The following guide is designed to help you identify the 20 breeding species of owls that can be found in the United States and Canada. Owls are divided into two groups or subfamilies: Tytoninae (barn and bay owls) and Strigidae (all other owls). Owls are basically nocturnal or crepuscular (active in the late morning or early evening). However, during winter, some species may be observed almost any time and in a variety of habitats because they are in search of food. Because most owls are active in times of low light or complete darkness, they have evolved a low- frequency vocal repertoire as a means of communication. Familiarity with these primary songs can greatly facilitate owl identifications.

Owls have two primary hunting methods: (1) "perch and pounce," which usually takes place from a low perch and is most common among forest owls, and (2) "quartering," which means flying low over the ground; it is most common among open-country owls.

Owls have evolved several important adaptations to help them cope with their lifestyles. Some of the most recognizable characteristics include: Large heads to accommodate large eyes and ears. Owls cannot move their eyes up, down, or side to side like humans can, so owls have evolved the ability to rotate their heads approximately 270 degrees. The ears in some species are asymmmetrical (the right ear is longer and situated higher on the skull), allowing them to calculate flight angles when sounds are heard but prey cannot be seen. Owl feathers in many species are structured so that sound created by flight is absorbed; Consequently, these owls can hear but not be heard by potential prey when flying. Owls usually vocalize at a low frequency. These sound waves carry long distances and are not absorded by barriers such as vegetation as quickly as high-frequency vocalizations.

The photos and accompanying text are designed to help you identify North American owls and provide some basic life history. In North America, female owls are larger than males, with the exception of the Burrowing owl. For identification purposes, owls are often separated into those with "ear tufts" or "horns" and those which are "round headed." In the owl descriptions that follow, we have used "tufts" instead of "eartufts" or "horns" to denote the specialized feathers arising from the heads of many owls. We have retained the use of "round-headed." If you're in the field and trying to identify North American owls, make the following items part of your check lists:

• Determine if the owl has tufts or is round-headed.
• Note the eye and bill color.
• Note the plumage color and other distinctive markings.
• Note relative size of the owl.
• Note details of the owl's habitat and check distribution maps.

By using a combination of these field tips, you should be well on your way to identifying any owl you might see in North America.