Bear Biology

The brown bear is the predominant bear along the Chilkoot River.  Brown bears and grizzlies are really the same species. Brown bears are just the coastal version of grizzlies and because of the abundance of fish they tend to be larger than the inland grizzlies.  Black bears have been seen along the river but this is a rare occurrence. 

Range: Based on collar studies done by the Alaska Department of Fish and Game, the Chilkoot bears home range is roughly a 30 square mile range.  In the summer and fall they use the majority of the Chilkoot River watershed.   The females are basically the only bears that are observed along the river.

Appearance: The bears along the river are usually dark brown in color, though they can vary from a light creamy shade through to black. When they come out of hibernation in the spring they are generally light in color and as the summer progress become darker in color.  The long guard hairs over the shoulders and back are often light colored at the tips which, from a distance, give a grizzled appearance. They have a distinctive hump on the shoulders.  The hump is a mass of muscle that enables the bear to dig and use their paws as a striking force.  Their face is a slightly dished profile to the face. The long claws on the front paws are curved and range in color from yellow to brown.  The claws are used to dig up plant roots and excavate their dens.

Weight:  The two collared females along the river weigh between 300-500 lbs.  The males do not come down to the river so their weights are not known.  Determining representative weights is difficult as there are seasonal considerations to take into account-for instance, some bears can weigh almost twice as much in the fall as they might weigh in spring.. At birth, cubs weigh 11 ounces to 1 pound 6 ounces.  By the end of their first year of life, they can weigh 150-200 pounds.

Longevity: Longevity in the wild is 20 to 25 years although rarely animals in excess of 35 years of age have been reported.  Two prevalent bears along the Chilkoot River are over 24 years old. 

Top Speed: 35 mph although a brown bear in Denali National Park in Alaska was clocked at 41 mph!

Reproduction: Female brown bears reach sexual maturity at four-and-a-half to seven years of age. Males may become sexually mature at a similar age but are probably not large enough to be able to enter the breeding population until they are eight to ten years old.  Mating takes place from early May to the middle of July but implantation does not occur until about October or November.  The young are born from about January to March.  The litter size ranges from one to four, but two is most common. Cubs remain with their mothers usually for at least two-and-a-half years, so the most frequently a female can breed is every three years.

Social system: Under most circumstances, the bears along the river live as lone individuals, except for females accompanied by their cubs. During the breeding season, a male may attend a female for up to two weeks for mating. Brown bears are distributed in overlapping home ranges and male home ranges are larger than those occupied by females. Despite their propensity for a solitary existence, the bears may congregate where food is abundant, such as at salmon streams.

Diet:  The bears mainly eat vegetation such as grasses, sedges, plant bulbs, berries and roots. In the early summer, one female and her cubs were observed eating eulachon.  As July progresses and the pink salmon enter the Chilkoot River, they become the primary source of food for the bears.

Making a Living: Most bears are active during the morning and early evening hours.  During the daytime they rest in day beds, often constructed in dense cover to escape the heat.  During the late summer and fall months, when they are fattening up for the long months of hibernation, bears may be active throughout the day.  As food items become scarce, the bear's territory increases.  Within their home range, bears use a wide variety of habitats.  Bears travel from alpine food sources to estuaries, to berry patches, to salmon spawning sites - visiting each site when its particular food source is available

Dens: Dens must provide protection and security during the winter months.  Brown bears can excavate a den but often use rock caves and hollow trees.  Dens are dug in dry, stable soil where winter temperatures will remain above freezing.  Usually the den site terrain is sloping.  As snow falls it covers and helps to insulate the den.  Generally the den is just large enough to accommodate the bear.  The entrance to the den leads to a tunnel that slopes downward to the actual sleeping chamber.  This sloping tunnel allows stale air to escape.  Most dens are used only once.