Transition periods in spring (May, June) and fall (Sept., Oct.) separate a winter period when white-tailed ptarmigan (Lagopus leucurus, avian family Tetraonidae) browse on buds and twigs of a few genera of shrubs, from a summer period when they eat a variety of leaves, flowers, and fruits as well as some invertebrates. The sample of 167 crops studied showed berries of Empetrum and Vaccinium to be more important to ptarmigan in fall in British Columbia and Alaska than in Colorado. Alaskan and British Columbian white-tailed ptarmigan also consumed much more Alnus (catkins and buds) in winter than Colorado specimens. This may be due to the greater abundance of Alnus in alpine areas in the north, but also could be influenced by competition from Lagopus lagopus and L. mutus that winter in the same places as L. leucurus in northern British Columbia and Alaska.