Winter Ecology of Bighorn Sheep in Yellowstone National Park

Abstract

Bighorn sheep (Ovis c. canadensis) were intensively studied on the northern Yellowstone winter range during the winter of 1965-66, with additional data gathered the following two winters. Censuses showed a stable or slowly increasing population of about 250 animals. Grass and browse utilization was moderately high. During the winter of 196546, bighorns ate 61 percent grass, 17 percent forbs, and 22 percent browse. Bluebunch wheatgrass ( Agropyron spicatum ) was the most common species in the diet. Snow cover was light that winter, and competition with elk (Cerrus canadensis) was slight to moderate. ECOLOGY OF SHEEP IN YELLOWSTONE * Oldenxeyer et al. 257 Kleberg Research Program in Wildlife Ecology, College Station, Texas. 25pp. 1969. Texotics. Texas Parks and Wildl. Dept. Bull. 49. 46pp. SANKHALA, K. S. 1964. Wildlife sanctuaries of Rajasthan. J. Bombay lVat. Hist. Soc. 61(1): 27-34. SCHALIER, G. B. 1967. The deer and the tiger: a study of wildlife in India. The University of Chicago Press, Chicago and London. 370pp. \ILKINSON, L. F. 19:57. Defense against brush. Pages 709-712. In T. Lea [Editor], The King Ranch. Little, Brown and Co., New York. 838pp. Receirecl for publicatiowl August 28, 1970. Little research has been conducted on Rocky Mountain bighorn sheep in Yellowstone National Park since the studies of Greer ( 1931 ), Mills ( 1937 ), Murie ( 1940 ), and Gammill ( 1941 ) . Buechner ( 1960 ) included information from most of these studies as well as from his own research in his comprehensive analysis of the past, present, and future status of bighorn sheep in the United States. Annual reports of the Park Superintendent, beginning in the early 1 The National Park Service, the National Wildlife Federation, the Wildlife Management Institute, and the Yellowstone Library and Museum Association financed this study, which provided thesis uaterial for the senior author's Master of Science degree at Colorado State University, Fort Ciollins. 2 Present address: Denver Wildlife Research Center, Bureau of Sport Fisheries and Wildlife, Denver, Colorado. 3 Present address: Department of Conservation, College of Agriculture, Cornell University, Ithaca, New York. l900's, contain general statements about the status of bighorn sheep. Systematic censuses of bighorn sheep in the northern part of the park have been made periodically since the early 1930's, with some counts made from fixed-wing aircraft and from helicopters since 1955. Except for these reports, information gathered in recent years prior to our study has been limited to miscellaneous observations. Woolf ( 1966 ) conducted a summer ecology study concurrently with this study. Historical records leave little doubt that bighorn sheep were abundant and widely distributed in and around Yellowstone National Park prior to the arrival of modern man ( Henderson n.:d., Murie 1940, Haines 1965, Buechner 1960 ). Population decline apparently began in the late 1800's. Since 1903 the number of bighorn sheep in the northern part of the park has varied This content downloaded from 207.46.13.48 on Wed, 12 Oct 2016 05:52:11 UTC All use subject to http://about.jstor.org/terms 258 Journal of Wildlife Management, Vol. 35i, No. 2, April 1971 horn sheep; (3) to determine bighorn food habits and daily activity patterns of bighorn sheepl on winter rang;e; ( 4 ) to evaluate utilization of impjortant forage pllants; and (S) to evaluate prossible completitive relationships between bighoirn sheepl and other ungulates, primarily elk, oin winter range. R. E. Howe was instrumental in obtaining approval for the study from the National Park Service, and in securing funds. Professor D. R. Smith of Colorado State University supplied valuable technical assistance to the study and offered suggestions on the manuscript. R. E. Pillmore and Ann H. Jones, Denver Wildlife Research Center, critically reviewed the manuscript. K. R. Greer, Montana Fish and Game Commission, kindly provided results of elk rumen