Odocoileus hemionus

Mule Deer live in a broad range of habitats - forests, deserts, and brushlands. Mountain populations migrate to higher elevation in warmer months, looking for nutrient-rich new-grown grasses, twigs, and shrubs. They maintain separate summer and winter ranges, connected by a migratory pathway. In milder climates, they do not migrate. They live in small social groups of about three, except during the winter, when large groups may come together to feed in open meadows. Females tend to stay close to where they were born. Males disperse farther, establish their own territories, and compete for access to females during the October and November breeding season. The males lose their antlers after breeding and grow new ones yearly, with each set becoming larger than the previous one. Newborns, with spotted coats, are well-camouflaged.

Adaptation: The remarkable evolution of running adaptations is evident in comparing the same (homologous) wrist and hand bones of the Mule deer, Odocoileus hemionus (image on the left), with a primitive type of versatile hand, like that of a Hedgehog, Erinaceus europaeus (image on the right).

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More info for the term: tundra

Figure 2. Mule deer distribution and habitat in the western United States. Map courtesy of Remote Sensing and GIS Laboratory, Mule Deer of the Western United States. 2005. Utah State University, Logan, Utah. http://www.gis.usu.edu. Click on map for a larger image.

Mule deer are native to western North America. Scattered populations occur as far east as western Minnesota and Iowa. In Mexico, they occur south to Baja California (including some islands in the Sea of Cortez) and the southern end of the Mexican Plateau. They have been introduced in Hawaii and several islands in Prince William Sound [215]. Major gaps in mule deer distribution occur in the Mojave and Sonoran deserts in southeastern California, southern Nevada, southwestern Arizona, and northwestern Sonora, Mexico; the high-elevation or cold deserts and plains grasslands of northeastern Arizona and southeastern Utah; the Central Valley of California; and probably the Great Salt Lake desert region. Otherwise, mule deer occur in all of the biomes of western North America north of central Mexico, except the arctic tundra [7,345]. Within the mule deer's distribution, black-tailed deer occur along the northern Pacific Coast from central California north to southern Alaska [215].

States and provinces:
United States: AK, AZ, CA, CO, ID, KS, MT, NE, NV, NM, ND, OK, OR, SD, TX, UT, WA, WY
Canada: AB, BC, MB, NT, SK, YT [234]
Mexico [215]

Odocoileus hemionus occurs throughout western North America from Alaska and Western Canada through the Rocky Mountains and Western Plains States of the United States south to the Peninsula of Baja California, Cedro Island, Tiburon Island and Northwestern Mexico. The southernmost distribution reaches central Mexico, but the historical boundary is not very clear (Sanchez- Rojas and Gallina 2007)

Odocoileus hemionus occurs over most of North America west of the 100th meridian from 23 degrees to 60 degrees N. The eastern edge of the usual range extends from southwestern Saskatchewan through central North and South Dakota, Nebraska, Kansas, and western Texas. Isolated occurrences have been reported from Minnesota, Iowa, and Missouri. Major gaps in geographic distribution are in southern Nevada, southeastern California, southwestern Arizona, and the Great Salt Lake desert region. Apart from these gaps, O. hemionus occurs in all of the biomes of western North America north of central Mexico, except the Arctic tundra (Anderson 1984).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Native range extends from southeastern Alaska south through Canada and most of the western United States and Great Plains, to Baja California (including some islands in the Sea of Cortez) and the southern end of the Mexican Plateau (Sonora and northern Tamaulipas, according to Grubb, in Wilson and Reeder 1993). The species has been introduced in Hawaii (Tomich 1986) and Argentina.

Mule deer vary in size depending upon region. The largest occur in the Rocky Mountains and the smallest, the black-tailed deer, occur along the northern Pacific coast [215,324]. Males are typically larger than females. Field-dressed carcass weights of ≥1.5-year-old male mule deer (bucks) on the Roosevelt National Forest averaged 148 pounds (74 kg), and ≥1.5-year-old female mule deer (does) averaged 118 pounds (59 kg) [6]. In Lake County, California, black-tailed deer bucks in good condition typically weighed 90 to 130 pounds (45-65 kg), and does weighed 70 to 90 pounds (35-45 kg) [92].

The pelage of Odocoileus hemionus ranges from dark brown gray, dark and light ash-gray to brown and even reddish. The rump patch may be white or yellow, while the throat patch is white (Geist 1981). The white tails of most mule deer terminate in a tuft of black hairs, or less commonly in a thin tuft of white hairs. On some mule deer, a dark dorsal line runs from the back, down the top of the tail, to the black tail tip. All markings vary considerably among O. hemionus, but remain constant throughout the life of an individual. O. hemionus possess a dark V-shaped mark, extending from a point between the eyes upward and laterally. This mark is more conspicuous in males. Growth in O. hemionus during the first year is roughly parallel in males and females. Thereafter, males, in general, exceed females in carcass weight, chest girth, neck circumference, body length, head length, cranial breadth, shoulder height, hindfoot length, and hoof length (Anderson 1984). Carcass weight ranges from 45 to 150 kg in males, and 43 to 75 kg in females. Chest girth ranges from 80 to 117 cm in males, and 78 to 97 cm in females. Neck circumference ranges from 30 to 65 cm in males, and 26 to 38 cm in females. Body length ranges from 126 to 168 cm in males, and 125 to 156 cm in females. Head length ranges from 28 to 35 cm in males, and 27 to 33 cm in females. Cranial breadth ranges from 11 to 16 cm in males, and 10 to 14 cm in females. Shoulder height ranges from 84 to 106 cm in males, and 80 to 100 cm in females (Wallmo 1981).

Range mass: 43 to 150 kg.

Sexual Dimorphism: "Males are usually heavier than females. "

Length:
Range: 1.3-1.7 m males; 1.3-1.6 m females

Weight:
Range: 40-120 kg males; 30-80 kg females

Length: 199 cm

Weight: 215000 grams

Comments: Mule deer occupy many types of habitats in mountains and lowlands, including various forests and woodlands, forest edges, shrublands, grasslands with shrubs, and residential areas. They are often associated with successional vegetation, especially near agricultural lands, but in southeastern Alaska they use old growth forests almost exclusively in winter and spring (Schoen and Kirchhoff 1990). Mule deer are scarce or absent in portions of the Mohave and Sonoran deserts, particularly where permanent water is absent during the summer dry season (Rautenstrauch and Krausman 1989). In southern Arizona, mean distance of mule deer from permanent water in July was less than 3 km (most females averaged less than 2 km) (Hervert and Krausman 1986); in early and late summer mule deer averaged 1.1-1.2 km from permanent water (compared to about 1.3 km for random locations) (Ordway and Krausman 1986). In winter, mule deer tend to be on warmer slopes or other areas with minimal snow cover. Snow depth in excess of 25-30 cm can impede movement, and snow depths greater than 51-60 cm discourage continuous occupation (Loveless 1967, Gilbert et al. 1970). Populations in Hawaii occur in moderately dry native and introduced forest.

In Nevada, mule deer inhabit most areas above the Lower Sonoran Life-zone; Hall (1946) observed that areas heavily grazed by domestic sheep have far fewer deer than those utilized only by cattle (possibly a result of competition for browse).

In northern Arizona, mule deer live in areas vegetated by yellow pine, buckbrush, snowberry, and aspen; elsehere in Arizona they inhabit chaparral and more xeric habitats, except those in the far southwestern portion of the state (Hoffmeister 1986). Deer that occur in yellow pine and spruce-fir habitats in spring and summer migrate to lower elevations (pinyon-juniper) for winter (Hoffmeister 1986).

In southern Arizona, mule deer used and preferred mountainous vegetative associations, but males also used nonmountainous associations (Ordway and Krausman 1986).

A survey along the lower Colorado River (California-Arizona border) in 1910 yielded no evidence at all of mule deer, but in earlier years deer apparently were numerous "both in the river bottom and back through certain desert ranges, where there are springs which the deer could visit regularly for water" (Grinnell 1914). In 1902 deer were said to be common on both sides of the river near Cibola (Grinnell 1914).

More info for the terms: avoidance, cover, forb, formation, wildfire

A review stated antipredator strategies of mule deer include early detection and outmaneuvering of predators; avoidance of areas frequented by predators; formation of groups with other mule deer; and restriction of movements to areas close to cover or escape terrain (e.g., steep slopes, riverbanks, and areas with low obstacles such as deadfall). Mule deer may also defend themselves against predators such as bobcats and coyotes [119,121]. Geist [121] suggested that the mule deer's antipredator strategies in part determine the species' preference for areas with broken terrain and steep slopes with obstacles.

Presence of predators may alter mule deer habitat use, movements, diet, and behavior (e.g., [4,239,258]). At the Three Bar Wildlife Area, summering female mule deer in enclosures with coyotes used areas with denser vegetation than females in enclosures without coyotes. Four habitats occurred in the enclosures: burned and unburned interior Arizona chaparral and burned and unburned Sonoran desertscrub. Burns resulted from a severe spring wildfire 4 years earlier. Vegetation was denser in burned and unburned chaparral than in desertscrub. Thus, mule deer may have selected chaparral for its escape and hiding cover from coyotes. However, they may have selected it for its greater thermal and security cover or for its greater forb biomass [239]. In the eastern Sierra Nevada, where mountain lions accounted for 68% of predator-caused mortality, male and female mule deer selected locations at higher elevations with more antelope bitterbrush, an important winter forage species, than random locations. Mountain lion kill sites were in relatively more open locations than locations in which mule deer foraged (P<0.05 for all variables). Therefore, mule deer did not appear to be confronted with a trade-off between predation risk and forage abundance when selecting habitat [258].

Predation risk from human hunting may also alter mule deer habitat use, movements, diet, and behavior [78]. For example, near Fort Collins, Colorado, hunting resulted in mule deer moving to areas with dense cover within their home ranges [182].

More info for the term: cover

Adult male and adult female mule deer may select habitats differently, whereas young males and young females use similar habitats as adult females [286]. During their 1st or 2nd year, young males typically shift from habitats used by females to those used by adult males. Often, this shift is made during the fawning or rutting periods (see Dispersal and Social behavior). Female mule deer may select habitats with more ground cover than males (King and Smith 1980, Main and Coblentz 1996, cited in [233]). In the Southwest, males may be found at higher elevations than females [286,290]. For example, in Arizona adult females always used habitats in the Picacho Mountains, whereas adult males used the creosotebush-velvet mesquite (Larrea tridentata-Prosopis velutina) flats surrounding the mountains. Adult males and adult females were generally found together only during the rut [286]. However, in the eastern Sierra Nevada, male and female mule deer selected habitats similarly [258].

More info for the term: cover

Edge habitat is generally considered important to deer because of high habitat diversity within ecotones and easy access to more than one habitat type [27,176]. Mule deer commonly use edges between burned and unburned habitats (see Size and shape of burned areas). Their use of edge habitats varies depending upon the interspersion of habitats providing forage and cover. A review stated that studies showing an apparent preference by deer for edge habitats tended to be conducted in areas where forage and cover were not available within the same habitat or where forage and cover habitats were not well interspersed. Studies finding little response of deer to edges tended to be in areas that had a high degree of interspersion of forage habitats and cover habitats or had a fine-grained interspersion where forage and cover were available in the same habitat [176].

More info for the term: succession

Mule deer occur in habitats in all stages of succession. With perhaps the exception of black-tailed deer that reside along the northern Pacific Coast, mule deer generally benefit from early successional vegetation that establishes after logging or fire [215,347]. Many mule deer forage species are characteristic of seral plant communities created after fire and other disturbances [91,236]. Disturbances that open the forest canopy and create early successional plant communities may provide deer with more forage than closed-canopy, old-growth forests in regions where snow does not become too deep [88]. Where snow is deep, mule deer forage in the understories of forests with structurally diverse, multilayered canopies, such as old-growth forests [58]. In general, the length of time that successional vegetation benefits mule deer varies with the type of disturbance, habitat type, soils, climate, and other factors [147,215]. For more information, see Habitat management and Indirect Fire Effects.

More info for the terms: cover, phenology, selection

Mule deer forage-site selection is based in part on forage quantity and nutritional quality, which are influenced by plant species composition, plant phenology and related changes in nutrition, site characteristics (soil, shade, and topography), successional stage, grazing and browsing pressure (see Livestock grazing), and weather. Mule deer forage-site selection is also affected by predation risk and proximity of foraging sites to drinking water and habitats providing cover.

Weather affects mule deer forage availability and thus foraging-site selection throughout the year. For example, black-tailed deer along the northern Pacific Coast in British Columbia and southeastern Alaska largely depend on canopy cover in mature forests [135,347,350]. A review of black-tailed deer habitats in southeastern Alaska, where black-tailed deer used forests year-round, stated that the 2 most important features of forest vegetation for black-tailed deer are a productive understory of high-quality forage and an overstory that intercepts and/or redistributes enough snow that understory forage remains available throughout the winter [135]. Patterns of forest use by black-tailed deer in southeastern Alaska shift through the winter and spring with changes in snow conditions and plant phenology [135]. In high snow areas in British Columbia and Alaska, "critical" winter rangelands include areas at low elevations; areas with southern aspects on moderate to steep (40%-100%) slopes; forests with multiple canopy layers; small, interspersed openings; and dense forest patches with well-developed crowns that intercept snow [58]. Black-tailed deer in areas of deep snow along the northern Pacific Coast largely depend upon old-growth western hemlock-Sitka spruce stands of moderate to high volume (≥20,000 board feet/acre) with an understory of huckleberry, bunchberry, and strawberryleaf raspberry (Rubus pedatus) due to the high degree of snow interception by the canopy and high-quality forage in the understory. In areas of low snow, however, forest stands with more open canopies and lower densities may be relatively more important [135]. In spring, the most important habitats for black-tailed deer are those with early snowmelt because these areas provide abundant, early succulent vegetation. Open areas such as clearcuts, rocky outcrops, and open forests have rapid snowmelt and early initiation of spring growth [58]. Wet sites, particularly those with patches of skunk cabbage (Lysichiton americanus), also provide abundant early new growth and are important spring foraging habitats [135].

Mature chaparral stands provide essential cover and forage for mule deer during parts of the year [345]. Mule deer summer foraging sites in California chaparral include riparian areas, seeps, springs, streams, and ponds. In fall, foraging sites include stream bottoms, ridge tops, and northern slopes. In winter, mule deer forage on south slopes and sheltered ridges [14]. A review stated that mule deer carrying capacities in chaparral are largely determined by weather and its effects on forage quality and quantity. "Good deer years" have weather conditions that promote herbaceous forage production and acorn production and/or extend forage succulence through the summer and fall [14]. Diversity of habitats is important to mule deer in California chaparral. Biswell [39] stated water availability, combined with chamise chaparral on south-facing slopes and mixed chaparral on north-facing slopes and in drainages, favored black-tailed deer in Lake County, California, because the combination provided diverse browse. In California oak woodlands, black-tailed deer use all successional stages, but Anderson and Pasquinelli [10] considered oak woodlands with abundant seedlings and saplings most important.

More info for the terms: cover, shrub

Mule deer require cover for security, thermal protection, and snow interception [34,58,102,119,215,347]. Cover influences the energetic costs of maintaining body temperature; the abundance of forage; security from predators and humans; and the costs of movement through snow [58]. According to a review, concealment cover is provided by vegetation within 7 feet (2 m) of the ground. Olson [241] described patches of concealment cover as "any vegetation capable of hiding 90% of a mule deer from human view at a distance ≤200 feet (60 m)". Conifers and other evergreen plants provide some of the best cover for mule deer in winter [241,287]. Topographic features such as boulders, river breaks, irregular topography, and ledges also provide concealment cover for mule deer [58,253]. Thermal cover is provided by vegetation and topography that ameliorate temperature and wind. During high wind, mule deer seek pockets of calm air below the crests of hills and in dense forests [102,119]. The importance of thermal cover varies with season, weather, and the age, size, and nutritional condition of the animal [58]. Based upon a simulation model using data from 14 years in shrubsteppe and shrub-woodland winter ranges in Colorado, mule deer doe and fawn thermal cover requirements under severe winter weather conditions were inversely correlated with the physical condition of the animal. However, under less than severe weather conditions, enhancing thermal cover on shrubsteppe and shrub-woodland winter ranges appeared unlikely to improve mule deer condition, although loss of cover could markedly alter patterns of mortality [150].

Snow interception cover is provided by forest and shrub canopy cover and topography. According to Bunnell [58], the degree of canopy closure has the most influence on the proportion of snowfall that will be intercepted by a forest >30 feet (10 m) tall. Forest stands with high canopy closure have shallower snow beneath, which reduces the cost of movement and increases forage availability [58]. In coastal British Columbia, mean snow depths across 4 mountain hemlock stands of different ages decreased linearly with mean canopy closure (r²=0.87, P<0.05). The stands included a 200-year-old forest with 60% canopy closure, an 80-year-old stand with 90% canopy closure, a 20-year-old stand with 36% canopy closure, and a recently clearcut stand with 0% canopy closure. The 2 oldest stands had less snow and a harder crust than the recent clearcut. Thus, mean black-tailed deer sinking depths were lower in those stands [60]. Clearcuts in western redcedar-western hemlock-western white pine forests in northern Idaho accumulated more snow than mature forest. However, spring snow melted faster from clearcuts than mature forest. Clearcuts on south-facing slopes had exposed forage soonest in spring [138]. A sagebrush canopy intercepts snow in addition to providing frequently melted-out areas around large plants, allowing for access to forage. Near Dubois, Wyoming, big sagebrush stands with about 50% cover accumulated more snow than open grasslands. In spring, snowmelt began earlier and proceeded at greater rates in and adjacent to big sagebrush crowns [158]. Because the amount and duration of snow varies within and among years, the value of canopy cover to mule deer also varies [253].

Mule deer are attracted to canopy openings by abundant forage but may make little use of the centers of large openings because of distance from cover [351]. See Edge habitat for more information.

More info for the terms: cover, forbs, selection, shrubs

Mule deer require water and forage—particularly grasses, forbs, and shrubs—that is palatable and nutritious year-round. For this reason, they usually require several plant communities throughout the year. Thus, diversity of habitats in close proximity is important in mule deer habitat selection (e.g., [14,39,135]). Open areas and early-seral communities are important mule deer foraging habitats in many areas. Mule deer may require forested areas or dense thickets of shrubs for escape, thermal, and snow interception cover. Because of their needs for forage and cover, mule deer often prefer edges over open or closed habitats. Mule deer use habitats differently based on age and gender, with adult males and adult females usually occupying separate ranges, except during the rut [34,58,102,119,215,233,253,347].

• Topography
• Cover
• Foraging sites
• Successional status of mule deer habitats
• Edge habitat
• Age and gender
• Predation risk
• Other factors

More info for the terms: codominant, cover, fire regime, hardwood, mesic, natural, shrub, shrubs, tundra

Mule deer are the most widely distributed and abundant of all large mammal species in western North America. They occur in diverse habitats from moist, dense coniferous forests to dry, open plains and deserts, and alpine habitats [129]. A review stated that "the multitudinous habitats of the mule and black-tailed deer are so diverse as to defy generalization" [347]. Mule deer occur in tallgrass, mixed-grass, and shortgrass prairies of the Great Plains, in shrublands, woodlands, and forests of the Rocky Mountains, and in sagebrush (Artemisia spp.) communities, pinyon-juniper (Pinus-Juniperus spp.) woodlands, and desert scrub of the Southwest. They are absent, however, from many desert communities of the Southwest because succulent forage occurs too infrequently to maintain populations [347]. In terms of elevation, they occur from coastal communities up to subalpine and alpine communities [119,215,347]. See the Fire Regime Table for a list of plant communities in which mule deer may occur and information on the FIRE REGIMES associated with those communities.

Canadian boreal forest: Mule deer occur in boreal forests of the 4 major forest types: quaking aspen (Populus tremuloides) parkland; mixed woodlands of quaking aspen, balsam poplar (P. balsamea), paper birch (Betula papyrifera), resin birch (B. glandulosa), white spruce (Picea glauca), and balsam fir (Abies balsamea); lower foothills dominated by lodgepole pine (Pinus contorta), quaking aspen, and balsam fir with white spruce and black spruce (Picea mariana); and northern foothills of black spruce, white spruce, subalpine fir (A. lasiocarpa), and pine (Pinus spp.). The boreal forest-subarctic woodland ecotone marks the northern limits of mule deer's distribution. In the boreal forest ecosystem, mule deer prefer open grassland-parkland types [347]. In Yukon, mule deer habitats are largely open, south-facing grassy slopes bordered by quaking aspen, and recently burned areas. Mule deer expanded their natural range into Yukon around the 1930s [152].

Alaska, Pacific Northwest, and California: In Alaska, black-tailed deer occur in Sitka spruce (Picea sitchensis), western redcedar (Thuja plicata), and western hemlock (Tsuga heterophylla) forests. Inland these forests transition to alpine tundra [135]. In coastal regions of northern California and southern Oregon, redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii) dominate black-tailed deer habitats. To the north, throughout habitats in Washington, British Columbia, and Alaska, Sitka spruce, western redcedar, and western hemlock dominate [135,215,347]. Inland in northern California, Oregon, Washington, and British Columbia, black-tailed deer occur in western redcedar, incense-cedar (Calocedrus decurrens), western hemlock, and/or Douglas-fir forests. On the Coast Ranges, they occur in Douglas-fir and silver fir (A. alba) forests [135]. In the Cascades Range, silver fir-Douglas-fir, subalpine fir-mountain hemlock (T. mertensiana), and ponderosa pine (Pinus ponderosa)-shrub forests are common mule deer habitats, whereas in the Sierra Nevada, mule deer commonly occur in mixed-conifer forests (white fir (A. concolor), incense-cedar, sugar pine (P. lambertiana), ponderosa pine, and Douglas-fir), red fir (Abies magnifica) forests, and subalpine forests (lodgepole pine, whitebark pine (P. albicaulis), foxtail pine (P. balfouriana), and/or mountain hemlock) [347,348]. Throughout coastal and inland California, mule and black-tailed deer occur in mixed-evergreen forests comprised of incense-cedar, Pacific madrone (Arbutus menziesii), California bay (Umbellularia californica), Coulter pine (P. coulteri), canyon live oak (Quercus chrysolepis), and/or coast live oak (Q. agrifolia) [52,347]. Throughout California, mule deer are particularly common in oak woodlands and chaparral. California oak woodlands are dominated by a mixture of oaks including coast live oak, canyon live oak, blue oak (Q. douglasii), valley oak (Q. lobata), and interior live oak (Q. wislizeni), and pines such as gray pine (Pinus sabiniana) and Coulter pine [347]. California chaparral communities occupied may be monospecific communities dominated by chamise (Adenostoma fasciculatum), manzanita (Arctostaphylos spp.), or ceanothus (Ceanothus spp.) or diverse mixtures with oaks (Quercus spp.) and other shrubs [340,347]. From California north to Washington and east to Wyoming, mule deer occur in sagebrush steppe. Antelope bitterbrush (Purshia tridentata) and snowberry (Symphoricarpos spp.) are important shrubs browsed by mule deer in this ecosystem and may be codominant in some areas [287,347].

Southwest: Mule deer occur in a range of habitats in the Southwest, including desert shrublands at the lowest elevations, semidesert shrubland-grassland communities, chaparral, mountain shrub, woodlands at midelevations, and some forests at high elevations [347]. Desert grasslands without shrubs do not have mule deer unless they contain rugged topography or riparian areas. Dry washes are important to mule deer in semidesert grasslands because they provide food as well as resting, escape, and travel cover throughout the year. In parts of the Mojave, Sonoran, and Chihuahuan deserts, mule deer are restricted almost entirely to riparian habitats [290]. In the Sonoran Desert, they are most abundant on upper bajadas in desert scrub either in or near ecotones with interior chaparral, grassland, or woodland [340]. Interior Arizona chaparral provides good year-round habitat for mule deer [290,345].

Great Basin: In the Great Basin, mule deer occur in semidesert shrublands of sagebrush, saltbush (Atriplex spp.), Stansbury cliffrose (Purshia mexicana var. stansburiana), and winterfat (Krascheninnikovia lanata) [215,347]. At high elevations, mule deer occur in juniper-pinyon woodlands and in forests of lodgepole, ponderosa, Great Basin bristlecone (P. longaeva), and/or limber (P. flexilis) pine [101,347]. Great Basin conifer woodland [53,290] and Great Basin montane scrubland [54] also provide good habitat for mule deer. Pinyon-juniper woodlands are used as year-long mule deer rangeland but are particularly valuable as winter rangeland [290,305]. Montane and subalpine conifer forests, particularly those near mountain meadows or quaking aspen communities, serve primarily as summer rangelands [51,290].

Rocky Mountains: In northern mountainous areas of the West, montane and subalpine forest communities dominate summer ranges and open, shrub-dominated slopes and ridges are the primary winter rangeland [215]. Forests of quaking aspen, grand fir (A. grandis), western larch (Larix laricina), western white pine (P. monticola), western redcedar, and/or western hemlock, meadows, and alpine communities are common mule deer habitats. In valleys and piedmonts of the Rocky Mountain region, grasslands and open ponderosa pine forests are common mule deer habitats [347,348]. Sagebrush steppe, juniper-pinyon woodland, and true mountain-mahogany (Cercocarpus montanus)/oak scrub are the most extensive winter rangeland types in northern mountainous regions [66,348].

Mule deer use a wide variety of habitats in southern mountainous areas. The "most significant" are sagebrush, juniper-pinyon woodland, mountain shrub, montane forest, and subalpine forest. At low elevations, big sagebrush (A. tridentata), juniper (e.g., oneseed (Juniperus monosperma), Utah (J. osteosperma), alligator (J. deppeana), and Rocky Mountain juniper (J. scopulorum)), and pinyon occur in various combinations. The true mountain-mahogany/oak shrub type and many pine and Douglas-fir types occur at midelevations. In subalpine forests, subalpine fir, blue spruce (P. pungens), and Engelmann spruce (P. engelmannii) are most prevalent to the south and lodgepole pine, subalpine fir, and Engelmann spruce are most prevalent to the north. Mule deer occur in quaking aspen habitats in montane and lower subalpine zones [347].

Great Plains: In the prairies of the northern United States and southern Canada, rough, forested, or nonforested breaks along river drainages, badlands, and shrubby stream courses and draws—especially near agricultural lands—provide mule deer habitat. Level and rolling grasslands provide poor habitat for mule deer [215,287,347]. Mule deer populations diminish abruptly at the transition from shortgrass or mixed-grass prairie to tallgrass prairie [347]. Mule deer occur in the quaking aspen parklands of Alberta and Saskatchewan [287]. Mule deer prefer shrubby draws dominated by western snowberry (S. occidentalis), common snowberry (S. albus), silver buffaloberry (Shepherida argentea), chokecherry (Prunus virginiana), golden currant (Ribes aureum), and rose (Rosa spp.); hardwood draws dominated by green ash (Fraxinus pennsylvanica), American elm (Ulmus americana), boxelder (Acer negundo), and hackberry (Celtis occidentalis); and floodplains dominated by eastern cottonwood (Populus deltoides) with willow (Salix spp.) and saltcedar (Tamarix spp.) in the understory. Slopes with Rocky Mountain juniper are also important [287,288]. In Prairie County, Montana, over all seasons and years, mule deer generally used sagebrush-grasslands, bunchgrass prairies, badlands, mesic shrublands, and hardwood draws more than expected based on availability [365].

Numerous reviews describing the biology of mule deer are available and cited frequently in this review. These include the following sources: [7,58,120,135,215,241,324]. Among these sources, this review relies most heavily on "Mule and black-tailed deer of North America" (compiled and edited by Wallmo [346]), particularly the following chapters: [5,66,77,78,88,119,216,265,287,293,340,345,347,348,351]. This review includes information for many aspects of mule deer life history but focuses on those most relevant to fire.

• Life history
• Diet

Habitat and Ecology

Systems

• Terrestrial

Odocoileus hemionus is remarkably adaptable. Of at least sixty types of natural vegetation west of the 100th meridian in the United States, all but two or three are or once were occupied by O. hemionus. Several additional vegetation types are inhabited in Canada and Mexico as well. The vegetation types in Mexico are similar to the types occurring in the United States. However, the tropical deciduous vegetation at the tip of Baja California is unique. In Canada, O. hemionus occupies five boreal forest types that do not occur in the United States. O. hemionus occupies a wide range of habitat provinces (regions of land containing particular vegetation types) in western North America. These habitat provinces include the California woodland chaparral, the Mojave Sonoran desert, the Interior semidesert shrub woodland, the Great Plains, the Colorado Plateau shrubland and forest, the Great Basin, the Sagebrush steepe, the Northern mountain, and the Canadian boreal forest (Wallmo 1981).

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; mountains

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

In mountainous regions, mule deer tend to migrate (up to 100+ km) from high summer range to lower winter range. For example, in Nevada, deer migrate in autumn from areas where snow lies deeply in winter (e.g., higher mountains) to areas where there is little or no snow (generally lower elevations); in some areas the climate is mild enough to allow deer to occupy the same locations all year (Hall 1946). In southeastern Alaska, deer migrated from low elevation heavily forested winter range to higher elevation summer range in open canopy subalpine and alpine habitats (Schoen and Kirchhoff 1990). In the arid southwest, deer reportedly migrate in response to rainfall patterns (Longhurst and Chattin 1941), but this has not been documented. In southwestern Arizona, some mule deer were nonmigratory whereas others migrated seasonally between summer-dry-season ranges that had permanent water sources to other areas that lacked permanent water (Rautenstrauch and Krausman 1989). Mule deer are not migratory in many plains regions. They exhibit high fidelity to individual seasonal ranges (e.g, see Kucera 1992).

Dispersal distances range up to around 100-200 km (Anderson and Wallmo 1984).

Home range size varies with season, gender, age, body mass, habitat, and other factors. Within a single season, home range size may be as small as around 30-40 hectares or as large as several hundred hectares; generally, mule deer do not move very far on a daily basis (Mackie et al., in Chapman and Fledhamer 1983).

More info for the term: parturition

Mule deer may be year-long residents in foothills, occupy seasonal ranges that include footslopes in winter and adjacent mountain slopes in summer and fall, or migrate between distinct, widely separated winter-spring and summer-fall ranges. Mule deer may move from high-elevation montane ranges in summer to low-elevation ranges in fall and winter [215]. In mountainous regions of the West, most mule deer are migratory, spending summer in the mountains and fall in foothills and valleys. Some mule deer live at low elevations year-round and in the absence of snow, most migratory mule deer remain at high-elevation summer ranges during winter [66,159,348]. Generally when snow is deep, mule deer move down from high elevations; move up from areas of low relief to slopes of southern or western exposure or to windswept ridges; or move into forests where snow is shallow. In regions with snow, fall migration usually depends upon the timing of snowfall and the depth of snow on summer and transitional ranges, whereas timing of spring migration is associated with snowmelt, the appearance of succulent forage on transitional and summer ranges, and perhaps the timing of parturition [7,135,215]. In the arid Southwest, mule deer may migrate in response to rainfall patterns [7].

Not all mule deer in a population migrate. Only 7% of female mule deer migrated in the Rocky Mountain foothills of eastern Colorado [183]. In the Poudre Canyon area of the Roosevelt National Forest, about 80% of mule deer were migratory [204]. In the Green River Basin of western Wyoming, 95% of mule deer were migratory [285]. In populations of north-central Colorado, the average proportion of mule deer that migrated was 52% but ranged from 0% to 100% [75].

Reviews stated that migration distances vary from <1 mile up to nearly 100 miles (2-160 km) [135,215]. Migrations may take from 4 to 7 weeks [7]. In the Green River Basin, mule deer took 9 to 13 weeks to complete their migration in spring and fall, spending 4 to 5 months each year on midelevation transitional ranges [285].

Mule deer are active throughout the day and night [102,327]. According to reviews, they are most active in early morning, late afternoon, and early evening [102,241].

Mule deer are most likely to disperse during the fawning period or during the rut [119]. One- to 2-year-old mule deer are most likely to disperse. Males are more likely to disperse than females [59,215,274,288,365]. In a migratory population in west-central Utah, few mule deer dispersed as fawns, but 60% of yearling males and 35% of yearling females apparently dispersed by 16 months old [274]. In the Missouri River Breaks, 70% of yearling males and 16% of yearling females dispersed [129].

Dispersal distances vary but are typically short. On Vancouver Island and in western Washington, male black-tailed deer dispersed 9.4 miles (15.2 km) and females dispersed 7.6 miles (12.2 km) on average. The maximum dispersal distances were 20 miles (32 km) for a male and 19 miles (30 km) for a female [59]. In Prairie County, Montana, migration distances ranged from 7 to 87 miles (11-140 km) for males and 8 to 16 miles (12-26 km) for females. Wood and others [365] suggested that long migration distances may be more characteristic of mule deer in patchy environments where suitable habitats are widely separated. The longest dispersal distance reported as of this writing (2012) was for a male mule deer in west-central Utah that dispersed at least 150 miles (240 km) [274].

More info for the terms: cacti, competition, ferns, forb, forbs, lichens, litter, phenology, prescribed fire, selection, shrub, shrubs, succession, vine

Along the continuum from grazers to browsers, mule deer are classified as intermediate or mixed feeders and can switch from a diet composed primarily of grasses and forbs to one primarily of browse [7,119,216]. Mule deer are opportunistic, concentrate selectors. Compared with other ruminants, they have small rumens and gut lengths relative to body size; thus, they must eat small volumes of high-quality, easily digested food [121,192,215]. Mule deer consume the stalks, flowers, fruits, and seeds of grasses and forbs. They eat the buds, fruits, seeds (particularly acorns), stems, leaves, and bark of trees and shrubs [88,119,215,293]. They also eat fungi, lichens, algae, mosses, and ferns [135,185,215,293,340]. Cacti and other succulents may be seasonally important in mule deer diets in some areas [215,340]. Mule deer may eat aquatic vegetation, but according to Cowan [81], they do not normally feed in water >8 inches (20 cm) deep. Mule deer can only access forage that is <5 feet (1.5 m) tall [119,145,327]. They avoid dense thickets when feeding [81,102,141,145,181,327]. Reviews of mule deer diets are available: [88,185,340,348].

The foods eaten by mule deer are extremely varied [119]. For example, a review listed 202 species of trees and shrubs, 484 species of forbs, and 84 species of graminoids eaten by Rocky Mountain mule deer [185], which occur from Yukon and Alberta south to Arizona and Texas [185]. In the Southwest, a review of 12 studies across Arizona, New Mexico, and southwestern Texas found that 327 plant species were consumed by mule deer [290]. Although mule deer utilize a large number of species, relatively few make up a large part of their diet. For example, in Colorado pinyon-juniper woodland in Fort Bayard, New Mexico, tame mule deer sampled 113 of the 194 plant species found in the area, but only 10 comprised ≥92% of the diet [157].

Forbs and grasses are the most important mule deer forages during the growing season in most regions, whereas browse is often most important during the dormant season [41,42,88,101,241,290,327,330,340]. In the coastal forests of southern Vancouver Island, mule deer annual diets consisted of 67% browse, 15% lichens (mostly beard lichens (Usnea spp.)), 11% forbs, 5% fungi, and 2% graminoids, ferns, horsetails (Equisetum spp.), and quillworts (Isoetes spp.). Mule deer fed on 92% of available browse species, 64% of forbs, 56% of graminoids, and 74% of ferns, horsetails, and quillworts throughout the year [81]. In conifer forest in the North Coast Ranges of California, browse, including acorns, were eaten consistently throughout the year (48% of annual diet), forbs were eaten mostly in summer (28% of annual diet), and graminoids were important in cool months (24% of annual diet) (California Wildlife Investigations Laboratory cited in [88]). Forb quality and quantity appeared to increase the productivity of 2 mule deer herds in Utah. On a summer range with forage that was 52% forbs, a herd averaged greater carcass weights and greater fawn production than a herd on a range where only 12% of forage was forbs [250].

Typical genera browsed by black-tailed deer along the northern Pacific Coast include maple (Acer spp.), alder (Alnus spp.), wintergreen (Gaultheria spp.), currant (Ribes spp.), blackberry (Rubus spp.), willow (Salix spp.), elderberry (Sambucus spp.), and huckleberry (Vaccinium spp.) [324]. "Staple" forage plants for black-tailed deer in California chaparral include chamise, interior live oak, and wedgeleaf ceanothus (Ceanothus cuneatus) [36]. Oak foliage and acorns are important in regions where they occur [10,36,48,57,236,327]. In the Great Basin, antelope bitterbrush, mountain-mahogany (Cercocarpus spp.), sagebrush, and juniper are major components of the mule deer's winter diet [41,42,290,348,354]. Other important browse plants include ceanothus, manzanita, serviceberry (Amelanchier spp.), desert peach (Prunus andersonii), and rose [41]. Forage species important to Rocky Mountain mule deer are shown below [185].

Table 1. Forage species most valuable to Rocky Mountain mule deer in at least one season [185]

Browse antelope bitterbrush big sagebrush chokecherry curlleaf mountain-mahogany (Cercocarpus ledifolius) Gambel oak (Quercus gambelii) hollyleaved barberry (Mahonia aquifolium) ponderosa pine quaking aspen rabbitbrush (Chrysothamnus spp.) Rocky Mountain juniper rose Saskatoon serviceberry (Amelanchier alnifolia) snowberry skunkbush (Rhus trilobata) snowbrush ceanothus (Ceanothus velutinus) true mountain-mahogany willow Graminoids bluegrass (Poa spp.) brome (Bromus spp.) fescue (Festuca spp.) sedge (Carex spp.) wheatgrass (Agropyron spp., sensu lato) wildrye (Elymus spp.) Forbs alfalfa (Medicago spp.) aster (Asteraceae) balsamroot (Balsamorhiza spp.) beardtongue (Penstemon spp.) buckwheat (Eriogonum spp.) cinquefoil (Potentilla spp.) clover (Trifolium spp.) dandelion (Taraxacum spp.) fleabane (Erigeron spp.) lupine (Lupinus spp.) phlox (Phlox spp.) pussytoes (Antennaria spp.) sagebrush vetch (Vicia spp.) thistle (Cirsium spp.) yarrow (Achillea spp.)

Forage preferences of mule deer vary among rangelands, seasons, and years, and appear strongly related to forage availability and plant phenology [41,215,327,348]. When green and succulent, forbs and grasses are selected over browse, but as forbs and grasses dry up, browse becomes increasingly important in the diet [41,215,236,241,327,348]. Leafless twigs are consumed only when other forage is scarce [348]. Severson and Medina [290] ranked mule deer food preferences in the Southwest from highest to lowest as follows: 1) fruits, flowers, and mushrooms; 2) new green herbage, particularly forbs and new leaves of deciduous shrubs; 3) new twigs and mature green herbaceous material; 4) new leaves and twigs of evergreen species, and 5) mature leaves and twigs of evergreen species. In general, mule deer forage is most abundant during the growing season and declines progressively in quantity, variety, and quality after annual growth ceases. On most mule deer rangelands, succulent forage is scarce in winter. However, in the mediterranean climatic region of California, succulent forage is abundant during spring, late fall, and winter and relatively scarce in summer. In some areas, mule deer forage is green and available year-round [88]. A review of mule deer diets in the Chihuahuan Desert reported that browse dominated diets in dry years and forbs dominated diets in wet years [340]. During a drought year in southeastern Arizona, mule deer and white-tailed deer diets changed from succulent deciduous forage to drought-tolerant evergreen species. The author suggested that competition with livestock may accentuate the effects of drought on mule deer and white-tailed deer diets [11]. See Livestock grazing for more information.

Deep snow makes forage less accessible to mule deer [348]. For example, on a treeless area of the Tillamook Burn, Crouch [87] estimated that 12 inches (30 cm) of snow would reduce available forage for black-tailed deer from about 224 kg/ha to 34 kg/ha [87]. Mule deer may paw through snow to feed, but they prefer to feed where there is no snow [119]. When other forage is buried by deep snow, conifer browse and arboreal lichens are important in mule deer diets in many regions [13,58,124,134,215,355].

Fire may affect mule deer diet composition. After a September prescribed fire on the east slope of the Colorado Front Range, mule deer diets in a montane shrub community contained more grass and less browse on burned plots compared with controls for 2 postfire years. In a montane grassland community, mule deer diets contained more grass and less browse on burned plots relative to controls during the 1st postfire year, but during the 2nd postfire year, there were no differences in grass and browse content [306]. For more information, see Indirect Fire Effects.

Nutrition: Protein content in preferred mule deer browse changes seasonally, reaching its lowest levels in winter. The time of year in which browse plants reach their highest nutritional level varies with the plant species [109,340]. Nutrients in mule deer forage species also change with seral stage [133]. Thus, diversity in browse composition and age is important for mule deer nutrition. For a review of the chemical composition of mule deer forage, see Kufeld and others [185].

Mule deer may select the relatively more nutritious foods from among those available (e.g., [223,325,327]). In interior Arizona chaparral near Globe, Arizona, combined mule deer and white-tailed deer use of sprouting shrubs during the first spring after a mid-September prescribed fire was positively related to moisture levels and crude protein content and negatively related to crude fiber content. For example, heavy use of true mountain-mahogany during the spring was associated with highest crude protein values and comparatively low crude fiber values, and selection of Wright silktassel (Garrya wrightii) during the summer growing season coincided with increases in moisture and crude protein and decreases in crude fiber [267]. However, in the Tillamook Burn in February—approximately 24 years after the 1951 fire in an area that had been salvaged logged—mule deer did not appear to select among 6 forage species (cascara (Rhamnus purshiana), red huckleberry (V. parvifolium), Douglas-fir, California hazelnut (Corylus cornuta subsp. californica), red alder (Alnus rubra), or vine maple (Acer circinatum)) based upon chemical composition, except that moisture tended to be higher in the most preferred species [262]. For more information, see Indirect Fire Effects.

Mule deer foraging effects: Because mule deer forage selectively, they can influence plant species composition and diversity by consuming palatable species, which may allow unpalatable species to gain dominance [80,135,315]. They can influence rates of nutrient cycling by altering litter quantity and quality and via urination and defecation. Also, mule deer may affect growth of stems and leaves and alter levels of plant nutrition [80]. Deer exert cascading effects on animals both by competing directly for resources with other herbivores and by indirectly modifying the composition and physical structure of habitats [3,80,264]. Reviews describing mule deer foraging effects are available: [24,80,220]. For information about mule deer effects on postfire succession, see Mule deer interactions with fuels and fire effects.

Odocoileus hemionus is a small ruminant with limited ability to digest highly fibrous roughage (Short 1981). Optimum growth and productivity of individuals and populations are dependent upon adequate supplies of highly digestible, succulent forage. Diets consisting primarily of woody twigs cannot meet the maintenance requirements of O. hemionus. Based on its stomach structure and its diet of woody and herbaceous forage in approximate equal proportions, O. hemionus is classified as an intermediate feeder. Because nutritious forage is in poor supply for much of the year, O hemionus has an annual cycle of metabolic rates. A higher energy flux and food intake in the summer enables O. hemionus to capitalize on abundant high-quality forage for growth and fat storage. A lower energy flux in the winter permits O. hemionus to survive on a lower intake of poor-quality forage while minimizing the catabolism of stored fat for body functions. The estimated rate of food intake is about 22 g/kg body weight/day. In adult males, food intake drops abruptly with the onset of rut (Anderson 1984). O. hemionus frequently browses leaves and twigs of trees and shrubs. Green leaves are very succulent and, except for epidermal tissue and structural ribs, consist largely of easily digestible cell contents. Dead and weathered leaves have little protein and high cell-wall values. As a result, they are of very low digestibility. O. hemionus also eats acorns, legume seeds, and fleshy fruits, including berries and drupes, that have moderate cell-wall levels and are easily digested (Short 1981).

Comments: Browses on wide variety of woody plants and grazes on grasses and forbs. May feed on agricultural crops. Also commonly consumes mushrooms, especially in late summer and fall (Great Basin Nat. 52:321). In northern California, reproductive success apparently was reduced due to selenium deficiency (Flueck, 1994, Ecology 75:807-812).

More info for the terms: duff, long-term effects, prescribed fire, shrubs

Fire may reduce the numbers of external and internal parasites that affect mule deer and other animals [27,146,209], although the effect is likely brief. Fires can reduce winter tick (Dermacentor albipictus) populations [144]. After a May prescribed fire in mature quaking aspen forest and willow habitat in Elk Island National Park, Alberta, the number of engorged adult female ticks and larvae immediately declined. Winter tick survival was highest where the burn was patchy and duff consumption was least [103]. According to a review, the number of winter ticks killed also depends on the habitat type and season of burning because most ticks are found on the tops of shrubs in spring [146]. Although winter tick populations may be reduced in the short term, fire's long-term effects on winter tick populations were unknown as of this writing (2012).

Fire in wetland habitats may help reduce giant liver fluke (Fascioloides magna) populations, which may be detrimental to mule deer and white-tailed deer [327]. Giant liver flukes have a complex life cycle that involves an intermediate aquatic snail host for the embryonic stage, aquatic vegetation for the larval-cyst stage, and an ungulate host for the juvenile and adult stages [331]. In east-central Alberta, deer, elk, moose, and American bison (Bos bison) populations were heavily infected with giant liver flukes (Swales 1936 cited in [331]). In order to control these infestations, dead aquatic vegetation was burned and aquatic snails were controlled with chemicals. This "apparently eradicated" giant live flukes in ungulates in the area; limited examinations found no giant liver flukes in deer harvested by hunters (Stock 1978, Pybus 1990b, cited in [331]). Following the Tillamook fires in Oregon, black-tailed deer were free of liver flukes (Fascioliasis) and lungworms (Strongylida) that had been prevalent before the fires. Apparently, fire had killed the dryland snail that is the intermediate host for liver flukes and some lungworms [160,369].

Odocoileus hemionus (bighorn sheep, wapiti, mule deer) is prey of:
Gulo gulo
Ursus arctos

Based on studies in:
USA: Montana (Tundra)

This list may not be complete but is based on published studies.

Odocoileus hemionus (bighorn sheep, wapiti, mule deer) preys on:
alpine vegetation

Based on studies in:
USA: Montana (Tundra)

This list may not be complete but is based on published studies.

More info for the term: density

According to a review, mule deer population density ranges from <0.1 to >29 mule deer/km² [215]. Winter concentrations in mountainous areas may be up to 130 mule deer/km² [243]. Mule deer densities in prairie habitats tend to be low [215]. In open northern prairie and plains habitats, population density in spring ranged from 0.6 to 3.3 mule deer/km² [365]. In prairie breaks and badlands, where topography and habitat are more diverse, density is usually higher, ranging from 1.4 to 4.4 mule deer/km² in spring [129]. In desert shrublands in Arizona, density ranged from 5.5 to 10.3 mule deer/km² (Smith and others 1969 cited in [215]). In mountainous areas, habitats tend to be heterogeneous and support high mule deer densities. In mountain-foothill type rangelands in Utah, density was about 16 mule deer/km² (Robinette and others 1977 cited in [215]). Hanson and McCulloch (1955 cited in [345]) considered the carrying capacity of mule deer in Arizona chaparral to be 4 to 5 mule deer/km². Mule deer in California chaparral have medium population densities (4-8 mule deer/km²) [324,327]. If oak woodland is interspersed with chaparral, density may be as high as 22 to 28 mule deer/km² [324]. In coastal forests in California, density tends to be about 2 to 8 mule deer/km², but in areas opened by logging or fire, density may be as high as 15 to 19 mule deer/km² [324]. For more information, see Logging and Indirect Fire Effects. Desert shrubland and grassland habitats tend to be "marginal" for mule deer, and wide oscillations in population density are typical, with low maximum densities compared with those in other habitats [340]. In the Southwest, mule deer populations fluctuate with annual precipitation (see Malnutrition and weather).

Slope, aspect, and elevation influence mule deer habitat use, particularly through effects on snow depth [135] and ambient temperature [327]. In general, high elevations tend to have more snow than low elevations, and south- and west-facing slopes tend to have less snow than other aspects due to solar radiation. Steep south-facing slopes are probably useable longer in fall, winter, and spring than shallow south-facing slopes or any north-facing slope. Shading, wind direction, and other topographical features are also important [66,135].

Figure 3. Mule deer herd on a snowy slope. Photo courtesy of David Heffernan, USFWS.

During hot weather, mule deer in the Southwest tend to forage on north- or west-facing slopes in dense vegetation, to bed in shade, and to seek shelter in washes [290]. In Lake County, California, black-tailed deer use mostly south-facing slopes in winter. In late spring they use mostly cool, northern exposures until fall, although they sometimes move to streambeds during hot weather and use south-facing slopes at night. They also move up and down elevation throughout the day and year, using areas near ridgelines in cool weather and deep canyon bottoms during hot weather [14,327]. In Fort Bayard, New Mexico, mule deer used all slopes throughout the year. The author concluded that a diversity of slopes and aspects likely benefited mule deer by providing diverse forage and protection from weather [157].

More info for the terms: density, hardwood, mesic, presence, xeric

Adult mule deer establish and traditionally use seasonal or year-round home ranges. According to reviews, mean annual home range sizes for mule deer vary from 74 to 34,220 acres (30-13,850 ha) [7,135,215]. Nonmigratory black-tailed deer have among the smallest home ranges [324].

According to a review, mule deer in "open, simple, and more variable habitats" tend to have larger home ranges than those in "closed, diverse, and stable environments" [215]. For example, in open, nonforested northern prairie habitat in Prairie County, Montana, year-long home ranges of migratory and nonmigratory adult mule deer ranged from 452 to 16,306 acres (183-6,599 ha) [365], whereas in forested prairie breaks habitat, year-long home ranges of migratory and nonmigratory adult mule deer were smaller, ranging from 114 to 8,253 acres (46-3,340 ha) [129]. According to Wood and others [365], seasonal home ranges tend to be small among mule deer in mesic mountainous habitats and large in more xeric, desert habitats. In the northern Great Plains in South Dakota, mule deer occupying rough terrain had smaller home ranges than those in relatively level terrain [288]. In Prairie County, Montana, nonmigratory mule deer had small home ranges and relatively high local population densities in areas with interspersed hardwood draws and badlands. Mule deer ranged over larger areas and occurred at lower densities in areas where badlands and hardwood draws were lacking or more widely separated [365]. In arid mixed woodland-grassland communities in north-central New Mexico, larger home ranges tended to have a greater proportion of grasslands (r²=0.18, P=0.037) [29].

Males tend to have larger home ranges than females [7,135,215]. In the Bridger Mountains of Montana, winter home ranges averaged 613 acres (248 ha) for males and 603 acres (244 ha) for females. Summer home ranges averaged 593 acres (240 ha) for males and 437 acres (177 ha) for females [243]. In the Missouri River Breaks region, the presence of fawns-at-side was the most important factor in determining home range sizes of adult females, with adult females with fawns-at-side having smaller home ranges than nonreproductive females. Home range sizes of adult females were not related to population density, forage condition, or age of females [129].

Seasonal movements and daily activity patterns may be strongly influenced by air temperature, wind, and/or snow depths [92,215]. In Colorado, mule deer tended to move within their winter habitats to areas with temperatures of 16 to 45 °F (-9 to 7 °C). When temperatures were below 16 °F, they tended to increase their metabolic rate (Mautz and others 1985 cited in [215]). During cold weather mule deer tend to use south-facing slopes, and during warm weather they tend to use north-facing slopes (see Topography) [92]. High winds appear to influence mule deer movements only during periods of cold weather, when mule deer seek shelter and reduce their activities [92,215]. According to Mackie and others [215], snow depth probably has the most influence on mule deer movements. Deep snow makes forage less accessible, increases energy expenditure, and may increase an animal's vulnerability to predation [78,135,237,348]. Snow depths of about 12 inches (30 cm) generally impede mule deer movement, especially that of young animals, and may cause mule deer to move to areas with less snow [78,135,204,215].

In regions with snow, winter ranges are often smaller than summer ranges. In the Bridger Mountains of Montana, average snow depths and patterns restricted mule deer to <20% of their total year-round range in winter. Under severe snow conditions only 20% to 50% of the winter range was considered usable [243]. Gilbert and others [122] concluded that because snow was too deep (>18 inches (46 cm)) in Middle Park, Colorado, during 2 of 3 winters, >90% of mule deer winter range was uninhabitable. In cold and snowy periods on Vancouver Island, mule deer used <40% of the area used during mild winters (McNay and Doyle 1987 cited in [58]).

In the arid Southwest, summer ranges may be smaller than winter ranges because of limited water. In Maricopa County, Arizona, mule deer had smaller home ranges in summer than winter, possibly due to greater dependence on limited water sources during periods of hot weather [115]. The 400,000-acre (162,000 ha) summer range of the Kaibab mule deer herd in Arizona was smaller than its winter range [156].

Fidelity to traditional home ranges can be so great that deer will "starve to death" rather than travel "a few kilometers" to abundant forage (Dasmann and Taber 1956 cited in [135]). During a fire, mule deer may not leave their home ranges even as their home ranges burn. If they do leave, they typically return soon after fire. Shantz [291] noted that mule deer and white-tailed deer returned to their home ranges so soon after fire that they burned their feet. Humphrey (1926 personal communication cited in [291]) noted that mule deer on the Manti-La Sal National Forest, Utah, returned to their burned home ranges "even though the forage was practically all destroyed". For more information, see Travel patterns. Although mule deer are unlikely to explore unfamiliar but favorable areas even if these areas are only a few kilometers away, they may shift their use of an area over time to exploit changes in resource availability [58]. Livestock grazing may affect the use of mule deer home ranges. For more information, see Livestock grazing.

Follow this link to the U.S. Forest Service Fire Effects Information Service to see a table with fire regime information that may be relevant to habitats in which this species occurs

Mule deer may inhabit the same range throughout the year or migrate to separate summer-fall and winter ranges [159,215]. Migratory mule deer are generally found in mountainous regions, where they move up and down along elevational gradients in response to weather and seasonal changes in vegetation. Transitional ranges are used in spring and fall as mule deer move between summer and winter ranges [159,215]. Nonmigratory individuals tend to occur at low elevations year-round [135]. In the prairies of the northern United States and southern Canada, mule deer tend to be nonmigratory but exhibit local shifts in habitats among seasons [215]. In other regions, a single population may be comprised of migratory and nonmigratory individuals. Individuals generally retain the same ranges from year to year and travel the same routes between ranges [159,215].

• Daily activity
• Seasonal movements and migration
• Dispersal
• Home range

Home range size may be 30-240 hectares or more; directly correlated with availability of food, water and cover. Deep winter snows are major factor limiting population size in Pacific Northwest (Schoen and Kirchhoff 1990). Predators include: mountain lions; coyotes; dogs.

See Hatter and Janz (1994) for information on apparent demographic changes associated with wolf control on northern Vancouver Island.

Mule deer males use glands on their forehead to apply scent marks to trees. These scent posts communicate the presence and physiological status of the deer and seem to be important in the social and reproductive biology of the species.

More info for the terms: cover, presence

Social structure in mule deer is organized around family groups consisting ≥2 generations of related females and their male and female offspring [215]. Bucks older than yearlings are absent from these groups [102]. Adult bucks may form groups, although they often remain solitary [97,102]. In late spring and early summer, adult females drive off previous year's young and isolate themselves in fawning areas, where they remain until late summer or fall [102,119,215]. Other associations during summer include small groups of adult males, mixed yearling-adult male groups, and groups of nonreproductive adult females that may have lost young-of-the-year. In late summer and fall, mixed family groups re-form. In late fall, winter, and spring, mule deer may concentrate in large groups on winter rangelands. Winter aggregations may be comprised of >100 individuals [97,102,215]. The largest groups form in the northern part of the species' distribution in areas where deep snow restricts access to forage. Large groups may also form in early spring where green, succulent forage is available [215]. Group size may be related to presence of cover. On the eastern and western slopes of the Cascades Range in southwestern Washington, the size of black-tailed deer groups was inversely related to canopy cover. Group sizes in open grassland-woodland ranges on the east side were significantly larger than those in forested rangelands on the west side [28]. Within groups, the largest and oldest individuals tend to be dominant [102,215].

Comments: Throughout the year most activity occurs at dawn and dusk, though nocturnal and daytime activity is common.

Males grow antlers from late winter (March) through summer and into fall (October). Antler shedding occurs from December through April (mostly January-February).

More info for the terms: cover, litter, parturition, severity

Fawn mortality is generally higher than that of adults. It is often highest at or immediately following parturition [58,77,77,163,215,283]. According to a review, 25% to 30% of fawns are commonly dead by fall, 50% more by early winter, and up to 75% or more by spring [215]. For example, in the declining North Kings River mule deer herd in oak-grassland and chaparral habitats in California, about 50% to 70% of fawns died within the first month of life, whereas winter fawn losses were "minor". The largest cause of mortality was coyote predation. The authors hypothesized that low fawn recruitment and population decline were due to reduction in the occurrence of fire and other disturbances on summer and transitional ranges that led to a decline in nutritional quality of mule deer forage during the last trimester of pregnancy and the lactation period [283].

Fawn survival may be related to fawn weight and gender, litter size, and other factors. In Colorado, Idaho, and Montana, where the average annual mortality of mule deer fawns was 66%, the heaviest fawns at the start of winter had the highest overwinter survival (P<0.001). Predation and malnutrition accounted for most deaths [338]. On 3 winter ranges in southwestern Idaho, the probability of winter fawn mortality increased with lower body mass (P=0.007) and being male (P=0.018) [31]. In the scablands of eastern Washington, twin fawns had a risk of dying 2.6 times higher than that of single fawns [163]. In north-central New Mexico, mule deer fawn survival was related to birth mass, birth date, litter size, maternal body fat, and total and seasonal precipitation (P<0.009 for all variables). The authors concluded that fawn survival was driven in part by an interaction between total and seasonal precipitation and effects of these factors on plant production, with consequential effects on female nutrition, and ultimately, fawn birth attributes [198].

Weather may affect fawn survival. In several plant communities in central Oregon, mule deer fawn survival during winter was closely related to temperature, wind, and snow cover and depth. Fawn survival decreased as the combination of these factors increased in severity (Leckenby and Adams 1986 cited in [106]). In Prairie County, Montana, there were significant relationships between the total amount of precipitation occurring from July to April prior to fawning and percent of fawns in the population the following winter (r=0.75, P=0.01) and spring (r=0.76, P=0.01). Average or greater precipitation during summer apparently resulted in relatively good summer forage conditions during those years, leading fawns to have ample fat reserves that could carry them through even severe winters. On the other hand, fawn winter mortality rates were relatively high in years with extreme drought and resultant poor summer forage, even when winters following the drought were mild [365].

Several other studies reported relationships between precipitation or forage production on summer ranges and herd productivity or population fluctuations (e.g., [129,164,250,303]).

Cover is important in fawning areas. Cattle (Bos primigenius) grazing may result in a loss of hiding cover for fawns, possibly increasing fawn predation mortality [197]. See Livestock grazing for more information.

More info for the terms: cover, forb, severity, wildfire

Malnutrition is often the leading cause of mule deer deaths. On Utah juniper-big sagebrush rangelands in southeastern Utah, winter mule deer mortality varied inversely with the amount of available browse [277]. Prolonged, continuous snow cover may result in substantial mortality due to malnutrition and starvation [78,88]. For example, in Oregon, a mule deer die-off occurred after snow covered the Cedar Creek Enclosure for >50 consecutive days; the die-off occurred about 23 years after the last wildfire [148].

In the prairies of the northern Great Plains, annual variations in amount and timing of precipitation influence vegetation production and thus mule deer mortality due to malnutrition [365]. In Prairie County, Montana, overwinter fawn mortality rates of mule deer were positively correlated with winter severity during 4 of 12 years (r=0.94, P=0.03). During the other years, fawn survival rates appeared to be mainly influenced by drought and poor forage the prior summer. Total amount of precipitation occurring in the area from July to April prior to fawning and percent of fawns in the population in spring were positively correlated (r=0.76, P=0.01) during the 12 years [365].

In the arid Southwest, precipitation may indirectly affect mule deer mortality through its effects on plant productivity [217,219,347]. A study in the Sonoran Desert of California found positive correlations between rainfall and the proportion of mule deer in good physical condition (r=0.60, P=0.064) and fair physical condition (r=0.70, P=0.017), whereas the proportion of mule deer in poor physical condition was negatively correlated with rainfall (r= -0.72, P=0.20) [218]. In the Trans-Pecos region of Texas, abundance of adult mule deer (R=0.645, P≤0.001) and fawn production (R=0.553, P≤0.003) were correlated to the Palmer Hydrologic Drought Index, indicating that the mule deer population was negatively affected by drought [352]. At Three Bar Wildlife Area in Arizona, survival of mule deer fawns in a given year varied with total rainfall during the previous winter. This relationship appeared to result mainly from the influence of precipitation on production of winter-growing forbs: Variation in forb production accounted for about 75% of the total variation in fawn survival during the 8-year study [303]. A severe, year-long drought in desert grassland of southeastern Arizona caused an apparent decline in local mule deer and white-tailed deer populations [11].

Black-tailed deer may have high mortality during hot, dry summers in California chaparral [14,90,323,324]. In this habitat, there is typically an abrupt decline in forage quality in June and July as vegetation desiccates. During dry summers, black-tailed deer mortality may be high if forage desiccates early, while fawns are nursing. In addition, years of low acorn production may lead to high mortality in August and September. Conversely, because the acorn drop is coincident with the breeding period, years of good acorn production may improve breeding conditions of bucks and does, resulting in increased fawn production [14,323].

Major predators of mule deer include coyotes (Canis latrans), mountain lions (Puma concolor), gray wolves (Canis lupus), bobcats (Lynx rufus), brown bears (Ursus arctos), American black bears (Ursus americanus), and humans [7,78,121,215]. Golden eagles (Aquila chrysaetos) are common predators of young [7,78,215]. Predators may kill mule deer of all sexes and ages and in all physical conditions [44,78,154]. For more information, see Predation risk.

According to reviews, the oldest male from a captive population was 22 years old, and the oldest female was 16 years old [215]. In wild populations, the oldest male was 19 years old, and the oldest female was 20 years old [7]. However, in wild populations, males seldom live longer than 8 years, and females seldom live longer than 14 years [215].

• Predators
• Diseases and parasites
• Malnutrition and weather
• Fawn survival

Average lifespan
Status: captivity: 22 years.

Maximum longevity: 22 years (captivity) Observations: One captive female lived 20.5 years (Richard Weigl 2005). A semicaptive reportedly lived 22 years (Ronald Nowak 1999).

More info for the terms: cover, density, parturition, shrubs, wildfire

Gestation ranges from 183 to 218 days [7,58,215]. In the northern part of the mule deer's distribution, parturition occurs primarily from late May to mid-July [215]. In the southern part, parturition occurs primarily in July and August [215,290]. Extreme birth dates occur as early as mid-May and as late as early October [7]. Like the rut, fawning periods tend to occur within a short period. In Utah (Robinette and others 1977 cited in [5]) and Colorado (Anderson and Medina 1967 cited in [5]), for example, about 85% of fawns were born within a 32-day period. However, a long fawning period may be more typical in arid areas of the Southwest where rainy seasons are unpredictable. In Arizona, fawning coincided with the summer monsoon season and in one study ranged from 5 August to 5 October [115].

Growth: As parturition approaches, pregnant females move to fawning areas. Does with fawns may remain in these areas until late summer or fall [215]. Fawns weigh from 4.5 to 11 pounds (2.0-5.0 kg) [5,7,215]. Singletons weigh more than fawns from litters with ≥2 fawns [5]. Males and females tend to weigh the same at birth [5], although among sets of twins of opposite sex, males may be heavier [7]. A fawn's birth weight may affect its survival. A review stated that the effect of a maternal doe's physical condition on fawn birth weights is unclear. However, females in good physical condition the year before parturition may have a shorter gestation and/or give birth earlier than females in poor physical condition [215].

Newborn fawns hide and may be separated from their mothers for long periods. The hiding period lasts for 6 to 8 weeks [119]. Fawns begin to consume green vegetation at 2 weeks old and are weaned in fall, when their mothers breed again [7,14,102,215]. Young remain with their mothers until the following spring, when their mothers drive them away before giving birth [215]. For more information, see Social behavior.

Fawns grow rapidly, with males tending to be heavier than females. Yearling females weigh about 10% less than yearling males on average [215]. Anderson and others [6] concluded that male mule deer on the Roosevelt National Forest continued to gain weight throughout their lives, whereas females reached their maximum body weight at about 8 years old. In contrast, Mackie (1964 cited in [215]) concluded that males in Montana gained weight until at least 7.5 years old, whereas female weight changed little after 2.5 years old.

Most mule deer attain sexual maturity and can breed as yearlings [215]. However, yearling males are frequently prevented from mating by older males [215]. Fawns may become pregnant, but this is rare in the wild [215,322]. The age at first parturition is influenced by nutritional condition. In severely malnourished populations, the age at first parturition may be ≥3.5 years old [215].

Pregnancy and twinning rates: Adult mule deer commonly produce twins, whereas yearlings usually produce singletons; triplets and quadruplets are rare [5,77,215]. Pregnancy rates are influenced by local environmental conditions and nutritional status of does. In the Missouri River Breaks region of Montana, mule deer produced an average of 44% singletons, 55% twins, and 1% triplets during 12 years. During times with the poorest range conditions, mule deer produced 75% singletons, 25% twins, and no triplets. During times with the best conditions, they produced 27% singletons, 70% twins, and 3% triplets [129]. According to a review, triplets are born mainly to >4-year-olds [5].

Pregnancy rates range from 70% to >90% among adult (≥1.5-year-old) females. Yearlings typically have lower pregnancy rates than adults [215]. At Hopland Research and Extension Center, California, wild black-tailed deer fawns bred when the population was experimentally reduced from 25 to 10 black-tailed deer/km². The author suggested that the reduced population density resulted in rapid body growth and early maturation [227]. In the Missouri River Breaks region, 4-, 5-, and 6-year-old mule deer females were the most productive segment of the population. Reproduction declined sharply at 7 years old. Females ≥8 years old had reproductive levels similar to that of 3-year-olds, which were 12% to 21% lower than levels of 4-, 5-, and 6-year olds [130]. Reproduction in males may decline at 7 years old [5].

The number of fawns per doe varies with range quality [293]. The number of mule deer fawns per doe on "poor" Utah juniper/big sagebrush rangeland in south-central Utah was 64% of that on "good" Utah juniper/big sagebrush rangeland in southern Idaho [164]. In California chaparral, the black-tailed deer fawn:doe ratio was <85:100 in dense, tall chaparral. It was 147:100 in areas where repeated prescribed fires and seeding of grasses and legumes resulted in a mosaic of grasslands with scattered areas of dense chaparral, and it was 116:100 in an area burned in a summer wildfire 2 years previously that had large areas of small shrubs and very little herbaceous cover [320,322]. Taber [323] suggested that a diet low in protein and phosphorus resulted in low ovulation and reproductive rates of black-tailed deer living in the dense chaparral.

In the arid Southwest, the abundance of forage is frequently controlled by seasonal rainfall, and Hungerford [156] suggested that precipitation during the summer may be the most important factor regulating mule deer fawn production and survival. On the Kaibab Plateau in Arizona, a dry summer resulted in the lowest fawn production on record (28 fawns:100 does) [319]. In another study, fawn production on the Kaibab National Forest, north-central Arizona, averaged 90% 5 years after about 10% of the mule deer summer rangeland was treated. Slash piles were burned and grasses, legumes, and shrubs were seeded in forested areas. Some forested areas were also logged. Meadows, which were historically overgrazed, were disked and seeded. Fawn production during the 5 years prior to treatments averaged 66%. The author suggested the increased fawn production was a result of increased forage productivity due to the treatments [156].

More info for the term: polygamous

One review described mule deer as polygamous, with bucks wandering about extensively and seeking individual does in estrus [215]. Other reviews described them as polygynous [7,119], with a tending bond system where a doe seeks out a dominant buck and the buck tends to the doe until she is bred [7,119,121]. The largest bucks with the largest antlers are dominant and breed most often [7,215].

The breeding season (rut) begins as early as September and ends as late as March, depending upon location [7,215]. Within a given location, however, breeding tends to occur within a short period [7]. For example, in the Missouri River Breaks region of eastern Montana, 75% of pregnant does conceived between 21 November and 1 December [129]. A single buck may breed many females, and a single doe may breed several times during a single estrous period [58,215]. Yearling (1- to 1.5-year-old) females tend to breed 3 to 4 weeks later than adults [14,102].

The interval between estrous periods ranges from 22 to 29 days, although in black-tailed deer the estrous cycle may shorter. True estrus lasts 24 to 36 hours [5,7,58,215]. As many as 5 estrous periods may occur when does repeatedly fail to conceive [7,102].

Odocoileus hemionus is a polygynous species, having a tending-bond type breeding system. Courtship and mating occur within the group (Geist 1981). A dominant male tends an estrus female until mating or displacement by another male occurs. Dominance is largely a function of size, with the largest males, which possess the largest antlers, performing most of the copulations (Kucera 1978). Most O. hemionus females conceive during their second year and only rarely during their first year. The breeding peak in O. hemionus occurs mainly from late November through mid-December. The average gestation length is 204 days. The peak birth period in O. hemionus is estimated to be from June 16th to July 6th, with most births occurring in June. The time of birth varies according to the environment. Robinette (1977) calculated that a 305-m rise in elevation is associated with a 7-day delay in the birth period. The mass at birth of O. hemionus ranges from 2 to 5 kg. Mass at birth is affected by litter size and sex, with males being heavier. The common liter size is two, with mothers in their first or second breeding year most frequently producing singletons. Weaning begins at about 5 weeks of age and usually is completed at age 16 weeks. Full development of most skeletal attributes occurs at about 49 months of age in males and 37 months of age in females. However, gains in carcass mass are continuous until an age of 120 months in males and 96 months in females. In O. hemionus, male neonates predominate when poor nutrition prevails about 6 weeks before, and during, the breeding period. Ovulation in female O. hemionus occurs about 12 to 14 hours after estrus terminates. Approximately 27 to 29 days elapse between conception and implantation in female O. hemionus. Among male O. hemionus, testicular mass and volume are maximal during November and minimal during April and May (Anderson 1984).

Average birth mass: 2950 g.

Average gestation period: 207 days.

Average number of offspring: 1.5.

Average age at sexual or reproductive maturity (male)
Sex: male: 503 days.

Average age at sexual or reproductive maturity (female)
Sex: female: 478 days.

Mule deer mate in autumn, often mainly late November to mid-December. Gestation lasts about 203 days Births occur in late spring, mostly in May-June in much of the range, sometimes as late as July or August. Litter size is 1-2, depending on age and condition of female. Fawns are born with spotted pelage and initially stay hidden. They lose their spots generally by late summer or early fall. Weaning begins at about 5 weeks, usually completed by 16 weeks. Males usually first breed at 2 years, males at 3-4 years.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

There are 2 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

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Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 13
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 1996
  Lower Risk/least concern

All federal, state, and provincial land and wildlife management agencies recognize the fundamental need to maintain O. hemionus ranges and keep them habitable. To counter the trend of agricultural development, rangeland conversion, mining, road and highway construction, and the development of housing tracts, many states and provinces have purchased critical areas, especially winter ranges, to maintain the various habitats of O. hemionus. But, due to political opposition to government acquisition of privately owned lands, plus a scarcity of funds for this purpose, only a small fraction of O. hemionus ranges has been acquired by the government. The effects of reduced O. hemionus ranges can be mitigated by better management of the remaining lands to maximize their productiviy for O. hemionus. Various habitat management programs include the manipulation of livestock grazing, the manipulation of cultivative communities, and the manipulation of vegetative communities. For O. hemionus, the optimal successional stages are subclimax plant communities that can be perpetuated only through the influence of humans. Since O. hemionus production is not the primary management goal on most private or public lands in western North America, O. hemionus habitat improvement programs typically involve a complex process of coordination among bureaucracies with missions that are usually not compatible (Wallmo 1981).

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Comments: Extensive, intensive land use by humans can reduce, eliminate, or displace local mule deer populations, but many kinds of human activities, particularly those that generate patches of early successional growth in heavily forested areas, may improve the habitat for deer. Grazing/browsing by domestic sheep in dry environments reduces the capacity of the habitat to support deer (e.g., see Hall 1946).

Grinnell (1914) suggested that an absence or extreme scarcity of mule deer along part of the lower Colorado River (Arizona-California) probably was due to "rapid settlement of the river bottom." Presumably this involved habitat loss as well as excessive hunting (Grinnell suggested that hunting by miners eliminated bighorn sheep from Riverside Mountain, also along the lower Colorado River).

Chronic wasting disease (CWD) is a transmissable spongiform encephalopathy of mule deer, white-tailed deer, elk, and moose. It is caused by infectious agents known as prions (an abnormal form of a normal protein). Symptoms include lesions on the central nervous system, behavioral abnormalities, and, most obviously, chronic weight loss.CWD is always fatal. First recognized in captive mule deer in Colorado, CWD now occurs in the wild and has spread to at least dozen states and two Canadian provinces. It may be spread from one animal to another via saliva, feces, or possibly other body fluids. CWD does not cause rapid, widespread die-offs of deer, but there is concern about the long-term effects of the disease. No practical methods of CWD eradication are known; the focus thus far has been on learning more about CWD and how it is transmitted, and on preventing the disease from spreading by banning the transportation of live cervids across state lines.

More info for the terms: cover, fire exclusion, fire frequency, forbs, frequency, fuel, litter, presence, succession, xeric

Mule populations were reduced substantially following European settlement. By 1900 populations had declined due to overgrazing by livestock, overharvesting, drought, agriculture, and land development [30,287,340]. From the 1910s to the 1950s, however, widespread logging, fire, and predator reduction programs benefited mule deer, and populations in some areas were higher than they had been historically [340]. Encroachment of woody plants onto some areas of the Southwest and Great Basin that were formerly dominated by grasses due to livestock grazing, alterations of fire patterns and fire exclusion, and possibly climatic shifts, have increased winter cover and forage for mule deer [17,127,216,290,340]. Increases of woody plants were followed by dramatic increases in mule deer populations [17,340]. However, such changes also resulted in reduced summer rangelands, and intensive cultivation and development further reduced habitats for mule deer [340]. By the 1940s and 1950s, many mule deer populations exceeded carrying capacity [330,340]. In the mid-1960s and early 1970s, mule deer populations declined sharply over much of the United States [201,340]. The decline was attributed to habitat losses from urbanization and other land development, fire exclusion, vegetation succession, conversion of shrublands to grasslands, and deterioration of winter ranges due to excessive use by large ungulate populations [153,201,340]. In some areas, repeated wildfires have resulted in the conversion of native shrub-grass habitats to environments dominated by nonnative invasive plants such as cheatgrass (Bromus tectorum). These changes have had substantial negative impacts on mule deer [330]. Beginning in the late 1970s and early 1980s, mule deer numbers continued to decline in some areas but remained stable or increased in others [340].

Threats to mule deer populations include overharvesting, increased human disturbance, and nonnative invasive plants:

Human disturbance: Mule deer may habituate to human presence and become nuisances in some areas. However, human development generally reduces mule deer use of developed areas [215,347].

Nonnative invasive plants: Spread of nonnative invasive grasses and forbs may harm or benefit mule deer. Some researchers found that mule deer commonly consume nonnative invasive plants, including spotted knapweed (Centaurea maculosa) (e.g., [50,105,190,206,244,270,278,368]). Along the Selway River in Idaho, mule deer ate spotted knapweed seedheads, particularly when snow was on the ground, because the seedheads were easily obtainable above the snow. In fact, they were one of the few herbaceous plants readily available to mule deer in open areas when snow was >12 inches (30 cm) deep. Mule deer also ate large amounts of spotted knapweed rosettes, particularly in spring after snowmelt [368]. Mule deer consumed green shoots of cheatgrass and rosettes of tumble mustard (Sisymbrium altissimum) in late winter and spring after several wild and prescribed fires in Lava Beds National Monument, California [261].

Some sources suggested that the carrying capacity of rangeland for mule deer and livestock may be reduced by nonnative invasive plants that displace more palatable native grasses and forbs (e.g., [46,105,206,271]). In the Bitterroot Valley, Montana, mule deer rarely used spotted knapweed-dominated open areas [360]. However, along the Selway River in Idaho, where densities ranged from 0.03 to 0.17 mule deer/ha during winter, spotted knapweed infestations of xeric south and west-facing slopes on year-round rangeland did not appear to affect mule deer carrying capacity in winter when compared with Saskatoon serviceberry/bunchgrass-sedge shrubfields [368]. Wright and Kelsey [368] attributed differences between the studies to lower mule deer densities, greater availability of agricultural lands, and less snow cover in the Bitterroot Valley study.

Mule deer may contribute to the spread of nonnative invasive plants by ingesting, transporting, and disseminating viable seeds of nonnative invasive plants in their feces [25,89,139,240,244,342,343]. In maritime chamise-La Purissima manzanita (Arctostaphylos purissima) chaparral habitats in Santa Barbara County, California, mule deer dispersed seeds of hottentot fig (Carpobrotus edulis), a nonnative invasive plant, into recently burned areas [89].

The spread of cheatgrass has important indirect effects on mule deer and other wildlife by increasing fuel loads and fire frequency, which may alter the structure and composition of native plant communities. Because sagebrush communities provide important winter rangelands for mule deer and sagebrush is easily killed by fire, cheatgrass invasion may be particularly detrimental to mule deer in sagebrush habitats [270,371]. Buildup of medusahead (Taeniatherum caput-medusae) litter may also lead to increased fuel loads and more frequent fires in low sagebrush (Artemisia arbuscula) and other sagebrush communities [271]. For more information, see FEIS reviews of cheatgrass, medusahead, and other species of interest.

Major Threats

More info for the term: density

Mule deer are hunted by humans throughout their range [78]. Hunting can alter population density, sex ratios, behavior, movements, and life span [78,327]. Historically, overhunting has reduced mule deer populations (See Threats). See Connelly [78] for a review of hunting effects on mule deer populations.

More info for the terms: cover, density, dispersion, fire management, forbs, hardwood, mast, natural, prescribed fire, presence, shrub, shrubs, succession, tree

Disturbance can produce habitat for mule deer by favoring forage growth and by creating ecotones between areas of dense cover and more open feeding areas. Conversely, loss of cover over large areas can be detrimental to mule deer [135,215]. Several researchers suggested that resource managers may need to consider proximity of food, cover, and water before implementing actions that may impact mule deer habitats [153,215,216].

• Prescribed fire
• Logging
• Other treatments
• Livestock grazing
• Water management

Prescribed fire: For information on the use of prescribed fire in mule habitats, see Fire Management Considerations.

Logging: With the exception of black-tailed deer in British Columbia and southeastern Alaska, which are dependent upon canopy cover in mature forests [134,135,215,325,350], mule deer generally benefit from early successional vegetation that establishes after logging and other disturbances [135,215]. Logging may benefit mule deer because early-seral habitats often contain a greater variety, quantity, and quality of mule deer forage than mature forests (e.g., [39,72,98,137,269,290,304,310,325,349]). However, forage quantity and quality may not increase immediately in logged areas and may last only 20 to 30 years (e.g., [134,147,215,269,310,350]). In addition, cover may be reduced [310]. A review stated that clearcutting of old-growth forests in southeastern Alaska has 4 potential effects may decrease the carrying capacity of habitat for black-tailed deer: 1) sun-grown plants in open clearcuts may have lower digestible protein concentrations than shade-grown plants in forests; 2) large amounts of logging slash may increase energy costs of locomotion for black-tailed deer and reduce the area of usable habitat; 3) snow may accumulate and persist more in open clearcuts than in forests; and 4) understory production may be reduced to extremely low levels when the conifer canopy closes; this may occur at about 20 to 30 years after logging and persist for 100 years or more [134].

In general, the duration of logging benefits to mule deer varies with forest type, soils, climate, and other factors. Use of prescribed fire, herbicides, soil scarification, planting of seeds and seedlings, and other site preparation may shorten or lengthen the time a logged site is used by mule deer [134,147,215]. For example, burning young clearcuts in southeastern Alaska may benefit black-tailed deer by reducing shrub and conifer biomass and increasing the diversity of herbaceous forage plants, thus potentially delaying conifer canopy closure [134]. In addition, succession following clearcutting may be affected by heavy mule deer browsing. For more information, see Mule deer foraging effects. Mule deer use of logged areas is modified by opening size, logging slash, predisturbance movement patterns, and weather, particularly snow depth. Reviews of logging effects on mule deer are available: [72,134,351].

Opening size: The size and distribution of clearcuts in space and time are important to mule deer; this is likely also true of burned sites. In the boreal forest zone in western Alberta, the size and dispersion of 2- to 9-year-old clearcut blocks and type of treatment best explained mule deer and white-tailed deer use of clearcuts (R²=0.21, P<0.01). Deer showed a strong preference for clearcut blocks that were <40 acres (16 ha); because they preferred areas within clearcuts that were <330 feet (100 m) from cover, they favored configurations that provided a high degree of edge per unit area. They also preferred clearcuts that were scarified or scarified and burned under prescription compared with untreated clearcuts. The authors suggested that such treatments may have led to greater abundance of preferred herbaceous species and reduced logging slash, which benefited deer. Clearcut blocks in clumped patterns appeared unfavorable [334]. Some authors suggested that many small, scattered, irregularly shaped clearcuts may be preferable to fewer, large, block-shaped clearcuts because multiple small treatments would contact the home ranges of more mule deer [135,334]. A review stated that deer used natural and created openings in ponderosa pine forests similarly, particularly when thinned stands occurred nearby, but in dense stands, deer likely benefited from small openings [72]. For more information, see Edge habitat. See the review by Wallmo and Schoen [351] for management recommendations regarding sizes of clearcut openings in various regions.

Logging slash: Depending upon its density, logging slash may be a benefit or a detriment to mule deer. Reviews stated that abundant logging slash generally impedes mule deer movements and may act as a barrier to mule deer use of clearcut openings and selectively logged areas [63,135,351]. Conversely, some logging slash can provide cover for mule deer [351]. In quaking aspen stands on the Apache and Coconino National Forests, Arizona, deer use was lower in thinned quaking aspen stands without slash removal despite greater density of perennial grasses, forbs, and quaking aspen sprouts in these stands compared to unthinned stands. Apparently, the amount of woody debris in thinned stands prohibited deer use [268]. In southeastern Alaska, dense logging debris apparently impeded black-tailed deer use of 1- to 2-year-old clearcuts in western hemlock-Sitka spruce forest. Dense logging debris continued to impede black-tailed deer until 15 to 20 years after logging [350]. Mule deer pellet group counts in clearcut strips in subalpine lodgepole pine and spruce-fir forest in Colorado were less than those on adjacent uncut sites during the first year after logging, possibly due to the deep tangle of residual slash and disturbance of logging operations. However, 10 years after strip clearcutting, pellet group counts were 2 times higher on clearcut strips than on adjacent uncut strips [344]. In a selectively cut ponderosa pine forest in Arizona, deer pellet groups were more numerous where slash was undisturbed after logging. Slash abundance was 1.7 times greater where slash was undisturbed than where it was piled and burned, but forbs were more abundant where slash was piled and burned, which should have attracted deer. The author suggested that deer may have preferred the site where slash was undisturbed because the slash provided protective cover [266]. In north-central Arizona, mule deer use was higher on clearcuts where the slash had been piled and burned than on clearcuts where slash had been piled but not burned [189]. In Arizona, Neff (1980 cited in [72]) found that deer showed no preference for either the presence or absence of slash in small (1-10 acres (0.4-4.0 ha)) openings in ponderosa pine stands.

A review recommended prescribed fire in southeastern Alaskan forests after clearcutting to reduce logging slash, reduce shrub biomass, favor herbs, reduce conifer regeneration, and prolong the useful life of clearcuts for mule deer, at least in snow-free seasons or areas [135]. In juniper woodlands in Texas, Bryant [57] suggested that 10% to 15% of cleared areas should contain slash to provide cover for mule deer. Black-tailed deer may also benefit from reduced logging slash that potentially impedes their movements [134]. For more information, see Indirect Fire Effects.

Logging and weather interactions: Mule deer may not use clearcuts because of deep snow compared to forests [357]. In the interior western redcedar-western hemlock subzone near Horsefly, British Columbia, mule deer tracks during a year of low snowfall were half as abundant in clearcuts as in uncut forest. Snow was 17 inches (44 cm) deep in openings and just 10 inches (26 cm) deep in forests, suggesting that deep snow in clearcuts may have reduced forage access and thus use of clearcuts [357]. For more information, see Foraging sites.

Other treatments:
Sagebrush and pinyon-juniper: Removal of shrubs and trees in sagebrush and pinyon-juniper ecosystems is a common management practice on mule deer rangelands. In sagebrush and pinyon-juniper ecosystems, large areas have been treated mechanically, with prescribed fire, or with herbicides to try to convert them to grass-shrub or grass types [66,347]. Such treatments in sagebrush communities may reduce important winter forage for mule deer [91]. Partial or complete removal of trees in pinyon-juniper communities may result in substantial increases in production of grasses, forbs, and shrubs, which could potentially increase mule deer carrying capacity [66], but according to a review, this practice produces mixed results. Some studies showed increased mule deer use of treated pinyon-juniper sites, typically due to greater amounts of forage and browse on treated areas, while other studies did not show increased mule deer of treated areas, typically because of reduced cover in these areas [2]. On the Zuni Indian Reservation in western New Mexico and eastern Arizona, mule deer pellet groups increased with the number of pinyon and juniper trees removed (R²=0.95, P=0.03) [2]. A similar increase did not occur on 2- to 24-year-old pinyon-juniper rangelands in Utah that were chained and seeded with grasses, forbs, and shrubs. The authors suggested that treated sites were used despite decreased cover because of increased forage [299]. At Fort Bayard, New Mexico, mule deer abundance in Colorado pinyon (Pinus edulis)-juniper habitat was higher before than after tree removal. Mule deer forage increased after tree removal, but the authors concluded that the absence of cover reduced mule deer use [294]. In a review, Phillips [256] stated that chained pinyon-juniper stands did not benefit mule deer and other wild ungulates until trees and shrubs established [299]. Other researchers reported that treatment of pinyon-juniper rangelands did not affect mule deer habitat use. Mechanical and herbicide treatments on 5,200 acres (2,100 ha) of pinyon-juniper rangeland in Arizona resulted in no differences in mule deer use of the area (Neff 1980 cited in [290]).

Mule deer use pinyon-juniper woodlands in all stages of succession [2]. How long each stage is utilized depends in part on site, composition of the understory prior to disturbance, the type of disturbance, weather conditions, postdisturbance treatments such as seeding, and livestock grazing [290]. In general, the usefulness of pinyon-juniper habitats to mule deer declines as the understory and midstory decline [295]. Based upon studies in west-central Utah, posttreatment production of forbs and grasses generally diminishes to pretreatment levels in <20 years; shrubs increase up to 40 years after treatment; and at 40 years, juniper and pinyon again dominate the site [21]. In Nevada, annual and perennial forbs dominated for 1 to 2 years after canopy removal; perennial grasses dominated in the 2nd year and reached maximum abundance in the 4th year. Shrubs reached a peak after grasses, between the 1st and 3rd posttreatment years, and trees regained dominance in <15 years [329].

According to a review, published literature is "nearly unanimous" in recommendations for pinyon-juniper management for mule deer and other wild ungulates: 1) keep openings small and close to escape cover, usually 0.1 to 0.2 mile (0.16-0.32 km) maximum; 2) locate projects near areas of historical big game usage; and 3) leave browse plants untreated or reestablish following treatments [2]. These authors provide management recommendations for mule deer and other ungulates in pinyon-juniper communities: [57,290,295]. See Great Basin woodlands for information about fire effects on mule deer in pinyon-juniper communities. For a review of the effects of management practices in sagebrush steppe on mule deer—including topics not discussed here such as management of sagebrush with herbicides, fertilizing sagebrush habitats, and reseeding after sagebrush reduction—see Carpenter and Wallmo [66]. See Great Basin shrublands for information about fire effects on mule deer in sagebrush communities.

Gambel oak: Gambel oak is an important mule deer forage species; both its mast and browse are used extensively. It may form almost pure stands in some areas. Because of its growth habit, however, it often forms impenetrable thickets that are too tall or inaccessible for mule deer [66,186]. Methods used to treat Gambel oak communities include prescribed fire, logging, and herbicides. Clearcutting patches in Gambel oak habitat may produce abundant browse because of Gambel oak's sprouting ability, but this would temporarily reduce acorns. Selective cutting, in which the best acorn-producing trees are left, was recommended by Severson and Medina [290] to ensure both browse and acorn production at a single location. A review stated that treating Gambel oak stands with prescribed fire or mechanical methods may increase mule deer use of treated stands up to 4 times but that use declines as time since treatment increases and stands become dense and inaccessible [186]. In Colorado, dense Gambel oak stands were sprayed with herbicides. Two years after spraying, grasses increased 44% compared with pretreatment levels, while shrubs decreased 29% and forbs decreased 15%. Five years after spraying, grasses were 17% below pretreatment levels and shrubs were 7% below pretreatment levels. Consequently, herbicide treatment was considered beneficial to mule deer for only a brief time, and frequent retreatment was considered necessary to maintain high-quality habitat for mule deer [180]. See Southwest shrublands for information about fire effects on mule deer in Gambel oak communities.

Livestock grazing: Influences of livestock grazing on mule deer can be detrimental, neutral, or beneficial [67,153,216,290]. Grazing, as well as the physical presence of cattle, domestic sheep (Ovis aries), and other livestock can have negative impacts on mule deer not only by reducing forage and changing ratios of live to dead plant material [8,153,290,361,362], but by causing changes in movements and behavior and altering activity budgets [67,67,169,216,263,290]. However, some researchers reported few or no effects of livestock grazing on mule deer in areas where livestock grazing intensity was low or moderate [18,67,153,290]. Livestock grazing in many perennial grasslands historically increased shrub and annual grass-forb types, potentially benefiting mule deer (see Threats) [153,216,290]. In other areas, heavy livestock grazing reduced shrubs and herbs important as mule deer forage [216]. Reviews noted that livestock grazing on the northern Great Plains has extensively reduced or eliminated hardwood tree and shrub cover along drainageways, which has limited the occurrence of mule deer in some areas [287,290]. In the Sierra Nevada, cattle grazing during peak fawning season reduced hiding cover for fawns in both quaking aspen and meadow-riparian habitats compared with areas without cattle grazing [169,197]. Reviews stated that livestock management practices and factors that may affect mule deer include weather, topography, water availability, rangeland type, grazing intensity, animal distribution, livestock species, grazing system, and timing and duration of grazing. Timing of livestock grazing was considered particularly important to mule deer, which are particularly susceptible to adverse effects during fawning [17,67,153,169,215,216,290,290].

Water management: On some arid ranges of the Southwest, water development and better distribution of water sources for livestock can benefit mule deer by permitting year-round or seasonal use of rangelands from which they may have been excluded by a lack of free water (see Water) [153,215,216,280]. Mule deer numbers increased during the 5 years following development of permanent water sources on areas of Fort Stanton, New Mexico, that had little or no free water previously. In one area, use increased from <1.6 to >13 mule deer/mile² in 5 years. In another area, use increased from 14.2 to 19.2 mule deer/mile² in 1 year, dropped to 9.4 mule deer/mile² in the 4th year when water sources deteriorated, and increased to 22.1 mule deer/mile² in the 5th year when water was again available [367]. However, water developments may concentrate livestock and deer, leading to degradation of some habitats [153,215,216]. Furthermore, redistribution of livestock through water development may increase overlap of mule deer and livestock on areas previously occupied by mule deer but not livestock [153,216]. For more information, see the review by Mackie and others [215].

Federal legal status: The Cedros Island mule deer is Endangered [337].

Other status: Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe, although recent changes in status may not be included.

Other management information:

• Threats
• Habitat management
• Population management

Conservation Actions

Management Requirements: Cattle grazing results in loss of hiding cover for fawns, possibly may increase rate of loss of fawns to predation (Loft et al. 1987). On summer range in the Sierra Nevada in California, cattle evidently competed with deer, particularly at high stocking rates and during a year of below-average precipitation; adverse effects could be reduced by reducing or eliminating cattle grazing during early summer on all or part of a grazing allotment (Kie 1991; see also Loft et al. 1991 for further evidence of cattle-induced habitat shifts by mule deer).

See Wood and Wolfe (1988) for discussion of viability of intercept feeding to reduce deer-vehicle collisions.

See Andelt et al. (1991) for information on the relative effectiveness of various repellents for reducing damage to plants (when the deer were moderately hungry, even the best repellents failed to deter browsing).

Douglas fir and Ponderosa pine are of major economic importance for commercial timber. However, these trees are browsed heavily by O. hemionus. Browsing of other trees is seldom considered an economic problem. In the Douglas fir region, O. hemionus browses on trees during both the dormant and growing seasons. Practices that encourage the growth of O. hemionus populations can therefore also encourage damage. Douglas fir is harvested mainly by clearcutting and is regenerated by planting with nursery-grown stock. O. hemionus is attracted to clear-cuts, and Douglas fir is an acceptable and sometimes preferred forage species. This situation invites browsing of sufficient intensity to influence forest regeneration in many areas (Wallmo 1981).

Odocoileus hemionus is of tremendous interest to hunters. Populations of O. hemionus that are large enough to support hunting during two or three weeks in autumn offer countless recreational opportunities for the public. This desire to hunt generates revenue for the economy (Wallmo 1981).

Comments: Browsing on juvenile fruit trees in northern Utah had no effect on tree growth or initial fruit production (Great Basin Nat. 52:352).