Black Bears (Ursus americanus)
The American black bear is a medium-sized bear native to North America. It is the continent’s smallest and most widely distributed bear species. The American black bear is the world’s most common bear species. It is listed by the IUCN as Least Concern, due to the species’ widespread distribution and a large global population estimated to be twice that of all other bear species combined. Although they live in North America, American black bears are not closely related to brown bears and polar bears; genetic studies reveal that they split from a common ancestor 5.05 million years ago. Both American andAsian Black Bears are considered sister taxa, and are more closely related to each other than to other species of bear.
Their entire life evolves around food. When they are not hibernating, bears spend most of their time looking for food.
From the time they come out of hibernation until berry crops are available, bears live off their stored fat and the limited energy provided by fresh spring greens. They get most of their food energy by feeding on summer berry crops like blueberries, strawberries and raspberries. In the fall, they turn their attention to hazel nuts, mountain ash, acorns and beech nuts.
While black bears will eat carrion, insects, fish, deer and moose calves, the bulk of their diet is plant material. Their natural preference is to find lots of high energy food – like huge berry patches – that will help them fatten up fast. Their survival and ability to have and raise young depend on their ability to double their weight before going into winter hibernation.
Black bear weight tends to vary according to age, sex, health, and season. Seasonal variation in weight is very pronounced: in autumn, their pre-den weight tends to be 30% higher than in spring, when black bears emerge from their dens. Black bears on the East Coast tend to be heavier on average than those on the West Coast, although black bears follow Bergmann’s Rule and bears from the northwest are often slightly heavier than the bears from the southeast. Adult males typically weigh between 57–250 kg (126–550 lb), while females weigh 33% less at 41–170 kg (90–370 lb).
(Note: Bergmann’s Rule states that the farther north a species lives the larger they tend to grow. This is usually to help survive in colder climates. There are other adaptations within certain species to the far north as well that do not follow Bergmann’s Rule, but in general the rule hold across a majority of species.)
The fur is soft, with dense underfur and long, coarse, thick guard hairs. The fur is not as shaggy or coarse as that of brown bears. American black bear skins can be distinguished from those of Asiatic black bears by the lack of a white mark on the chin and hairier footpads. Despite their name, black bears show a great deal of color variation. Individual coat colors can range from white, blond, cinnamon, or light brown to dark chocolate brown or to jet black, with many intermediate variations existing. Bluish tinged black bears occur along a portion of coastal Alaska and British Columbia. White to cream colored black bears occur in coastal islands and the adjacent mainland of south-western British Columbia. Albino specimens have also been recorded.
Black bears are extremely adaptable and show a great variation in habitat types, though they are primarily found in forested areas with thick ground vegetation and an abundance of fruits, nuts, and vegetation. In the northern areas, they can be found in the tundra, and they will sometimes forage in fields or meadows.
Black bears tend to be solitary animals, with the exception of mothers and cubs. The bears usually forage alone, but will tolerate each other and forage in groups if there is an abundance of food in one area.
Most black bears hibernate depending on local weather conditions and availability of food during the winter months. In regions where there is a consistent food supply and warmer weather throughout the winter, bears may not hibernate at all or do so for a very brief time. Females give birth and usually remain denned throughout the winter, but males and females without young may leave their dens from time to time during winter months.
Black Bears mate during the summer, Sows tend to be short tempered with their mates after copulating. The fertilized eggs undergo delayed development and do not implant in the female’s womb until November. The gestation period lasts 235 days, and litters are usually born in late January to early February. Litter size is between one and six cubs, but 2 is the usual number. At birth, cubs weigh 280–450 g (0.62–0.99 lb), and measure 20.5 cm (8.1 in) in length. They are born with fine, gray, downlike hair, and their hind quarters are underdeveloped. They typically open their eyes after 28–40 days, and begin walking after 5 weeks. Cubs are dependent on their mother’s milk for 30 weeks, and will reach independence at 16–18 months. At the age of six weeks, they attain 900 g (2.0 lb), by 8 weeks they reach 2.5 kg (5.5 lb) and by the age of 6 months they weigh 18 to 27 kg (40 to 60 lb). They reach sexual maturity at the age of three years, and attain their full growth at 5 years.
References: Wikipedia, Ontario Ministry of Natural Resources.