Natural History Overview
CDFW's mission is "to manage California's diverse fish, wildlife, and plant resources, and the habitats upon which they depend, for their ecological values and for their use and enjoyment by the public." Mule deer are an important large mammal in California. They provide wildlife viewing, recreational and ecological value, as well as economic value to the public. An understanding of factors affecting mule deer populations is important for effective management.
The Inland Deserts Region has diverse habitats for mule deer, ranging from desert, both low and high, to foothills and mountain peaks. Each of these areas provides unique management challenges.
Description and Life History
The mule deer (Odocoileus hemionus) can be recognized by its large ears (mule-like) and black tipped tail. The male is a buck, female is a doe, and young is a fawn. The word “ deer” is an irregular noun; “ deer” is the same in the singular form and plural form.
The buck has a set of branching antlers, with each side branching into two main beams, and each beam forking into two tines. The number of forks, or points, is dependant on the buck's age, nutrition, and genetics. Antlers are shed each year in January or early February after the breeding season. New antlers, covered by a soft velvety skin begin growing in late spring. During mid-summer, after normal growth of the antlers is complete, the velvety skin gradually dries and is shed from the antlers. In early fall, as the breeding season approaches, bucks will go into rut. During the rutting or mating period bucks spar for females, and become more aggressive as they compete with other bucks for mates. Mule deer are serially polygynous, one buck mates with many does. Gestation period is about 200 days. Does can give birth to one, two, or three fawns, though triplets are rare. Fawns are born in late spring to mid-summer and are spotted at birth but loose their spots within a few months. Fawns are weaned in the fall after about 60-75 days and continue to stay with their mothers during the first year. Fawns will become sexually mature at a year and a half.
Deer are generally crepuscular, foraging activity occurs mostly around dawn and dusk, but deer may be active day or night depending on other variables, such as human activity or other disturbances in the area. Deer diets differ across their range, but high quality digestible forage is selected when available. Not all plants are nutritious for deer. Deer feed on grasses and forbs in the spring and summer, however they are primarily browsers. High quality forage items like young tender shoots, young shrubs, leaves of plants that are high in nutrients, succulent grasses, and forbs are selected. Also, deer eat items such as bark, buds, and acorns. In the high deserts and chaparral, some common plant species that deer forage are: bitterbrush, sagebrush, blackbrush, ceanothus, and mountain mahogany. In the diets of desert mule deer, Marshal et al. (2006) identified 34 plant taxa, including desert-ironwood, mesquite, brittle-bush, palo verde, burro-weed, and wild buckwheat.
Deer may be migratory or resident. In California, long distance migration is rare among large mammals, and mule deer are one of the few that migrate. Migrating deer herds, in Mono and Inyo counties, make a year-long round trip from summer range to winter range, with corridors and holding areas in between. Summer range in typically high elevation and utilized for its nutritious green forage and fawning areas. However, these high elevation areas are covered in snow during the winter, so prior to deep snow, deer must migrate to lower elevations. At low elevations, deer are confined to relatively small winter ranges, which support deer for a short period of time because forage is limited. In fact, some migrating deer will hold up in the snow until there is springtime green-up to feed on at the lower elevations.
In the San Bernardino Mountains, deer make a seasonal shift to lower elevations, but not the long distance migration seen in the north. In the Colorado Desert, the desert mule deer will migrate to different seasonal ranges based on the distribution of water and location of key forage.
Because deer don't recognize county or state line boundaries, CDFW staff need to coordinate deer management efforts with adjacent Regions in California, and adjacent states, Nevada and Arizona. CDFW and the Nevada Department of Wildlife have an Interagency Agreement that states particular goals and objective for management of the East Walker and West Walker deer herds (Mono County), which spend summers in California and migrate throughout the area and into Nevada during the fall and winter.
There are six subspecies of mule deer (Odocoileus hemionus) in California:
- O. h. californicus - California mule deer (Westside of Sierra Nevada down to southcoast)
- O. h. eremicus - Desert/burro mule deer (southwest California, northwest Mexico and Arizona)
- O. h. fuliginatus - Southern mule deer (Southernmost California and Baja California)
- O. h. hemionus - Rocky Mountain mule deer (Northwest California, western and central North America)
- O. h. inyoensis - Inyo mule deer (Sierra Nevada, California)
- O. h. columbianus - Columbia Black-tailed deer (Northern California and Pacific Northwest).
The Inland Deserts Region has four of the six mule deer subspecies: the Rocky Mountain and Inyo subspecies in the north and the California, Southern, and Burro subspecies in the south.