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 di sturbance by human observers. The effects of human disturbance during resea rch activities were assessed in a colony of South American Tems (Sterna hir undinacea) by comparing hatching success between visited and unvisited nest s during incubation. Predation be a mustelid, probably the Little Grison (G alictis cuja), was the main cause of nest failure during incubation. Hatchi ng success and daily nest survival rates during incubation did not differ b etween visited and unvisited nests.