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Predators & Scavengers

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1 Predators & Scavengers on Mon Aug 15, 2011 2:26 pm



Grizzly Bear
Most female grizzlies weigh 150 - 350 kilograms (330 - 770 pounds), while males weigh on average 230 – 450 kg (500 - 1000 lb). Newborn bears may weigh less than 500 grams. Although variable from blond to nearly black, grizzly bear fur is typically brown in color with white tips. A pronounced muscular hump occurs on their shoulders which strengthens their front limbs for digging and running; they can attain speeds of 55 km/hr (35 mph). The hump is also a good way to determine a black bear from a brown bear, as black bears do not have this hump.
Although grizzlies are of the order Carnivora and have the digestive system of carnivores, they are normally omnivores, since their diet consists of both plants and animals. They have been known to prey on large mammals, when available, such as moose, deer, sheep, elk, bison, caribou,and even black bears. Grizzly bears feed on fish such as salmon, trout, and bass, and those with access to a more protein-enriched diet in coastal areas potentially grow larger than interior individuals. Grizzly bears also readily scavenge food, on carrion left behind by other animals.
Plants make up approximately 80%–90% of a grizzly bear's diet. Various berries make up a large portion of this. These can include blueberries, blackberries, salmon berries, cranberries, buffalo berries, and huckleberries, depending on the environment.
Grizzlies are normally solitary, active animals, but in coastal areas, the grizzly congregates alongside streams, lakes, rivers, and ponds during the salmon spawn. Every other year, females (sows) produce one to four young (commonly two) which are small and weigh only about 500 grams (one pound). A sow is protective of her offspring and will attack if she thinks she or her cubs are threatened.
Most notable in Yellowstone have been the interactions between gray wolves and grizzly bears. With the reintroduction of gray wolves to Yellowstone, many visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the grey wolf. Typically, the conflict will be in the defense of young or over a carcass, which is commonly an elk or caribou killed by wolves. The grizzly bear uses its keen sense of smell to locate the kill. Then, the wolves and grizzly will play a game of cat and mouse. One wolf may try to distract the bear while the others feed. The bear then may retaliate by chasing the wolves. If the wolves become aggressive with the bear, it is normally in the form of quick nips at its hind legs. Thus, the bear will sit down and use its ability to protect itself in a full circle. Rarely do interactions such as these end in death or serious injury to either animal. One carcass simply is not usually worth the risk to the wolves (if the bear has the upper hand due to strength and size) or to the bear (if the wolves are too numerous or persistent).
Picture Source - U.S. Fish and Wildlife Service, public domain

Black Bear
Black bear weight tends to vary according to age, sex, health and season. Seasonal variation in weight is very pronounced: in autumn, their pre-den weight tends to be 30% higher than in spring, when black bears emerge from their dens. Black bears on the East Coast tend to be heavier on average than those on the West Coast. Adult males typically weigh between 57-250 kg (125 and 550 lb), while females weigh 33% less at 41-109 kg (90–275 lb). Although they are the smallest species in North America, large specimens exceed the size of all other bears except the brown and polar bears. The biggest wild American black bear ever recorded was a male from North Carolina, shot in 1998, that weighed 400 kg (880 lb) and measured 2.4 m (7.95 ft) long. Adults have a typical size range of 120-200 cm (47-79 in) in length, and 70-105 cm (28-42 in) in shoulder height. The tail is 7.7-17.7 cm (3-7 in) long.
The fur is soft, with dense underfur and long, coarse, thick guard hairs. The fur is not as shaggy or coarse as that of brown bears. American black bear skins can be distinguished from those of Asiatic black bears by the lack of a white mark on the chin and hairier footpads. Despite their name, black bears show a great deal of color variation. Individual coat colors can range from white, blond, cinnamon, or light brown to dark chocolate brown or to jet black, with many intermediate variations existing. Bluish tinged black bears occur along a portion of coastal Alaska and British Columbia. White to cream colored black bears occur in coastal islands and the adjacent mainland of south-western British Columbia. Albino specimens have also been recorded. Black coats tend to predominate in moist areas such as New England, New York, Tennessee, Michigan and western Washington. 70% of all black bears are black, though only 50% of black bears in the Rocky Mountains are black.
Up to 85% of the black bear's diet consists of vegetation, though they tend to dig less than brown bears, eating far fewer roots, bulbs, corms and tubers than the latter species. Young shoots from trees and shrubs during the spring period are important to black bears emerging from hibernation, as they assist in rebuilding muscle and strengthening the skeleton and are often the only digestible foods available at that time. Berries, fruits, grasses, nuts and buds are often eaten. During this period, they may also raid the nut caches of squirrels. Black bears are fond of honey, and will gnaw through trees if hives are too deeply set into the trunks for them to reach them with their paws. Once the hive is breached, black bears will scrape the honeycombs together with their paws and eat them, regardless of stings from the bees.
Black bear interactions with wolves are much rarer than with brown bears, due to differences in habitat preferences. The majority of black bear encounters with wolves occur in the species' northern range, with no interactions being recorded in Mexico. Despite the black bear being more powerful on a one to one basis, packs of wolves have been recorded to kill black bears on numerous occasions without eating them. Unlike brown bears, black bears frequently lose against wolves in disputes over kills. Wolf packs are known to kill black bears during their hibernation cycle.
Picture © worldstart.com


Gray Fox
The gray fox ranges from 800 to 1125 mm (31.5 to 41.3 inches) in length. Its tail measures 275 to 443 mm (10.8 to 17.5 inches) and its hind feet measure 100 to 150 mm (4.9 to 5.9 inches). It weighs 3.6 to 6.82 kg (7.9 to 15 lbs).
The gray fox is a solitary hunter and is largely omnivorous. It frequently preys upon the Eastern Cottontail, though it will readily catch voles, shrews, and birds. The gray fox supplements its diet with whatever fruits are readily available and generally eats more vegetable matter than does the Red Fox.
Tree Climbing
The gray fox's ability to climb trees is shared only with the Asian raccoon dog among canids. Its strong, hooked claws allow it to scramble up trees to escape many predators such as the domestic dog or the coyote, or to reach tree-bound or arboreal food sources. It descends primarily by jumping from branch to branch, or by descending slowly backwards as a house cat would do. The gray fox is nocturnal or crepuscular and dens in hollow trees, stumps or appropriated burrows during the day.
Picture © Ian and Rachel

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