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Disturbance is the most important factor controlling the availability of food. Heavy shooting pressure keeps geese away from favorable habitat. Riders are less disturbing, and sometimes can approach geese within 46 m. Helicopters are extremely disturbing, and low-flying, small planes can cause geese to fly to roost or refuge areas. Barnacle geese (Branta leucopsis) at Caerlaverock were sometimes raised by small aircraft at a distance of 1.6-3.2 km. Even brant (Branta bernicla) can become indifferent to larger planes. Noise is less important than visual cues, but sudden sounds usually affect geese. Greater white-fronted geese (Anser albifrons) spend about 3% of their undisturbed time alert, but any forced increase of vigilance takes time away from feeding. Avoidance values" were calculated for 47 fields at Slimbridge by giving arbitrary points for distance from roost (0-2), size of field (0-20), extent of hedges or banks (0-5), shepherding frequency (0-15), distance from roads or canals (0-10), distance of bordering roads or canals from field center (0-30). The sum of the avoidance values for each field plotted against mean goose use for four seasons resulted in a correlation coefficient of -0.809 (P = 0.1). Greater white-fronted geese can spend more than 2% of their daytime drinking. If water is not freely available, birds have to fly to drink and bathe. Pink-footed geese (Anser brachyrhynchus) at Loch Leven travelled several miles to the roost at midday to drink. Geese relying on food of low nutritive value cannot afford such an expenditure of time and energy.