Species Description

Classification

Within the class of animals we call mammals there are 2 groups of animals that walk on hooves. These animals are commonly called Ungulates, from the Latin unguis, meaning "claw" or "toe nail." The hooves are simply highly developed toe nails upon which these animals walk. The order Artiodactyla contains all ungulates with an even number of toes (2 or 4) such as cattle, deer, goats, antelope, pigs, and camels. The name for these animals which walk on an even number of toes comes from the Greek Artios = "even", and daktulos = "a finger or toe".

There are nine families within Artiodactyla but only four occur naturally in North America: Bovidae (sheep, cattle, goats, bison), Antilocapridae (pronghorn antelope), Tayassuidae (collared peccary/javelina), and Cervidae (deer, elk, moose).

The deer family (Cervidae) includes all moose, elk/red deer, caribou/reindeer, Eurasian deer, and medium-sized American deer. Cervids, as members of the family are called, no longer have a digit #1 (thumb or big toe) and walk on the hooves (toe nails) of the 3rd and 4th toes. The 2nd and 5th toes have been reduced and assume a nonfunctioning role as the short toes we call "dew claws."

Worldwide, there are about 17 genera in the deer family, but only Alces (moose), Rangifer (caribou), Cervus (elk), and Odocoileus (deer) are found in the United States. The Genus Odocoileus includes the only two species of medium-sized deer in the United States: white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus). The genus name Odocoileus comes from the hollow pits, called infundibula, in the chewing surface of the premolars and molars; Odous means "tooth" and koilos means "hollow."

Description

The mule deer was first described in North America in 1817 based on the field notes made by Charles LeRaye while he was a captive of the Sioux tribe on the Big Sioux River in South Dakota. The scientific name hemionus literally means "half-mule," because its ears are so big they were said to resemble a mule's.

Adult males of this medium-sized member of the deer family can range from 150 to 300 pounds and stand about 3 feet tall at the shoulder. Besides having larger ears, mule deer differ from whitetails in several ways. The most commonly mentioned difference -- but not the best characteristic -- is the unique antler shape. Mule deer antlers have small or missing browtines with main beams that sweep out and upward, forking once and then each fork divides again in mature bucks (dichotomous branching). Mature bucks typically have eight total points or 10 if the browtines are present (four point western count). It is not at all unusual for whitetails to have forked tines like a mule deer or to see a mule deer with all tines arising from the mainnbeam; antlers can not be relied on as the sole identifying characteristic.

Mule deer tails appear rope-like and are usually (not always) white on the back side with a distinctive black tip surrounded by a large, obvious white rump. Some mule deer may have a thin black line running along the back (dorsal) side of the tail. Mule deer along the west coast differ from inland mule deer by the presence of a dark dorsal (back) surface of the tail (similar to whitetails) and relatively short metatarsal glands on the hind legs; these deer are referred to as black-tailed deer.

The mule deer does not "flag" its tail and normally bounces away in a motion called "stotting" where all four hooves push off at the same time. Blacktails, which live in habitat more similar to whitetails, may lift their tails but do flag in the same manner as whitetails. Mule deer escape behavior is not as fast as a whitetail's, but in rugged terrain it is effective in keeping obstacles between the predator and itself.

The breeding season (rut) occurs in the late fall (November-December) with single or twin fawns born in the summer (June-August). Males grow antlers covered with a skin called ‘velvet' throughout the summer. In the early fall (August-September) the velvet dries and is rubbed off to reveal the bony, sharp antlers in time for the rut. The antlers are shed in spring and regrown annually, with antler size increasing each year until peaking when the buck reaches 6-8 years of age. Mule deer are primarily browsers, with a majority of their diet comprised of weeds and leaves/twigs of brush. Mule deer have a small rumen and must forage on high quality foods. Frequently high quality foods are those that are green and growing. Mule deer will eat grass especially when the grass is green and actively growing. Like cows and other animals with a 4-chambered stomach, deer process food by chewing cud (ruminating). This reprocessing of food, along with beneficial bacteria in the stomach, allows deer to digest fibrous leaves and twigs. Populations in mountainous areas migrate seasonally from higher summer elevations to snow-free lower winter ranges.

Distribution

Mule deer (including the blacktails) are distributed throughout North America from the coastal islands of Alaska to the Mexican state of Zacatecas. With this wide latitudinal range, comes a great diversity of different climatic regimes and vegetation associations. Mule deer are very adaptable in their ability to make a living in coastal rain forests (200 inches of rain per year), icy mountains, prairie grasslands, and hot southwest deserts (4 inches of rain per year). With this range of habitats, comes an incredibly diverse diet that defies generalization.

Many species vary from one portion of its range to another. These variations come about as individuals in localized areas adapt to habitat, forage, or climatic conditions they are exposed to. Depending on the source, there have been between 7 and 11 subspecies of mule deer described in North America. Many of these were deemed "different" based on only a few individuals and the overlap in characteristics among most subspecies is so great that no list of differences can be written that will allow biologists or hunters to differentiate them. Without geographic separation between subspecies, maps of their boundaries are merely crude attempts to describe regional differences throughout the range of mule deer.

                                                                 
                                                                                       -- Jim Heffelfinger, RegionalGame Specialist
                                                                                          Arizona Game and Fish Departmenti