White-tailed Deer

Scientific Name	Odocoileus virginianus
Survival Strategy	Active all winter
Conservation Status	Least Concern

Phenology

Spring
Deer are rebuilding their fat supplies all spring, and antlers on bucks begin growing in April. Females may drop one to three fawns in May through June.

Summer
Does are nursing fawns throughout summer and are also feeding to build their fat reserves. To avoid the summer heat, deer are often active before sunrise and after sunset.

Bucks form bachelor groups in the summer and continue to feed. They are rubbing their fully grown antlers on small trees to shed the velvet covering by late August. (This will not end well for the young trees!)

Fall
The rut (breeding season) runs from late October through mid-November. The bachelor groups break up and bucks scrape the ground and small trees as a form of scent marking. The deer’s diet shifts to include acorns if they are available. Breeding takes place in late October through November.

Winter
White-tailed deer go into survival mode as winter sets in. Their fat reserves are dwindling, and they are losing more calories than they are consuming. To conserve energy, deer limit travel and stay near high caloric food sources such as cornfields. Most females endure the winter with the added challenge of pregnancy. Does with more fat reserves at the end of winter tend to have stronger newborn fawns. Triggered by reduced sunlight and testosterone, bucks’ antlers fall off around January and February.

Behavior

Deer Yards
For most of the year, white-tailed deer live in family groups consisting of a doe and her fawns. Bucks travel alone. When the snow is deep, deer will form herds, called “yards,” in conifer stands that can involve many individual animals. These deer yards serve to block wind, limit snow depth, and reduce heat loss. In extreme conditions, they are less active, sometimes dropping their metabolism by half.

Physiology

A Warm Coat
The deer’s winter coat consists of darker hollow guard hairs and dense woolly underfur. The darker winter coat absorbs more solar energy. Sebaceous glands in the skin produce oil that makes the fur water-repellent.

Fat as Fuel
Like other mammals, white-tailed deer store brown fat (BAT) around internal organs and under their skin, insulating and providing energy reserves. Brown fat reserves can be up to 30% of a deer’s body mass.

Diet

The white-tail deer’s winter diet includes small twigs, grasses, acorns, fruits, and corn stubble.
White-tail deer need to eat about 8 pounds of plant matter per 100 pounds of body weight daily.
Because deer are browsers and not grazers, deep snow does not put their food supply entirely out of reach.

Fermenting Food
White-tail deer are ruminants and have a four-chambered stomach, which, with the help of a symbiotic relationship with a microorganism, they can ferment food high in cellulose. This process makes the nutrients available to the deer.

Lifespan and Mortality

The average lifespan of a white-tailed deer is 4.5 years. The average buck lives 2.9 years, while the average doe lives 6.5 years.

Causes of Mortality
White-tailed deer are preyed on by bears, wolves, coyotes, bobcats, and humans. A four-year study ranking the causes of deer mortality found the following: human hunting 43%, starvation 9%, coyote 7%, wolf 6%, and roadkill 6%.

Winter Severity Index
Wildlife biologists calculate the Winter Severity Index (WSI) between December 1 and April 30 by adding the number of days with 18 inches or more snow depth to the number of days when the minimum temperatures are below 0°F. When the Winter Severity Index is higher than 100, winter mortality (starving to death) can be above 20%. (Visit Winter Severity Index page from the main menu)

Climate Vulnerability

Researchers found that climate change is fueling the northward expansion of the white-tailed deer range. Another study suggests that Midwest deer populations will increase in response to less severe winters, and moose populations will decline.

Never stop learning

Etymology: The scientific name for the white-tailed deer is Odocoileus virginianus. Odocoileus is a contraction of the Greek words “odōn,” which means tooth, and “koilos,” which means hollow. Virginianus indicates the species is indigenous to the state of Virginia.

References

White-Tailed Deer | EEK Wisconsin https://eekwi.org/critter/mammal/fawn.htm

How do deer survive harsh winter weather https://now.tufts.edu/articles/how-do-deer-survive-harsh-winter-weather

Enjoy Winter: White-tailed Deer https://natlands.org/enjoy-winter-white-tailed-deer/

Video: The Deer Study – A Closer Look at the White-tailed Deer https://youtu.be/LYeinlgY6es

The Process of Deer Antlers https://blog.snapshotwisconsin.org/2019/04/16/the-process-of-deer-antlers/

Dawe KL, Boutin S. Climate change is the primary driver of white-tailed deer (Odocoileus virginianus) range expansion at the northern extent of its range; land use is secondary. Ecol Evol. 2016 Aug 18;6(18):6435-6451. doi: 10.1002/ece3.2316. PMID: 27777720; PMCID: PMC5058518.

Weiskopf, S.R., Ledee, O.E. and Thompson, L.M. (2019), Climate change effects on deer and moose in the Midwest. Jour. Wild. Mgmt., 83: 769-781. https://doi.org/10.1002/jwmg.21649

A year in the life of a white-tailed deer – Off the Record Podcast Ep. 19, Wisconsin Department of Natural Resources. https://youtu.be/VJEmHnbAxnE