Also known as brown bears for their signature coloring, grizzly bears live in harsh, cold environments like Alaska, Siberia and the Rocky Mountains. They're only able to survive in these areas because of their physical and behavioral adaptations, which allow them to hunt for food, shelter themselves for the winter and reproduce in a way that helps to ensure the survival of their cubs.
Searching for Food
Grizzly bears are effective hunters and scavengers, with a sense of smell that can detect a rotting corpse from two miles away. This highly attuned sense enables them to find and eat carrion such as moose, mountain goats and even other bears. They also have long, sharp claws, which are useful for digging. With these claws, they easily can uproot plants and demolish the burrows of small, ground-dwelling animals such as mice and squirrels, digging them out of their homes and eating them.
Chasing Down Prey
Though grizzly bears can weigh more than 1,300 pounds, their bodies are adapted for running. This adaptation is what gives grizzly bears the distinct back humps around their forelegs. These humps are where the bones and muscles have adapted to make grizzlies powerful runners, capable of chasing down large, nimble prey such as caribou and moose. The humps also give grizzly bears the upper body strength to be more effective diggers, though they are unable to climb.
Because grizzlies live in environments that are cold during winter, they are adapted to hibernate. As winter approaches and their food supplies start to dwindle, grizzly bears forage and hunt more often so that they can build up body fat. Using their long, sharp claws and powerful digging strength, they dig dens for themselves where they nest through the winter. In their dens, grizzly bears enter their hibernation state, during which their body temperature and heart rate drop. During this period, they do not need food or water, nor do they need to relieve themselves -- they simply sleep.
To give their cubs the greatest chance at survival, grizzly bears are adapted to a particular breeding cycle that is dependent on their annual hibernation. After mating in the three-month period between May and July, females don't give birth until the period between January and March. This is because the embryo doesn't implant itself right away -- it remains in limbo for several months, until the body has gained enough weight for hibernation and to successfully carry the pregnancy. If a female doesn't gain enough weight, she simply reabsorbs the embryo and tries again the next year. Because the birthing months fall during the hibernation period, a new mother can remain awake to care for the cubs inside the den while maintaining her low-energy level.
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Tom Ryan is a freelance writer, editor and English tutor. He graduated from the University of Pittsburgh with a degree in English writing, and has also worked as an arts and entertainment reporter with "The Pitt News" and a public relations and advertising copywriter with the Carnegie Library of Pittsburgh.