California Black Bear (Ursus americanus californicus)
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).
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.
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).
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).
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).
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).
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.
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.