The United States population of American Oystercatchers (Haematopus palliatus) is of special concern. Biologists attribute low numbers and reduced reproductive success to excessive predation and human disturbance; however, researchers have not documented nest predators positively and the mechanism by which human presence reduces reproductive success is not well understood. During the 2003 and 2004 breeding seasons, I video-monitored American Oystercatcher nests (n = 32) to document causes of nest failure and observed oystercatcher behavioral responses to human activity at Cumberland Island National Seashore. Hatching and fledging success were 45% and 33%, respectively. Predation was the primary cause of nest failure (44% of nests). Pedestrian activity reduced reproductive behavior during incubation. Vehicular activity reduced foraging behavior during brood rearing. Presence of boats did not affect behavior. Oystercatchers were fairly intolerant of pedestrian activity 137 m of nests during incubation. During brood rearing, oystercatchers reacted to pedestrian activity 137 m of chicks.