Grizzlies are surprisingly fast for such big animals. They can run at around 50 km/h, faster than the fastest human sprinter. They are also brilliant swimmers and can climb trees when they're young (older bears get too heavy for the branches).
Grizzlies eat almost anything. They love berries, roots, nuts, fish, and small animals. In late summer, when salmon swim up rivers to lay eggs, grizzlies gather at waterfalls to scoop them out of the air as the fish jump. A single bear can eat 30 fish in a day at this time of year.
Before winter, grizzlies eat as much as they can - up to 40 kilograms of food a day - to build up a thick layer of fat. Then they find a den, often a cave or a hole they dig themselves, and sleep for around five months. Their heart slows right down. Mother bears sometimes give birth during this winter sleep, and the babies stay tucked into her warm fur for months.
Baby grizzlies are tiny when they're born - about the size of a squirrel. By the time they come out of the den in spring, they are about the size of a small dog. They stay with their mother for two to three years, learning to find food, swim and climb. They watch her closely - she is their teacher.