San Francisco State University
Department of Geography

Geography 316:  Biogeography  12/07/00

The Biogeography of the 
American Black Bear ( Ursus americanus )

by Sandra Summers, student in Geography 316, Fall 2000                                                                               

                                                                                                                 
 Photo of Black Bears by Sandra Summers
Taken on 12/02/00 at Folsom Zoo, Folsom, CA.

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Carnivora

Family: Ursidae

Genus: Ursus

Species: Ursus  americanus

Description of Species:
     Although called American black bears, Ursus americanus actually range in color.  Black and brown are the most common colors but there are some that have white or light bluish coats.  Both of the subspecies found in California are usually indeed black with some slight color variations among the individuals.  U. americanus are rather impressive creatures.  A male black bear will weigh between 125 to 660 pounds.  Females are usually considerably smaller, weighing between 90 and 175 pounds (Stirling 1993).  They range from 4 ½ to 6 feet in length and stand 35 to 40 inches tall.  The amount and availability of food and the age of the bear are the predominant factors that determine where they fall in this range of sizes.  U. americanus have a convex facial profile and rounded ears.  They have short tails and are lacking the shoulder hump seen in Ursus arctos, known also as brown bears (Stirling 1993).  Both the heel and the toe of the foot make contact with the ground as the bear walks, giving the bears a walking style similar at least in this one way to humans.  The hind feet have five toes and longer claws than the front paws.  The front claws are curved for digging and tree climbing and short enough that they are not seen from a distance. They can move surprisingly fast, up to 25 miles per hour over short distances (Middleton 1997). 

Habitat:

     Forests are a necessary element of U. americanus’ habitat.  The trees and brush provide cover for the bears as well as food.  Fallen logs, caves and hollow trees provide den sites for hibernation during the cold season.  Trees also provide an escape from danger with a quick climb.  The dense brush along stream banks also provides cover as the bears often travel along stream corridors when moving from one feeding location to the next.  Grazing on the fruits, nuts, berries and other consumable vegetation in these areas provides about 75% of the bears’ nutrition (Middleton 1997).  The forest vegetation also offers shade during the hot part of the day, when the bears are less active. 

 

 

 

 

Natural History:
      Black bears feed during the cool morning and evening hours, preferring to rest in the shade away from the hot midday sun.  They are omnivorous and will eat almost anything that they can find.  The bulk of their diet consists of plant matter such as fruits, nuts, berries, grasses, roots, tubers and such. Insects are also readily consumed, as are animal carcasses and some small mammals and fish (Smith 1985).  The bears will increase their food consumption in late summer and early fall in preparation for hibernation, gaining up to 30 pounds per week. Despite a reduced metabolic rate, the bears will lose up to 40% of their body weight during hibernation (Smith 1985).

     The lifespan of a black bear living in the wild can exceed 25 years.  Females reach sexual maturity between 3 and 5 years of age and mate every other year (Ewer 1973).  Males mature in 5 to 6 years.  Mating season for black bears falls in the months of June, July and August. The females give birth during hibernation and emerge from their dens with cubs in tow in late spring, usually around May or June.  With the exception of a mother bear and her cub, black bears are solitary animals.  Each has a home territory that it will defend from other black bears of the same sex.  The territory of a male will usually overlap that of several females, which he will defend from other males and will mate with when they become receptive (Wilson and Ruff 1999).  They interact very little outside of mating season but will tolerate shared feeding sites to some extent. 
 

Evolution:
       The order Carnivora is comprised of mammals that originally evolved as predators. Mammals first appeared on the earth in the upper Triassic period, about 190 million years ago, as rather small creatures by today’s standards.  Of these early mammals one group, called Pantoteria, developed stronger jaws and more efficient teeth than it’s contemporaries.  During the Tertiary period this group evolved further into the Miacidae.  The Miacidae were small forest dwelling mammals with wide paws and partially opposing digits that suggest they were tree climbers.  They also began to develop carnassial teeth meaning that they are used in a shearing manor (Ewer 1973).  Flowering plants began to evolve during the Cretaceous period and flourished well into the Tertiary period.  This abundant plant life fed a rapidly growing population of herbivores.  With a healthy number of prey species now available, the stage was set for the carnivores to evolve. Two distinct groups developed, the Canoidea and the Feloidea.  The Feliodea evolved in the tropical forested regions and the Canoidea in the temperate regions.  The Canoids dispersed, using the Bering Straits land bridge to move between the Old and New worlds. Four families developed from the Canoids.  These families are the Canidae, the Procyonidae, the Mustelidae and the Ursidae.  The Ursidae are the least predacious family of the Carnivora. Ursidae have developed a unique dentition in reponse to the high vegetable content of their diet. They have highly modified molars that are used for crushing and grinding food and notably reduced premolars. They have also developed an interesting variation in their scapula.  They have a long narrow scapula with a wide flange, called a post-scapular fossa, which is connected by muscle tissue to the humerus (Ewer 1973).  This allows them to heft their considerable body weight with their fore limbs, as they do when climbing trees, without separating the shoulder joint. American black bears (Ursus americanus) are one of several species belonging to the family Ursidae.
 

Distribution
     The American black bear, (Ursus americanus), is widely distributed in North America.  Its range extends from the arctic south into Mexico’s Sierra Madre mountain range and across 32 states in the U.S.  Two subspecies of Ursus americanus are found in California.  Ursus americanus altifrontalis, also called the Olympic black bear is found in coastal regions of California.  It’s relative Ursus americanus californiensis, also called the Califronia black bear, is found in interior regions of California (Wilson 1999).  Black bears prefer forests and woodland areas but they are occasionally seen roaming about in grassy meadows and increasingly in urban areas.  They can be found near sea level around coastal towns as well as in areas of considerable elevation such as the Sierra Nevada and San Bernardino mountain ranges (Zeiner, Laudenslayer, Mayer and White 1990).  Having been driven out of much of their historic range, they have proven themselves to be rather adept at transitioning to new habitats and finding new exploitable food sources, such as urban landfills and dumpsters.
 
 

   Map of Distribution of American Black Bears In California  by Sandra Summers

                                                                                                              
   
Other interesting issues:
     Black bears face an increasing threat from their human counterparts.  Large numbers of them are killed by poachers every year to supply a rapidly growing illegal market.  Their gall bladders sell for top dollar in asian markets for their supposed medicinal properties. 

Bibliography

Bcadventure.com. November 2000.  Black Bear Ursus americanus.  Available:  http://www.fishbc.com/adventure/wilderness/animals/blackbear.htm   

 

Blomstrom, David. Montana Fish, Wildlife and Parks.  November, 2000.  Geozoo.  Available:  http://geobop.com/mammals/carnivora/ursidae/Ursus_americanus/index.htm

 

Ewer, R.F. 1973.  The Carnivores.  Ithica, New York. Cornell University Press.

 

Ingles, Lloyd G. 1965.  Mammals of the Pacific States.  Stanford, California.  Stanford Unversity Press.

 

Middleton, Don. August, 1997. The Bear Den.  Available:   http://www.nature-net.com/bears/black.html

 

Sedgwick County Zoo. March, 2000. American Black Bear.  Available:  http://www.scz.org/animals/b/abbear.html 

 

Smith, Richard P. 1985.  The Book of the Black Bear.  New York, NY. Winchester Press.

 

Stirling, Ian 1993.  Bears, Majestic Creatures of the Wild.  Pennsylvania. Rodale Press.

 

U.S. Fish and Wildlife Service.  November, 2000. Wildlife Species.  Available:  http://species.fws.gov/bio_bear.html  Current Information from the U.S. Fish and Wildlife Service.

 

Wilson, Don E. and Sue Ruff 1999. The Smithsonian Book of  North American Mammals.  Washington and London, U.K. Smithsonian Institution Press.

 

Zeiner, David C., William F. Laudenslayer, Jr., Kenneth E. Mayer and Marshall White 1990.  California’s Wildlife,  Volume 3 – Mammals.  Sacramento, CA. State of California Resources Agency, Department of  Fish and Game. 
 
 

send comments to bholzman@sfsu.edu
 

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