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Up to 400,000 snow geese (Chen caerulescens) congregate on the North Slope where they accumulate energy for fall migration. This study documented undisturbed behavior and evaluated effects of overflights. Snow geese were observed at five camps along the North Slope during 663 hours for over 175 flocks; behaviors occurred during 73 natural disturbances and 163 non-experimental overflights. Experimental overflights at 2.5-hour intervals with a Cessna 185 Bell 206-B helicopter were made. Undisturbed snow geese spent 57% of daylight hours feeding (juveniles alone 65-70%). Snow geese were equally prone to flush from fixed-wing aircraft and helicopters, flushed at greater distances from helicopters, but flew longer in response to fixed-wing aircraft. Snow geese accommodated to a varying extent to increased frequencies of overflights. Non-experimental aircraft disturbances averaging 0.25 per daylight hour resulted in a potential decrease of 2.6% in time spent feeding. Experimental overflights at 2-hour intervals by fixed-wing aircraft caused an 8.5% decrease in feeding time, and could cause a reduction of 20.4% in energy reserves for juveniles; the corresponding figure for a helicopter is 9.5%.