Two hundred species, fourteen neck bones, near-silent wings
Owls (Strigiformes) number over two hundred mostly nocturnal raptors with forward-facing eyes, facial discs, and flight feathers tuned for quiet. They can turn their heads about 270 degrees thanks to fourteen neck vertebrae—twice the human count.
The order splits into two families, the typical owls of Strigidae and the barn and bay owls of Tytonidae. Most are solitary night hunters, although the northern hawk-owl hunts by day and the burrowing owl lives in groups. They take insects, small rodents, rabbits and hares, and other birds, and a few specialise in fish. Owls live everywhere except the polar ice caps and certain remote islands, and in English a gathering of them is a parliament.
Their senses are built for darkness. Unlike most raptors, whose eyes sit on the sides of the head, owls look straight ahead, gaining the depth perception needed in dim light. The eyes are so large for the skull that they have become tube-shaped, and owls find their way at night without echolocation. A ring of feathers around each eye, the facial disc, can be adjusted to channel sound toward ear openings set at different heights, helping the bird pinpoint prey. Plumage is mostly camouflaged, though ear tufts, face masks and bright irises may serve as signals in the gloom.
Turning the head so far needs special plumbing. The holes in the neck vertebrae that carry the arteries are around ten times wider than the vessels themselves, instead of matching them as in people, so blood keeps reaching the brain. Slow, near-silent flight comes from unusually large feathers with a softened structure, an advantage for nocturnal species hunting prey that listens hard. Barn owls pay for it: they skip oiling their feathers from the preen gland, so the plumage is not waterproof and heavy rain grounds them. They once sheltered to hunt inside barns, which have become scarcer.
Females are usually the bigger sex. Explanations include small males being nimbler hunters that supply the nest, heavier females surviving long stints brooding eggs, and males needing agility to escape aggressive mates.
Source: Owl
