OWLS.
The Night Hunters
By Chuck Fergus
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. They have been doing it for ages; owls fossils found in Midwestern 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 horned, barred and long-eared owls are permanent residents; the short-eared owl is basically a winter 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 then they actually are. Their drab-colored feathers blend into the background of shaded daytime roosts and the darkness of night; the feathers on owl’s legs provide insulation and protect against bites by prey. Both sexes are colored essentially alike, but females are usually larger and heavier then 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 then 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 accommodate 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 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.
The leading parts of a night hunter’s wings-which cut the air when the bird flies-have soft, serrated edges. These soft leading edges, lightweight wings and a large wing surface area let an owl fly and glide in total silence. As its flight is noiseless, an owl easily hears other sounds while hunting. It descends to its target in a silent, mothlike glide.
An owl grips and kills prey with its talons. Two of these strong, sharp claws branch off the front toes of the foot, and two off the back toes. If the prey is small enough, the owl swallows it whole; otherwise it holds the kill with its talons, tears the carcass apart with its hooked beak and bolts the pieces. The owl’s stomach absorbs nutritious portions and forms indigestible matter (hair, feathers, bones, claws, insect chitin) into round pellets regurgitated about seven hours later.
Pellets, also called castings, can be found under daytime roosts or nighttime feeding stations. Generally, the larger the owl, the larger its pellets. Pellets can be broken apart and the hard bony parts separated from the fur and feathers. Close examination of the hard items gives insight into the owl’s diet.
Most owls call to attract members of the opposite sex during mating season and to announce individual territory. They also call softly for short-range communication between mates or between parents and offspring. When cornered or frightened, owls hiss or make clicking noises by snapping their mandibles (upper and lower parts of the bill).
Owls don’t build nests, preferring to take to abandoned crow or hawks nests or use holes in trees or banks. They may add lining material to existing nests. Early nesters, some even lay eggs in late winter; by the time fledglings leave the nest, offspring of other wildlife abound and are fairly easy prey for the inexperienced young owls.
Owl eggs are founded, white and undecorated, usually 3-5 in number. Incubation is generally the female’s responsibility, while the male hunts and brings food to the female. After the eggs hatch, both female and male feed the young.
The nestlings wear thick white or light gray down. Young found in the same nests are invariably of different sizes, because incubation starts as soon as the female lays the first egg (unlike most other birds, which begin incubation only after all eggs are laid), and therefore this egg hatches first. As much as two weeks may pass between the laying and hatching of the first and last egg. Young hatched latest will die if the parents can not find enough food in the area around the nest, as they can’t compete with the larger, older nestling. This natural check balances predator population with food supply and ensures that surviving fledglings are strong.
During the day, most owls stay in hollow trees or dark, dense stands of vegetation. They hunt mainly at night-occasionally at dusk or on cloudy days-quartering the ground in silent flight or scanning it from a convenient perch.
Owls generally kill what’s easiest to catch or find. As with most predators, they are blamed for killing more game and poultry than they actually do. In reality, they are beneficial birds that prey on many pest species. Mice and wood rats form a major part of the larger owls’ diets; smaller owls eat insects and small mammals. All Pennsylvania owls are protected by the Game Law and federal regulations.