Natural History of the Black Bear

Introduction and General Description:
The black bear, Ursus americanus, is the most prevalent bear species in North America.  The average length of the black bear ranges from four to seven feet in length from nose to tail.  Although coloration is often black or brown, individual color varies within the species.  Males are typically larger weighing up to five hundred pounds while females, usually smaller, are found between one and three hundred pounds.  Black bears are excellent climbers.  Cubs often climb trees to escape predators and other forms of danger.  In any terrain, black bears can easily outrun humans.  A bear's top speed can reach more than thirty miles per hour.

Habitat and Range:
For the most part, the habitat of the black bear is a forest abundant in fruit and nuts.  Black bears can be found in deciduous, coniferous, or mixed forest regions.  The home range of an American black bear varies depending on the location, the season, food availability, and the density of individuals. The home range of a male is normally larger than that of a female; the male may roam an area anywhere between ten and sixty square miles while a female may wander an area of fifteen square miles.  In Minnesota, black bears are most common in forests and wetlands of the northeast, and found sometimes as far south as Anoka County.

Population in Minnesota:
Minnesota's Department of Natural Resources (DNR) has come up with a unique, but useful way to estimate black bear numbers in the state.  Bait bags containing bacon laced with tetracycline are hung in areas of bear activity.  When ingested, tetracycline incorporates itself into any newly forming tooth and bone material.  It shows up as a fluorescent mark when examined under ultraviolet light.  Hunters are asked to provide the DNR  with a tooth and small piece of rib bone from any black bear they harvest.  Using this method, biologists estimate the current Minnesota black bear population to be 22,000 to 23,000 individuals.

Social Structure:
Since food is not concentrated in one area, black bears cannot feed together, and often travel alone, except for mother and cubs.  Mother bears will defend territories for themselves and their offspring from her current and past litters.  

Hunting and Food:
The black bear’s sense of smell is seven times sharper than a bloodhound’s.  Bears rely on their sense of smell to locate mates, detect and avoid danger, identify their cubs, and locate food.  Their color vision also aids them in finding their next meal.  Despite being classified in the order, Carnivora, due to their large teeth and claws, they rarely eat anything larger than an insect.  Their long canine teeth are used for biting into rotting logs to find insects and their claws are used for tree climbing to locate acorns, nuts and fruit.  The main diet of a black bear includes fruit, nuts, plants, and insect larvae.  Their large bodies, which are designed to store fat, are incapable of catching large, fast prey. 

Communication:
Black bears typically do not vocalize.  The most common bear sounds are grunts, used when playing, and loud blowing, indicating the black bear is nervous or afraid.  The black bear uses a resonant voice to exhibit strong emotions and most often used by cubs.  Adults will use their resonant voice when they are in pain or are frightened.  Bears also communicate by marking their scent by urinating, defecating, and rubbing, scratching, and biting trees.   Scent discloses a bears reproductive status and identity. 

Hibernation:
Black bears are not true hibernaters.  Their behavior is more accurately described as denning.  Minnesota's black bears tend to nest on top of the ground, but some seek caves and more sheltered areas.  A black bear must gain fifty to sixty pounds of fat in the late summer and fall to sustain itself through the winter.  Black bears are able to reduce their metabolic rates by more than fifty percent in response to reduced temperatures and low food abundance.  Bears will sleep for months without eating, drinking, urinating, or defecating.  Denning can last up to seven months in the Northern regions but is often shorter in the South where food is available more readily.  The length and depth of hibernation is genetically programmed to match the average availability of food for that region.     

Mating and Breeding:
Male bears will compete for females and will mate with as many partners as possible.  Black bears mate from late May until early July.  Although mating occurs anytime between late May and July, implantation of the fertilized egg is delayed until November.  The embryo will not implant in the uterus until adequate fat and nutrients have been built up for the winter.  Cubs are born in January or February and weigh ten ounces when born.  A litter usually consists of two cubs.  Cub mortality for the first year of life ranges from thirty to fifty percent.  Bear cubs remain with their mother for approximately seventeen months.  When their mother is ready to mate again she forces her offspring to stop traveling with her.  Father bears do not help in raising the cubs.  Black bears are solitary, except when breeding.

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