|American Black Bear, Ursus americanus Common Names: black bear, American black bear
General Description Ursus americanus is one of the most familiar wild animals in North America today. The name, however, can be very misleading in terms of a basic description of the mammal. Ironically, the black bear is not always black-although the most common colouring is black with a brownish muzzle and often a white patch below the throat, it can also be light brown, cinnamon beige, or even a blue-white colour. No matter what the shade, it would be a very intimidating mammal to meet up with in the wild. They can range from about 89 to 102 cm tall when on all fours, with a length of about 140 to 180 cm. There is quite a significant weight range, from approximately 57 to 272 kg (although most are in the vicinity of 135 kg). Females, within a geographic area, usually weigh about one-third less than males. Although they have been known to live for 20 to 25 years, few bears live for more than 10 years (due to a variety of factors, including environmental conditions, and even because of legal hunting). Their eyesight is relatively poor, but they have well-developed senses of hearing and smell to compensate. The black bear is not to be confused with a close relative-the grizzly bear (Ursus arctos). Ursus americanus lacks the shoulder hump customary to the grizzly, and it also has shorter front claws, adapted for tree climbing. And although they are, of course, land animals, they are good swimmers, which aids them in their hunt for food. These mammals are large enough that it makes it difficult for them to be in an area without “leaving their mark”. When bears itch, they often scratch by standing on two legs and rubbing their backs on a tree or telephone pole, leaving behind them a sign that they were there.
Geographical Distribution and Habitat Requirements Ursus americancus is basically a North American mammal, and has representatives throughout most of the northern hemisphere. They range from the northern tree limit of the Arctic far to the south through most of Canada and US, and even as far south as Mexico. It’s not found on Prince Edward Island, in northern Alberta, northern Saskatchewan, or in extreme northern Ontario. The preferred habitat is forests with occasional open areas such as meadows, and they can be found all across the province of New Brunswick. Maximum populations are probably attained in areas of mixed coniferous-deciduous forests, where densities are about 1 bear for every 3 to 4 km2, with the males’ territory being about 4 times larger than the females’. All bears have a feeding territory of their own, although one male’s territory may overlap those of several females.
General Biology As is apparent in their bulky, thickset appearance, the black bear is not a selective feeder. Of course, the diet depends on the seasonal availability of food and geographic location of the mammal, but they will dine on virtually anything edible (they are omnivorous). More than 75% of the diet is vegetable matter, but black bears are not against eating animal matter such as decaying carcasses, fish, moose calves, small marine animals, ants, or any other food of this type. They prefer to feed in the early morning or the cool of the evening, simply to avoid the midday sun. It is also logical that the density of food resources is a factor in determining the home range of bears-the more concentrated the food sources, the smaller the necessary range. Home range and dispersal plays a role in the reproductive success of Ursus americanus as well. Dispersal may expose males to a larger number of available female mating partners, which is important because of the “promiscuous mating system” that bears follow. The parental involvement by males is minimal, and reproductive success is limited by the number of females they encounter and with whom they successfully breed. Females normally mature at about 3 to 5 years, and mating usually takes place in June or early July. Females usually mate with several males over 2 to 3 weeks of breeding season, every other year. The cubs are born in January or February, while the mother is still in “hibernation”, after a process of “delayed implantation”. This is a defense mechanism by the female, and it means that the embryo doesn’t attach to the uterine wall until after about 6 months, just in case the mother doesn’t have enough nutrients stored up to support herself and her cubs. 8 weeks after this, the cubs are born- the number varies from 1 to 4, with 2 being the average (though the litter size increases as the mother gets older). They are hairless and tiny at birth (240 to 330 g), but within 5 weeks they are developed enough to leave the den with the mother. Technically, bears often “den” in the winter, though they do possess many characteristics of true hibernators. Although the body temperatures are only slightly lower, heart rates are greatly reduced (from 40 to 70 beats per minute to about 8 to 12), and metabolism slows by half. In addition, unlike many small mammal hibernators, bears do not have to eat or eliminate waste, but survive entirely on their stored fat. However, black bears are not true hibernators and most could be aroused if prodded enough. If the weather is favourable enough, some bears may wake up and even wander around for short periods during the typical “hibernating months”. The denning period usually lasts about 4 to 7 months, and the mammals leave the den over a period of about half a month, communing April or May. Normally, adult males emerge first, and females with small cubs last. All of them have lost substantial amounts of weight over the long winter period, but it doesn’t take them long to return to their old foraging pattern. Most bears continue this pattern from dawn until dark, but those that are in the area of high human activity are often mainly nocturnal, to minimize contact between the two groups.
Conservation Ursus americanus is the most widespread and numerous bear in North America, with a population estimated somewhere between 400 000 and 750 000 individuals. Areas of heavy deforestation have seriously limited the ranges of some bears, but aside from this human interference, the American black bear has a healthy, stable population throughout most of the continent.