Odocoileus hemionus (Mule Deer)
Written by Matthew Trujillo (Mammalogy Lab--Fall 2003)

Edited by Karah Gallagher and Jennifer Bailey

Map prepared by Greg T. Lewellen

The geographic distribution of Odocoileus hemionus and it subspecies occurs over most of western North America.  It is indicated Odocoileus hemionus has occurred as far south as San Luis Potosi, Mexico to as far north as the Yukon Territories (Wallmo 1981; Cowan 1956).  The eastern edge of the mule deer's range is southwestern Saskatchewan.  Odocoileus hemionus and its subspecies are common to Alaska, British Columbia, Alberta, North Dakota, South Dakota, Nebraska, Kansas, Colorado, Utah, New Mexico, Arizona, Nevada, California, Oregon, Washington, and western Oklahoma (Wallmo 1981).  Sightings have also occurred in Minnesota, Iowa, and Missouri (Robinette 1966; Wallmo 1981).

Distribution in Texas occurs over most of the Trans-Pecos and panhandle regions.  Most of these populations are the result of introductions (Anderson 1981; Davis and Schmidly 1994; Koerth et al. 1985; Sowell et al. 1985).

wpe4D.jpg (56020 bytes) Photo courtesy Texas Parks & Wildlife 2003

Physical Characteristics:

Odocoileus hemionus is a medium-sized deer.  The pelage colors change from summer to winter (Hall 1981).  In winter, colors may be a dark brown to gray, dark and light ash-gray to brown and even cinnamon buff.  The colors are more reddish during the summer.  A dark brown patch extends nearly to the eyes on the forehead.  A brown patch occurs on each side of the nose.  The rest of the face is white or gray.  Ears are big and black on the front border with whitish on the inner surface.  The  inner sides of the buttock, legs, abdomen and throat are white.  The throat may have one or two white patches; two is most common.  The tail is short and the tip is black, with the remainder being white. Antlers are dichotomously branched and occur almost entirely in males (Cowan 1956; Davis and Schmidly 1994; Geist 1981; Hall 1981).

The dental formula of Odocoileus hemionus is: i 0/3, c 0/1, p 3/3, m 3/3 with a total of 32 teeth (Davis and Schmidly 1994).

External measurement averages of male and female Odocoileus hemionus are:  total length 1453-1755mm, tail length 152-175mm, hind foot length 475-555mm, metatarsal gland length 129mm, mass 57-150kg (Davis and Schmidly 1994).

Natural History:

Food Habits: The diet of Odocoileus hemionus consists primarily of browse, forbs, and grass species.  Studies have shown woody and herbaceous forage to be equal in dietary requirements (Short 1981).  Other studies have shown that diets are comprised of 70-75% browse, 16-26% forbs and 2-3% grasses (Anderson et al. 1965; Boeker et al. 1972; Krausman 1978).  It has been noted that Odocoileus hemionus feed on green leaves, green herbs, weeds and grasses during the summer, when they are more plentiful than browse.  But when winter arrives the deer feed primarily on browse (Davis and Schmidly 1994).  Forbs are more nutritious than browse and benefit the diet more.  However, forbs are not available at all times.  So, browse species are sufficient enough in nutrient values and in abundance that they provide an adequate year round diet (Boeker et al. 1972).  This may show why browse species are such a big part of their diet.

The primary foods of the Trans-Pecos area of Texas are the flowering plants of lechuguilla, the basal parts of sotol, mesquite, juniper, and a number of forbs (Davis and Schmidly 1994).

 Reproduction: The breeding season for Odocoileus hemionus can start as early as October and can continue to the latter part of January or into February (Davis and Schmidly 1994; Wallmo 1981).  The gestation period is approximately seven months and the fawning period extends over June, July and August.  This is a period of high temperatures, precipitation, and when most of the quality forage is most available.  At birth fawns are spotted and weigh about 2.5kg (Anderson 1981; Davis and Schmidly 1994; Kucera 1978).  Litter sizes range from 1-4 fawns (Kucera 1978). 

Weaning can begin as early as 5 weeks of age and is usually completed by 16 weeks of age (Davis and Schmidly 1994; Short 1981). 

Sexual maturity begins at the age of about 18 months in does and young bucks do not usually participate until the age of 3 or 4 (Davis and Schmidly 1994; Wallmo 1981).

Hybridization may occur between Odocoileus virginianus and Odocoileus hemionus.  This poses a serious problem for mule deer populations.  Many times, hybrids are sterile and this could impact a population greatly (Cronine et al. 1988; Stubblefield et al. 1986).

 Behavior: Odocoileus hemionus are active during the early morning and late afternoon hours and also after sundown.  They usually bed down during the afternoon hours (Davis and Schmidly 1994; Robinette 1966).

When alarmed, Odocoileus hemionus escape by a method known as stotting.  This is a high bouncing gait that includes the bounding motion of all four legs striking downward and backward at the same time.  They can cover a lot of rough terrain and escape from predators by employing this method (Cowan 1956; Davis and Schmidly 1994; Wallmo, 1981).

Speeds are variable of Odocoileus hemionus.  When forced, they are capable of attaining speeds up to approximately 58km/hr for a short distance.  Average speeds are around 30km/hr (Davis and Schmidly 1994; Wallmo 1981).

Common predators of Odocoileus hemionus are: gray wolf (Canis lupus), mountain lion (Puma concolor), coyote (Canis latrans), bobcat (Lynx rufus), black bear    (Ursus americanus), and grizzly bear (Ursus arctos) (Ballard et al. 2001; Robinson et al. 2002).

Odocoileus hemionus do not raise and wave their tails like Odocoileus virginianus (white-tailed deer).  But, O. h. hemionus raises its tail slightly, but no more than horizontal and  O. h. columbianus and O. h. sitkensis carry their tails erect, but never wave it from side to side (Cowan 1956).

Odocoileus hemionus may shift their home ranges, in relation to changes in food availability (Koerth et al. 1985).  Migration takes place between winter and summer home ranges (Peek and Forseth 2003; Wallmo 1981). Distances traveled range from a few miles up to 100 miles (Gruell and Papez 1963; Wallmo 1981; Wright and Swift 1942; Zalunardo 1965).

Odocoileus hemionus is polygynous and does not form or defend harems.  Instead, a tending bond system is formed.  The dominant buck generally allows no other bucks to court does. He prevents this behavior by making threats.  The dominant buck allows subordinate bucks in the group only if they pay no attention to does (Kucera 1978; Robinette 1966).

The antlers are shed annually from December-April.  As soon as they are dropped, new antlers begin to grow.  They grow from March-October or until the velvet is shed. Velvet is supplying nutrients to the growing antlers and is used as protection.  After the velvet is shed, the antlers are fully formed, only to be lost after the breeding season is complete (Anderson and Medin 1971; Davis and Schmidly 1994).

 Habitat:  Odocoileus hemionus occurs in all the biomes of western North America, north of central Mexico, except the Arctic tundra (Wallmo 1981).  Odocoileus hemionus prefers open, arid environments in which sagebrush, juniper, pinyon pine, yellow pine, bitter brush, and mountain mahogany are predominate (Davis and Schmidly 1994; Wallmo 1981).

Economic Importance for Humans:

Odocoileus hemionus is economically important as a big game animal throughout the U.S. (Davis and Schmidly 1994; Wallmo 1981).  Odocoileus hemionus have been valued as a source of food and as a trophy recreational opportunity (Wallmo 1981).  Farmers and ranchers are also supplementing their incomes, by allowing  the legal harvesting of these game animals on their properties (Sowell et al. 1985).

Conservation Status:

Odocoileus hemionus population numbers are not as high as they used to be (Wallmo 1981). Many factors have contributed to the decline in numbers:  habitat loss or manipulation, severe weather, starvation, changes in age and sex structure, predation, competition with livestock and other wildlife species, hunting, and disease (Wallmo 1981).

A major disease, Chronic Wasting Disease or CWD, has really affected the mule deer populations of the West. Over the last few years, this has been an emerging epidemic (Miller et al. 2000).  CWD is a transmissible spongiform encephalopathy or prion disease that affects free-living cervids (Miller et al. 2000; Williams and Young 1980).  Since the epidemic has surfaced only recently, both its origins and future are still uncertain.  A long term committement will be needed to control this disease and its harmful effects (Gross and Miller 2001).  Proper management of all the factors listed above will insure that Odocoileus hemionus numbers will rise and prosper (Wallmo 1981).


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