![]() ![]() ![]() Pregnant females den at higher elevations than other females and male bears (Haroldson et al 2002). ![]() In the Yellowstone ecosystem, grizzly bears tend to dig or locate dens on the mid to upper one-third of 30°-60° slopes with northern exposures between 6,562-10,006 ft, =8103 ft (2,000-3,050 meters, =2,470 m) in elevation (Judd et al. The sucking and licking action apparently helps toughen the new footpads so bears can walk on them without pain or difficulty when they emerge from the den and begin searching for food (Beecham et al. This idea most likely arose from observations of bears licking the bottom of their paws during the last half of the denning period when their old, callused footpads slough off (Rogers 1977). It was also once believed that bears obtained nutrients from sucking their paws during hibernation. It is possible this plug may keep the bear from defecating inside the den during hibernation as fecal plugs are found just inside or outside the dens of bears that have just emerged (Rogers 1981). Bears continue to produce some feces during hibernation yet they do not defecate (Rogers 1981). Actually, the plug, made up of feces, dead intestinal cells, hair, and bedding material, forms during hibernation and not before (Rogers 1981). It was once thought that bears ate roughage prior to den entrance to scour their digestive tract and form a plug in the anus to prevent them from eating any more food that fall. Bears may lose 15-30 % of their body weight during hibernation (Rogers 1981). Bears lose fat and may actually increase lean-body mass while hibernating due to this nitrogen recycling (Wickelgren 1988). The urea produced from fat metabolism (fatal at high levels) is broken down and the resulting nitrogen is used by the bear to build protein, which allows them to maintain muscle mass and organ tissues (Rogers 1981). Waste products are produced, however, instead of disposing of their metabolic waste, bears recycle it. Bears live off of a layer of fat built up during the summer and fall months prior to hibernation. Grizzly bears and black bears generally do not eat, drink, defecate, or urinate during hibernation. Mammals that experience lower body temperatures during hibernation, such as chipmunks and ground squirrels, must awaken every few days to raise their body temperature, move around, urinate, and eat (Rogers 1981). They experience a drop in heart rate from 40-50 beats per minute during the summer to 8-19 beats per minute during hibernation. ![]() Respirations in bears decrease from 6-10 breaths per minute normally, to 1 breath every 45 seconds during hibernation. Due to the highly insulating pelts of bears and their lower surface area to mass ratio than smaller hibernators, body heat is lost slowly which enables bears to cut their metabolic rate by 50-60% (Craighead and Craighead 1972 Rogers 1981). Many scientists now consider bears to be super hibernators. This allows bears to react to danger quicker than hibernators whose body temperature may be less than 40° F (4° C) and who have to warm up before they can move quickly (Bagget 1984). Body temperature for hibernating bears remains above 88☏ (31☌) which is within 12☏ (11☌) of their normal body temperature of 100°–101☏ (37.7°–38.3☌) (Bagget 1984). Mammals considered true, or deep hibernators, such as chipmunks and ground squirrels, experience a drastic decrease in body temperature during hibernation. The denning period in Yellowstone National Park is approximately 5 months.įor many years some people did not consider bears to be true hibernators. Duration of winter denning is dependent upon latitude and varies from a few days or weeks for black bears in Mexico to 6 months or more for bears in Alaska (Kolenosky and Strathearn 1987, Haroldson et al. Bears hibernate during the winter months in most areas of the world. Hibernation is an adaptation to a seasonal shortage of food, low environmental temperatures, and snow cover on the ground (Craighead and Craighead 1972 Tietje and Ruff 1980). ![]()
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