Annual, seasonal, and habitat-related variation in feeding habits of the arctic fox (Alopex lagopus) on St. Lawrence Island, Bering Sea

Small rodents, especially northern voles (Microtus oeconomus), were the most frequently occurring prey in the stomach contents and scats of arctic foxes collected on St. Lawrence Island between 1955 and 1970. Annual variations in the winter occurrence of voles in the stomach contents correlated well with variations in population density of the voles in the previous summer. However, when the foxes' summer dens were in or near large marine bird colonies, birds predominated in the diet. Even in winter, birds tended to occur more frequently in the diet of foxes trapped on bird cliffs than on the tundra. Since the birds are absent from the cliffs in winter, these evidently were from cached supplies. In terms of biomass, birds were of equal or greater importance than voles in the overall diet, and marine mammal carrion became most important in winter and early spring, when live prey were scarce. Although populations of live prey were abundant and readily accessible in summer, they were absent or inaccessible in winter; hence, even in this area of abundance, storage of food was essential for survival of foxes through the cold months.