Moose are active during the day. They live alone, but in winter they sometimes form small groups. Moose eat grass, leaves, twigs, willow, birch, maple shoots and water plants. After a pregnancy of 8 months, the female gives birth to one or two calves. Females can first become pregnant when they are between two and three years old. Young moose stay with their mother for a year; after one year they leave and live alone. Moose usually live to fifteen years old, but they can reach as old as twenty-seven years old. A mother moose will aggressively protect her young. Moose calves are hunted by bears and wolves.