25 Mar Deer Adaptations to Survive Winter
In the fall, deer grow a specially designed winter coat and begin to store fat. The winter coat has hollow guard hairs for insulation with a fine hair underfur for warmth – this helps them retain body heat, thus reducing energy demands to stay warm. The fat reserve provides nutrition over winter. In addition, deer decrease their metabolic rate during the winter, which reduces food requirements to approximately one half of what they need in the summer. Research at the Cusino Wildlife Research Station in the Upper Peninsula (UP) showed that fawn growth rates even slowed to allow the deer to put on fat reserves for the winter. All these factors contribute to substantially decreased winter energy demands for a deer. Those demands can be met with limited natural browse, supplemented with the fat reserves.
In locations where a severe winter is an annual event, deer migrate to wintering habitat complexes, which are areas with thick overhead cover and natural winter browse available. These complexes provide thermal cover and sufficient natural food for deer to survive winter. They have been called “green barns” and the description is appropriate because they substantially reduce wind chill and the snow is often shallower under conifers. Deer substantially reduce their activity in these wintering complexes; reduced movement requires less energy.
All these adaptations: winter coat, fat storage, reduced metabolism, thermal cover, and sedentary behavior, help deer survive severe winters. Even with all the food they want, deer use their fat reserves and lose weight over winter. Deer in relatively good condition can fast for several weeks without harmful effects.