Next Species
Previous Species

Search
Browse
Home Page
Help

Comments
Copyright Information

  The Mammals of Texas - Online Edition

Mule Deer
Order Artiodactyla : Family Cervidae : Odocoileus hemionus (Rafinesque)

Mule Deer (Ocodoileus hemionus).  Photo by Frank Aguilar, courtesy of Texas Parks and Wildlife.Description. A moderately large deer with large ears; antlers typically dichotomously branched and restricted almost entirely to males; metatarsal gland 8-12 cm long, narrow, and situated above midpoint of shank; upperparts in winter cinnamon buff suffused with blackish, more reddish in summer; brow patch whitish; ear grayish on outside, whitish on inside; tail usually with black tip and white basal portion; underparts white. Dental formula: I 0/3, C 0/1, Pm 3/3, M 3/3 X 2 = 32. External measurements average: (males) total length, 1,755 mm; tail, 152 mm; hind foot, 555 mm; metatarsal gland, 129 mm; (females) 1,453-175-475 mm. Weight, 57-102 kg.

Species distribution mapDistribution in Texas. Occurs over most of the Trans-Pecos and Panhandle regions of Texas and in some areas immediately east thereof, partly as a result of introductions.

Habits. Mule deer occupy to some extent almost all types of habitat within their range but, in general, they seem to prefer the more arid, open situations in which sagebrush, juniper, pinyon pine, yellow pine, bitter brush, mountain mahogany, and such plants predominate. In western Texas, rocky hillsides covered with lechuguilla, sotol, juniper, and pinyon pine provide the essentials.

The mule deer is noted for its peculiar, high-bouncing gait. Estimates of their speed vary, but Donald McLean was able to force one to a speed of 58 km an hour on a dry lake flat in California. After the first short burst of speed, the animal dropped to about 35 km an hour and was badly winded after a chase of less than 1.5 km. When allowed to choose their own gait, they are able to travel at about 30 km an hour for a considerable period of time. In rough, broken country they are at their best. There, the long, high bounds send them over the rocks and brush much faster than the average running animal can go through or around the obstructions. The longest bounds are generally made when the animals are going downhill or leaping across gullies. McLean measured two flat jumps that were 5.9 and 7.1 m, respectively. A downhill bound on a 7% slope measured 8.7 m. They can easily clear a fence 2 m high.

Although equipped with acute senses of sight and hearing, these deer rely largely upon the sense of smell in detecting danger. Stationary objects are easily overlooked by them, but they readily detect any that are in motion.

Mule deer of both sexes normally do most of their feeding in early morning before sunrise or in late afternoon and evening after sundown. They spend the middle of the day bedded down in cool, secluded places. In summer, the bucks retire as soon as the sun shines where they are feeding and go to the dense shade of some grove to bed down for the day. In general, mature bucks prefer rocky ridges for bedding grounds because there they seem to feel more secure from the approach of danger. Does and fawns are more likely to bed down in the open. In winter, however, they often seek out sunny places well screened on at least three sides by vegetation. At night, they usually bed down in the open away from trees and bushes.

The food of the mule deer is quite varied. In Trans-Pecos Texas, the flowering stalks of lechuguilla, the basal parts of sotol, mesquite, juniper, and a number of forbs contribute to their diet. Feeding time varies with the weather, the phase of the moon, the time of the year, and type of country. During cold, snowy, winter months when food is difficult to obtain and a considerable amount is required to maintain body heat and energy, deer feed at all times of day and night. During the rutting season, feeding is often erratic, especially with bucks. During the hunting season, when many hunters are on the range, bucks do the major part of their feeding at night. Deer are more prone to feed on dark nights and are relatively quiet and bedded down when the moonlight is intense. In spring and summer, mule deer tend to feed to a greater extent upon green leaves, green herbs, weeds, and grasses than they do upon browse species; the reverse is true in fall and winter.

The rut begins in the fall, usually in November or December, but varies with locality and climatic conditions and continues until the latter part of January or even into February. During this period, the bucks have terrific battles in which the antlers are used almost exclusively. Bucks that are evenly matched in size and strength may fight until almost exhausted before one or the other is the victor. The animals are polygamous. The stronger, more virile bucks attract females to them and attempt to defend them against the attentions of the younger bucks. Small, persistent bucks can lead a large buck a miserable life, leaving him little time to take care of family duties or even to eat, because of his continued attempts to drive them away. In this period the necks of bucks become swollen, a development that is closely associated with reproduction.

The gestation period is approximately 210 days, and the fawning period extends over several weeks in June, July, and August. The female sequesters herself and drops her fawn in a protected locality where it remains for a period of a week or 10 days before it is strong enough to follow her. At birth fawns are spotted and weigh approximately 2.5 kg. They are nursed at regular intervals by the female, 10 minutes of nursing usually sufficing for a full meal. The young ones are weaned at about the age of 60 or 75 days, at which time they begin to lose their spots. The weaning time is a critical one because if green forage is not available, the fawns seldom make their transfer from milk to a diet of vegetation. If the fawn is not weaned, both mother and fawn are likely to experience difficulty in surviving a severe winter. Sexual maturity is attained at the age of about 18 months in does but ordinarily, young bucks are not allowed to participate actively in the rut until they are 3 or 4 years old.

Antlers are shed after the breeding season, from mid-January to about mid-April. Most mature bucks in good condition have lost theirs by the end of February; immature bucks generally lose them a little later. New antler growth begins immediately following the shedding of the old. Growth is extremely rapid, and massive antlers develop fully in about 150 days. While the antlers are growing, the bucks remain on the open slopes and benches where the brush is short or scattered to avoid injuring the soft, new growth. Mature bucks normally have four main points on each antler, but beyond the third year there is little or no correlation between the number of points and the age of the deer. Beyond the prime of life, the so-called "Pacific buck" type may develop, which consists of only two points, or a spike, on each side of a large set of antlers.

The age of mule deer can be determined fairly accurately up to about 24 months. At birth the fawn is equipped with upper premolars, the third and fourth lower premolars, the lower canines, and the entire lower incisor series. The second lower premolar may erupt shortly after birth or within the first 60 days. By the age of 3 months, the first upper molar is functional. At the age of approximately 1 year, the middle lower incisor is shed and replaced by a permanent one. Each permanent incisor is wider than its predecessor. At the age of 15-18 months, the molars erupt and take their place in the series, and at the age of 24-25 months, the premolars are replaced by the permanent dentition.

Mule deer are of considerable economic importance as a big game mammal. Statewide, the population was estimated to be about 198,000 in 1991 and the harvest by hunters that year was estimated at 7,900. On the other side of the ledger, there is some competition between mule deer and livestock on the range, particularly in spring and early summer. Furthermore, such maladies as hoof-and-mouth disease can be transmitted from deer to livestock, and vice versa, so that once the disease is established in wild animals drastic measures must be taken to curb it. Anthrax is also said to be propagated and spread by deer, and these animals are also capable of harboring the causative agents of tularemia or rabbit fever.

Remarks. Sympatric populations of mule deer and white-tailed deer (Odocoileus virginianus) in western Texas have been found to interbreed and produce hybrid offspring. Genetic analyses indicate that these hybrids are more characteristic of white-tailed deer than of mule deer; thus, it appears that hybridization may be one factor contributing to the displacement of mule deer by white-tailed deer in this region.

Photo credit: Frank Aguilar, courtesy of Texas Parks and Wildlife.