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

The study was conducted in the Chisos Mountains and surrounding foothills and mesas, an area of approximately 20 square miles (52 km²), in Big Bend National Park (Fig. 1). Headquarters were maintained at the Naturalist Workshop in Panther Junction (Fig. 2). Paved roads to the north of the Chisos and up Green Gulch and dirt roads into Pine and Juniper canyons (Fig. 2) served as access routes to the mountains via pickup trucks and a trailbike; travel on the study area itself was by foot. Field observations and collections were the basic methods of obtaining data, but National Park Service records and museum specimens served as additional information sources.

Climate

Weather information was collected from U.S. Weather Bureau stations, maintained by the National Park Service at Panther Junction and in the Basin. These data were supplemented with readings from rain gauges set up over the study area.

Deer Description and Distribution

Descriptions of Carmen deer were based on field observations made with 8x35 binoculars and a 20x spotting scope, and on examinations of collected animals. All collections were by authority of a U.S. Department of the Interior, National Park Service, Class B, Collecting Permit.

Weights and measurements were taken whenever deer were collected. Measurements taken with a flexible steel tape to the nearest millimeter were as follows:

Body length: The distance from the tip of the nose to the base of the tail when the tail is held 90° to the dorsal side. The animal was straightened on its side as much as possible and the tape was passed along the curvatures of the dorsal side.

Tail length: The distance from the base of the tail held 90° to the dorsal side to the end of the last caudal vertebra.

Total length: Body length plus tail length.

Heart girth: The circumference of the chest cavity taken behind the forelegs.

Rear leg: From the top of the right tibia to the tip of the hoof.

Height at withers: The vertical distance from the tip of the hoof of a foreleg to the top of the scapula.

Neck circumference: The circumference of the midpoint along the extended neck.

Outside ear: The length of the ear from the base to the tip.

Supplemental cranial material used in describing Carmen deer were obtained from the Museum of Vertebrate Zoology, University of California at Berkeley, and the Bird and Mammal Laboratories of the National Museum of Natural History in Washington, D.C. Skulls collected during this study are deposited in the Texas Cooperative Wildlife Collections, Texas A & M University, College Station.

Distribution of Carmen deer was established by examination of potential habitat and confirmation of deer presence in these areas.

Population Estimates

Prior to the start of the present study, Atkinson (1975) established pellet plot transects (Eberhardt and Van Etten 1956) throughout the Chisos Mountains. Transects consisted of 20 pellet plots, for a total of 0.2 acres (O.08 ha) per transect. Each of 12 transects was this size; the upper Juniper Canyon transect consisted of only 10 pellet plots comprising 0.1 acre (O.04 ha). Transects were composed of two parallel lines of plots 72 feet (22 m) apart, with paired plots along each line located at 289 foot (88 m) intervals.

The plots were read in August, November, February, and June of each year. Pellet groups were removed after each reading. Additional information was obtained from 10 pellet plot transects established by the National Park Service in whitetail habitat.

Sex and Age Classification

A total of 1,218 individual observations of whitetails was made. Deer observed in the field were classified as fawns, adult females, adult males, and yearling males or females when possible. Tooth wear (Taber 1969) served as an aging criterion when jaws were available.

Group Size and Activity

Group size and activity were recorded for each field observation. Field work was concentrated during crepuscular hours. An indication of early nocturnal activity was obtained by spotlighting both sides of Green Gulch from Campground Junction to Basin Junction (Fig. 2). Spotlights were handled by two observers, in the bed of a pickup truck, each working one side of the road, as a third member drove 5 miles per hour (8 km per hr). Spotlighting was conducted monthly between June 1972 and January 1973.

Reproductive Activity and the Fawning Season

Development of secondary sex characteristics and male rutting behavior were dated as observed. Several embryos were backdated to determine conception dates and observations of newborn fawns and pregnant females were recorded. When collected, testicles were examined for active spermatogenesis.

Mortality

Deaths were placed into three categories: predation, accidents, and undetermined. Predator-related and undetermined deaths were discovered in the field, while most accidents (i.e., road-kills) were reported by the park staff.

Parasites, Disease, and Deer Condition

All animals collected were examined for external parasites; concentrated searches were made on and in the ears, around the head, between the hooves, neck, back, flanks, genitals, and anus. External parasites were preserved in 70% ethyl alcohol, labeled, and sent to the Department of Veterinary Parasitology, Texas A & M University for identification.

Lung, liver, spleen, kidney, heart, testicle, ovary, and muscle samples from collected deer were labeled and preserved in 10% formalin. Tissues were examined at the Washington Animal Disease Diagnostic Laboratory, Washington State University, Pullman.

An indication of the condition of deer was provided by visual examination of marrow color and consistency, and omental, kidney, and heart fat. Classification was good, fair, or poor (Hornocker 1970).

Predator Scat Analysis

Fecal droppings (scats) from mountain lions, coyotes, and bobcats were collected throughout the study period. One hundred and sixty-one lion scats, 128 bobcat scats, and 245 coyote scats were analyzed. Lion and bobcat scats were found in the field, while most coyote scats were picked up along paved or dirt roads. Upon collection, droppings were identified, labeled, placed in bags, and preserved with mothballs until analyzed.

A reference collection of hair-scale impressions from prey species was made in fingernail polish (Williamson 1951). Drawings of medulla characteristics of hairs, compound microscope hair prints prepared by D. E. Atkinson, and scale photographs (Adorjan and Kolenosky 1969) also were referred to for identification. Teeth, claws, hooves, and cranial material of prey species were sometimes used in determining scat contents.

Individual scats were broken apart and different hairs sorted into isolated piles. Hair mounts were then made of representative hairs from each isolate, studied microscopically, compared to the reference series, identified, and recorded. Volumetric makeup of each hair group was ocularly estimated.

Food Habits

Twenty-five whitetail rumens were analyzed for forage content. One was collected by a hunter outside the park, while all others were obtained in the park. Table 2 lists the sex, age class, and number of animals collected. Collections by special permission were random. In addition, observations of browsing deer were used to determine other plants consumed.

TABLE 2. Sex, age, and numbers of Carmen deer collected for analysis of rumen content in Big Bend National Park.

Rumen contents were washed in water, labeled, placed in plastic bags, and frozen. Sampling was performed following the technique of Chamrad and Box (1964). Foods observed in the rumen but not sampled are listed as trace items in the diet.

Food samples from rumens were viewed under a binocular microscope and compared to reference collections of seeds and plants for identification. A complete, verified herbarium of study-area vegetation was also available. Scientific names of plants follow Correll and Johnston (1970).

Seasons are based on plant phenology, climate, and deer activity. Summer includes May, June, and July; late summer is August, September, and October; winter extends from November through January; and February, March, and April are spring months.

Competitive Interactions

Measurements of association between mule deer and whitetails were determined from coefficients of association (Dice 1945) and were subjected to a chi-square examination for determining statistical significance. Competition was also evaluated through habitat and forage use between the two deer species.

Vegetation

Vegetative sampling was done between July and November 1973. The sampling technique followed Dix (1969). Several habitat comparisons were made, with a similarity index as described by Curtis (1959:83).

Utilization of various areas by the two species of deer was determined by differences in pH values of pellets deposited by mule and white-tailed deer (Krausman et al. 1974).