Mule deer are one of the most iconic and beloved wildlife in the American West. They are so-named because of their large ears that look like a mule’s ears. During summer, these deer are a tannish-brown color and in winter they are brownish-gray. There is a white patch on their rump and they have a small white tail tipped with black.
In this post Pritish Halder gives a brief description on the mule deer, (Odocoileus hemionus) is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer.
Mule deer inhabit most of the western area of North America, from the Alaskan coastal islands, down to southern Baja Mexico. They also occur from the northern border of the state of Zacatecas in Mexico and northwards through the Great Plains to Canada, in the provinces of Saskatchewan, British Columbia, Alberta, and the south of Yukon Territory. Mule deer migrate from low elevation winter ranges to high elevations summer ranges.
Although not all individuals in populations migrate, some will travel long distances between summer and winter ranges. These animals inhabit forests, grasslands, shrubland, fields, desert, and semidesert depending on the season, preferring arid, open regions and rocky hillsides.
Habits and Lifestyle
Mule deer are a social species and typically stay in groups of multi-generational families of related females with their offspring. Bucks that are older than yearlings will often group together, otherwise, they remain solitary. In the late summer and autumn, mixed family groups join together to form larger groups for protection during the winter. The largest males, having the biggest antlers, are the dominant ones, and they breed most often during the season of mating.
Mule deer are primarily active during the morning, evening, and moonlit nights. In the middle of the day, the mule deer will rest in a cool, secluded area. Males prefer to bed down on rocky ridges, while females and fawns prefer open areas. Seasonal movements involve migrations from the summer ranges in higher elevations to lower winter ranges and are associated with lowering temperatures, severe snowstorms, and deep snow, which reduce food supply and mobility.
Diet and Nutrition
Mule deer are herbivorous (folivorous, graminivorous) animals that eat a wide variety of vegetable matter, such as fresh green leaves, lower branches of trees, twigs, and various grasses. They particularly like blackberry and raspberry vines, mistletoe, grapes, mushrooms, and ferns. They are able to eat so carefully that they can even eat the fruit of cacti.
Mule deer are ruminants, meaning they employ a nutrient acquisition strategy of fermenting plant material before digesting it. Deer consuming high-fiber, low-starch diets require less food than those consuming high-starch, low-fiber diets. Rumination time also increases when deer consume high-fiber, low-starch diets, which allows for increased nutrient acquisition due to greater length of fermentation.
Because some of the subspecies of mule deer are migratory, they encounter variable habitats and forage quality throughout the year. Forages consumed in the summer are higher in digestible components (i.e. proteins, starches, sugars, and hemicellulose) than those consumed in the winter. The average gross energy content of the consumed forage material is 4.5 kcal/g.
Due to fluctuations in forage quality and availability, mule deer fat storage varies throughout the year, with the most fat stored in October, which is depleted throughout the winter to the lowest levels of fat storage in March. Changes in hormone levels are indications of physiological adjustments to the changes in the habitat. Total body fat is a measure of the individual’s energy reserves, while thyroid hormone concentrations are a metric to determine the deer’s ability to use the fat reserves. Triiodothyronine (T3) hormone is directly involved with basal metabolic rate and thermoregulation.
Mule deer are polygynous, with courtship and mating occurring within the group. From November to February, bucks evenly matched in strength and size compete in battles for access to mate with females. Gestation lasts 6 to 7 months and one or two fawns are born in early summer. There are often twin births after the first pregnancy. Nursing fawns stay hidden during the day in the underbrush while their mothers are away.
They begin to accompany their mothers within a few weeks. The weaning process begins when the fawns are around 5 weeks old and it is usually completed by the time they are 16 weeks old. They usually stay with their mothers for their first full year. Does are sexually mature at about 18 months old but young bucks are not permitted to mate until the age of 3 or 4 years.
The fawns have a spotted coat. The bucks (males) have forked antlers, which are shed in mid-February. Their next set of antlers then starts to grow immediately. Antlers have a covering of velvety skin until they are fully formed, at which point the buck scrapes off this layer. Females (does) do not have antlers.
Today the most serious threat to wild Mule deer is the prevalence of Chronic Wasting Disease (CWD). This has been diagnosed in deer in the United States Rocky Mountains region, as well as other mid-western states. Further threats include great numbers in predator populations (e.g. feral dogs), competition for grazing with livestock, habitat loss, and other actions by humans.
Their habitat in many regions is being lost, and in others dramatically fragmented, due to the human population growth, development, and natural events. Road construction, urban expansion, catastrophic wildfire, and the spread of invasive plant species also have led to habitat loss.
The total number of the Mule deer population is unknown today, but according to the Gohunt resource, specific populations were estimated in these regions: Colorado – 408,000 deers; Nevada – 106,000 deers; Utah – 80,600 deers. Overall mule deer numbers are stable today and they are classified as least concern (LC) on the IUCN Red List.
Fun Facts for Kids
- Mule deer lack front teeth; they just have a hard palate.
- Males grow forked antlers that have 8 to 10 points and spread as much as 4 feet (1.2 m).
- Mule deer have very good night vision and can detect the movement of predators as far away as 600 meters. They have a sense of smell that is 1000 times the accuracy of the human sense of smell. They are able to detect water that is two feet underground.
- Mule deer are not choosy about where they sleep and will make temporary “beds,” of flattened grass or leaves. If they use an area often, they will scratch a crude nest in the earth with their hooves.
- When Mule deer are threatened by potential danger, they try to escape by “stotting” (bouncing on the ground on their four feet all at the same time).