North American Black Bear, Ursus americanus
North American black bears are common although listed as threatened in Louisiana, Mississippi and Texas by the U. S. Fish and Wildlife Service. International Union for the Conservation of Nature Status: Least Concern; population increasing.
They are the smallest of the bears weighing 200-600 pounds and measuring 2-4 feet high at the shoulders and 5-6 feet in length. They do not have the shoulder hump of the grizzly bear. They have a short tail almost concealed in its fur, small rounded ears, and are plantigrade (walk on the entire foot like humans). Although called black bears, they come in various colors: black, brown, blonde, cinnamon, creamy white, and blue-gray. The latter two color variations are limited to small populations in southwestern Canada and the southern Alaskan islands.
Habitat and Range
The black bear can be found throughout Canada and the United States and as far south as the Sierra Madre Mountains of northwest Mexico, usually in thick forest. Eastern black bear habitat is more restricted, roughly following the Appalachian Mountains. A couple small populations occur in Florida.
They are omnivorous. A majority of their diet is plant material: grass, seeds, vegetables, roots, nuts, honey etc. When the opportunity arises they will eat fish, eggs, rodents, insects, carrion, and garbage. Though able to hunt and kill prey, spend more time foraging, which reduces energy demand.
In times of plenty females will reach maturity at 3-4 years of age. They will typically breed every two years and raise 2-3 cubs. Black bears mate in June-July. The process of delayed implantation allows the fertilized egg to float in the uterus without implanting until approximately November when the mother attains a suitable fat reserve to sustain pregnancy. If the female fails to reach these fat levels, her body reabsorbs the egg. The cubs are born in winter (January or February) while the mother is hibernating. They weigh approximately one pound at birth and are naked and blind. Cubs remain with their mother, nursing until spring. They are weaned by August, but stay and hibernate with their mother their first winter. Cubs disperse by late spring the following year.
They are typically solitary animals, except for females with cubs. They will den in fallen trees, hollow logs, under roots or in caves for 4-6 months during their winter dormancy. During their active months they are generally crepuscular, meaning they are most active in twilight hours. Generally, their activity pattern adjusts according to local human activity.
Some researchers refer to bear hibernation as winter sleep, winter dormancy, or carnivoran lethargy to differentiate this behavior from the deeper hibernation of smaller mammals such as ground squirrels. These smaller mammals are said to enter “true hibernation” due to the extremity of the changes in body temperature (some drop to freezing), respiration, and heart rate (almost imperceptible in some species).
Normally, bears do not eat, drink, urinate, or defecate during winter dormancy. Instead, they rely solely on breakdown of fat reserves. They burn approximately 4,000 calories per day for a total of 20-27% of their body fat during the entire denning period. Since bears do not burn protein for energy during winter dormancy, they do not accumulate large enough amounts of urea to necessitate urination. The small amount of urea that is produced is recycled into proteins which are used in rebuilding muscle and other body tissues, preventing muscular atrophy. Other hibernators awaken periodically to consume food stored in their burrows. They also must eliminate wastes during these brief waking periods.
During winter dormancy, bear heart rates decrease from 40-50 beats per minute (bpm) to 8-10 bpm. Blood flow to peripheral areas, such as limbs, reduces. Body temperature and metabolic rates drop, but not as dramatically as in the “true hibernators.” Because bears maintain relatively high body temperatures during winter dormancy, they can be aroused more easily. Therefore, bears react more quickly to danger, especially mothers needing to respond to their offspring’s needs.
- They can run at least 30 mph for short distances.
- They may smell strong scents from two miles away under appropriate conditions.
- The average lifespan for a wild black bear is 10 years, although there is great variation regionally. Bears in the Sierra Nevada mountains live 15-20 years while those in Florida or in captivity may live up to 30 years.
- Adult black bears can climb trees.
- Sometimes they choose dens in tree-trunk cavities as high as 60 feet above the ground.
- They are classified as carnivores because of their teeth and hunting abilities, although we refer to them as omnivores due to their varied diet.
- Males are boars and females are sows.
- When they walk, the legs on one side move together instead of alternating like most four legged animals.