Effects of Research Activity on Hatching Success in a Colony of South American Terns

-Determination of breeding success of birds requires a variable amount of disturbance by human observers. The effects of human disturbance during research activities were assessed in a colony of South American Terns (Sterna hirundinacea) by comparing hatching success between visited and unvisited nests during incubation. Predation by a mustelid, probably the Little Grison (Galictis cuja), was the main cause of nest failure during incubation. Hatching success and daily nest survival rates during incubation did not differ between visited and unvisited nests. Received 29July 1998, accepted 6January 1999. Resumen.-La determinaci6n del 6xito reproductor supone ciertas molestias a las aves por los investigadores. Estas molestias fueron valoradas en una colonia de Charrin Suramericano (Sterna hirundinacea), comparando el 6xito de eclosi6n en nidos visitados y no visitados durante la incubaci6n. La depredaci6n por un mustilido, probablemente Galictis cuja, fue la principal causa de fracaso reproductor durante la incubaci6n. El 6xito de eclosi6n y la supervivencia diaria de los nidos durante la incubaci6n no difiri6 entre nidos visitados y no visitados.