FORAGE SELECTION BY MULE DEER ON WINTER RANGE GRAZED BY SHEEP IN SPRING

Late spring grazing by sheep altered the amount of several forage categories available to deer the subsequent autumn and winter. Total herbaceous plant material was much reduced by spring-time sheep grazing, but regrowth following fall precipitation increased the proportion of green herbaceous material available. Current year’s growth of bitterbrush was also increased relative to the nongrazed situation due to the release of moisture and nutrients accompanying the removal of herbaceous plants by sheep. Subsequently winter diets of mule deer on the sheep-grazed area were higher in herbaceous components but lower in shrub components than on the adjacent area where sheep had not been previously grazed. Implications of these findings are that quality of deer diets was not detrimentally affected where sheep had grazed during the preceding spring and a much greater animal yield is possible through dual use. A deficit of winter forage apparently limits mule deer (Odocoileus hemionus hemionus) population over much of their range (Aldous 1945; Doman and Rasmussen 1944). This can be viewed in terms of both extent of winter rangeland and quantity of forage (principally shrubs) produced there. The Utah Division of Wildlife Resources estimates that there are approximately 7,424,000 ha of mule deer winter range in Utah, including some 1,149,000 ha dominated by the sagebrush complex, primarily big sagebrush (Artemisia tridentata). However, big sagebrush is viewed as only moderate quality winter forage for deer because of its low acceptability (Smith and Hubbard 1954). This is a particular problem where sagebrush exists in stands devoid of more palatable shrub species. Winter deer losses in Utah appear to be inversely related to the amount of palatable browse species available (Robinette et al. 1952). The grazing of deer winter ranges by domestic livestock is common throughout the Intermountain West. Such ranges are grazed in spring when forage is typically in short supply for the livestock industry. Hence, the generally low state of productivity of these ranges is viewed as a limitation to livestock production (Cook and Harris 1968) as well as to deer production. Recent research indicates that with properly designed grazing strategies, livestock-big game competition can probably be minimized (Jensen et al. 1972; Jensen et al. 1976). Moreover, these same studies suggest that livestock may be used to manipulate vegetation on deer winter ranges to effectively Authors were research assistant, associate professor, and research assistant, respectively., Department of Range Science, Utah State University, Logan 84322. Smith and Fulgham are now, respectively, assistant professor of animal science, Angelo State University, San Angelo, Texas 76901, and assistant professor of animal and range sciences, New Mexico State University, Las Cruces 88003. This report is Journal Paper No. 2249 of the Utah Agricultural Experiment Station, the supporting institution for this research. Authors also acknowledge the Utah Division of Wildlife Resources (UDWR) for providing the study site, the experimental animals, and logistic support. Charles H. Jensen, game biologist, UDWR, assisted in site selection and study design. -Dr. Charles Romesburg and Mr. Kim Marshall, US/IBP Desert Biome Project, were both especially helpful in the data analysis phase of the project. Manuscript received November 14, 1977. increase quantities of browse available to wintering deer. However, the specific responses of mule deer to such grazing systems have not been well established. Thus, the study reported in this paper was designed to determine: (1) the plant species present and available to wintering mule deer following spring-time sheep grazing and (2) the relative proportions of the various plant species in the diets of mule deer during the winter following the spring sheep grazing treatment.