The Rocky Mountain Mule Deer (Odocoileus hemionus) is only one of several subspecies of mule deer native to western North America. Others include the California mule deer, Inyo deer, the burro deer of the hot southwestern deserts, the Sitka deer of coastal Alaska and British Colombia, and the Columbian black-tailed deer found from British Columbia to central California. Modern mule deer are believed to have developed during the transition from the Pleistocene to the current Holocene period, 10,000-12,000 years ago. They are consequently one the world’s most recently evolved mammals. They developed from hybridization of white-tailed deer and primitive black-tailed deer, and then spread throughout North America after the megafaunal extinctions (such as the native North American camels, horses, mammoths, mastodons, and pronghorn) left vacated ecological niches for new animals to fill.

Rocky Mountain mule deer are opportunistic concentrate feeders, meaning that they seek and select high quality plant material. As the seasons progress, diet selection will change to whatever plants currently contain the highest quantity of protein and energy. Mule deer are frequently described as primarily browse feeders, but most data indicates their foraging behavior is far more complex. Mule deer overall have been found to feed on 484 species of forbs, 202 species of shrubs and trees, and 84 species of sedges and grasses. They are thus able to adapt to a wide range of habitats, as long as a diversity of plant types are available.

Mule deer tend to be migratory, especially in areas with a broad range of altitude. Individual animals and family groups tend to migrate between the same seasonal ranges year after year, unlike elk, whose migratory patterns are highly erratic. Large aggregations are common on winter ranges, but after fawning and throughout lactation, does tend to remain isolated with their fawns. Females without fawns do tend to remain in larger bands all through the year. In Colorado, rutting behavior peaks in November, with the bulk of fawning taking place in June. Daily feeding patterns within home ranges are highly unpredictable, especially in areas with high predator populations.

The mule deer buck is second only to the white-tailed deer as North America’s most hunted big game trophy. Mature bucks stand three to four feet at the shoulder and can weigh up to 300-400 lbs. Currently, it is estimated that 5.5 million mule deer survive in North America, with nearly one million annually killed by sport hunters.

Sources: Geist, V. 1998. Deer of the World. Stackpole Books Nowak, R.M., ed. 1999. Walker’s Mammals of the World, Volume 2, Sixth Edition. The Johns Hopkins University Press