Brown Bear

"To him [the grizzly bear] almost everything is food except granite." -John Muir

 

NPS/Matt Cameron

Long before national parks existed, bears were central to the stories, legends, and mythologies of cultures around the world. Brown bears—icons of Alaskan wilderness—are found throughout the rugged landscape of Gates of the Arctic National Park and Preserve. Brown bears in Gates of the Arctic are physically and behaviorally distinct from brown bears found in the vastly different environment of Alaska’s southern coast.

 

A comparison of black and brown bear body sizes, for males and females, across latitudes in North America.

In the south coastal areas, brown bears grow to massive proportions gorging on salmon from the world-renowned runs in Katmai and Lake Clark National Parks and Preserves. Faced with a super-abundance of food, brown bears in these parks tolerate the presence of other bears and readily congregate at high densities. In contrast, food is scarce on the tundra and in the boreal forests of Gates of the Arctic, where bear density is about 1 brown bear per 15 square miles of land. However, the northern bears do not miss out entirely on nutrient rich salmon! Salmon can be found in the tributaries of the Noatak and Kobuk Rivers, hundreds of miles from the Chukchi Sea. Apart from this short-lived salmon feast, brown bears in Arctic Alaska, including Gates of the Arctic, are primarily solitary and must roam far afield to find sustenance in the form of green vegetation, berries, and live prey or carrion. With high-calorie food harder to come by, they do not grow as large as brown bears found along Katmai and Lake Clark coasts.

 

You are what you eat

One of the most fundamental questions scientist seek to understand about wild animals is: What do they eat? One commonly used method of determining the diet of wild animals is called stable isotope analyses, based on the principle that "you are what you eat." Biologists sampled hair from bears in Gates of the Arctic NPP, Lake Clark NPP, Katmai NPP , and Kodiak Island to determine what nutritional resources used by bears are most important, and when they matter. All this from a single hair sample collected at one point in time.

 

Brown bears have impressive claws that are excellent for digging.

NPS/Kent Miller

Surviving the long Arctic winter—where food is scarce and wind chills can dip to -95°F—requires a strategy to conserve energy; for brown bears this means denning. After spending much of the very short Arctic summer fattening up, brown bears excavate dens for use during the long Arctic winter. In Gates of the Arctic, winter can last up to eight months, the location and provisioning of the den site is important to a bear’s survival. Relying on experience, brown bears choose den sites that maximize energy conservation.Though they rarely reuse the same den in Gates of the Arctic, brown bears typically return to the same area each winter to den. Using their long, powerful claws, brown bears excavate dens on steep slopes (31° on average) to optimize drainage and stability. Brown bears typically select areas with deep snowpack for insulation, and they further insulate their dens by lining the floors and entrances with vegetative material such as grass and moss. Biologists believe bears in Gates of the Arctic build new dens each year because most dens collapse during the intervening summer as the ground thaws. While denning, a bear's heart and breathing rates slow (a state called torpor that is not considered full hibernation as observed in Arctic ground squirrels), it doesn’t eat, and sows (adult females) give birth and nurse cubs without fully waking.

 

NPS/Kent Miller

Recruitment of young into adulthood is paramount for a population to sustain itself. For brown bears in Alaska, survival of young is strongly influenced by age and size of sows. Larger and more experienced brown bear sows recruit more cubs than smaller and less experienced sows. Researchers found that the small sows in Gates of the Arctic and the interior of Lake Clark recruit fewer cubs than the larger sows in Katmai and on Kodiak Island.

 

Maintaining healthy brown bear populations in Alaska’s parks is an important mission for NPS. Reliably estimating the size of the low-density population of brown bears across the 8.5 million acres of Gates of the Arctic, in addition to the 8.8 million acres of the neighboring Noatak National Preserve, Kobuk Valley National Park, and Cape Krusenstern National Monument, is not an easy task, yet it is critical for setting harvest regulations. Hunting is an important traditional aspect of life in Alaska, and brown bears are harvested by subsistence hunters throughout Gates of the Arctic and sport hunters in the Itkillik and Kobuk Preserves. Biologists and pilots conduct population surveys from small fixed-wing aircraft across these large areas. Photographs of individual bears recorded on one flight are used to identify bears and distinguish them from bears seen on a second flight in the same area. These surveys help us track population trends and manage the effects of human activities that directly affect brown bear survival.

Population size is not the only measure of the health of a population; genetic characteristics of individuals can help scientists understand how resilient the population may be to environmental changes and disease. Brown bears in Gates of the Arctic have lower levels of gene transcription (gene expression that directs how cells in the body function) than bears in Katmai and Lake Clark. This is a sign that brown bears in this area are more physiologically challenged than bears from southern coastal populations and may be more susceptible to stressors like disease. This kind of microscopic information can alert us to environmental stressors that affect individual bears, their populations, and even their habitat.

 

Exposure to pathogens

Scientists discovered that brown bears in Gates of the Arctic, and others from five locations throughout Alaska, have been exposed to numerous pathogens (infectious agents that can cause disease). These pathogens are linked to previously documented bear deaths and some may potentially infect humans. Information on the exposure of bears to pathogens may be useful for making informed management decisions for declining bear populations or those of conservation concern and in developing recommendations for the public regarding safe processing, handling, and consumption of harvested animals.

 

On top of a caribou carcass, a brown bear rests.

NPS/Matt Cameron

Ninety-five percent of brown bears in the United States live in Alaska, and Gates of the Arctic is an important refuge for brown bears adapted to life in the Arctic. The Arctic is changing rapidly, and the potential impacts to brown bear populations are not fully understood. We will continue to monitor, study, and conserve brown bears in Gates of the Arctic to ensure that these magnificent animals remain a vital part of the Park and Preserve’s ecosystem for generations to come.