By Misi Stine Environmental Educator and member of the MN Herpetological Society
When Europeans settled what is now Minnesota, the white-tailed deer range was limited to the southern and central parts of the state. When the new settlers cleared forests for wood products and agriculture, it forever changed the landscape. By the 1880s, degraded habitats from agricultural conversion, hunting for both subsistence and to supply markets with meat, reduced the deer population significantly. Subsequent changes in management practices have resulted in an amazing rebound in the number of deer, primarily due to the landscape alterations, which opened new habitats and allowed white-tailed deer to move into areas they had not previously occupied. Today the white-tailed deer population in Minnesota is much larger than it was at the time of European settlement, and they are found throughout the state. (Minnesota Department of Natural Resources, n.d.)
White tailed deer are adapted to Minnesota winters with fur coats made up of hollow guard hairs and a thick undercoat to provide insulation and maintain body heat. They produce oil that allows their coat to repel water. Building their fat stores and adapting their behaviors to slow their metabolism is part of winter survival. Deer also use their environment to protect them from winter conditions by spending time in stands of conifers that provide shelter from the elements. In milder winters, they can often find enough food to browse on to get by. However, winter can be difficult for deer when it is considered severe, with the cold temperatures and deep snow that persist over a prolonged period. (Whittier, 2018) (Minnesota Department of Natural Resources, n.d.)
A Deer_Winter_Virginia State Parks staff, CC BY 2.0
Winter severity is calculated with a point system: considering the number of days where the air temperature is below zero and the number of days with snow depths of 15 inches or deeper. Severe winter conditions that impact the survival of white tailed deer, include: the number of days where the snow depth remains at or above 15 inches, how long severe winters last, successive years of severe winters, how early the landscape starts to green up as part of the transition to spring, the amount and quality of the food available, how dense the deer population is in a given area, the age, and sex of the herd. (Minnesota Department of Natural Resources, n.d.)
In addition, are the white-tailed deer in wolf range, if so, how many wolves are living in the same area? Wolves do better in severe winters because they adapt better to those deep snow conditions with their large wide paws that act like snowshoes, whereas deer have “boot” like feet that sink in the deep snow. Wolves take advantage of the deer who are not fairing as well nutritionally.
One of the most fascinating aspects of white-tailed deer and the outcomes of severe winter survival is research conducted by Dr. David Mech and others in 1991, which uncovered evidence of what is called the “grandmother effect.” This effect is found where grandmothers who were pregnant when they survived a difficult winter gave birth to fawns whose later offspring were shown to be in poorer condition even when the mother was not pregnant during a severe winter themselves. This research was confirmed by later studies. (L. David Mech, 2015)
Wildlife103_USDA NRCS, Public domain, via Wikimedia Commons
One final note, while it can be difficult to hear the challenges of the whited tailed deer, with the spread of Chronic Wasting Disease (CWD) and other diseases, most wildlife experts recommend not feeding white-tailed deer. CWD is a disease caused by the formation of abnormal proteins called prions which are transmitted from animal to animal through direct contact or contact with infected materials like feces, urine, and saliva. The disease is always fatal, and these prions are persistent in the environment. In many places, it has been made illegal to feed white-tailed deer in an attempt to slow the spread of CWD. Many believe that CWD has the potential to significantly limit the white-tailed deer, and other ungulate populations in the future.
References
L. David Mech, et al. (2015). Wolves on the Hunt. Chicago: University of Chicago Press.
Minnesota Department of Natural Resources. (n.d.). How winter impacts deer survival. Retrieved from Minnesota Department of Natural Resources: https://www.dnr.state.mn.us/mammals/deer/management/wsi.html#:~:text=Their%20winter%20coats%20of%20hollow,temperatures%20can%20increase%20deer%20mortality
Minnesota Department of Natural Resources. (n.d.). Natural History of Deer in Minnesota. Retrieved from Minnesota Deparment of Natural Resources: https://www.dnr.state.mn.us/mammals/deer/management/history.html#:~:text=Odocoileus%20virginianus,deer%20were%20absent%20or%20rare
Saunders, D. A. (1988). Adirondack Mammals. In D. A. Saunders, Adirondack Mammals (p. 216). New York: New York State Series.
Todd M Kautz, e. a. (2020). Influences of body mass and environmental conditions on winter mortality risk of a northern ungulate. Evidence of a late-winter survival bottleneck. Ecology and Evolution, 1666-1677.
Whittier, C. (2018, January 30). How do deer survive harsh winter weather. Retrieved from Tufts Now: https://now.tufts.edu/articles/how-do-deer-survive-harsh-winter-weather