Grissly Bear Management Concepts Grizzly Bear Management









The Bear Necessities about Grizzlies


Grizzly 101

Grizzly bears, Ursus arctos horriblils, are a subspecies of the brown bear.  This being so, not all brown bears are grizzlies, but all grizzlies are brown bears.  This is not to say that the color of all grizzly bears is brown.  Natural variation in pellage occurs, and colors can range from black to blonde to brown (shown in above photo).  This variation makes the distinction between black bears and grizzly bears difficult for some people, but, unlike their cousins, grizzly bears have a hump between their shoulder blades.  This is easily noted in the latter two photos above, and it is this characteristic that serves as the easiest way to differentiate between the two species when observed from a distance.


Evolution and phylogeny


Brown bears are distributed throughout the holarctic regions of North America, Asia, and Europe.  It has long been believed that the bears first evolved either in Europe or Asia, migrating to Alaska during the Pleistocene (Kurten 1968).  After the retreat of the ice sheets, the bears were able to expand their range south into what are currently Canada, the contiguous United States, and northern Mexico.  Molecular data support this hypothesis, as phylogenetic trees made from both nuclear (DNA obtained from the nucleus of a cell that is inherited from both parents) and mitochondrial DNA (obtained from the mitochondria of a cell that is maternally inherited) put Eurasian bears at the base, followed by three clades (groups) of bears in Alaska, and one in the lower 48.  Interestingly, these genetically based trees also show that polar bears (Ursus maritimus) are closely related to one of the Alaskan clades, specifically those bears located in the ABC (Admiralty, Baranof, Chichagof) Islands in the SE part of the state.  This means that polar bears most likely evolved from brown bears after they crossed the Bearing Straight.


Diet and adaptations

Grizzly bears, contrary to the belief of many, are not man-eating monsters.  In fact, grizzly bears are omnivores, and much of their diet consists of plants, berries, roots and seeds, as well as moths, carrion, and cutthroat trout.  Examination of the teeth of grizzly bears clearly demonstrates this, as in addition to their carnassial pair, a set of teeth generally designed for consuming flesh, grizzly bears have well defined bunodont molars (short cusped) that are common in most omnivores, including humans.


Humans and grizzly bears

Being reclusive animals, it is thought by many that bears prefer areas with low human densities.  This is most likely due to the fact that the bears have found humans to be inhospitable neighbors (though some are trying to remedy this).  Humans are the primary cause of mortality for the bears, in large due to fear and other such views.  This has only been compounded by the fact that bears are huge, males ranging from 300-800 pounds, depending upon the quality of their habitat.  Excessive human induced mortality has resulted in ESA listing of grizzly bears, as well as a recent concern about their genetic diversity.




Like most carnivores, rates of fecundity for grizzly bears are low.  This is compounded by the fact that it takes several years for bears to reach sexual maturity, as they generally live to be about 20 years of age.  Mating generally occurs between themonths of May and July, and females delay implantation of the blastocyst (fertilized egg) until late summer or autumn.  Gestation from the time of insemination until parturation (birth) is usually between 180 - 250 days, with the bears giving birth in winter while still in their dens (Feldhammer 1999). 


Did you know…

Grizzly bears do not undergo true hibernation?  Each winter, bears undergo torpor, which is similar to hibernation, in that the animal’s metabolic rate is slowed and body temperature drops.  Due to the fact that a bear’s body does not reach ambient temperature, it is said to undergo carnivorian lethargy, or “false hibernation.”  This is not unique to bears, though.  Nothing larger that marmots, which are a bit bigger than house cats, are capable of true hibernation due to the energy requirements for raising the body temperature to a functioning level (Feldhammer 1999).