Mule deer
The mule deer is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer.
Mule deer are found only on the western Great Plains, in the Rocky Mountains, in the southwest United States, and on the west coast of North America. Their range is much smaller than the related white-tailed deer, which are 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 have also been introduced to Argentina and Kauai, Hawaii.
Taxonomy
Mule deer can be divided into two main groups: the mule deer 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, 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 group:
- *O. h. californicus – California mule deer. This widespread subspecies is found throughout much of California, with high densities in Orange and Los Angeles Counties to coastal Santa Barbara, Ventura, and San Luis Obispo; from Morro Bay to Santa Cruz, along the coast, its range is somewhat patchier. Inland, the California mule deer is known from around San Bernardino to as far north as Lassen; many deer inhabit the areas in and around Sequoia National Park, Yosemite, Plumas National Forest, and of course, the Sierra Nevada, its range partly overlapping with that of the Inyo subspecies. It is notably absent from the Central Valley and the agricultural districts of the state ; north of San Francisco, it is replaced by the Columbian subspecies. It is also known to range across the border into west-central Nevada, between Reno and Carson City.
- *O. h. cerrosensis – Cedros or Cerros Island mule deer, after Cedros Island, off of the southwestern Pacific coast of Baja California state, the subspecies' sole habitat.
- *O. h. eremicus – Desert or burro mule deer. Primarily found in the Lower Colorado River Valley, Southern California's Inland Empire, the areas around Las Vegas and extreme southern Nevada, much of Arizona and parts of southern New Mexico. In Mexico, it is primarily known from Sonora, having been known from as far south as Hermosillo; it has also been observed in Coahuila, Chihuahua and Durango.
- *O. h. fuliginatus – Southern mule deer. Mainly found in Southern California and along the U.S.-Mexico borderlands, into the northern half of the Baja California Peninsula, where it has been sighted as far south as El Rosario. Notably high population densities occur to the west of Anza-Borrego Desert State Park and in and around the region of Julian, California.
- *O. h. hemionus – Rocky Mountain mule deer. Primarily found in western and central North America, as far south as Colorado and as far north as Yukon and the Northwest Territories, including inland British Columbia.
- *O. h. inyoensis – Inyo mule deer. This deer is primarily found within the Sierra Nevada and Yosemite, within inland Central California, and has been sighted as far south as Death Valley and as far north as the Stanislaus National Forest.
- *O. h. peninsulae – Baja or Peninsular mule deer; found across the majority of the state of Baja California Sur, Mexico.
- *O. h. sheldoni – Tiburón Island mule deer, also called the venado bura de Tiburón in Spanish. This deer is only found on Tiburón Island, Mexico, in the Gulf of California.
- Black-tailed deer group:
- *O. h. columbianus – Columbian black-tailed deer; found primarily in coastal temperate rainforest habitats of the Pacific Northwest and Northern California
- *O. h. sitkensis – Sitka black-tailed deer ; found in similar temperate rainforests as the Columbian subspecies—though with a more northerly range—from the central coast of British Columbia throughout Southeast Alaska, with smaller populations further north to Anchorage, the Kenai Peninsula, and Kodiak Island. Found typically in dense, lush habitats, such as the Great Bear Rainforest and Tongass National Forest.
Description
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, 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 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. 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 and largest in early gestation.
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 attack only fawns or infirm specimens, or they may eat a deer after it has died naturally. Bears and small 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:| Shrubs and trees | Forbs | Grasses and grass-like plants | |
| Winter | 74% | 15% | 11% |
| Spring | 49% | 25% | 26% |
| Summer | 49% | 46% | 3% |
| Fall | 60% | 30% | 9% |
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, and berries. Carbon isotopic study of mule deer in Yellowstone has shown them, along with elk, to be the most generalist large herbivores of the region.
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 the following:
- Among trees and shrubs: Artemisia tridentata, Cercocarpus ledifolius, Cercocarpus montanus, Cowania mexicana, Populus tremuloides, Purshia tridentata, Quercus gambelii, and Rhus trilobata.
- Among forbs: Achillea millefolium, Antennaria species, Artemisia frigida, Artemisia ludoviciana, Aster species, Astragalus species, Balsamorhiza sagittata, Cirsium species, Erigeron species, Geranium species, Lactuca serriola, Lupinus species, alfalfa, Penstemon species, Phlox species, Polygonum species, Potentilla species, Taraxacum officinale, Tragopogon dubius, clover, and Vicia americana.
- Among grasses and grasslike species: Agropyron, Elymus, Pascopyrum species, Pseudoroegneria spicatum, Bromus tectorum, Carex species, Festuca idahoensis, Poa fendleriana, Poa pratensis, and other Poa species.
Humans sometimes engage in supplemental feeding efforts in severe winters in an attempt to help mule deer avoid starvation. Wildlife agencies discourage such efforts, which cause harm to mule deer populations by spreading disease when deer congregate for feed, disrupting migratory patterns, causing overpopulation of local mule deer populations, and causing habitat destruction from overbrowsing of shrubs and forbs. Supplemental feeding efforts might be appropriate when carefully conducted under limited circumstances, but to be successful, the feeding must begin early in the severe winter and must be continued until range conditions can support the herd.
Mule deer are variably gregarious, with a large proportion of solitary individuals and small groups. Reported mean group size measurements are three to five and typical group size is about seven.