Nutrition of Willow Ptarmigan in Northern Alaska

West, George; Meng, Martha

Analyses were made of the crop contents of 540 Willow Ptarmigan collected throughout the year at four localities in the Brooks Range of northern Alaska. In winter, the birds depend on the buds and twigs of willow (Salix spp.) for their nutrition; up to 94 per cent of the total diet is willow and 80 per cent of that may be of a single species (S. alaxensis). After fall migration southward, the population spreads out over 200 miles from the Colville River at the north to the Koyukuk River to the south of the Brooks Range. Variations in amount of snow cover and height of plants restrict the use of certain willow species and dwarf birch reach greater heights and remain available throughout the winter. Alder (Alnus crispa) is abundant but is seldom used, perhaps because of its chemical composition which may make it unpalatable. As snow melts, the birds depend more on willow leaves, herbaceous plants, and berries. Caloric values of foods eaten by ptarmigan indicate that birch has a higher caloric content than willow at any season. The caloric content of willow remains relatively constant during winter but rises in spring when catkin buds swell prior to development. In early summer, opened catkins have a low value. Leaves were approximately equivalent in value to winter buds. The caloric content of the average diet remains nearly constant throughout the winter, but drops in summer, because of the use of hervaceous plants and berries whose caloric equivalents are less than that of winter willow buds. Birds wintering in the south of the range consume a diet which is higher in caloric content than that of birds farther north because of the former's use of larger amounts of birch. From this study and others it is apparent that Willow Ptarmigan are well adjusted to deriving their nutritional and energy requirements from a number of different diets. The chief dietary component is willow when it is readily available in the locality in which the birds occur, but it is not a necessity for existence of the species.

Nutrition of Willow Ptarmigan in Northern Alaska

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