Foods of Rock and Willow Ptarmigan in Central Alaska with Comments on Interspecific Competition

Weeden, Robert

A collection of 743 Rock Ptarmigan crops from all seasons of the year and 663 Willow Ptarmigan crops from August through April was analyzed for oven-dry weight of food items. Throughout Alaska, Rock Ptarmigan eat mainly buds and catkins of dwarf birch in winter (11 October to 9 May). In spring (10 May to 5 June) the transition to the varied early summer (6 June to 31 July) diet of leaves and flowers is fairly quick. The late summer (1-31 August) diet is characterized by decreased consumption of leaves and flowers and increased consumption of berries and seeds. Animal matter is taken opportunistically, but rarely in large amounts. The fall period is essentially a long transition from the seeds and fruits of August to the monotonous diet of buds and catkins of winter. The pattern among Willow Ptarmigan seems similar to that of Rock Ptarmigan from August to early spring in central Alaska. In coastal areas where there is little snow, Willow Ptarmigan eat a wider variety of foods in winter, but still feed heavily on buds and twigs of deciduous shrubs. Throughout Alaska the main winter food of Willow Ptarmigan is Salix spp. buds and twigs. Given the demonstrated heavy dependence of the Rock and Willow Ptarmigan on a very few types of winter food, quantitative or qualitative shortages in winter foods could have serious direct and indirect population effects. The short period of dietary transition in spring could be critical also, as heavy energy demands for molting and breeding occur at that time. Interspecific competition may have a bearing on winter foods selected by Rock, Willow, and White-tailed Ptarmigans in areas of sympatry. Bill shape seems to be an adaptive feature correlated with the winter food specializations observed, and behavioral specializations such as perching or scratching for food may be important too.

Foods of Rock and Willow Ptarmigan in Central Alaska with Comments on Interspecific Competition

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