Army cutworm moths fly long distances in early summer from farm fields on the Great Plains up to alpine slopes in the mountains. Bears feeding on moths on talus slopes can eat 40,000 to 60,000 moths in one day.
Army cutworm moths provide 8 kilocalories per gram, the richest documented food for grizzly bears in the Greater Yellowstone area. In summer, some grizzlies climb to high mountain slopes where moths gather, and eat them.
A grizzly's hearing is about like ours, and its sense of smell is the one it depends on most. A brown bear can follow the scent of a rotting carcass for more than two miles.
An adult grizzly stands about 3.5 feet (about 1 meter) tall at the shoulder. In the lower 48 states, adult males average 400 to 600 pounds (200 to 300 kilograms).
Hyperphagia is the time in fall when a grizzly eats far more than usual and turns the extra food into fat; it lasts two to four months before the bear enters its den. In the fall, a grizzly bear may gain as much as 3.64 pounds (1.65 kilograms) in a single day. The fat a bear stores for winter gives it energy and also keeps it warm.
In the lower 48 states, average yearly home ranges of adult female grizzlies run from 130 to 358 square kilometers, and those of adult males from 475 to 2,162 square kilometers. Young female grizzlies usually set up a home range about 6 to 9 miles from the middle of their mother's, while young males move farther, about 19 to 26 miles.
Some brown bears travel hundreds of kilometers in autumn to reach salmon streams or places with lots of berries. Where fish are plentiful, a brown bear can eat up to 90 fish in a single day. Once salmon-eating brown bears are less hungry, they eat only the eggs, brains and skin of the salmon, the most nutritious and fatty parts.
Salmon left in the forest by bears give nutrients to the trees: studies in Alaska found that a large share of the nitrogen in riverside trees came from salmon.
Words to know
- talus: loose rock slope
- hyperphagia: eating a lot
- kilocalories: energy units
- nutrients: body food
