Associations Between Bighorn Sheep and Elk in the Tom Miner Basin, Montana

Abstract

One of the hypotheses proposed for declines of bighorn sheep (Ovis canadensis) is competition for forage between bighorns and elk (Cervus elaphus). We tested the rationale underlying this hypothesis in the Tom Miner Basin, Montana. Bighorn numbers in this area declined by 70 percent or more between the mid-1970s and mid-1990s. Elk numbers apparently increased substantially during the same period. Pellet counts and vegetation surveys in 1975 and 1994-1995 indicated an increase in elk use of areas near bighorn wintering sites but no negative changes in vegetation composition. During 1994-1995, elk pellets were found in >40 percent of plots in bighorn wintering areas that contained bighorn pellets. This evidently represented elk summer use of bighorn winter habitat because we did not observe elk using bighorn wintering areas during the winter. Multivariate habitat models indicated proximity to escape terrain was the primary factor determining use of specific sites on bighorn winter range, but tree analysis indicated a secondary negative association between elk and sheep pellet densities in 1995. Our measurements of summer utilization of forage in 1994 and 1995 did not indicate that use of sheep range by elk had detectable impacts on availability of forage for sheep during winter.