In West Texas the white-tailed deer is a species that attracts a wide range of opinions. Many deer managers, protective of their prized mule deer herds, resent the “invasion” of the white-tailed deer into areas previously unoccupied by the “lesser species.” Others view the white-tailed deer as an additional source of recreation (hunting, photography, observation, etc.) and/or income. The western Edwards Plateau (Crockett, Terrell, and eastern Pecos counties) is known for its high white-tailed deer numbers, a direct result of intensive predator control associated with the sheep and goat industries. High numbers of deer and livestock, combined with limited precipitation, commonly result in small-bodied, modest-antlered deer. However, on a few properties where animal numbers are kept below carrying capacity, a year of average rainfall can produce some impressive white-tailed bucks.
Population Status and Distribution.
In general, white-tailed deer in west Texas are slowly increasing in numbers and gradually expanding in distribution, although populations in some areas have stabilized. Deer numbers in the extreme western Edwards Plateau range from 10-25 acres per deer (depending on the ranch and the respective management practices) and have existed at this density for some time. The white-tailed deer is expanding westward into Pecos and Brewster counties, primarily along brushy draws and drainages. They are also expanding south along brushy draws and canyons toward the Rio Grande River in Terrell and southeast Brewster counties (rugged country previously occupied exclusively by mule deer). There are a few exceptions to this trend in Terrell and eastern Pecos counties, where white-tailed deer numbers are decreasing and mule deer numbers are increasing. These are localized situations that involve substantial reduction of woody cover, which favors the behavior and survival of mule deer.
White-tailed deer numbers are relatively low in the Permian Basin (Upton, Crane, Ector, Midland counties), but numbers are gradually increasing along with increasing woody cover. The primary factors limiting deer numbers in this area are lack of woody cover and high predator numbers (coyotes and bobcats). Low deer numbers and relatively deep soils contribute to a high nutritional plane for most deer herds. This area can produce some exceptional bucks. Most white-tailed deer herds in the Permian Basin exist among light numbers of mule deer.
The Carmen Mountain white-tailed deer population is relatively stable and occurs in several mountain ranges is southern Brewster County and western Presidio County. The primary habitat of the Carmen subspecies is the pinyon-juniper-oak associations of the Chisos Mountains. There is some debate concerning the subspecies of white-tailed deer that occurs in the Davis Mountains (pinyon-juniper woodlands) at higher elevations. Whether they are the Carmen subspecies or the more common Texas white-tailed deer (or an intergrade), this population is relatively stable in areas with abundant woody cover and free-standing water.
The primary factor providing for the expansion of white-tailed deer in west Texas is the steady encroachment and increasing density of woody plants (primarily mesquite). Improved water distribution as a result of livestock management is also a contributing factor. Intensive predator control efforts have resulted in increased fawn survival in localized areas.
The primary factors deterring population increases in some far-west habitats are minimal amounts of woody cover and low fawn survival. Low fawn survival is primarily attributable to coyote, bobcat, and lion predation and nutritional factors associated with frequent drought.
White-tailed and Mule Deer Interactions
A question often asked by west Texas landowners and hunters is “Are white-tailed deer driving out the mule deer?” White-tailed deer do not physically “drive out” mule deer from an area; however, in some areas mule deer numbers are declining while white-tailed deer numbers are increasing. This change in species composition gives the appearance that the mule deer are being physically displaced. What actually is occurring is a gradual change in the vegetation that favors white-tailed deer.
In areas where the height and density of brush is increasing, the habitat is becoming more suitable for white-tailed deer and less desirable for mule deer. Research indicates that mule deer in Texas prefer a brush canopy cover of 40 percent or less, while white-tailed deer numbers increase dramatically in areas with a brush canopy exceeding 50 percent (Wiggers and Beasom 1986). The greatest white-tailed deer numbers were found in areas that consisted of about two-thirds brush cover. When the two species occupy the same area, they often are segregated-- mule deer preferring the high, rougher canyons and open hillsides and white-tailed deer occupying the brushy draws and lowlands. An exception to this generality occurs in Jeff Davis County where white-tailed deer occur on the densely wooded mountain tops and mule deer occur in the relatively open lower slopes and flats.
Where mule deer and white-tailed deer coexist, interbreeding does occur. The long-term effects are unknown, and for most areas, the extent of hybridization is not known. The highest incidence of hybridization in the Trans-Pecos occurs in the eastern part of the region where high populations of mule deer and white-tailed deer coexist. Using a technique called “polyacrylamidel electrophoresis,” Stubblefield et al. (1986) estimated that up to 14 percent of deer may be hybrids where both species occupy the same range, although the average occurrence of hybrids was only about 5%. Many ranches where the 2 species overlapped showed no evidence of hybridization. Using a more accurate technique (DNA sequencing), Cathey et al. (1998) found that 7.7% of 26 deer sampled were hybrids in the West Texas zone of contact (Terrell, Pecos, and Brewster counties). DNA sequencing was also used to determine the extent of hybridization in the Panhandle (Donley County) where the ranges of both species overlap. The results of a small sample of deer (n= 40) indicated a hybridization frequency of 8% (F. Bryant, pers. comm.). Observations by Texas Parks and Wildlife biologists during the hunting season indicate that true hybrids are extremely rare. Out of several hundred deer that are checked each year, it is rare to find a single hybrid.
Antler characteristics, tail coloration, and ear length are not reliable in recognizing hybrids. First generation hybrids often can be identified by the length of the metatarsal gland that is located on the outside of the rear leg between the hock and the hoof. It typically will measure about ¾-inch long in whitetails and about 4 inches long in mule deer. The metatarsal gland of hybrids is intermediate in length, measuring about 2 inches long. Second generation hybrids can not be identified by their appearance. The predominant successful breeding among hybrids is between white-tailed bucks and mule deer does (Carr and Hughes 1993, Cathey et al. 1998), but interbreeding also can occur between mule deer bucks and white-tailed does. Hybrids appear to have at least a limited degree of fertility (Whitehead 1972, Derr et al. 1991, Cathey et al. 1998).
Carr, S. M., and G. A. Hughes. 1993. Direction of introgressive hybridization between species of North American deer (Odocoileus) as inferred from mitochondrial- cytochrome-b sequences. J. Mammal. 74: 331-342.
Cathey, J. C., J. W. Bickham, and J. C. Patton. 1998. Introgressive hybridization and nonconcordant evolutionary history of maternal and paternal lineages in North American deer. Evolution 52(4): 1224-1229.
Derr, J. N., D. W. Hale, D. L. Ellsworth, and J. W. Bickham. 1991. Fertility in an F1 male hybrid of white-tailed deer (Odocoileus virginianus) x mule deer (O. hemionus). J. Reprod. Fertil. 93: 111-117.
Stubblefield, S. S, R. J. Warren, and B. R. Murphy. 1986. Hybridization of free-ranging white-tailed and mule deer in Texas. J. Wildl. Manage. 50: 688-690.
Whitehead, Jr., C. J. 1972. A preliminary report on white-tailed and black-tailed deer crossbreeding studies in Tennessee. Proc. of the Annual Conf. of the Southeast. Assoc. of Game and Fish Commissions. 25: 65-69.
Wiggers, E. P., and S. L. Beasom. 1986. Characterization of sympatric or
habitats of two deer species in west Texas. J. Wildl. Manage. 50: 129-134.