Winter Feeding Program of Alaska Willow Ptarmigan Shown by Crop Contents

Irving, Laurence; West, George; Peyton, Leonard

Crops of 1192 Willow Ptarmigan (Lagopus lagopus) from the Brooks Range of Alaska progressively increased in weight from October to December and January and diminished in weight monthly until April. In October and November migration of this population is southward; from January to May migration is northward. In January the weight of crops increased during the few hours of light and attained weights of around 100 g (15 per cent of the weight of ptarmigan without crop) three hours after noon. November and February accumulations in crops were less and later in the day, and in October and March the accumulation diminished further and occurred later. In April and May there were no clear times of maximal accumulation. These records are related to the duration of light (sunlight plus nautical twilight) and indicate that feeding extends for less than eight hours on clear midwinter days to provide for a resting time of 16 hours. In autumn the increasing accumulations in crops are related to shortening days. After midwinter in lengthening days, the diminishing accumulations in crops represent the results of prolonged feeding and activity that in May brings about migratory activity during much of the 24 hours that are then continually light. The concentration of feeding is related to shortening of daylight, and prolongation of feeding is related to lengthening day. Cold and snow cover continue after midwinter into May, so that accumulation in crops is not in phase with the prolongation of arctic winter into spring, or with the cycle of migratory activity.

Winter Feeding Program of Alaska Willow Ptarmigan Shown by Crop Contents

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