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Habitat
 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.
Suggested Readings:
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.
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