Boreal owls range over a much larger area than do other owls of similar size. The reason for this behavior is probably that the small mammals on which owls feed are especially scarce in the forests where boreal owls live, and the relative scarcity of prey requires the owls to range more extensively to find sufficient food.
The statement 'The boreal owl requires less food, relative to its weight, than is required by members of other owl species' most helps to confirm the explanation above.