Significance of Brooding to the Energy Demands of Alaskan Rock Ptarmigan Chicks

Rock ptarmigan (Lagopus mutus) chicks are brooded periodically during the first few days of life; longer in cold and rainy weather. Computed minimum foraging time in adverse weather conditions is 96 minutes/24 hours. Crop analysis and calo- rimetry of the 6 major food items show that a full crop may contain up to 0.47 kcals. Energy requirements were calculated for both an 18-gram chick and a 30-gram chick. The 18-gram chick required between 34 and 50 crop loads per 24 hours. With 96 minutes foraging time, and the observed pecking rates, this was considered possible. The 30- gram chick required twice as much foraging time but since it was approaching homeo- thermy,. it was tentatively concluded that neither was that chick being handicapped by brooding. Vagaries in early survival of rock ptarmigan chicks, therefore, afe not due to differences in post-hatch weather.