Seabird distribution in the gulf of Papagayo, Costa Rica, during non-upwelling conditions

Abstract

The Gulf of Papagayo off the northwestern coast of Costa Rica is one of a series of upwelling localities along the coast of Central America. We surveyed its marine avifauna during the non-upwelling season in 1988, using transects at sea and inspection of islands for nesting birds. The most common species at sea was Black Tern Chlidonias nigra, although these were only seen on one transect. We found a density of 3.76 (SD 6.8) birds/km2 or 2.1 birds/km2, if the Black Terns are removed. Despite differences in transect methods and timing, these values are generally comparable to estimates from the Bay of Panama upwelling but much lower than from upwellings off Peru and California. Sea surface temperature did not appear to affect bird numbers. Breeding numbers on the islands were small, either because of human disturbance or because it was the non-upwelling period. These small upwellings may be important to North American seabirds as migratory stopovers or wintering grounds.