Brown bears and grizzly bears are considered to be the same species and a differentiated by geographical location. Brown bears are those that live near the coast and have access to salmon, whereas the grizzly bears live in the interior of Alaska without access to salmon and re primarily vegetarian. Brown bears resemble black bears but the brown bear is larger, has a large shoulder hump and longer straighter claws. The coloration of brown bears can vary from being dark brown to blond. Weights vary according to the time of year but during late summer and fall, a mature male brown bear weighs 400 – 900 pounds. Females weigh one half to three quarters as much as the males.
Brown bears mate anytime from May through July. A mated pair may remain together for up to a month but otherwise they are generally solitary. Males will occupy a home range up to 1500 square miles that encompasses several females’ home ranges so they have more of a chance to mate each year. In areas of high bear density, a female may mate with more than one male. In the circumpolar north, females reach sexual maturity about age 6.
When a female brown bear becomes pregnant, the blastocyst (fertilized egg) does not attach to the uterine lining as it does in other mammals. Instead the blastocyst remains dormant and unattached inside the uterus. The blastocyst will no attach to the uterine wall and resume its development until the brown bear begins its semi-hibernation. This process is known as delayed implantation. Since semi-hibernation may not begin until October or November and the cubs are born in January or February, the actual gestation is only 3 months long. If the female does not have enough fat reserves to support herself and her young, the blastocyst may not implant itself and will be aborted.
The cubs are born in the den and are altricial (dependent) being blind, weighing only about a pound and covered with fine gray hair. Litter size ranges from one to four cubs, with a litter size of two being most common. Upon leaving the den in the spring, cubs will weigh about 15 pounds and upon denning in their first fall, they weigh 60-70 pounds.
The cubs will remain with their mother through the second year and sometimes even through their third year. Only after driving her cubs away, will the sow come into estrus again.
Pregnant females are the first to den and the last to re-appear in the spring. In the Arctic, where weather is severe and food supplies scarce, grizzlies den up to 8 months.
Brown bears are omnivorous, feeding on plants and young shoots, carrion, and moose and caribou wit can capture them. It is most common for brown bears to take calves in the spring but some bears are capable of taking an adult moose or caribou in the summer and fall.
Bears are unusual hibernators because of their large size. They don’t fall into torpor and decreased consciousness like most true hibernators. Bears must be alert because they give birth and raise babies in their dens. The sleep but are not out cold. Bears are also unique because they have adapted to recycle their waste products. A fecal plug forms to help keep waste inside.
Alaskan Wildlife can be seen in Denali National Park. Kantishna Wilderness Trails provides Alaska Wildlife Day Tours while Kantishna Roadhouse offers Denali lodging and accommodations for Alaska Travel and Alaska Vacations deep into Denali National Park.