Field Guide to Mammals of Southern California Nelson’s Bighorn Sheep

Nelson’s Bighorn Sheep (Ovis canadensis nelsoni)



General Distribution

Populations of Nelson’s bighorn sheep are found in four areas on National Forest System lands in southern California. The San Rafael Peak/Cobblestone Mountain population is a small, reintroduced population that was established in the 1980s. This population inhabits an area in the southern part of the Los Padres National Forest. Nelson’s bighorn sheep in the San Bernardino Mountains are considered to constitute two separate populations: the larger population (San Gorgonio Herd) occurs in the vicinity of Mount San Gorgonio in wilderness; the other population (Cushenbury Herd) occurs on the northern edge of the range in desert-facing canyons (e.g., Furnace, Bousic, Arctic, and Marble Canyons). Finally, the population in the San Gabriel Mountains is concentrated primarily in the Bear Creek drainage; the upper East Fork of the San Gabriel River and Cattle Canyon (both in the Sheep Mountain Wilderness); San Antonio Canyon; Cucamonga Canyon; and the South and Middle Forks of Lytle Creek (Stephenson and Calcarone 1999).

Systematics

The term “desert bighorn sheep” is used to describe those subspecies of bighorn sheep inhabiting dry and relatively barren desert environments. In the past, these subspecies included Nelson’s bighorn sheep (O. c. nelsoni), Mexican bighorn sheep (O. c. mexicana), Peninsular bighorn sheep (O. c. cremnobates), and Weems bighorn sheep (O. c. weemsi) (Manville 1980). However, new genetic evidence and a recent reanalysis of morphometric data resulted in changes in the accepted taxonomy for Nelson’s bighorn sheep and the Peninsular bighorn sheep (U.S. Fish and Wildlife Service 2001). After their analysis, Wehausen and Ramey (1993) placed Peninsular bighorn sheep within the Nelson subspecies.

Habitat Requirements

Desert bighorn sheep inhabit dry, relatively barren, desert mountain ranges throughout North America. Escape terrain is identified as the single most important habitat component for bighorn sheep in these mountains. Escape terrain is defined as steep slopes (80 percent or steeper) with abundant rock outcrops and sparse shrub cover (canopy cover of 30 percent or less). Nelson’s bighorn sheep in the San Gabriel Mountains occur at elevations of 3,000-10,064 feet (914-3,068 meters [i.e., to the summit of Mount San Antonio]). During the winter and spring, Nelson’s bighorn sheep occur primarily in escarpment chaparral in the lower canyons at 3,000-6,000 feet (914-1,829 meters).

Reproduction

The breeding season of Nelson’s bighorn sheep generally begins in November with the rutting season. Following a six month gestation period, ewes give birth to single lambs (occasionally twins) from late April through early July. During the first few weeks after giving birth, ewes remain alone with their lambs in steep terrain until they join a nursery group. Lambs are weaned at 1–7 months, and juveniles remain with the ewes until they reach sexual maturity (U.S. Fish and Wildlife Service 2000b). Rams are believed to be sexually mature at 6 months of age (U.S. Fish and Wildlife Service 2000a). In the San Gabriel Mountains, the duration of the rut was from mid-September to late December with a peak in late October through the first half of November (De Forge 1980). During the height of the rutting period, mature rams seemed to have little fear of humans and made movements up to 2.5 miles to find ewes.

Daily/Seasonal Activity

In general, bighorn sheep feed in the early morning, at midday, and in the evening, lying down and chewing their cud at other times, and bedding down for the evening. Foraging and bedding spots may be used for years (McMahon 1985). Daily foraging and resting cycles also vary depending on forage quality (U.S. Fish and Wildlife Service 2000a). Seasonal activity depends on availability of water, forage, and escape cover. Typically, bighorn sheep congregate near dependable water sources from May through October, when temperatures are highest. This aggregation of individuals also corresponds with breeding activities. Young bighorn sheep learn locations of escape terrain, water sources, and lambing habitat from older individuals in the group (U.S. Fish and Wildlife Service 2000b). Bighorn sheep migrate between winter and summer ranges, generally moving downslope in winter and spending summer in alpine habitats. Water restricts movement of the species during hot summer months (Zeiner and others 1990).

Diet and Foraging

Nelson’s bighorn sheep graze and browse on succulent grasses and forbs. Sedge, grasses, and small alpine forbs constitute the chief food (Ingles 1965). Browse is an important component of the diet for populations in arid habitats (Zeiner and others 1990).

Territoriality/Home Range

Young ewes learn home range boundaries from their mothers and/or older females and demonstrate a high degree of philopatry to these traditional home ranges throughout their lives (Geist 1971). Rams do not exhibit the same site fidelity as ewes and tend to move among ewe groups. Home ranges in one study were found to average 9.8 square miles (25.5 square kilometers) and 7.8 square miles (20.1 square kilometers) for rams and ewes, respectively (U.S. Fish and Wildlife Service 2000a). De Forge (1980) working in the San Gabriel Mountains found ewe home ranges from 1.84 and 3.06 sq. km (.71-1.8 sq. mi.) and a ram home range to be 17.9 sq. km (6.9 sq. mi.).

Predator-Prey Relations

Recently, mountain lion predation has been documented as a threat to some ewe groups in the Peninsular Ranges. Predation by other species such as coyotes and bobcats may also reduce lamb recruitment (U.S. Fish and Wildlife Service 2000a). Holl (2002) and Holl and others (2002) both implicated predation by mountain lions as a primary cause of the huge decline of the San Gabriel Mountain sheep herd.

Literature Cited

Clark, J.L. 1970. The great arch of the wild sheep. Norman, OK: University of Oklahoma Press. De Forge, J.R. 1980. Ecology, behavior, and population dynamics of desert bighorn in the San Gabriel Mountains of California. Pomona, CA: California State Polytechnic University. M.S. thesis. Geist, V. 1966. The evolutionary significance of mountain sheep horns. Evolution 20: 558-566. Geist, V. 1971. Mountain sheep – a study in behavior and evolution. Chicago, IL: University of Chicago Press. Hamilton, K.M. 1983. Effects of people on bighorn sheep in the San Gabriel Mountains, California. Las Vegas: University of Nevada. M.S. thesis. Hansen, C.G. 1967. Bighorn sheep populations of the desert game range. Journal of Wildlife Management 31: 693-706. Holl, S.A.; Bleich, V.C. 1983. San Gabriel mountain sheep: Biological and management considerations. San Bernardino, CA: Unpublished report on file at the San Bernardino National Forest. Holl, S.A.; Torres, S.G.; Bleich, V.C. 2001. Population dynamics of bighorn sheep in the San Gabriel Mountains, 1967-1998. Paper presented at the September 27, 2001 annual meeting of The Wildlife Society in Reno, Nevada. Holl, S.A. 2002. Conservation strategies for bighorn sheep in the San Gabriel mountains, California. Report prepared for the Los Angeles County Fish and Game Commission, Los Angeles, CA. Lawson, B.; Johnson, R. 1982. Mountain sheep. In: Chapman, J.A.; Feldhamer, G.A., eds. Wild mammals of North America. Baltimore, MD: John Hopkins University Press. Ingles, L.G. 1965. Mammals of the Pacific states- California, Oregon, Washington. Stanford, CA: Stanford University Press. Leslie, D.M., Jr.; Douglas, C.L. 1979. Desert bighorn sheep of the River Mountains, Nevada. Journal of Wildlife Management Wildlife Monograph 66. Light, J.T., Jr.; Weaver, R. 1973. Report on bighorn sheep habitat study in the area for which an application was made to expand the Mt. Baldy winter sports facility. San Bernardino, CA: Unpublished report on file at the San Bernardino National Forest. Manville, R.H. 1980. The origin and relationships of American wild sheep. In: Monson, G.; Sumner, L., eds. The desert bighorn: Its life history, ecology, and management. Tucson, AZ: University of Arizona Press; 1-6. McMahon, J.A. 1985. The Audubon Society nature guides: Deserts. New York: Alfred A Knopf. Shackelton, D.M. 1985. Ovis canadensis. No. 230. Mammalian Species. Published by the American Society of Mammalogists. Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment: Habitat and species conservation issues. General Technical Report GTR-PSW-172. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture.. Torres, S.G.; Bleich, V.C.; Wehausen, J.D. 1994. Status of bighorn sheep in California, 1993. Desert Bighorn Council Transactions 38: 17-28 Torres, S.G.; Bleich, V.C.; Wehausen, J.D. 1996. Status of bighorn sheep in California, 1995. Desert Bighorn Council Transactions 40: 27–34. U.S. Fish and Wildlife Service. 2000a. Recovery plan for bighorn sheep in the Peninsular Ranges, California. Portland, OR: U.S. Fish and Wildlife Service. U.S. Fish and Wildlife Service. 2000b. High priority biological opinion on activities related to trails, dispersed recreation, and developed recreation on the peninsular bighorn sheep. U.S. Fish and Wildlife Service. 2001. Final rule to designate critical habitat for the peninsular bighorn sheep distinct population segment. Federal Register. Wehausen, J.D.; Ramey, R.R., II. 1993. A morphometric reevaluation of the peninsular bighorn subspecies. Desert Bighorn Council Transactions 37: 1-10. Zeiner, D.C.; Laudenslayer, W.F., Jr.; Mayer, K.E., eds. 1990. California’s wildlife. Volume I: Mammals. Sacramento, CA: California Statewide Wildlife Habitat Relationships System, California Department of Fish and Game.

Share

Field Guide to Mammals of Southern California Mule Deer

Mule Deer (Odocoileus hemionus)

General Distribution

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.

Systematics

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.).

Habitat Requirements

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).

Reproduction

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).

Daily/Seasonal Activity

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.

Territoriality/Home Range

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).

Predator-Prey Relations

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).

Literature Cited

Anderson, A.E.; Wallmo, O.C. 1984. Odocoileus hemionus. Mammalian Species 219: 1-9. Published by the American Society of Mammalogists. Bowyer, R.T. 1981. Management guidelines for improving southern mule deer habitat on the Laguna-Morena demonstration area. USDA Forest Service, 40-9AD6-9-622. Bowyer, R.T. 1984. Sexual segregation in southern mule deer. Journal of Mammalogy 65: 410-417. Bowyer, R.T. 1986. Habitat selection by southern mule deer. California Fish and Game 72: 153-169. Bowyer, R.T.; Bleich, V.C. 1984. Effects of cattle grazing on selected habitats of southern mule deer. California Fish and Game 70: 240-247. Bunnell, F.L.; Harestad, A.S. 1983. Dispersal and dispersion of black-tailed deer: Models and observations. Journal of Mammalogy 64: 201-209. Cowan, I.M. 1933. The mule deer of southern California and northern lower California as a recognizable race. Journal of Mammalogy 14: 326-327. Cowan, I.M. 1956. Life and times of the coast black-tailed deer. In: Tylor, W.P., ed. The deer of North America. Washington, DC: Wildlife Management Institute. Dasmann, R.F.; Dasmann, W.P. 1963. Mule deer in relation to a climatic gradient. Journal of Wildlife Management 27: 196-202. Geist, V. 1981. Behavior: Adaptive strategies in mule deer. In: Wallmo, O.C., ed. Mule and black-tailed deer of North America. Lincoln, NE: University of Nebraska Press.?Hall, E.R. 1981. The mammals of North America. 2d ed. New York: John Wiley & Sons. Kufield, R.C.; Wallmo, O.C.; Feddema, C. 1973. Foods of the Rocky Mountain mule deer. USDA Forest Service. Resident Paper RM-111. Loft, E.R.; Armentrout, D.; Smith, G.; Craig, D.; Chapel, M.; Willoughby, J.; Rountree, C.; Mansfield, T.; Mastrup, S.; Hall, F. 1998. An assessment of mule deer and black-tailed deer habitats and populations in California: With special emphasis on public lands administered by the Bureau of Land Management and the United States Forest Service. Sacramento, CA: California Department of Fish and Game, Wildlife Management Division. Longhurst, W.M.; Leopold, A.S.; Dasmann, R.F. 1952. A survey of California deer herds: Their ranges and management problems. California Department of Fish and Game Bulletin No. 6. Mackie, R.J.; Hamlin, K.L.; Pac, D.F. 1982. Mule deer (Odocoileus hemionus). In: Chapman, J. A.; Feldhamer, G.A., eds. Wild mammals of North America: Biology, management, and economics. Baltimore, MD: The Johns Hopkins University Press. Mackie, R.J.; Pac, D.F.; Jorgensen, H.E. 1978. Population ecology and habitat relationships of mule deer in the Bridger Mountains, Montana. In Montana Deer Studies. Progress Report. Federal Aid in Wildlife Restoration Project, W-120-R-9. Helena, MT: Montana Department of Fish and Game. Miller, F.L. 1970. Distribution patterns of black-tailed deer (Odocoileus hemionus columbianus) in relation to environment. Journal of Mammalogy 51: 248-260. Nicholson, M.C. 1995. Habitat selection by mule deer: Effects of migration and population density. Fairbanks: University of Alaska. Ph.D. dissertation. Nicholson, M.C.; Bowyer, R.T.; Kie, J.G. 1997. Habitat selection and survival of mule deer: Tradeoffs associated with migration. Journal of Mammalogy 78: 483-504. Robinette, W.L. 1966. Mule deer home range and dispersal in Utah. Journal of Wildlife Management 30: 335-349. Robinette, W.L.; Baer, C.H.; Pillmore, R.E.; Knittle, C.E. 1973. Effects of nutritional change on captive mule deer. Journal of Wildlife Management 37: 312-326. Schaefer, R.J. 1999. Biological characteristics of mule deer in California’s San Jacinto mountains. California Fish and Game 85: 1-10. Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment: Habitat and species conservation issues. General Technical Report GTR-PSW-172. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. Vaughan, T.A. 1954. Mammals of the San Gabriel mountains of California. University of Kansas Museum of Natural History Publication 7: 513-582. Wallmo, O.C. 1981. Mule and black-tailed deer distribution and habitats. In: Wallmo, O.C., ed. Mule and black-tailed deer of North America. Lincoln, NE: University of Nebraska Press. Zeiner, D.C.; Laudenslayer, W.F., Jr.; Meyer, K.E.; White, M., eds. 1990. California’s wildlife. Volumne III: Mammals. California statewide wildlife habitat relationships system. Sacramento, CA: California Department of Fish and Game.

Share

Field Guide to Mammals of Southern California

California Black Bear (Ursus americanus californicus)

California Black Bear
General Distribution

Black bears are not native to southern California. Their absence from this region is believed to have been a result of competitive exclusion by California grizzly bear (Ursus arctos californicus). California grizzly bear was extirpated in California near the turn of the century, and black bears began appearing in Ventura and Santa Barbara Counties (Grinnell and others 1937). In the early 1930s, the California Department of Fish and Game initiated a translocation (introduction into the San Gabriel and San Bernardino Mountains) of 28 black bears into southern California to supplement the natural range expansion (Stephenson and Calcarone 1999).

Current black bear populations are known from Ventura and Santa Barbara Counties on the Los Padres National forest; the San Gabriel Mountains on the Angeles National Forest; and the San Bernardino and San Jacinto Mountains on the San Bernardino National Forest. Several sightings have more recently been reported from Palomar Mountain, Buckman Springs, and the Agua Tibia Wilderness Area on the Cleveland National Forest (Tremor and Botta 2000).

Systematics

Of the 16 subspecies of black bear (Ursus americanus) recognized by Hall (1981), northwestern black bear (U. a. altifrontalis) and California black bear occur in California. These two subspecies are separated geographically by the crest of the Klamath Mountains (California Department of Fish and Game 1998). California black bear is the only subspecies that occurs on the four southern California national forests.

Habitat Requirements

Black bear occupies a variety of habitats, but populations are densest in montane hardwood, montane chaparral, and mixed-conifer forests with a wide variety of seral stages (California Department of Fish and Game 1998). Vegetative and structurally diverse habitats are important to black bears because they provide a variety of food types. Black bears may also seasonally inhabit annual grasslands and valley foothill hardwood habitats (California Department of Fish and Game 1998). In the southern California mountains, black bears will follow riparian corridors down into low-elevation habitats (Stephenson and Calcarone 1999). Recently burned or logged forest can provide high-density fruit and berry production, whereas unmanaged and mature hardwood forests provide a variety of nuts and acorns (Lariviere 2001). Female black bears require secure, dry den sites for bearing and rearing young. Dens are also used by both sexes during periods of seasonal dormancy in the winter. Den sites have been found in hollowed-out trees, slash piles, root excavations, under large rocks, and occasionally on open ground (California Department of Fish and Game 1998, Lariviere 2001).

Reproduction

Female black bears reach sexual maturity generally between 3 and 5 years of age (Pelton 1982). Black bears breed in June and July and young are born during January or early February. Litter size ranges from one to four cubs and is probably influenced by the physical condition of the mother in early winter (Lariviere 2001). Although black bears are capable of breeding yearly, the frequency of breeding varies from 1 to 4 years (Lariviere 2001) and is strongly correlated with food availability (California Department of Fish and Game 1998).

Daily/Seasonal Activity

Black bears can be active during the day or night. They are typically crepuscular, concentrating most of their activity during the early morning and evening (Tremor and Botta 2000). In areas inhabited by humans, black bears become predominantly nocturnal and secretive (Lariviere 2001). Black bears in southern latitudes are active year-round, whereas bears in northern latitudes tend to undergo a period of seasonal dormancy in the winter (Tremor and Botta 2000). Because southern California generally has a mild climate, seasonal dormancy is less common and black bears are usually active year-round. However, pregnant females are less active and often den in the winter (Tremor and Botta 2000).

Diet and Foraging

Black bears are omnivores and consume a variety of plant and animal material including grasses, berries, nuts, acorns, wood fiber, insects, reptiles, birds, small mammals, and carrion (Tremor and Botta 2000). Seasonal variations exist in the type of foods eaten by black bears. In the spring, black bears consume mostly new vegetative growth and animal carcasses. During summer, their diet consists primarily of herbaceous material and fruits. During autumn, berries and mast (acorns and nuts) comprise the bulk of their diet (Lariviere 2001). The diet of urban California black bears in the San Gabriel Mountains was analyzed by examining bear scat collected from urban areas (Van Stralen 1998). Based on the total content of all scat analyzed, about 57 percent was native plant material (hollyleaf cherry, manzanita, redberry, grasses, and coast live oak); 26 percent was nonnative plant material (figs, peaches, apples, apricots, avocados, and domestic cherries); 14 percent was human garbage (paper, plastic, and metal); and 3 percent was animal matter (fly pupae and bird bones).

Territoriality/Home Range

The home ranges of black bears vary considerably and are determined by sex, age, season, and population density. The size of a home range is also largely dependent on food availability; concentrations of certain food resources can result in temporary range expansions (Pelton 1982). Black bears in northwestern Montana have been known to travel more than 100 miles (160 kilometers) to take advantage of available food supplies (Rogers 1987). Past studies have shown that the home range size of adult males is often 3-8 times larger than the home ranges of adult females. Using radio-telemetry, Van Stralen (1998) determined (with 95 percent confidence) the home range size of three urban males to be 2.9-11.0 square miles (7.4 to 28.4 square kilometers). The single female in this study had a home range of 2.1 square miles (5.4 square kilometers). Previous studies in southern California have reported home range sizes of 3.3, 7.5, and 9.7 square miles (8.6, 19.5, and 25 square kilometers) (Van Stralen 1998). Adult female black bears in northwestern Montana established territories in the summer (Rogers 1987). During other times of the year, black bears establish temporal spacing between each other and maintain these areas through a dominance hierarchy system (Pelton 1982).

Predator-Prey Relations

Black bears have very few natural predators. Bobcats, coyotes, or other black bears may occasionally kill young bears (Lariviere 2001). Most black bear mortality is human induced, predominantly by hunting. Bear mortality occurs when problem bears are removed from the population to protect property or for public safety. Vehicles also kill a number of bears annually.

Literature Cited

Bean, R.A. 2001. California’s black bear population is healthy and growing. California Game & Fish Magazine.
Big Game Hunt. 2002. Expanded elk and black bear hunting proposed – Expanded_Elk_and_Black_Bear_Hunting_Proposed_03080212.html [Homepage of California Department of Game and Fish], [Online]. Available: http://www.biggamehunt.net/sections/California/ California Department of Fish and Game. 1998. Black bear management plan. Sacramento, CA.
Grinnell, J.; Dixon, J.; Lindsdale, J. 1937. Furbearing mammals of California, their natural history, systematic status, and relations to man. Volume 2. Berkeley, CA: University of California Press. Hall, E.R. 1981. The mammals of North America. 2d ed. New York: John Wiley & Sons.

Lariviere, S. 2001. Ursus americanus. Mammalian Species 200: 1-7. Published by the American Society of Mammalogists.

Pelton, M.R. 1982. Black bear Ursus americanus. In: Chapman; J.A.; Feldhamer, G.A., eds. Wild mammals of North America: Biology, management, and economics. Baltimore, MD: The Johns Hopkins University Press; 504-514.

Rogers, L.L. 1987. Effects of food supply and kinship on social behavior, movements, and population dynamics of black bears in northeastern Minnesota. Wildlife Monograph 97.

Stephenson, J.R.; Calcarone, G.M. 1999. Southern California mountains and foothills assessment: Habitat and species conservation issues. General Technical Report GTR-PSW-172. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture.

Tremor, S.; Botta, R. (Eds.). 2000. Ursus americanus American black bear. San Diego Natural History Museum field guide [Homepage of the San Diego Natural History Museum], [Online]. Available: http:// www.sdnhm.org/fieldguide/mammals/ursu-ame.html.

Van Stralen, G.E. 1998. Home range size and habitat use of urban black bears in southern California. Northridge: California State University. Master’s thesis.

Share