To determine if the quality of winter diet is related to winter-habitat sexual segregation, Lagopus lagopus L. (Willow Ptarmigan) were collected in three wintering areas of Labrador between December and April 1998–2000 (n = 310). Crop contents were used to evaluate diet differences according to sex, age, and area. The most prominent item in ptarmigan crops was Salix spp. (willow; range 45–89%). The crops of adult females contained approximately 60% more willow, the most nutritious food in their diet, and 45% more calories than those of adult males. All birds collected from western Labrador contained more willow twigs and buds and more calories than those collected in central or eastern Labrador. The Gardarsson hypothesis suggests that males winter adjacent to breeding areas to improve competition for territories, and females choose areas with greater abundance and quality of food to enhance reproductive success. We could not reject this hypothesis since the wintering site with the most female-biased sex ratio was where diets had the greatest mass of willow and total calories.