Studies were conducted to determine the botanical composition of the diet of tame pronghorns (Antilocapra americana) on a grama-buffalo grass (Bouteloua-Buchloe) prairie under light and heavy cattle grazing regimes. Results indicated that pronghorns consume a wide variety of plant species when available. The diet was composed of 44, 54, and 2 (light use treatment) and 52, 43, and 5 (heavy use treatment) percent grass, forbs, and shrubs, respectively. Comparisons of foods eaten by tame and wild pronghorns indicated some differences in forage preferences, but only fringed sagewort (Artemisia frigida) occurred at a significantly (P < 0.05) different frequency. Comparisons of forage preferences of three wild herds of pronghorns also indicated differences in plant species. A comparison of foods eaten by four ungulates grazing together showed that pronghorn diets were less similar to bison (Bison bison) and cattle diets than to domestic sheep diets. J. WILDL. MANAGE. 40(3):469-478 Foods eaten by the pronghorn throughout its current range have been studied and reviewed by many investigators (Beale and Smith 1970, O'Gara and Greer 1970, Mitchell and Smoliak 1971, Taylor 1972, Sundstrom et al. 1973). In other studies workers have examined the extent of competition between domestic livestock and pronghorns (Buechner 1947, Severson and May 1967, Campbell 1970). Data collected by Hoover et al. (1959), Hoover (1966), and Hoover (1971) related information on foods of pronghorns on the shortgrass prairie and competition between pronghorns and domestic livestock. Yoakum (1972) reviewed historical and current (as of 1964) distribution of pronghorns in North America. His findings showed that the pronghorn was historically an animal of the prairie grasslands and was closely associated the bison. Yoakum (1972:173) further stated that with the advance of white man's agriculture civilization, the herds of high density buffalo [sic] and antelope were extirpated from the majority of the grassland plains. It, therefore, appears that the majority of the vast prairie lands which produced millions of antelope in pristine times, are now so intensively farmed that antelope no longer inhabit them, and antelope today exist only in peripheral ranges which historically produced low density populations. Bison and pronghorns do not coexist on v st areas of the shortgrass prairie today, so opportunities to study their food habits in close association are limited. Part of the Grassland Biome (IBP) analysis of the shortgrass prairie ecosystem involved determining the forage habits of four grassland herbivores (cattle, sheep, bison, and pronghorns) under two grazing regimes. The four ungulates shared common pastures, so differences in their food habits were attributed to the animals rather than to the environment. The purpose of our study was to determine in detail the botanical composition of the diets of tame pronghorns relative to forage availability through the year and to compare these feeding habits those of wild pronghorns. We also make comparisons to diets of cattle, sheep, and bison reported by other investigators (Peden et al. 1974, Peden 1972) during this study. 1 This paper reports on work supported in part by National Science Foundation Grants GB-13096, GB-31862X, and BMS73-02027 A02 to the Grassland Biome, U.S. International Biological Program, for Analysis of Structure, Function, and Utilization of Grassland Ecosystems. J. Wildl. Manage. 40(3):1976 469 This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 05:38:38 UTC All use subject to http://about.jstor.org/terms 470 PRONGHORN DIETS IN COLORADo Schwartz and Nagy We acknowledge K. Miller and S. Kerr for their assistance pronghorn care and training and R. Souther for maintenance of animals at the Pawnee Site. J. Hoover aided study design. M. Travis assisted throughout the study data collection. We also thank the many members of the IBP Grassland Laboratory who aided in various phases of data collection and analysis: C. Dickinson for plant biomass estimates, S. Woodmansee for fecal analyses, D. Swift for computer programming, M. Campion for statistical analysis, and J. Ellis and L. Menges for manuscript review.