Mule Deer

Genus: Odocoileus
Species: hemionus

Mule Deer

Mule deer are among the most beloved and iconic wildlife of the American West. Found west of the Missouri River especially in the Rocky Mountain region of North America, mule deer get their name from their big, mule-like ears.

For decades, western Colorado has been home to some of the country’s largest mule deer herds. Herds in a portion of northwestern Colorado were so prolific that the area was dubbed “the mule-deer factory.”

Now, declining deer populations have people wondering if the factory is running down. Mule deer populations have been dropping across the West for several years. State wildlife managers and wildlife groups are trying to determine what’s behind the declines in western Colorado. The renowned White River herd in northwest Colorado has plummeted from more than 100,000 in the early 1980s to the current estimate of 32,000 deer. A new fact sheet by the National Wildlife Federation, “Legacy in the Crosshairs: Colorado’s ‘Mule-Deer Factory’ on the Decline” homes in on shrinking habitat due to development, including increased oil and gas drilling, and a growing human population as likely contributors to the decreases.

Description: Mule deer’s defining characteristic are their large ears, which are about 3/4 the length of the head. They have a distinctive black forehead, or mask, that contrasts with a light grey face. In summer, mule deer are tannish-brown and in winter brownish-gray in color. They have a white rump patch and a small white tail with a black tip. When running, they bound in a motion called “stotting,” in which all four hooves push off the ground at the same time.

Black-tailed deer are a subspecies of mule deer found in the Northwest and as their name suggests, have black tails instead of white.

White-tailed deer are a different species but overlap in range with the mule deer in some places. Mule deer are slightly larger, have bigger ears, smaller tails, and have forked antler structure rather than having points grow from a central branch like white-tailed deer antlers. The easiest way to differentiate the species is to look at the tail. Only the underside of the white-tailed deer’s tail is white, while the mule deer’s tail is all white with a black tip and is much smaller. Also, mule deer do not flash their tails in alarm.

Size:  Mule deer range from 3 to 3-1/2 feet tall at the shoulder, 4-1/2 to 7 feet long and have a tail that is 5 to 8 inches long. They can weigh between 130-280 pounds. The female deer are smaller than the male.

Diet: Mule deer are browsers, feeding on herbaceous plants and the leaves and twigs of woody shrubs. Mule deer are selective feeders. Instead of eating large quantities of low-quality feed like grass, they must select the most nutritious plants and parts of plants. Because of this, mule deer have more specific forage requirements than cattle or elk that share their habitat.

Typical Lifespan:  Mule deer usually live 9-11 years in the wild.

Habitat:  Mule deer are adapted to arid, rocky environments. They thrive in habitat that has all of the following characteristics:

  • Early stages of plant growth. Plants that are young and emerging are more nutritious than mature trees and shrubs.
  • A mixture of plant communities.Many species provide better forage than any single species.
  • Diverse and extensive shrub growth.More shrubs are generally preferable to fewer shrubs.

Life History and Reproduction: Between November and February (depending on the locality), bucks that are evenly matched in size and strength engage in battles for the right to mate with females. They lock antlers and fight until the point of exhaustion, when one will back down and flee from the victor. These victorious bucks attract females to them and attempt to defend them against the attentions of other (often younger) bucks. Sexual maturity is attained at the age of about 18 months in does but young bucks are not allowed to participate in the rut until they are 3 or 4 years old.

The gestation period is approximately 210 days, and the fawning period extends over several weeks in the summer. The female sequesters herself and drops her fawn in a protected locality where it remains for a period of a week or 10 days before it is strong enough to follow her. At birth fawns are spotted and weigh approximately 5.5 lbs. The young ones are weaned at about the age of 60 or 75 days, at which time they begin to lose their spots.

Learn More about Mule Deer

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