What's in a Name?
Looks aren't everything, but if you're a deer in the West, looks play an important role in determining whether you're called a mule deer, black-tailed deer or white-tailed deer. Behavior and habitat contribute, as well.
Species and Subspecies
Subtle variations in characteristics such as size, behavior and appearance in deer occur because of local habitat, food or weather conditions. There have been as many as 11 subspecies of mule deer and 30 subspecies of white-tailed deer described – all of these subspecies belong to two recognized species of deer in the West; mule deer and white-tailed deer. Black-tailed deer are also found in the West, but they are actually a subspecies of mule deer. All deer are members of the Cervidae family, hoofed mammals that have antlers such as elk, moose and caribou.
Mule deer were first described in North America in 1817 based on field notes made by Charles Le Raye while he was held captive by the Sioux tribe on the Big Sioux River in South Dakota. The scientific name of the species, hemionus, literally means "half-mule,” because the ears are similar to those of a mule.
Differences Between Species
There are several ways to tell a mule deer from a white-tailed deer, a critical need for hunters who must be able to identify species in areas where both exist. Mule deer differ from white-tailed deer in several ways, but because of variation within each species, some mule deer and white-tailed deer cannot be quickly identified. Black-tailed deer further cloud the identification issue because they display characteristics similar to both white-tailed deer and other mule deer subspecies.
When used alone, some of the identifying characteristics can be confusing. Thus, it is important to use several characteristics to identify species.
White-tailed deer have a wide, flattened tail that is broad at the base and narrower at the tip. A darker backside contrasts the pure white underside. The darker tail is edged with white fringe hairs that are an extension of the white underside. White-tailed deer lack a large, conspicuous white rump, and have tails that are at least 7 1/2 inches long.
Mule deer tails appear cylindrical, or rope-like, and are usually white on the backside, with a distinctive black tip surrounded by a large, obvious white rump. Some mule deer may have a thin dark line running down the back surface of the tail. Mule deer tails are less than 7 1/2 inches long.
Antlers are the least reliable characteristic to use when trying to differentiate mule deer from whitetailed deer because of the variation in antler shape and form in both species. Antlers can, however, help identification when used in combination with other characteristics.
Mature mule deer bucks have antlers with main beams that sweep outward and upward, forking once and then forking again. Brow tines are not always present. Mature bucks typically have eight to 10 total points (including brow tines that exceed one inch). These bucks are considered 4-point bucks (the number of points on one side of the rack excluding the brow tines).
Typical white-tailed deer antlers have several antler tines that arise singly off a main beam that sweeps outward and forward from the bases. The brow tines are nearly always present and usually prominent. Mature white-tailed deer bucks frequently have eight total points, including the brow tines.
It is not unusual for white-tailed deer to have forked tines like those of a mule deer, or for mule deer tines to arise from the main beam like those of a white-tailed deer. Mule deer bucks less than three years of age are frequently mistaken for large white-tailed deer because the tines have not yet developed the characteristic fork.
There may also be regional differences in antler form. For example, the white-tailed deer in the Carmen Mountains of northern Mexico seem to have a high degree of forked antlers like a mule deer.
The forehead of a white-tailed deer is usually the same color as the rest of the face, although it can be slightly darker. The white eye rings and markings directly behind the nose are prominent.
A mule deer usually has a distinctive black forehead, or mask, that contrasts sharply with a light grey face. The lighter facial coloration makes the eye rings and muzzle markings seem less obvious.
White-tailed deer ears are generally 2/3 the overall length of the head (back of head to nose), while those of a mule deer are 3/4 the length of the head.
When alarmed, a white-tailed deer usually raises its tail, exposing the fluffy white underside to alert all other deer in the area of apparent danger. It then runs directly away from the source of danger.
A mule deer does not "flag" its tail, and often bounces away in a motion called "stotting," in which all four hooves push off the ground at the same time. A mule deer may not escape as fast as a white-tailed deer, but a mule deer is more effective in quickly moving through rugged terrain.
Both species may stop and look back at the source of potential danger, but this behavior is more typical of mule deer.
The best way to tell a whitetailed deer from a mule deer is the size and location of the metatarsal glands, but this is not a readily observable characteristic. The metatarsal glands of both species are located on the outside of the lower portion of the hind leg, and are sometimes confused with the tarsal gland on the inside of the leg (hocks).
White-tailed deer have metatarsal glands that are one inch or less in length, and always encircled with white hair. This gland is at midpoint or below midpoint on the lower shank of the leg.
Mule deer have much larger metatarsal glands that are encircled with white hair. The gland measures three to seven inches in length, and starts at the ankle joint and extends downward toward the hoof. It appears as a large, long tuft of hair.
There are regional differences in metatarsal glands within species. For example, metatarsal glands of mule deer in desert habitats are reported to be shorter than mule deer in more northern habitats.
The preorbital (“pre” means “in front of”, “orbital” means “eye”) gland is located in front of the eye and differs considerably between the two species. The preorbital gland of a white-tailed deer is very small, appearing as a small slit with a maximum depth of 3/8 inch. The preorbital gland of a mule deer is comparatively large, forms a substantial pocket with a depth averaging 3/4 inch, and commonly contains a small ball of yellow, waxy substance.
When two species breed, the offspring is called a hybrid. Different species of animals normally do not breed with one another because they use different habitats, or are geographically isolated. If similar species live in the same habitat, then they generally breed at different times or have different breeding behavior.
In the case of white-tailed deer and mule deer, courtship and breeding behavior are different enough that body language and scent cues from a female mule deer during rut are not normally "understood" by a white-tailed deer buck, and vice versa. In some cases where ranges overlap, this system breaks down and mule deer and white-tailed deer may mate and produce a hybrid deer.
Hybrid deer may have characteristics of both mule deer and white-tailed deer. But a young mule deer may look like a large white-tailed deer, especially if its tail has a dark stripe down the back.
Every year numerous hunters report seeing hybrid deer, however, it is unlikely a hunter will ever see a hybrid deer in the field. The low number of white-tailed deer that mate with mule deer, and the low survival rate of hybrid offspring, greatly reduces the chance of encountering a true hybrid in the wild. Hybrids are rare and difficult to accurately identify because of many varying characteristics.
Citation: Mule Deer Working Group. 2003. Mule Deer: Changing landscapes, changing perspectives. Mule Deer Working Group, Western Association of Fish and Wildlife Agencies.