American black bears usually hibernate during winter. During this time, the black bear's metabolism and heart rate both decrease in relation to one another. In fact, during hibernation, an American black bear's heart can stop for twenty seconds. The body temperature of black bears also decreases to 31 °C (88 °F) during hibernation. When hibernation is over, the black bear's body temperature returns to normal. They are omnivores. Black bears eat fish, rodents, rabbits, carrion, fruit, nuts, grasses, deer and moose calves.