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Brant (Branta bernicla), Canada geese (Branta canadensis taverneri), and emperor geese (Chen canagica) interrupted foraging and flew in response to helicopters. Disturbance caused by aircraft may be harmful to brant. In 1,912 hours of daylight observations, potential incidental disturbance events occurred at 1.07/hr. Aircraft (0.57/hr) and persons on foot (0.08/hr) were the most frequent human-related disturbances. Of all disturbances, bald eagles and boats elicited the greatest responses with brant. Canada and emperor geese responded most to bald eagles (Haliaeetus leucocephalus Linn.) and persons on foot. Using data grouped by altitude and lateral distance to the flock, brant and emperor geese reacted similarly to different types of aircraft and were more responsive than Canada geese. Noise rather than visual cues could trigger behavioral responses. For each additional aircraft disturbance that occurred daily throughout a 54-day fall staging period, the predicted total weight gain would be reduced by 7.4 g, equivalent to energy expended in 53 minutes or 73 km of migratory flight. Ten daily disturbances reduced body weight by 4% from the expected departure weight at Izembek.