NATIONAL PARK SERVICE Ecology of the Carmen Mountains White-Tailed Deer

Carmen deer have a larger geographic range than previously thought. It extends beyond the boundaries of Big Bend National Park in the United States. Population indexes and tissue analyses suggest that, within the park, the herd is healthy and stable. Although the Chinati, Christmas, and Rosillos mountains, and perhaps other ranges in the Big Bend area support Carmen deer, the Chisos Mountains provide conditions that will continue to support a viable herd. Carmen deer in other areas are not as secure due to smallness of ranges, livestock competition, hunting pressure, and marginal habitat. A single factor was not isolated regulating distribution and population levels, but several conditions were operative: interspecific behavior, habitat, water availability, and predation.

Interspecific aggression between mule deer and Carmen deer was minimal. However, 6% of mule deer—white-tailed deer encounters were aggressive, and avoidance was recorded 12% of the time (Table 18). This indicates that behavioral interactions may play a part in separation, but a more important point should be considered. In all encounters, the relationship was terminated by submissive actions of the younger individual, whether mule or white-tailed deer. Interspecific interactions, as described between mule deer and whitetails, at a young age may influence habitat selection as adults.

Whitetail habitat in the Chisos and other ranges has been described and obviously is a factor in distribution and abundance. Although exclusive mule and white-tailed deer habitats are distinctly different, the Sotol—Grassland Formation, which is sympatric range, provides a combination of desert shrub and woodland vegetation. Forage utilization by deer in this area was in response to availability and, although the potential for forage competition existed, it did not appear to be operative during this study.

Perhaps a more important consideration of whitetail distribution in areas of overlap is water availability. In other Carmen deer ranges, distribution was associated with water and relatively heavily vegetated canyons and washes. In the Chisos Mountains, as more xeric conditions prevailed toward the outlying desert, vegetational density and springs decreased as did the Carmen deer. Whitetail range in Big Bend is bordered by springs: Lower Juniper Spring, Rock Spring, Panther Spring, Moss Wells, Oak Spring, Cattail Rats, and Blue Creek. Even in marginal habitat, distribution is associated with water: Dodson Spring, Fresno Spring, and Smoky Spring (Fig. 2). More xeric areas between the bordering springs were void of whitetails. Historically, whitetails inhabited several mesas which now support only mule deer. Free-standing water had been made available by ranchers, and as their operations ceased, so did inhabitance by whitetails. Competition with livestock and mule deer and hunting were possibly the primary reducing factors, but the influence of water cannot be ruled out. Leopold (1933:135) claimed that, "A range is habitable for a given species when it furnishes places suitable for it to feed [including moisture acquisition], hide, rest, sleep, play, and breed, all within the reach of its cruising radius." Of these factors, water availability cannot be ruled out as an important influence, especially in areas of marginal habitat.

Data presented herein on predation primarily concern food habits and only begin to explore the understanding of predator—prey relationships in the park. Although numbers of deer are estimated, an indication of predator density is not available. Local reports and "gut feeling" estimates have been presented, but without a quantitative base. Without such data, accounts of predator—prey relationships will be as speculative as are estimates of predator populations. That predators, especially cougars, have an effect on the population is probably true. Other influences are those suggested by Hornocker (1970) that lions tend to distribute prey and dampen oscillations. In more xeric areas, lions may serve, in part, to distribute deer among water sources and contribute to limitations in distribution.

Man's direct influence has not been required to maintain a viable population of Carmen deer in the park. The future of this subspecies in other areas is uncertain due to previously discussed reasons. However, increased interest in the National Park System means greater use by man. At present, active management programs are unnecessary to maintain whitetails in Big Bend, but several factors should be kept in mind. Interference with natural water sources by visitors should be discouraged. Fences should be built only when necessary, and as has been proposed, minimal development and maximum reduction of permanent fixtures is warranted in the Basin. More importantly, the deer populations should be kept under surveillance, which need not require more than the simplest of quantifiable population indexes.

"The National Park Service is charged with the responsibility of preserving designated areas, selected samples of primitive America, in their natural condition for the enjoyment and study of present and future Americans. In line with this high purpose, the flora and fauna should be subjected to a minimum of disturbance. The natural interactions of the members of the fauna and flora and the environment have a place in such a scheme and serve to furnish significance and greater interest in the animal life" (Murie 1940). The Carmen Mountains white-tailed deer in Big Bend National Park are a desirable member of the assembly of animals and contribute to the interest and variety of this fauna.