The mule deer gets its name from the size of its mule-like ears. Rocky Mountain mule deer stand three to three and a half feet tall at the shoulder, with bucks (males) usually weighing 125 to 250 pounds, though some may weigh as much as 400 pounds. Does (females) usually weigh between 100 and 150 pounds. During the winter, mule deer have a heavy, dark grey coat of long guard hairs covering a dense underfur. This is shed in the spring for a lighter reddish-tan coat. Fawns are born with a light brown coat covered with numerous white spots. By the time the fawns are approximately three months old, the spots will have disappeared. The mule deer has a white rump patch and a narrow black-tipped tail. It holds its tail down when it runs, unlike its cousin the white-tailed deer, which raises its bushy white tail like a flag.

Antlers, found only on bucks, begin growing in late winter and will reach full growth by late summer. Developing antlers are covered with a skin-like “velvet” which supplies blood and nutrients to the developing bone. The velvet is shed by early fall and the antlers harden. The antlers have a main beam which splits or forks into two branches with each branch or tine (point) being approximately the same length. Typical four point antlers have secondary forks that arise from these branches. While antler points cannot be used to determine the age of a deer, with proper nutrition, older deer generally have larger antlers with more points than do younger deer. Antlers are shed yearly, usually by late December.

Distribution

The Rocky Mountain mule deer has the broadest distribution of any antlered game animal in North America, ranging from northern Canada to central Mexico

Behavior

The mule deer rut, or breeding season, occurs during November and December. As bucks prepare to enter the rut, they become more aggressive and hyperactive. Throughout the summer and early fall, the bucks have been “play fighting” one another, establishing a dominance hierarchy. During the rut, larger bucks will chase away smaller bucks. If two males of approximately equal size meet, they will posture and possibly lock antlers in a dramatic pushing contest to establish breeding rights. Mule deer bucks are promiscuous, and will breed with any mature doe that will accept them. Does can breed with more than one buck, creating the possibility that twins may actually be the offspring of different fathers.

In areas where late spring snow storms are common, does generally give birth in June and July. In drier desert areas or in wet, rainy areas, the schedule may be moved forward or back, depending on the weather and forage conditions. This strategy gives the young the greatest opportunity for growth before they face harsh winter weather.

Pregnant does leave their herds and find isolated thickets in which to have their fawns. Older does commonly have twins, while yearling does will usually have a single fawn. Triplets are uncommon. Fawns average about eight pounds at birth, and are able to suckle and follow their mother within a short time of being born. Fawns grow rapidly during the summer months, reaching weights of 70 to 80 pounds by November.

Though they are capable of walking and running soon after being born, fawns survive by hiding. They are odorless at birth, and their spotted coat provides excellent camouflage. If the fawn doesn’t move, it can usually hide from predators. If it were to try to escape by running, however, it could become an easy meal for a hungry coyote, cougar or bear.

When nervous, the mule deer’s walk becomes stiff and jerky, unlike its normal free flowing walk. When frightened, it bounds away on all four feet. This bounding gait, called stotting, allows for sure footed movement over rugged terrain. Mule deer can cover a distance of nine to seventeen feet with each stot, and can run at 25 miles per hour for short distances. When chased, a mule deer can change direction with each bound, leaping over rocks, logs and brush, placing these barriers between itself and a predator.

Diet

Deer are browsers, and rely on many different plants for their nutrition. While shrubs and brush such as sagebrush, bitterbrush, mountain mahogany, cliffrose, rabbitbrush, scrub oak and willow make up a major part of their diet, mule deer will eat a variety of plants. In fact, researchers have documented Rocky Mountain mule deer feeding on close to 800 different plant species. Of these, over 60% are forbs (non-woody herbaceous plants such as dandelions), 25% are shrubs or trees, and 12% are grasses. Mule deer are selective feeders, and rarely concentrate on any single species.

Feeding habits vary with the changing seasons, and many researchers believe that mule deer have the ability to pick and choose the plants with the highest nutritional value during each season of the year. From late spring to early fall, mule deer quickly gain weight and build up fat reserves by feeding heavily on succulent leaves of the plentiful forbs and grasses. In late fall, they feed primarily on the current year’s growth of leaves and stems of brush species. During the winter and early spring when there is little ground forage available, mule deer are on a starvation diet of twigs and branches. This dry, woody vegetation is difficult to digest and lacks enough nutritional value to maintain body condition. During these periods of inadequate nutrition, mule deer use stored body fat to survive. Studies of mule deer during these lean times show that an adult deer may lose up to 20 percent of its body weight under these conditions, and that mule deer may spend up to six months out of every year on this type of low quality diet. Ultimately, winter survival depends on the weather, stored fat reserves, and the deer’s individual ability to conserve precious energy.

Habitat

Mule deer living in areas of high snowfall, like mountain ranges, or in areas with drastically changing climates, like a desert or canyonland, will make seasonal migrations between winter and summer ranges. Generally, mule deer summer at high elevations and winter at low elevations, following the snow line. Bucks will generally use habitats higher in elevation than will does and fawns. During heavy mule deer may spend up to six months out of every year on this type of low quality diet. Ultimately, winter survival depends on the weather, stored fat reserves, and the deer’s individual ability to conserve precious energy.