Except for mating and caring for their young, grizzly bears in primarily lead solitary lives, spending most of their time foraging, or looking for food. The grizzly is North America 's largest omnivore, meaning it eats both plants and animals. About 80-90% of the grizzly's food is green vegetation, wild fruits and berries, nuts, and bulbs or roots of certain plants. Grizzlies also eat a great deal of insects, sometimes tearing rotten logs apart and turning over heavy stones in search of the insects or their larvae.
The remaining percentage of food is meat and that mostly comes from animal carcasses, or carrion, of big game animals. However it will sometimes prey on elk or moose calves or smaller mammals. The grizzlies along the west coast of Canada and in Alaska have salmon which is an important food source. In Yellowstone National Park , spawning trout also play a crucial role in the diets of some bears. Bears are also inclined to find other sources of nutrition including army cutworm moths but have traditionally eaten pine nuts or seeds from white bark pine trees as important sources of food. This has decreased due to disease that heavily impacts these plants.
During the six months of winter in its den,
it is crucial that grizzlies must eat enough to store huge amounts of fat needed to sustain it. The grizzly's ability to eat large quantities of rich food and store fat without suffering from heart disease or cholesterol problems is of great interest to medical scientists. By determining how this is accomplished, scientists could find information that may be useful in preventing human heart disease.
Adult grizzly bears have little to fear from other wild animals as they are at the top of the food chain. Their only enemy is man where habitat loss and mortalities caused by humans are the greatest threats to the bear's survival today.
Interestingly enough, grizzly bears begin looking for a proper place to dig their dens, and may travel many miles before finding a suitable area in the early fall. Generally they seek a high remote mountain slope where deep snow will lie until spring to serve as insulation.
They often dig beneath the roots of a large tree to create their dens by chewing up obstructing roots and thrusting loose rocks and earth through the narrow entrance by its powerful strokes.
By October or November, the grizzly will enter its den and will get no water or nourishment of any kind but will use up its accumulated fat for the next 5 to 6 months. However, some grizzlies have been observed throughout the year, including during severe winters, if there is sufficient food to maintain them. In particular, grizzlies have been observed in the North Fork of Glacier National Park during winter for the last several years. They seem to be following wolf packs and mountain lions in remote regions,
using those species as "providers" for meals of deer and elk.
By March or April, male grizzly bears usually emerge from the den while females emerge in late April and May. The first food it eats is sometimes carrion from animals that did not survive the winter. A grizzly bear will usually travel to lower elevations to reach vegetated, snow-free areas. This can bring the bear into direct conflict with humans who traditionally build their homes in lower elevations, along the very creeks and rivers that bears need to visit in order to find spring "green-up".
When bears begin to awaken from their long winter’s sleep, they are understandably hungry and ready for a feed. During this time, it is important that people are aware of this and take cautious steps when stepping into bear territory. At this vital period of the year, bears will seek carcasses of animals such as deer and elk as food sources, which have been killed in winter. To defend their meal, they will act in an aggressive matter particularly if they have been sprung upon. If you are entering bear country, keep your eyes open for scavenger birds and your nostrils aware of foul odors as they indicate if a carcass is around.
If for some reason you decide to approach the carcass, look at the surrounding area in case there are bears close by as bears usually will devour a meal, then rest and return to eating the unfinished food. Limiting your noise and disposing of trash thoughtfully will also avoid drawing the bears’ attention to you.
Although bears usually will stay within their habitat, when they are hungry they will travel long distances and in foreign soil to find food. People who live near bear territory are recommended to hide items containing food such as dog food, garbage, barbeques as well as bird feeders in order to prevent bears from finding them. Once they have accessed free food, they will return to find more. Unfortunately the consequences can be fatal for the bears and extremely dangerous for human beings. Bear pepper spray is available however bears usually exert more power and a gun is more appropriate in this instance. Killing a bear is not recommended therefore prevention is better than cure so follow the right steps during the aftermath of winter.