Mule Deer (Odocoileus hemionus)
Mule deer occur throughout the Los Padres, Angeles, San Bernardino, and Cleveland National Forests in DAU 9 (Central Coast [south]) and DAU 10 (South Coast). The Central Coast (south) DAU comprises approximately 15,600 square miles (40,400 square kilometers) from the San Francisco Bay and Delta south through Ventura County and east to Interstate 5. National Forest System lands in DAU 9 (all of which are on the Los Padres National Forest) account for 18 percent of the total unit area. The South Coast DAU comprises approximately 7,800 square miles (20,200 square kilometers) from Los Angeles County south to the Mexico border and east to Interstate 10. National Forest System lands in DAU 10 account for 34 percent of the total unit area and include the Angeles, San Bernardino, and Cleveland National Forests.
Cowan (1956) and Hall (1981) recognized 11 subspecies of mule deer in North America. Two subspecies are known to occur in the Central Coast (south) and South Coast DAUs. California mule deer (O. h. californicus) occurs in the northern portion of the Central Coast (south) DAU, and southern mule deer (O. h. fuliginatus) occurs in the southern portion of the Central Coast (south) DAU and throughout the South Coast DAU. O. h. fuliginatus differs from O. h. californicus in the following distinguishing features: the summer pelage is darker cinnamon, rather than cinnamon-buff; the dorsal area appears darker with many black-tipped hairs; and the dark spots on the sides of the lower lip are restricted and do not meet on mid-ventral lines (Cowan 1933). The coastal areas of the Los Padres also contains the Columbian black-tailed subspecies (O. h. columbianus) which often interbreed with the California subspecies (O. h. californicus) and these animals are typically very small in size compared to the normal California mule deer and have rump marking more typical of black tails (Freel pers. comm.).
Characteristics of habitat used by mule deer differ geographically. In the low-elevation mountain ranges that lack extensive conifer forests (e.g., the Santa Ana Mountains, mountains of San Diego County, and most of the Los Padres National Forest) mule deer reach their highest densities in oak woodlands, riparian areas, and along the margins of meadows and grasslands (Bowyer 1986). They occur in lower densities in open scrub and young chaparral, but tend to avoid dense brushfields. In chaparral habitats, mule deer thrive on early successional vegetation that is prevalent for 1–10 years after a fire (Bowyer 1981). In the low-elevation mountains of San Diego County (e.g., 4,900-foot [1,494-meter] East Mesa in the Cuyamaca Mountains) mule deer primarily occupy meadows, oak woodlands, and low-elevation pine forests (Bowyer 1984, 1986).
Meadows are particularly important fawning habitat. Deer grass (Muhlenbergia ridgens) is used extensively by fawns for cover, and adult deer typically bed down in oak and pine stands (Bowyer 1984, 1986). The availability of free water during summer is a critical habitat requirement for mule deer in arid regions. On the East Mesa in the Cuyamaca Mountains, mule deer are mostly found in areas within 0.6 mile (1 kilometer) of free water. Areas without sources of summer water are usually devoid of fawns (Bowyer 1986). The most common habitat manipulation used to benefit mule deer is prescribed burning, usually in chaparral. Burning creates openings in the brush and temporarily increases the quality of deer forage (Dasmann and Dasmann 1963).
After observing marked increases in deer harvested in San Diego County following the Laguna fire in 1970, Bowyer (1981) developed deer management guidelines that emphasize burning to rejuvenate browse. Bowyer (1986) points out that the proximity of burned areas to other vegetative types preferred by mule deer may be a critical factor in determining the response of deer populations to alterations in old-growth chaparral. Short-lived increases in forage quality in areas with few deer will do little to promote population growth. Thus, chaparral burns will be most effective when they are conducted in areas that adjoin meadow, oak, or pine vegetation types that contain summer water sources (Bowyer 1981).
Mule deer usually reach sexual maturity at 1.5 years (Mackie and others 1982), and most females breed during their second year (Anderson and Wallmo 1984). Breeding records from 23 separate studies indicate that mule deer breed from mid-September to early March. A peak in breeding appears to occur from late November through mid-December. Young are born from late spring to early autumn, and the peak birth period is generally from mid-June to early July. The most common litter size for mule deer is two. However, females in their first and second breeding year will often produce only one young (Anderson and Wallmo 1984).
Mule deer may be active day or night but are generally crepuscular, with most activity occurring in the early morning and at dusk (Zeiner and others 1990). Miller (1970) found that activity patterns in black-tailed deer (O. h. columbianus) in northern California are influenced by changes or extremes in temperature, precipitation, and relative humidity. Mule deer in the Central Coast (south) DAU are resident deer that do exhibit some upslope/downslope movement with seasonal changes in weather and food resources, but essentially constitute a nonmigratory population. Mule deer inhabiting the high-elevation mountain ranges (i.e., San Bernardino, San Gabriel, and San Jacinto Mountains and Mount Pinos) of the South Coast DAU commonly undertake elevational migrations between summer and winter ranges (Loft and others 1998).
Migratory movements of up to 15 miles have been noted in the San Bernardino Mountains (Loe pers. comm.). Mule deer inhabiting lower-elevation mountain ranges that lack extensive conifer forests (e.g., the Santa Ana Mountains and mountains of San Diego County) and coastal areas do not migrate, but exhibit some upslope/downslope movement with seasonal changes in weather and food resources (Loft and others 1998, Nicholson and others 1997, Vaughn 1954).
Migratory mule deer move upslope in the summer into well-watered habitats on north-facing slopes dominated by pine forest. These habitats also contain openings, meadows, and riparian habitats that the deer utilize. Nonmigratory mule deer spend the summer on lower slopes, primarily in oak woodlands and the limited pine forests that occur in these lower-elevation areas. In winter, mule deer congregate on lower south-facing slopes where they heavily use oak woodlands, as well as chaparral and sagebrush habitats (Nicholson and others 1997).
Diet and Foraging
Mule deer are herbivores and require adequate supplies of highly digestible, succulent forage (Robinette and others 1973). Although mule deer have traditionally been identified as browsers (consuming predominantly woody forage), studies of their diet and stomach structure have induced researchers to reclassify them as intermediate feeders (consuming equal proportions of woody and herbaceous forage) (Anderson and Wallmo 1984). The type of plants eaten by mule deer is highly variable. Kufield and others (1973) reported that a total of 788 species of plants were eaten by Rocky Mountain mule deer (O. h. hemionus). Of these species, 202 were shrubs and trees, 484 were forbs, and 84 were grasses, sedges, or rushes.
Migratory mule deer establish distinct summer and winter home ranges and use approximately the same home ranges in consecutive years. Nonmigratory mule deer maintain yearlong home ranges. The size of mule deer home ranges is highly variable and probably dependent on a number of factors including sex, age, body mass, season, race, and habitat. In general, home range size can vary among deer using the same general habitat; males use larger areas than females. Home range size increases as distance between food, cover, and water sources increase (Anderson and Wallmo 1984).
Common predators of mule deer include mountain lion, coyote, bobcat, golden eagle, and black bear (Anderson and Wallmo 1984). When a mule deer detects a predator nearby, it attempts to escape by placing obstacles such as boulders, trees, bushes, and steep slopes between itself and the predator (Geist 1981).
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