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Owls are birds of prey, occupying by night the hunting and feeding niches which the hawks hold by day. Superb, specialized predators, owls are adapted to find, catch and kill prey quickly and efficiently. And they've been doing it for ages; owl fossils found in midwestem United States in rocks of the Eocene period date back about 60 million years.

Eight species of owls either live in Pennsylvania or visit the state in winter. Barn, screech, great homed, barred and long-eared owls are permanent residents; the short-eared owl is basically a winter resident, here from November to April; the saw-whet owl is a rare resident, seen most often from November to February; and the snowy owl is occasionally spotted in winter, especially in Pennsylvania's northern counties.

Taxonomists divide owls (order Strigiformes) into two families, Tytonidae--barn owls--and Strigidae, a family to which all other Pennsylvania owls belong. Our barn owl ranges over most of the world, with related species in South America, Europe, Africa, Asia and Australia. Strigidae have near-worldwide distribution, including most Pacific islands and the arctic.

The plumage of owls is dense and soft, making them look heavier than they actually are. Their drab-colored feathers blend into the background of shaded daytime roosts and the darkness of night; the feathers on owls' legs provide insulation and protect against bites by prey. Both sexes are colored essentially alike, but females are usually larger and heavier than males of the same species.

Some unusual and highly effective adaptations help owls survive. Extremely large retinas make their vision 50 to 100 times more efficient than human sight at distinguishing small objects in dull light. Also, the retinas are packed with rods (light-gathering cells). An owl can't distinguish colors well, but it possesses binocular vision: each eye views the same scene from a slightly different angle, thus improving depth perception. Eyes are fixed in the skull; to look to the side, an owl moves its head, and some species can twist their necks over 270 degrees--almost all the way around.

An owl's head is large and broad to accomodate two widely spaced and highly developed ears. Owls hear sounds well below the threshold of human hearing; even in complete darkness a barn owl can catch prey by using its hearing alone. The conspicuous "ears" or "horns" of great horned, long-eared and screech owls are really tufts of feathers that have little effect on their hearing.

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