Barred owls can be found in dense forests right across North America. They feed on small mammals, fish, birds and small reptiles - pretty much anything that comes their way. The barred owl grows up to half a metre tall and has emerged as a very adaptable nocturnal predator. Whereas they have been long-thought to live in old-growth forests, they are now building up quite an urban population. In Charlotte, North Carolina, barred owls tend to nest in the cavities of the numerous willow oak trees that line the city's streets. Far from being endangered, the owls have expanded their range; and now, in some places, conservationists are worried about the effects they might have on other native species.