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The Grizzly or Brown Bear
Grizzly bears and brown bears are the same species, but following convention, we use the name grizzly bear here.
It’s estimated that up to 20,000 grizzly bears remain in western Alberta, the Yukon and Northwest Territories and British Columbia. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) lists grizzly bear as a "Special Concern" species due to characteristics that make it particularly sensitive to human activities or natural events. In Alberta, the grizzly bear is considered “May be at Risk”, while in British Columbia, it’s “blue-listed”. The current estimate of the grizzly bear population on provincial lands in Alberta is 500 - 1,000, and up to 17,000 in British Columbia. Within the Rocky Mountain National Parks, *population estimates are:
*Note: many of these bears do not spend their entire lives within the parks.
Mating takes place from mid-May to early July. Males will travel long distances to mate with available females. Bred females experience delayed implantation; the embryo does not implant in the uterus until November or December, but only if the bear has enough fat reserves to sustain her and the developing fetuses through hibernation. This highlights how important habitat quality and diet is to reproductive success. Cubs are born in the den in late January to early February and weigh about half a kilogram (~1 lb.). While the female dozes for another several months, the cubs nurse on milk rich in fat. By the time the sow emerges from the den with her cubs-of-year, they weigh around 8 kg (18 lbs.). A healthy, young-of-year cub can weigh up to 45 kg (~100 lbs.) by the time the family group dens in the fall. Grizzly bear cubs typically remain with their mothers for at least three years. During this time, the sow nurtures, protects and educates her cubs, which increases their chance of successful recruitment into the population (their chance of also reproducing as adults). While under their mother’s care, cubs learn how to forage and move through the landscape to access seasonal habitats. Natural mortality is highest for cubs-of-year and is usually related to nutrition. Adult male bears sometimes kill cubs. Bears that survive to become mature adults can live up 20-30 years in the wild; however, most die human-caused deaths at an earlier age. Grizzly bears have an excellent sense of smell, and good eyesight and hearing.
Food: Though classified as carnivores, grizzly bears are omnivorous. They selectively eat a variety of plants at specific stages of growth throughout the year; meat constitutes about 15 percent of their diet. When bears leave their dens in late March to early April, food is scarce. Snow lingers at higher elevations. The bears are lean and in need of nutrition. Avalanche chutes and steep sub-alpine grasslands with sunny west and south aspects become snow free first and support a diversity of grasses and flowering plants. Important food sources include the roots of the legume Hedysarum, and the bulbs of glacier lily and spring beauty. Winter killed wildlife offer an important pulse of protein and fat. Freshly emerging grasses and sedges in meadows, and along streams and rivers at lower elevations are also important foods. Introduced plants such as clover and dandelion, which green up early along roadsides and disturbed areas, also provide important forage for bears that will risk human presence associated with such sites.
By late spring, horsetail (Equisetum) becomes an important source of food along streamsides and in wet areas in mature spruce forests. Grizzly bears also prey on newborn calves of elk and other ungulates if the opportunity arises. By mid-summer, favoured cow parsnip flourishes on avalanche slopes and moist east and north facing slopes near treeline. Bears flip rocks to lick up insects such as ants and ant larvae. Insects are also torn out of rotting logs and trees.
By mid-July to early August, the fruits of berry producing shrubs begin to mature. In the Central Rockies, berries are the important high quality food source for bears. They concentrate their efforts where these sun-loving plants flourish – along dry forest edges and in open forest. On the drier east slopes of the Rocky Mountain, buffaloberry is most common. Near the Great Divide and on the moist west slopes of the Rockies, blueberry and huckleberry shrubs also grow. Burned forests are important sites that support berry producing shrubs and Hedysarum.
Once a hard frost hits, the larger berries drop and bears turn to the tiny berries of low-growing bearberry, crowberry and grouseberry. Whitebark pine nuts stashed in squirrel caches also provide important calories. Ground squirrels, fat after a summer of feeding, are dug out of their burrows. As winter approaches, bears enter a state called "hyperphagia" and may eat for 20-23 hours a day to store enough fat to survive through hibernation. In some years, the berry crop fails. Bears then rely heavily on Hedysarum roots. They must forage more widely and intensely, using precious energy. With fewer food options and wider travels, food-stressed bears are more likely to get into improperly stored human garbage and other artificial attractants.
Through late fall to hibernation, bears rely once again on Hedysarum roots. Depending on the individual bear and opportunity, ungulates such as elk may become prey. In the Rocky Mountains, grizzly bears have evolved with dynamic landscape events like fire, avalanche and flood – these natural disturbances cultivate the diverse habitats that bears and many other species rely upon. Shelter or Cover: For grizzly bears, trees and shrubs provide cover for security. Shrubs and forest edge allow sows with cubs and young bears to stay out of sight and avoid detection and close encounters with dominant bears or people. Bears also need cover for protection from the weather and climate. Bedding sites (day beds) are generally made near the inside edge of dense forest. Day beds are resting sites that allow bears to maintain a comfortable body temperature on a hot, or a cool day. Grizzly bears have adapted to living in food scarce wintry northern climates by hibernating for up to six months of the year. They dig winter dens into steep slopes with a north or east facing aspect in the sub-alpine where high snow accumulation insulates against the winter cold. Bears Need Space: Bears select for and use habitats based on social interactions with other bears and the presence or absence of human activity. Grizzly bears are not territorial but establish home ranges that vary in size depending on the individual bear and habitat quality. Home ranges may overlap and are usually not aggressively defended. Although the size of home ranges may vary greatly, the average home range in the Central Rockies is:
To survive and successfully raise cubs, adult female bears need safe, predictable, quality habitat within their home ranges. Female cubs establish their home range in the vicinity of their mother, but male cubs usually travel or disperse farther away.
The best, most continuous habitat and wildlife movement corridors sweep along major valley bottoms. Here bears are also most likely to encounter busy trails, roads and highways, railways, campgrounds, or townsites. These developments and human activity fragment habitat, and can potentially filter or even block wildlife movement. Bears that risk using habitat or travel routes near human developments are more likely to die human-caused deaths by being struck by vehicles or trains, or by becoming ‘problem’ bears that are destroyed as a public safety risk. As landscape connectivity is lost, bear populations may become isolated. Isolated populations are more likely to go extinct as they are vulnerable to disease; environmental changes such as drought and climate change; in-breeding, or even inability to find a mate. If connectivity remains, a large population can ‘rescue’ a small population from extinction by providing a source of immigrants. If we can maintain connectivity (habitat connections) across the landscape for grizzly bears, we are also likely to protect movement corridors and habitats for many other species.
Rub trees (trees that generations of bear repeatedly rub and scratch), droppings and urine also communicate a bear’s presence and perhaps social status. Social status is generally based on size as a reflection of sex and age. Adult male bears tend to be dominant. Dominant bears have the pick of the best habitat and food sources. Generally in this social ranking, after mature males, mature females with cubs follow, then single adult bears, and at the bottom of the social ladder, sub-adult (teenage) bears. Once independent of their mother, sub-adult bears must establish their own home ranges and ‘fit in’ to the landscape. These bears are curious and on a learning curve. On an evolutionary scale, this curious behaviour probably helped bears find food in a wide variety of landscapes. Today it also makes young bears vulnerable to danger from humans. Young ‘naïve’ bears are more likely to tolerate people in order to access high quality habitat near human activity and developments, consequently they are more likely die a human-caused death. Sows with cubs are also more likely to use habitat near people, both to avoid dominant males that pose a threat to their cubs, and to access much needed natural bear foods. Typically bears using habitat near people forage at night or early and late in the day when human activity is typically low. This avoidance behaviour helps prevent bear-human conflict, but usually with an energetic cost to the bear. If there are no good or bad consequences, the avoidance response can wane as the bear becomes more and more tolerant of human activity. They become bolder or less wary around people. The need to provide secure quality habitat where adult female bears and their cubs can forage on a daily basis with minimal human disturbance is vital to maintain wary bear behaviour, and the health of the regional bear population. It takes a big land base to support a self-sustaining population of grizzly bears; even the mountain national parks do not provide enough habitat by themselves. Cross-boundary cooperation and management is important to sustain grizzly bears; the will of society to do so, is vital. |
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