large-billed Terns (Phaetusa simplex) (n = 121), and Yellow-billed Terns (Sterna superciliaris) (n = 16) on an exposed sandbar in the Trombetas River, Brazil, were monitored during incubation and hatching in 1982. The species were interspersed throughout the colony, though Black Skimmers nested closer to the river than the other two species. Black Skimmers had larger clutches (2.83 eggs/clutch) than Large-billed (2.30 eggs) and Yellow-billed (1.94 eggs) terns. Abandonment and flooding accounted for the majority of nest and egg losses during incubation for Large-billed Terns (22 of 27 nest failures) and Yellow-billed Terns (two failures, one due to flooding). Black Skimmers lost no eggs or nests to flooding, but abandoned three nests (seven eggs) and three clutches disappeared (11 eggs). Black Skimmer clutches hatched on averaged of 5 d earlier than Large-billed Tern clutches, and 2 d earlier than Yellow-billed Tern clutches. Estimated number of young leaving the nest for Black Skimmers was 1.66 young/nest, 1.08 for Large-billed Terns, and 1.04 for Yellow-billed Terns.

PAM G. KRANNITZ, Journal of Field Ornithology: Vol. 60, No. 2, Spring, 1989