Owls are birds of prey with large heads, flat faces, forward-directed eyes and hooked beaks. The size of the beaks is often covered by facial feathers. They have strong legs, sharp claws, and soft feathers.
There are three scientific families of owls. One of these is extinct; These owls lived in North America about 45 million years ago. The remaining two families are the barn owls and the typical owls.
Most owls are nocturnal. However several, including the pygmy owls are crepuscular. This means they are active at twilight, hunting mainly at dawn and dusk. A few owls, such as the burrowing owl and the short-eared owl, are also active during the day.
The smallest owls are probably the pygmy owls. Some pygmy owls are only 13 cm long, and have a 32-cm wingspan. The pygmy owl might weigh only 50 g . The largest owls are the eagle owls which may reach 71 cm long, have a wingspan of just over 2 m. Their weight is about 4 kg .
The barn owl family contains two genera, with 10 or 11 living species and 11 known fossil species; the earliest record of the barn owls is from France and dates back about 19 million years ago.
Barn owls range from 27 to 53 cm in length and have relatively small eyes, a heart-shaped face. They have a comblike margin on the middle claw, and a light coloration and sparse markings on the underparts of the body.
The typical owls comprise 25-31 genera. Three of these genera have become extinct. Scientists believe that 25 species of owls have become extinct. There are reported to be 124-137 living species today. The earliest known typical owls first lived in Europe about 38 million years ago.
Typical owls range from 13 to 71 cm in length and have large eyes, a rounded or gogglelike face. Many species have feathered toes and two tufts of head feathers that resemble ears or horns. Usually owls have dark coloration and heavy markings on the underparts of their body.
Most owls see well in poor light, but all see well in bright daylight. Owls that live far north in the Arctic need to be able to see during the bright sunlight since an Arctic summer has very little darkness.
The owl's eyes are almost immovable, and the owl must turn its head to look elsewhere; however, some species can rotate their heads horizontally 270 degrees, or about three-fourths of a circle, and can turn their heads completely upside down (180 degrees).
The eyes are more forwardly directed in owls than in other birds. The visual fields of the two eyes therefore overlap, creating a binocular span of 60 degrees to 70 degrees, or about one-sixth of a circle. Since the fields of vision for each eye overlap, owls have good depth perception.
The owl's ear openings are located behind and to the side of the eyes. They are covered by sparse feathers. These feathers allow sound to travel past them easily.
Most owls have an ear opening about the size of the eye. However, a few species have extremely large ear openings that occupy the whole height of the head.
Owls can determine the direction of a sound source on a horizontal level by comparing the intensity of a sound heard in the two ears. Generally, the ear nearest the sound source will receive the highest intensity.
Owls also need to know the vertical direction of a sound to be able to strike prey concealed by vegetation or snow. For instance, if a rodent was moving along under the snow, the owl must be able to tell which direction the sound of the movement was coming from. The owl is able to do this with the help of its asymmetrical ears.
The soft feathers help the owl to fly quietly. This allows owls to surprise their prey.
The primary source for the information above was the online Groliers Academic American Encyclopaedia, and the images come from various online graphics libraries, primarily on CompuServe.
Thanks to the Smithsonian Institute, the National Forest Service, James
Armstrong, and a few unnamed professional photographers for their beautiful
owl photographs
This information was revised to accomodate our students' reading level from the Purdue On-Line Writing Lab Web Server Owl Info Page.