Once salmon arrive, the feast begins, as all bears gorge themselves on fish to put on enough weight before fasting all winter in their dens.
Black bears are not always black, and this variation is most apparent in British Columbia. Other colour phases that occur in British Columbia include cinnamon, brown, blonde, and of course white (Spirit Bears). The blue phase, or “glacier” bear, is sometimes seen in the extreme northwest corner of the province.
The bear family, Ursidae, contains eight species on four continents and includes the giant panda. Three species of bears – grizzly (brown), polar, and black – occur in North America, the latter nowhere else. The feet are flat-soled (plantigrade), with naked pads and five toes with relatively short curved claws that are well suited for tree climbing.
Black bears have low reproductive rates compared to many other mammals. Females usually don’t reach sexual maturity until four years of age and breed only every two to three years after that. In areas of abundant food, they may reach maturity sooner. Where food is scarce females might not bear their first litter until they are six or seven years old. Although some males can breed when they are one and a half years old, in most populations males don’t mature sexually until age five or six.
Black bears in British Columbia usually mate from early June to mid-July. However, in a phenomenon called delayed implantation, the embryo does not implant in the uterus and begin developing until October or November.
|Cubs are born in January or February, during hibernation. Black bears usually have two cubs, but litter sizes vary from one to five. At birth, cubs are hairless, blind, and weigh about 400 g. They nurse while the mother continues hibernating and weigh 3 to 5 kg when they leave the den in spring.
Cubs stay with their mother their entire first year and sometimes longer. During that time, she protects them and teaches them how to survive. They are weaned between July and September and hibernate with their mother the first winter. By the middle or end of their second spring, they are on their own. The mother drives the cubs away when she is ready to breed again.
At first they stay within her home range, and the mother may allow female cubs to set up home ranges that overlap hers. Male cubs usually stay within their mother’s home range for only a short time and then disperse to find a home range in a new area.
Hibernation is an important survival strategy for bears in regions such as British Columbia where their main foods – green vegetation, berries, salmon, and insects – are not available in winter.
|Black bears typically hibernate for three to five months on the south coast and for longer periods (probably five to seven months) in the interior and the north. Females, particularly the pregnant ones, hibernate longer than males. In coastal British Columbia, almost all black bear dens are in or under large-diameter trees, snags, logs, or stumps and may be up to 25 m above the ground. Bears in the interior also use tree cavities, but if big trees are not available, the bears often den in rock cavities, under brush piles, or in holes dug into the ground. When cold weather arrives, bears become increasingly lethargic and enter their dens. During hibernation their heart rate drops from about 50 beats per minute to around 10. Oxygen intake decreases by half, and body temperature drops by about 3ºC.|
In a most remarkable biochemical feat, hibernating black bears do not eat, drink, urinate, or defecate. They have a unique process for recycling metabolic wastes into nutrients. Black bears may lose up to a quarter of their body weight during hibernation.