Seasonal Starvation in Northern White-Tailed Deer

Abstract

White-tailed deer (Odocoileus virginianus) living in northern regions of the U.S. and southern Canada are subject to large seasonal variations in food supply. White-tails are browsing ruminants that consume leaves of forbs, shrubs, and low-hanging trees when available. When autumn frosts deprive them of that food supply, deer are commonly relegated to less nutritious twigs and evergreen fronds. Deep snows can restrict travel and foraging opportunities and increase energy demand, thus compounding winter’s nutritional challenges. Our studies of digestible energy (DE) and metabolizable energy (ME) requirements of white-tailed deer and the DE and ME supplied by typical winter browse show that maintenance energy requirements are rarely met, leading to increased winter mortality. Behaviors to minimize energy requirements include lying down on a sunny, wind-sheltered hillside, or seeking shelter on cloudy days or at night in protected locations such as cedar swamps. Here, deer curl up under overhanging branches to restrict radiant heat loss. Avoidance of death requires that sufficient accessible energy be stored in body fat depots during the previous summer and fall to sustain life until spring green-up. We have measured seasonal changes in food intake and lipogenic activity in subcutaneous and perirenal adipose tissue. These measures are markedly affected by photoperiod, presumably via the pineal gland and its response to day-length, and perhaps by other mechanisms. We also have reviewed and examined the effects of season, sex, and age on food intake and the corresponding morphological and physiological changes in white-tailed deer, along with other environmental factors that influence their welfare and that of other wild ruminants.