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American Black Bears
(Ursus americanus)
The name, the American black bear, is a misnomer given the many colour phases of this bear. While in eastern North America, most black bears are, in fact, black, such is not the case as one moves westward across the continent.
It is the one bear species which seems to have the greatest capacity to live in close proximity to man.
The American black bear is the most widespread and numerous bear in North America (see map). It is estimated that there are somewhere between 400,000 and 750,000 black bears throughout North America.
Its range extends from the northern tree limit of the Arctic far to the south through
most of Canada and the United States. It is found as far south as the range of the Sierra
Madre Mountains which are located in north-western Mexico.
Its preferred habitat includes forests with occasional open areas such as meadows. This includes the hardwood forests along the eastern side of North America as well as the coniferous forests found in the more central and western parts of the continent. The only habitat from which is excluded are those areas where heavy de-forestation has occurred.
This area encompasses 32 American states; all the provinces and territories of Canada excepting Prince Edward Island; and 5 Mexican states.
The American black bear is a large mammal whose size and weight show high variability
depending on food availability, climatic conditions, etc.
In general, adult black bears range from 89 to 102 centimeters (35 to 40 inches) tall
when on all fours and have a length of 140 to 180 centimeters (4 1/2 to 6 feet).
The weight of a black bear, which is highly variable, ranges from 57 to 272 kilograms (125 to 600 pounds) with males within a geographic area on average about a third larger than females. The largest American black bear to date was found in Riding Mountain National Park in Manitoba, Canada. It weighed in at 365 kilograms (805 pounds).
The lifespan of black bears in the wild can be twenty-five years or more.
Black bears have a heavy body, short tail, rounded ears, plantigrade feet (i.e., both
heel and toe make contact with the ground when walking in a manner similar to humans), and
a hind foot with five toes. They are much quicker than their appearance would suggest with
recorded speeds being in excess of 40 kilometers per hour (over 25 miles per hour) for a
short distance.
Black bears lack the distinct shoulder hump of the brown/grizzly bear and the claws on
the front paws are much shorter and generally not visible from a distance. Their curved
claws are highly adapted to tree climbing and all black bears are agile tree climbers.
While members of the order Carnivora , they have evolved primarily into vegetarians with accompanying changes in their dental structure and digestive tract.
The fur colour of the black bear is often, in fact, black but colour phases can also include light brown, dark brown, cinnamon, beige, and even a blue-white colour. There is evidence to suggest that in areas of relatively high rainfall, black bears predominate while in the drier inland areas of the continent, brown and blond bears are more common.
The Kermode bear, often referred to as the ghost bear, has beautiful cream-coloured fur. It is found only on three small, isolated islands found off the western coast of British Columbia. The brown eyes and black nose of these bears eliminate any possibility that the Kermode bears are an albino race.
Black bears, like most wild creatures, seek foods which will return the highest nutritional and protein value for the least expenditure of energy. Seasonal availability and geographic location are the biggest factors determining the primary food sources of bears.
Eating virtually anything edible, it has been determined that more than 75% of their diet consists of vegetable matter including, berries, flowers, grasses and sedges, herbs, tubers and roots, and nuts of all kinds. For the remaining portion of their diet, animal matter such as decaying animal carcasses, fish, small marine animals, ants and other insects, honey, elk and moose calves and a variety of other small mammals (e.g., ground squirrels, marmots, etc.) are consumed.
Black bears like to feed in the cool of the evening or in the early morning. During the heat of the day, they will often seek shade in the dense underbrush.
The size of the home range of an individual black bear will vary with the concentration of high energy food sources. Thus, the more concentrated the food sources, the smaller the range necessary to maintain an animal.
In general, females will have a home range which is 6.5 to 26 square kilometers (2 1/2 to 10 square miles) while males will normally have a home range which is four times larger at 26 to 124 square kilometers (10 to 40 square miles). The range of every adult bear is composed of an individual territory part of which constitutes its exclusive domain while the rest it co-habits with other bears. The home range of a mature male bear will often overlap the home range of several female bears.
Characteristically, a home range does not constitute one large area but rather is composed of several smaller food source areas connected by travel lanes. Open areas are usually avoided by black bears as they prefer wooded cover. Stream and creek beds are often used as travel lanes because of the thick undergrowth and a barrier-free escape route. This is particularly true in areas where there is heavy urban build-up.
Female black bears normally mature at 3 to 5 years of age with some waiting even later for their first mating. Copulation normally takes place in a manner similar to members of the canine (dog) family.
In warmer climates, mating may take place as early as May or June while in more northern (and therefore colder) locations, mating may be delayed until July or early August. Females will normally mate with several males over the two to three weeks of the breeding season. Females will normally breed every other year.
Through a remarkable process referred to as delayed implantation, the fertilized ovum divides a few times and then floats free within the uterus for about six months with its development arrested. Sometime around the denning period, the embryo will attach itself to the uterine wall and after a period of eight weeks (January/February), the cubs will be born while the mother is still in hibernation.
Delayed implantation clearly serves an important survival need for the mother. Should she not have enough fat reserves to carry her through the winter, the embryo will not implant and it is simply reabsorbed by her body.
The number of cubs born ranges from one to a maximum of four with two cubs being average. As a rule, the number of cubs a female will have increases as she gets older. Again, climate and food supply are important determinants of the size of the litter.
At birth, the cubs are blind, hairless and very tiny. They weigh from 240 to 330 grams (8 1/2 to 11 1/2 ounces). Virtually helpless, they are, however, able to move sufficiently to suckle on their mother who remains asleep. Her milk is calorically very rich containing over 20% fat. In contrast, human milk only contains about 4% fat.
Within the next five weeks, the cubs will develop rapidly on this rich diet such that they will be able to follow their mother when she leaves the den.
The survival of bear cubs is extremely tenuous with predation by adult male bears being quite common. Also, wolves, bobcats, eagles, mountain lions and, in more urban areas dog packs have been known to kill young cubs who become separated from their mother's side.
While the mother is foraging , the cubs are often placed under the shelter of a thicket or in a nearby tree. In the event of danger, the cubs will stay in the tree while their mother either takes guard on the forest ground below or climbs the tree after them.
The cubs will stay with their mother for the entire first year. They are generally weaned between July and September of their first year and stay with their mother through the first full winter. Their survival is totally dependent on the skill of the mother in both protecting them and teaching them the basics of what to eat, where and how to get it, where to den, and how to cope with danger.
As adolescents, the young bears are still in extreme danger. Normally they are driven off by their mother as she prepares to breed once more. They must now become rapidly self sufficient if they are to stay alive and find sufficient food to build up their fat reserves to last over the long winter. Occasionally, young bears will spend a period of time together after they have been driven off by their mothers.
During late summer and early fall, all bears have, as a survival imperative, the need to gain as much weight as possible. Through the harvesting of locally available nut crops, berries, etc., black bears normally make very large weight gains. Such gains may be as much as 14 kilograms (30 pounds) per week. At such times, foraging may occur around the clock with only short rest periods.
Most black bears, including all who live in areas with severe weather climates, will hibernate for between four and seven months. Where the weather is much more temperate and the period without food available is quite short, black bears may either not hibernate or they may simply nest in a thicket or other sheltered area for brief periodsof time.
In northern areas, the arrival of colder weather and/or snow precipitates the bear undergoing a remarkable metabolic transformation as it prepares for hibernation. Hibernation is an energy-saving process bears have developed to allow them to survive long periods when there is insufficient food available to maintain their body mass. As they stop eating and become increasingly lethargic, the bear will enter a cave; dig out a den; or hole up in a dense brush pile, hollow log or tree cavity.
While hibernating, a bear's heart rate drops from between forty to seventy beats per minute to only eight to twelve beats per minute and its metabolism slows down by half. Unlike many other animals who hibernate, its body temperature only undergoes a minor reduction of 3 to 7 degrees Centigrade (5 to 9 degrees Fahrenheit).
During the entire period of hibernation, the black bear will neither pass urea or solid fecal waste. While urea poisoning causing death would occur in all other animals, bears have developed a unique process of recycling the urea into usable proteins.
Most black bears vacate their winter dens over a one to two month period commencing in April or May. Both the climatic conditions (snow cover and temperature) and physiological factors such as the bear's age, the status of its health and its remaining fat reserves affect the exact timing of emergence from its den. Normally, adult males emerge first. Females with newborn cubs are usually the last to leave their dens.
During the hibernation period, all bears lose a great deal of weight. Adult males and adolescent bears lose between 15% and 30% of their weight while it is not uncommon for a female cub with newborn cubs to have lost as much as 40% of her weight.
The black bear will then resume its normal foraging pattern as it completes the cycle of life.
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