Bear (Ursus americanus) Biology

• General Information
• Description
• Reproduction and Social Behaviour
• Seasonal Food Habits
• Black Bear Chronology-One Year

General Information
The black bear is the only bear species native to Nova Scotia and is the smallest member of the bear family in North America. The black bear does not have a hump between the shoulders and the snout is straight (roman nose), whereas the grizzly bear does have a shoulder hump and a concave (dished) snout. The black bear also has small, tightly curved claws which are suitable for climbing trees. The black bear is a true omnivore, with 85-90% of its diet consisting of vegetable matter. The remaining 10-15% of its diet is made up of animal protein; primarily obtained from insects, such as ants and caterpillars. True carnivores, such as cougars, have flesh-cutting carnassial molars, whereas, black bears have low, flat-topped bunodont molars which are better suited for crushing hard mast. Bears can travel fast for short distances only (over 30 km/hour when necessary). Their style of walking is on the soles of their feet (plantigrade), while real predators have a faster style of toe walking (digitigrade). The bottom line is a bear's bulky body and flat feet are not designed to chase prey for long distances which is why they are opportunistic feeders.

Description
Although in western North America there can be different color phases in black bear fur, in Nova Scotia bears tend to be a glossy black color. The muzzle is generally a tan color, eyes are brown, and the ears are smooth and tapered. Bears also have a short tail and some animals exhibit a white chest patch. Ears look large on smaller bears and as bears grow, the ears appear correspondingly smaller. Adult male bears generally weigh between 60 and 200 kg and adult females weigh between 40 and 135 kg. Length of adult bears range from 125 to 200 cm, with males being larger than females. Bears see in colour and have good vision close up. They probably have twice the sensitivity for hearing that humans exhibit. A bear's sense of smell is unmatched by few animals and is generally seven times better than a dog. The nasal mucosa area on a bear is 100 times larger than humans. They are an intelligent mammal with navigation skills superior to humans and possess an excellent long-term memory. Black bears are also strong swimmers capable of traveling long distances in water.

Reproduction and Social Behavior
Other than females with cubs, black bears tend to be solitary animals. However, they will congregate in feeding areas (i.e. bait stations, garbage dumps, natural food sites, etc.) and mark territories and food sites extensively to communicate with other bears. Most bears become active just before sunrise, take a few naps during the day and bed down for the night a few hours after sunset. However, some bears will become active at night to avoid humans and other bears. The mating period usually occurs between late May to early July. A female bear is known as an "induced ovulator" which means that in order to ovulate, she has to have a male in attendance. Generally, the female only breeds every second year. After the female mates, implantation of the eggs are delayed until November, with the tiny cubs being born inside the winter den during January or early February. The number of cubs can vary, but in Nova Scotia the norm tends to be one to three cubs. Cubs only weigh approximately 250 to 450 gm at birth and nurse in the den until the family group emerges in the spring. Cubs usually stay with the mother until they are 17-18 months old. At this time, the female abandons the cubs and goes looking for a mate. Juveniles, particularly the males, can travel long distances in search of food and their own territory. Starvation is a leading cause of death in juveniles (and cubs). After mating, an adult female will allow her female offspring to set up adjacent territories to her, but she will drive off any of her male cubs that attempt to stay. Interestingly, the sex ratio of newborn cubs is generally 50/50, but after four years of age, only one-third of the adults are male. Black bears do not reach sexual maturity until they are at least two and a half years old and often not until they are older. Female range size is determined in part by habitat richness and is much smaller than the male range size. The adult male bear's mating range size is probably determined in part by the number of females in estrous he can successfully monitor.

Seasonal Food Habits
Black bears are opportunistic feeders that eat a variety of vegetable and animal matter. Their diet can vary depending on what they can find to eat and the time of year. During the spring, when food items are limited, their primary diet is the tender new growth of leaves (i.e. aspen, maple), buds, flowers (i.e. violets), roots and young plants. As plants mature, bears cannot digest the tougher cellulose because their digestive systems lack the complexity of a true herbivore. A bear's digestive tract is short, only 40% that of an equal-size herbivore and while a herbivore's digestive tract is 25 times it's body length, a bear's tract is only 5 to 8 times it's body length. Black bears depend on strong stomach muscles and low stomach ph (3.5) to break down food. Carrion, such as dead deer, can be an important food source in the spring and bears will also kill small mammals and birds, moose calves and deer fawns. Bears lose weight in the spring and don't exhibit weight gains until the summer months. As spring progresses and days grow warmer, ants and other insects are consumed by bears. During the summer and into the fall berries, fruit, acorns and nuts form a large part of their diet. It is at this time of year that black bears eat voraciously, and they can consume up to 20,000 calories a day trying to gain weight that will enable them to den successfully during the winter months. Black bears are instinctively driven to consume calories and they will do whatever is necessary to acquire food. This aspect of bear behavior often puts them in conflict with humans. When natural foods are in short supply, particularly in the late spring in Nova Scotia, black bears will approach human habitation for food sources such as domestic garbage, beehives, crops, and the occasional livestock.

Black Bear Chronology-One Year
Generally, black bears enter dens in October or November in Nova Scotia, although bear tracks have been reported on mild days in December. Black bears go to sleep after they enter the den and last for months without eating, drinking or passing bodily fluids. Hibernating bears cut their metabolic rate in half. Male bears den alone whereas females den with yearlings or give birth to newborn, sightless cubs during January. Pregnant females have to be a certain weight (>65 kg) in order to bring their fetuses to full term in the den. The young cubs nurse and develop in the den and emerge with the female in the spring (usually April). After leaving the den, bears are quite lethargic and don't eat for the first few weeks. When feeding resumes, new plant growth and carrion are primary food items until other sources become available. Females abandon yearlings (1 ½ yrs.) around the end of May and start looking for prospective mates. The mating period can run from June to July and both sexes are polygamous. As the summer progresses, the urge to consume calories (hyperphagia) becomes paramount, and bears literally become eating machines until the fall. Feeding slows down prior to bears entering their dens. Den sites in Nova Scotia can include brush piles, caves, cavities under rocks and the roots of blowdown. Ideal black bear habitat in Nova Scotia would include areas with a variety of forest types. Forest openings, vernal pools and wetlands provide many food items for bears. Larger rough-barked trees (i.e. white pine and eastern hemlock) are important refuge sites for female black bears with cubs. Females will use the base of these trees for bedding sites and cubs climb the trees at the first sign of danger. Studies in other areas have shown that black bears survive better in forested habitats that have minimal impact from humans (i.e. logging roads, forest cutting, etc.).