Mule deer and elk diet as an indicator of habitat competition. Frisina, Michael ^*,1, Wambolt, Carl^*,2, ¹ 1330 West Gold Street, Butte, MT, USA² 119 Linfiled Hall, MSU Campus, Bozeman, MT

ABSTRACT- Mule deer populations have gradually declined in recent decades, while elk have often increased on the same ranges. The cause is uncertain and a source of debate. Increasing elk numbers on these winter ranges may be causing competition for resources. We contrast winter diets of mule deer and elk to relate them to the population trends of both species on the Mount Haggin Wildlife Management Area in southwest Montana. From 1978 through 1996 elk populations were increasing. Mule deer populations were also increasing from 1978 through 1989, but decreasing from 1990 through 1996. The same 5 browse species comprised 95% and 52% of the mule deer and elk winter diets respectively. The diet overlap coefficient for these 5 browse species was 0.9, indicating a high degree of diet similarity. These data indicate there is a potential for significant competition between mule deer and elk sharing winter ranges. Because elk have a diet more varied (56% browse, 32% grass, 12% forbs) than mule deer (98% browse, 2% grass, 0.5% forbs) on this winter range, it is likely mule deer will be the most negatively impacted.

KEY WORDS: elk, mule deer, browse, food habits