Odocoileus hemionus

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.

Taxonomy

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.

Subspecies

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, 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

Description

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-tails.

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.

The mule deer is the larger of the three ''Odocoileus'' species on average, with a height of at the shoulders and a nose-to-tail length ranging from . Of this, the tail may comprise . Adult bucks normally weigh , averaging around , although trophy specimens may weigh up to . Does (female deer) are smaller and typically weigh from , with an average of around .

Unlike the white-tailed, the mule deer does not generally show marked size variation across its range, although environmental conditions can cause considerable weight fluctuations in any given population. An exception to this is the Sitka deer subspecies (''O. h. sitkensis''). This race is markedly smaller than other mule deer, with an average weight of and in males and females, respectively.

Seasonal behaviors

In addition to movements related to available shelter and food, the breeding cycle is important in understanding deer behavior. The " rut" or mating season usually begins in the fall as does go into estrus for a period of a few days and males become more aggressive, competing for mates. Does may mate with more than one buck and go back into estrus within a month if they did not become pregnant. The gestation period is about 190–200 days, with fawns born in the spring. The survival rate of the fawns during labor is about 50%. Fawns stay with their mothers during the summer and are weaned in the fall after about 60–75 days. Mule deer females usually give birth to two fawns, although if it is their first time having a fawn, they often have just one.

A buck's antlers fall off during the winter, then grow again in preparation for the next season's rut. The annual cycle of antler growth is regulated by changes in the length of the day.

The size of mule deer groups follows a marked seasonal pattern. Groups are smallest during fawning season (June and July in Saskatchewan and Alberta) and largest in early gestation (winter; February and March in Saskatchewan and Alberta).

Besides humans, the three leading predators of mule deer are coyotes, wolves, and cougars. Bobcats, Canada lynx, wolverines, American black bears, and grizzly bears may prey upon adult deer, but most often only attack fawns or infirm specimens, or eat a deer after it has died naturally. Bears and smaller-sized carnivores are typically opportunistic feeders, and pose little threat to a strong, healthy mule deer.

Diet and foraging behaviors

In 99 studies of mule deer diets, some 788 species of plants were eaten by mule deer, and their diets vary greatly depending on the season, geographic region, year, and elevation. The studies gave these data for Rocky Mountain mule deer diets:

The diets of mule deer are very similar to those of white-tailed deer in areas where they coexist. Mule deer are intermediate feeders rather than pure browsers or grazers; they predominantly browse, but also eat forb vegetation, small amounts of grass, and where available, tree or shrub fruits such as beans, pods, nuts (including acorns), and berries.

Mule deer readily adapt to agricultural products and landscape plantings. In the Sierra Nevada range, mule deer depend on the lichen '' Bryoria fremontii'' as a winter food source.

The most common plant species consumed by mule deer are:

* Among trees and shrubs: ''Artemisia tridentata'' (big sagebrush), '' Cercocarpus ledifolius'' (curlleaf mountain mahogany), ''Cercocarpus montanus'' (true mountain mahogany), ''Cowania mexicana'' (Mexican cliffrose), ''Populus tremuloides'' (quaking aspen), '' Purshia tridentata'' (antelope bitterbrush), ''Quercus gambelii'' (Gambel oak), and '' Rhus trilobata'' (skunkbush sumac).
* Among forbs: ''Achillea millefolium'' (western yarrow), '' Antennaria'' (pussytoes) species, ''Artemisia frigida'' (fringed sagebrush), '' Artemisia ludoviciana'' (Louisiana sagewort), '' Aster'' species, ''Astragalus'' (milkvetch) species, '' Balsamorhiza sagittata'' (arrowleaf balsamroot), ''Cirsium'' (thistle) species, '' Erigeron'' (fleabane) species, '' Geranium'' species, '' Lactuca serriola'' (prickly lettuce), ''Lupinus'' (lupine) species, alfalfa, ''Penstemon'' species, ''Phlox'' species, ''Polygonum'' (knotweed/smartweed) species, '' Potentilla'' (cinquefoil) species, ''Taraxacum officinale'' (dandelion), ''Tragopogon dubius'' (western salsify), clover, and ''Vicia americana'' (American vetch).
* Among grasses and grasslike species: ''Agropyron'', '' Elymus'' (wheatgrasses), '' Elytrigia'', '' Pascopyrum'' species ( wheatgrasses), '' Pseudoroegneria spicatum'' (bluebunch wheatgrass), '' Bromus tectorum'' (cheatgrass), ''Carex'' (sedge) species, ''Festuca idahoensis'' (Idaho fescue), '' Poa fendleriana'' ( muttongrass), ''Poa pratensis'' (Kentucky bluegrass), and other '' Poa'' (bluegrass) species.

Mule deer have also been known to eat ricegrass