Hybridization of Free-Ranging White-Tailed and Mule Deer in Texas

Abstract

We determined the occurrence and extent of hybridization between desert mule deer (Odocoileus hemionus crooki) and white-tailed deer (0. virginianus texanus) in the Trans-Pecos Region of Texas. Muscle samples were obtained from deer killed by hunters at 27 different locations in a 5-county area of southwestern Texas during the 1984 hunting season. Samples were analyzed by polyacrylamide gel electrophoresis to identify fixed albumin protein banding patterns for each species and for hybrids. Of 319 deer examined, the occurrence of hybrids varied among collection locations from 0 to 24%, with an average of 5.6% for the entire study area. J. WILDL. MANAGE. 50(4):688-690 Landowners in the Texas Trans-Pecos Region rely on desert mule deer hunting leases for income, and thus are concerned about the expansion of white-tailed deer into areas previously occupied by desert mule deer. Wiggers and Beasom (1986) linked this range expansion to encroachment of brushy vegetation that now favors white-tailed deer. Biologists in the TransPecos Region have noted a decline in mule deer and an increase in white-tailed deer numbers (Harwell and Gore 1981). About 30-40% of the Trans-Pecos Region is populated by both deer species (West 1985). Kraimer (1973) reported that mule deer bucks occasionally were attracted to white-tailed deer does during the rut, but sexual interactions between the 2 species were rarely documented. He suggested that differing morphology and scents prohibited interspecific courtships. However, free-ranging white-tailed deer x mule deer hybrids have been documented in Arizona (Day 1980) and Canada (Wishart 1980, McClymont et al. 1982). Wishart (1980) also found that some hybrids were fertile and produced viable offspring. Several landowners and deer biologists believe mule and white-tailed deer in the TransPecos Region are interbreeding (R. L. Marburger, pers. commun.; E. P. Wiggers, pers. commun.). Documentation of this phenomenon and its frequency is important in formulating ecologically sound deer management programs. Our objective was to determine the occurrence and extent of hybridization between free-ranging mule and white-tailed deer in the Texas Trans-Pecos Region. Collections of samples from deer over such an extensive area could not have been accomplished without the cooperation and assistance of numerous hunters, landowners, and wildlife professionals. Funding for this research was provided by the Caesar Kleberg Found. Wildl. Conserv. This paper represents Manuscript T-9428 of the College Agric. Sci., Texas Tech Univ. We thank R. K. Chesser, M. H. Smith, K. T. Sc ibner, and R. L. Marchinton for reviewing an earlier version of this manuscript. STUDY AREA AND METHODS The study area included Jeff Davis, Presidio, Brewster, Pecos, and Terrell counties in the Texas Trans-Pecos Region (Fig. 1). Geographically, the region varies from lowland flats to mountains with elevations from 760 to 2,600 m. Average annual precipitation for the area is 25-30 cm, most of which occurs in July and August. Vegetation is typical of the Chihuahuan Desert (Gould 1975). Species ratios vary from 1:19 (mule deer: white-tailed deer) in the eastern part to 8:1 in the western part of the study area (West 1985). In summer 1984, 30 cooperating landowners were provided prepared sampling packages, which consisted of freezer bags for muscle samples, and a card with instructions and information to be collected. Landowners distributed sampling packages to hunters during the 1984 'Present address: School of Forest Resources, University of Georgia, Athens, GA 30602. 2 Present address: Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77843.