Wildlife habitat is the environment that provides the essentials of food, cover, and space to a population of animals. These essentials are needed for reproduction, maintenance and growth of both the individual animal and the population. Grizzly bears have their own specific habitat requirements. In areas with very low levels of human development and activity, grizzly bear use of habitat corresponds to a large extent to the location of concentrated seasonal food sources. Ecological studies of grizzly bears in the Central Rockies Ecosystem have shown that grizzly bears use certain favorite plant and animal foods and will shift from one area to another in response to their seasonal abundance.
When grizzly bears come out of their dens in late March and April, food is localized and hard to come by. Some bears routinely travel to areas where they know there are carcasses of hoofed animals such as elk and moose. These areas include the winter range of these animals, railway tracks and roadsides, and the base of avalanche slopes where these animals may have been swept to their deaths. Other foods eaten by grizzly bears in early spring include the fresh shoots of grasses, the Hedysarum plant or “bear roots” , and overwintered bearberries that have aged and have a high sugar content. All of these food sources occur in greatest abundance on steep south-facing slopes, usually at lower elevations.
A little later in the spring, during May and early June, grizzly bears concentrate their activities in river valley bottoms. Bears will eat lots of the tips of the primitive plant called horsetail which is high in crude protein. Horsetail is usually found in mature stands of spruce forest along streams and rivers. Hedysarum roots are excavated along the levees of braided stream channels of larger river systems. Bears continue to find big game carcasses in these habitats and, in some cases, they will even hunt for elk and moose calves.
In late June, in low-lying areas, horsetails and grasses have grown too fibrous to be nutritious. Grizzly bears start to seek out lush areas of vegetation that have developed more slowly. These areas include high elevation avalanche slopes, groundwater seepage areas, and smaller stream courses at upper elevations. Typical foods in these areas are horsetails, Cow Parsnip, Glacier lily, Spring Beauty, Valerian, and a variety of grasses. Hedysarum roots are eaten in mid-summer but not nearly as much as in the spring and fall. The larvae of ants and wasps are eaten wherever bears can find dried out logs and rocks to flip.
Usually in early August, bears start to shift their diet to berries. At this time, some grizzly bears have been known to eat more than 200,000 berries in one day. On the drier east front of the Rocky Mountains, the buffaloberry is the main berry available. The most productive areas for buffaloberries are in open Lodgepole Pine forests in valley bottoms where soils are well drained and canopies are relatively open. In areas close to or west of the Continental Divide, grizzly bears eat blueberries and huckleberries during the months of August and September. These berries are prone to early fall frosts and bears are forced to switch to berries that stay on branches in spite of cold weather. These berries include Crowberry, Low bush Cranberry, and Mountain Ash. Ground squirrels are sought out in September when they are fat and slow. The diggings for ground squirrels are large and often trench-like. They reveal the large amount of effort that grizzly bears are willing to expend for this source of protein and minerals. During fall most grizzly bears supplement their berry diet with Hedysarum roots and even the nuts of Whitebark Pine trees.
When the opportunity arises, bears will eat human food and garbage — the “junk food” of their diet. They do so because of their large body size and huge appetites for high energy foods. Human food and garbage can be highly accessible and are found in predictable places. As is often the case, bears that become conditioned to these food sources present a threat to human safety and are usually translocated of destroyed.
Grizzly bears need a great deal of space to provide for their habitat needs. In order to access seasonally abundant and widely dispersed foods, grizzly bears must travel great distances. Grizzly bears that live in less productive habitat require much larger areas to feed in. The home range of grizzly bears in the eastern slopes of the Central Rockies Ecosystem is quite large, from about 500 sq. km for females to 1000 sq. km for males. Home range size in this region indicates that food sources are widely dispersed throughout the landscape rather than concentrated in local areas.
Not only do grizzly bears need large areas to live in, they need space with limited human access. Secure habitat where human activity is minimal allows grizzly bears to be 100% effective in their use of the landscape. Human activities and developments can make even the most productive habitat less attractive to a bear. As a result, grizzly bears will either live in these areas under stressful conditions or they will avoid them entirely. Overall, human developments and activities make habitat less effective in supporting the needs of bears.
In areas where grizzly bears may frequently encounter humans, they need tree and shrub cover that allows them to escape human detection and avoid close encounters. The alternative to avoiding humans is to become habituated and tolerant of their presence. Unfortunately, proximity to humans tends to increase the chance that a bear will be killed by humans. Bears also use the cover provided by closed-canopy forests to take refuge from the heat and to bed down for periods of the day.
ESGBP has conducted a lot of research into the nature of grizzly bear habitat. Habitat maps have been produced that give us an understanding of the overall quality and availability of habitat in the Central Rockies Ecosystem. Large-scale vegetation maps have revealed that grizzly bear habitat in the Central Rockies Ecosystem is patchy and occurs primarily in valley bottoms and mountain slopes. This patchiness has produced a naturally fragmented landscape where much of the area inhabited by grizzly bears consists of rock and ice. Researchers have also studied actual bear use of the landscape by visiting places where radio-collared grizzly bears have been located. Field researchers record the abundance of bear foods and the availability of cover for grizzly bears at these locations. In the near future, ESGBP will use both the bear use data and the habitat maps to get a really good feel for the specific habitat needs of grizzly bears in the Central Rockies Ecosystem in light of pressures from human development and activity.
Hamer, D. and S. Herrero. 1987. Grizzly bear food and habitat in the Front Ranges of Banff National Park, Alberta. Int. Conf. Bear Research and Management. 7:199-213.