The Mule Deer (Odocoileus hemionus) is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer.

Unlike the related white-tailed deer (Odocoileus virginianus), which is found throughout most of North America east of the Rocky Mountains and in the valleys of the Rocky Mountains from Idaho and Wyoming northward, mule deer are only found on the western Great Plains, in the Rocky Mountains, in the southwest United States, and on the west coast of North America. Mule deer have also been introduced to Argentina and Kauai, Hawaii.

Mule deer can be divided into two main groups: the mule deer (sensu stricto) and the black-tailed deer. The first group includes all subspecies, except O. h. columbianus and O. h. sitkensis, which are in the black-tailed deer group. The two main groups have been treated as separate species, but they hybridize, and virtually all recent authorities treat the mule deer and black-tailed deer as conspecific. Mule deer apparently evolved from the black-tailed deer. Despite this, the mtDNA of the white-tailed deer and mule deer is similar, but differs from that of the black-tailed deer. This may be the result of introgression, although hybrids between the mule deer and white-tailed deer are rare in the wild (apparently more common locally in West Texas), and the hybrid survival rate is low even in captivity. Many claims of observations of wild hybrids are not legitimate, as identification based on external features is complicated.

Some authorities have recognized O. h. crooki as a senior synonym of O. h. eremicus, but the type specimen of the former is a hybrid between the mule deer and white-tailed deer, so the name O. h. crooki is invalid. Additionally, the validity of O. h. inyoensis has been questioned, and the two insular O. h. cerrosensis and O. h. sheldoni may be synonyms of O. h. eremicus or O. h. peninsulae.

The 10 valid subspecies (some of which are in the following galleries), based on the third edition of Mammal Species of the World, are:

• Mule deer (sensu stricto) group:

  • O. h. californicus – California mule deer

  • O. h. cerrosensis – Cedros/Cerros Island mule deer; named after Cedros Island, the only place the subspecies is found

  • O. h. eremicus – desert/burro mule deer; found in the Lower Colorado River Valley, northwestern Mexico, southeastern California, and Arizona

  • O. h. fuliginatus – southern mule deer; found in southernmost California and Baja California

  • O. h. hemionus – Rocky Mountain mule deer; found in western and central North America

  • O. h. inyoensis – Inyo mule deer; named after Inyo County, California and found in the Sierra Nevada mountain range in California

  • O. h. peninsulae – peninsular mule deer; found in Baja California Sur

  • O. h. sheldoni – Tiburon Island mule deer; found on Tiburón Island

• Black-tailed deer group:

  • O. h. columbianus – Columbian black-tailed deer; found in the Pacific Northwest and Northern California regions

  • O. h. sitkensis – Sitka deer; named after Sitka, Alaska and found in the coastal area and islands off western British Columbia

The most noticeable differences between white-tailed and mule deer are ear size, tail color, and antler configuration. In many cases, body size is also a key difference. The mule deer's tail is black-tipped, whereas the white-tailed deer's is not. Mule deer antlers are bifurcated; they "fork" as they grow, rather than branching from a single main beam, as is the case with white-taileds.

Each spring, a buck's antlers start to regrow almost immediately after the old antlers are shed. Shedding typically takes place in mid-February, with variations occurring by locale.

Although capable of running, mule deer are often seen stotting (also called pronking), with all four feet coming down together.

California Mule Deer (Odocoileus hemionus californicus) - seen in many locations over many years in California

Columbian Black-tailed Deer (Odocoileus hemionus columbianus) - Seen in the Olympic Peninsula and Rainier area

Desert Mule Deer (Odocoileus hemionus eremicus) - Texas, Davis Mountains

Rocky Mountain Mule Deer (Odocoileus hemionus hemionus) Kaibab Plateau population - North Rim of Grand Canyon

Rocky Mountain Mule Deer (Odocoileus hemionus hemionus)

Inyo Mule Deer (Odocoileus hemionus inyoensis) - East Side of Sierra in June Lake Area

 Sitka Black-tailed Deer (Odocoileus hemionus sitkensis) - Knight Inlet British Columbia

The White-tailed Deer (Odocoileus virginianus), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced to New Zealand, all the Greater Antilles in the Caribbean (Cuba, Jamaica, Hispaniola, and Puerto Rico[3]), and some countries in Europe, such as the Czech Republic, Finland, France, Germany, Romania and Serbia.[4][5] In the Americas, it is the most widely distributed wild ungulate.

In North America, the species is widely distributed east of the Rocky Mountains as well as in southwestern Arizona and most of Mexico, except Lower California. It is mostly displaced by the black-tailed or mule deer (Odocoileus hemionus) from that point west except for mixed deciduous riparian corridors, river valley bottomlands, and lower foothills of the northern Rocky Mountain region from Wyoming west to eastern Washington and eastern Oregon and north to northeastern British Columbia and southern Yukon, including in the Montana valley and foothill grasslands. The westernmost population of the species, known as the Columbian white-tailed deer, was once widespread in the mixed forests along the Willamette and Cowlitz River valleys of western Oregon and southwestern Washington, but current numbers are considerably reduced, and it is classified as near-threatened. This population is separated from other white-tailed deer populations.

Texas is home to the most white-tailed deer of any U.S. state or Canadian province, with an estimated population of 5.3 million. High populations of white-tailed deer exist in the Edwards Plateau of central Texas and all of Pennsylvania. Michigan, Minnesota, Iowa, Mississippi, Missouri, New Jersey, Illinois, Wisconsin, Maryland, New York, North Dakota, Ohio, and Indiana also boast high deer densities. The conversion of land adjacent to the Canadian Rockies to agriculture use and partial clear-cutting of coniferous trees, resulting in widespread deciduous vegetation, has been favorable to the white-tailed deer and has pushed its distribution to as far north as Yukon. Populations of deer around the Great Lakes have expanded their range northwards, also due to conversion of land to agricultural use, with local caribou, elk, and moose populations declining.

Some taxonomists have attempted to separate white-tailed deer into a host of subspecies, based largely on morphological differences. Genetic studies, however, suggest fewer subspecies within the animal's range, as compared to the 30 to 40 subspecies that some scientists have described in the last century. The Florida Key deer, O. v. clavium, and the Columbian white-tailed deer, O. v. leucurus, are both listed as endangered under the U.S. Endangered Species Act. In the United States, the Virginia white-tail, O. v. virginianus, is among the most widespread subspecies. Several local deer populations, especially in the southern states, are descended from white-tailed deer transplanted from various localities east of the Continental Divide. Some of these deer populations may have been from as far north as the Great Lakes region to as far west as Texas, yet are also quite at home in the Appalachian and Piedmont regions of the south. These deer, over time, have intermixed with the local indigenous deer (O. v. virginianus and/or O. v. macrourus) populations.

Central and South America have a complex number of white-tailed deer subspecies that range from Guatemala to as far south as Peru. This list of subspecies of deer is more exhaustive than the list of North American subspecies, and the number of subspecies is also questionable. However, the white-tailed deer populations in these areas are difficult to study, due to overhunting in many parts and a lack of protection. Some areas no longer carry deer, so assessing the genetic difference of these animals is difficult.

Northern White-tailed Deer (Odocoileus virginianus borealis) - Illinois, suburban Chicago

Coues’ White-tailed Deer (Odocoileus virginianus couesi) - Cave Creek Ranch and Canyon and Madera Canyon Arizona

Dakota White-tailed Deer (Odocoileus virginianus dakotensis) - Badlands National Park, South Dakota