Life History, Ecology, and Range Use of the Pronghorn Antelope in Trans-Pecos Texas

Buechner, Helmut

The primary objective of the fifteen-month investigation was to determine antelope food habits and antelope-livestock competition. Most of the food-habits data in the literature pertain to stomach-content analyses; they indicate that pronghorns are largely browse feeders in the western States and consume only small quantities of grasses. The antelope population, reduced almost to the vanishing point late in the 19th century, has increased again to approximately 7,000 in Trans-Pecos Texas. Control of eagles and coyotes doubtlessly helped in the recovery of the pronghorn, but protection by ranchmen, game wardens, and later the public in general appears to be chiefly responsible for the substantial increase. The physical environment of the region is characterized by a climate of scant precipitation, rapid evaporation, moderate winters, and mild summers. Excessive overgrazing throughout the region intensifies the severe complex of ecological conditions under which the vegetation and animal life must develop and maintain themselves. The Trans-Pecos Region covers an area of 31,392 square miles in western Texas. Two physiographic subdivisions are recognized: (1) The western extension of the Edwards Plateau across the Pecos River and (2) the Mountains and Basins Area. The basins represent the easternmost of the desert basins of southwestern United States. The soils of the basins and plains are subdivided into three series: Reagan, light brown; Reeves, very light brown; and Verhalen, reddish brown. The grass-covered Reagan soils are among the best in the region and form an important part of several antelope habitats. As a group the extensive Reeves soils are low in productivity, being dominated mainly by desert-scrub vegetation. The heavy clay soils of the Verhalen series occur in large basins characterized by tobosa grass. Soils of the rough highlands and rolling hills are divided into the Ector and Brewster series, the former being derived from limestone, the latter from igneous, rock. The two principal biotic provinces are the Navahonian with its Pinon-Juniper and Oak-Juniper Life Belts and the Chihuahuan with its Desert Grassland and Desert Scrub Biotic Districts. Six grassland ecologic associations are recognized. The Desert Scrub is divided into four associations. Bluestem grasses were apparently abundant over much of the region at one time, associated with the bunch form of blue grama. In the "Marfa Flat Association," blue grama is dominant in the form of a short turf. Tobosa seems to have developed on broad flats formerly dominated by bluestems and gramas; under continued overgrazing it in turn is replaced by burro grass. When overgrazed, the several grassland associations become invaded by Desert Scrub; extensive areas have thus become dominated by woody vegetation. The sotol-lechuguilla community spreads with excessive grazing on limestone hills. Mixed scrubs, creosote bush, and mesquite associations invade grasslands of the basins. The extent, rapidity, and type of invasion depend upon local climatic conditions, soil type, slope gradient, exposure, and grazing pressure. Fawns were born from the first week in April to the latter part of May and possibly into the first week in June in 1947. Twin fawns, observed from birth until 31 hours of age, were active only 9 percent of the time between 5:30 a. m. and 9:00 p. m. of the second day of life. The same fawns were active 19 percent of the daylight hours when one week old. The breeding season extends from the last week in August to the first week in October. Gestation is from 7 to 7.5 months. Successful establishment and breeding of antelope herds are possible with a 50- to 75-percent loss in the theoretical breeding potential. Records of 84 deaths indicate that the greatest mortality is caused by old-age conditions and overgrazing by sheep. Two tagged does were 10- and 12-years old, respectively when retrapped. To determine the activity of antelope, specific herds were followed

Life History, Ecology, and Range Use of the Pronghorn Antelope in Trans-Pecos Texas

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