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Adult willow ptarmigan (Lagopus lagopus) were captured from the Brooks Range of northern Alaska and maintained in captivity out of doors under natural conditions of temperature and photoperiod similar to those prevailing in the southern part of the Brooks Range. Metabolized energy, molt, egg laying, body weight, and gross activity were recorded throughout the year. Maintenance energy did not differ between males and females except during egg laying. The amount of energy required in winter for thermoregulation was only slightly greater than that required by molting birds in summer. Egg—laying females had a higher energy requirement than non—laying but molting females and males. The gross activity of the captive ptarmigan began at the onset of civil twilight each day throughout the year. Therefore, in summer, activity continued for 24 hr. There were generally 2 activity peaks; the major peak occurred in the morning in spring and early summer but in the late afternoon in fall and winter. The total daily activity remained constant throughout the year except during May when males were undergoing courtship and territorial activities. Molt proceeded in the captives in the same sequence as in the wild population, but was slightly prolonged. All of the energy—demanding activities, such as seasonal change in weight, molt, egg laying, themoregulation, and gross activity, occur sequentially with only slight overlaps. Thus the total energy requirement is practically uniform throughout the year in captives. Determination of metabolic rates from crop fill and caloric values of natural diets as predicted from field collections closely approximate the laboratory determined rates.

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