Energetics and adaptations to cold in ptarmigan in winter

Ptarmigan Lagopus spp. inhabit arctic, subarctic and temperate alpine regions where winter is typically cold and snowy. Low ambient temperatures, however, have little effect on their energy budget. Ptarmigan have a highly insulative white winter plumage which contributes to a very low heat loss. They normally evade exposure to severe cold by roosting in the snow, where ambient temperature usually exceeds their lower critical temperature. Ptarmigan have a diurnal activity pattern and each day collect and store enough food in their crop-sack to last the long winter night. Their digestive system shows seasonal changes in length which apparently adapt the birds to a low quality winter diet. With the exception of high-arctic species, ptarmigan do not store substantial amounts of fat in the winter. The Svalbard Ptarmigan living at 77-80'N prepare for winter by depositing large stores of fat (up to 35% of body mass; BM) in autumn. Concurrently there is a marked.reduction in their daily energy expenditure which permits such fattening to occur despite the fact that food intake is simultaneously reduced.