Diets of Ungulates Using Winter Ranges in Northcentral Montana

Abstract

Dietary comparisons based on fecal analysis of mule deer, elk, bighorn sheep, and cattle using mule deer winter ranges along the east slope of the Rocky Mountains indicated that elk, bighorn, and cattle diets were much more similar to each other than to mule deer diets. The greatest overlap between elk, bighorns, and mule deer occurred during late winter when creeping juniper became an important dietary item for all 3 species. Rank-order comparisons indicate that rankings of items in the graminoid and forb forage classes for diets of the 4 ungulate species were significantly correlated with availability of these items. Correlations between availability and diet rank-order were poor for items in the woody forage class. Differences in the diets of the 4 ungulate species were more pronounced at the forage class level than at the plant species/genus level. Resource management along the East Front of the Rocky Mountains in northcentral Montana is becoming one of the most important land use issues in the state. The lo-km-wide strip where the prairie and mountains meet encompasses winter ranges for wild ungulates summering in the Bob Marshall Wilderness, supports a viable cattle industry, and has recently become the center of intense oil and gas exploration activity. Development of oil and gas reserves in the area could alter the existing relationship between livestock and game species by converting rangeland to well sites, roads, or storage facilities and by increasing disturbance and harvest of native ungulates. To contend with these changes in land use, range mangers will require more precise knowledge of the manner in which native and domestic ungulates use available forage than was necessary in the past. This study compares diets of mule deer (Odocoileus hemionus), elk (Cervus elaphus) bighorn sheep (Ovis canadensis), and cattle from sites where concentrations of native ungulates winter. A partial assessment of dietary selectivity is included. Study Area The study area, located approximately 110 km northwest of Great Falls, Mont. (Fig. l), was characterized by shortgrass prairie intergrading with a narrow foothill region of fescue (Festuca sp.)wheatgrass (Agropyron sp.) grassland and limber pine (Pinusflexilis)woodland/savannah. Mule deer, elk, and bighorn sheep winter along the foothill zone from December through May. Most cattle grazing in the foothills occurs from May through October on private, U.S. Forest Service, and Bureau of Land Management holdings.

Elk, Mule Deer, and Cattle Foraging Relationships on Foothill and Mountain Rangeland

“…The grass-dominated diets of cattle and elk reported in this study (Table 1) agree with results from previous studies on foothill and mountain rangeland in the northern Rocky Mountains (Stevens 1966;Miller and Krueger 1976;McLean and Willms 1977;Skovlin and Vavra 1979;Berg and Hudson 1982;Kasworm et al 1984;Vavra et al 1989;Ngugi et al 1992). For elk, graminoids were an especially important dietary component in winter and spring (66% and 72%, respectively; Table 1).…”

“…For elk, graminoids were an especially important dietary component in winter and spring (66% and 72%, respectively; Table 1). These values compare favorably with elk diets on foothill rangeland in northeastern Oregon (60% graminoids in winter-spring; Skovlin and Vavra 1979), southwestern Alberta (95% graminoids in winter-spring; Berg and Hudson 1982), north-central Montana (84% graminoids in winter and 65% graminoids in spring; Kasworm et al 1984), west-central Montana (77% graminoids in spring; Stevens 1966), and south-central Wyoming (84% graminoids in spring; Ngugi et al 1992).…”

“…Kasworm et al (1984) also reported that winter elk diets and summer cattle diets were highly correlated, and Berg and Hudson (1982) reported an astounding 98% dietary overlap between summer-fall cattle diets and winter-spring elk diets. In a companion study on 2 of the 4 ranches in our study area, Crane (2002) determined that elk in winter-spring preferentially selected feeding habitat where moderate cattle grazing had occurred during the previous summer-fall.…”

“…Feeding habitat overlap and dietary overlap also are typically low between mule deer and cattle in these habitats (Berg and Hudson 1982;McLean and Willms 1982;Kasworm et al 1984); however, foraging niche overlap can be significant in spring, when graminoids are succulent (Mackie 1981;Miller and Vavra 1982).…”

“…Significant dietary and feeding habitat use overlap often occurs on foothill and mountain rangeland between summerfall cattle grazing and elk or mule deer grazing in the winterspring (Kasworm et al 1984;Vavra et al 1989;Crane 2002). This overlap can be beneficial to wild ungulates, for example, when elk or mule deer preferentially select feeding sites where previous cattle grazing has improved forage palatability (Willms et al 1979;Grover and Thompson 1986;Jourdonnais and Bedunah 1990;Frisina 1992;Yeo et al 1993;Crane 2002).…”