Food Habits of Mountain Goats, Mule Deer, and Cattle on Chopaka Mountain, Washington, 1977-1980

Abstract

The seasonal food habits of mountain goats, mule deer, and cattle on Chopaka Mountain, Wash., (1977-1980) were determined by fecal analysis. Graminoids represented 84% of the fall diet of cattle, the only period when cattle occurred within the mountain goat range. Mountain goats utilized graminoids (42%) and shrubs (31%) primarily; whereas, mule deer consumed shrubs (45%) and conifers (29%). Dietary overlap was greatest between mt. goats and mule deer (37%) and mt. goats and cattle (32%), and minimal between mule deer and cattle (15%). Considerable intraand interseasonal variation was experienced for all 3 species. Local concern has been generated over the drastic decline of mountain (mt.) goats (Oreamnos americanus) on Chopaka Mountain, Wash., since the late 1940's. Advancing plant succession and competition with mule deer (Odocoileus hemionus) and cattle (Bos taurus) for available forage and space were thought to be the prime factors resulting in this reduction. Multiple use mandates upon the Bureau of Land Management made the determination of the interactive food habits of mt. goats, mule deer, and cattle imperative. Forage allocation without such data would be impossible. The purpose of this study was to determine the seasonal food habits and dietary overlaps for mt. goats, mule deer, and cattle on Chopaka Mountain, Wash. Historically, food habits studies have usually dealt with a single species of animal. Only recently has the fecal analysis food habits study methodology enabled investigators to quantify and compare herbivore diets (Storr 1961, Sparks and Malechek 1968, Hansenet al. 1973, Todd and Hansen 1973, Dearden et al. 1975). A number of comparative food habits studies are available for mule deer and cattle (Schwann 1945, Julander 1955, Mackie 1970 McKean and Bartmann 1971, Constan 1973, Hansen and Reid 1975, Hubbard and Hansen 1976, Hansen et al. 1977, Hansen and Clark 1977), but no comparative studies are available for mt. goats. Previous comparative food habits studies have demonstrated that ungulate food habits studies and their relationships vary considerably depending upon the specific ungulate involved, sampling techniques, location of study, year of study, and season of study. Generalization of food habits and their relationships are, therefore, rarely reliable. Mt. goat food habits studies (Anderson 1940, Harmon 1944, Casebeer 1948, Brandborg 1955, Saunders 1955, Hibb 1967, Kuck 1970) have been limited in scope and sample size due to the relatively inaccessible habitat of the animals. Authors are wildlife biologist, U.S. Bureau of Land Management, Safford, Ariz., and wildlife biologist, Washington Department of Game, Olympia, Wash. This study was supported by the U.S. Bureau of Land Management, Pittman Robertson Project 88R, and the Washington Department of Game. We appreciate the assistance of Bruce Davitt of the Wildlife Habitat Laboratory at Washington State University for microhistological fecal analysis and Jerry King and Bill Hebner of the Washington Department of Game for fecal sample collection. We also wish to acknowledge the critical review of the manuscript by Raul Valdez, David Kitchen, and R.M. Hansen. Manuscript received September 14, 1981. Study Area The study area, Chopaka Mountain, is located in northcentral Washington approximately 24 km west of Oroville. Mt. goats utilized approximately 2,400 ha of the mountain at elevations ranging from 2,388 m on Chopaka Mountain down to 360 m in the Similkameen Valley. Annual precipitation varied from 65 cm at the higher elevations to 38 cm in the valley. Snowpack averaged 2-3 m on Chopaka Mountain to 0.5 m in the Similkameen Valley. Seventy-one percent of the area is administered by the Bureau of Land Management, 25% is administered by the Washington State Department of Natural Resources, and 4% is privately owned. Geologically, Chopaka Mountain is an extension of the Cascade Mountain Range, although it borders the Okanogan Highlands and shares similar rock formations. The principal mt. goat range is on the eastern face of Chopaka Mountain where steep cliffs are interlaced with sharp, steep draws and hogback ridges. Cattle utilize the relatively flat terrain on the top and bottom of Chopaka Mountain. Mule deer utilize the entire area, except for the steepest cliffs. Substantial elevational changes, discontinuous wildfires, and geological outcrops have resulted in a diversity of climax and successional plant communities. The lower elevations are dominated by an open forest composed of ponderosa pine (Pinusponderosa), Douglas fir (Pseudotsuga menziesii), and bunchgrass (Agropyron spp.) communities. Mixed subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta), and whitebark pine (Pinus albicaulis) communities dominate the higher elevations. Bunchgrass communities dominate the developed soil sites; whereas, shrubs predominate near rock slides on the poorer soil sites. Bluebunch wheatgrass (Agropyron spicatum), Idaho fescue (Festuca idahoensis), pinegrass (Calamagrostis rubescens), Sandberg's bluegrass (Poa sandbergii), and cheatgrass (Bromus tectorum) are the predominant grasses. Dominant shrubs include buffaloberry (Shepherdia canadensis), currant (Ribes spp.), sagebrush (Artemisia spp.), serviceberry (Amelanchier alnifolia), Oregon grape (Berberis nersosa), ninebark (Physocarpus malvaceous), and snowbrush ceanothus (Ceanothus velutinus).