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Large boats and yachts rarely disturbed brant (Branta bernicla), but small boats with noisy outboards caused them to fly. In 168 hours of observation, human disturbance caused some birds to fly an average of once every 81 min. Forty-eight percent of disturbances were by people, most of whom were on shore; 39% by aircraft, chiefly small planes; 9% by loud noises; and 4% by small boats. Disturbances by aircraft caused about twice as many brant to fly as disturbances by people (d = 5.3; P < 0.001). Aircraft caused about 1.6 times as much disturbance as people. Without disturbance, brant spent an average of 1.1% of their time in flight. Total time spent flying was correlated with the amount of flying caused by disturbance (r = 0.93; n = 11; P < 0.001). Weekend disturbance stopped brant from feeding for as much as 11.7% of their time, and increased time spent flying as much as sevenfold. Overall, disturbance would probably have been unimportant if adequate food was available. However, food shortages probably prevented full compensation for disturbance.