Otus asio
eastern screech owl
(Also: eastern screech-owl)

Eastern screech-owls are found throughout much of eastern North America, from the Rocky Mountains in the West to the Atlantic coast and from Florida and southern Texas in the south as far north as southern Canada. (Gehlbach, 1995)

Eastern screech-owls have the broadest ecological niche of any North American owl. They are found in virtually all kinds of habitats below about 1500 meters elevation, from urbanized surroundings to boreal forests. They are generally found in wooded areas but do well in urban and suburban areas and acclimatize readily to human presence, often using bird boxes for nesting. These birds are cavity nesters and use natural cavities or those created by other animals. (Gehlbach, 1995)

Eastern screech-owls are small owls, from 16 to 25 cm in length. Females are generally larger than males, which is common in owls. Eastern screech-owls are dichromatic, they come in two distinct color morphs. They are either uniformly gray or uniformly rufous, with darker streaking on the body. Both color morphs make them very difficult to distinguish from surrounding tree bark. They have bold streaking on their breasts, yellow beaks and eyes, relatively large feet with feathered toes, and large "ear" tufts on either side of their head. Eastern screech-owls are distinguished from their close relative western screech-owls, by their yellow bill, descending trill call, and by the rufous coloration of some individuals. (Gehlbach, 1995)

Most eastern screech-owls form pair bonds for life with individuals of the same age. Some mate switching occurs after unsuccessful nesting attempts and some males have been observed nesting simultaneously and sequentially with more than one female. Both males and females crouch and trill when their mate approaches. (Gehlbach, 1995)

Eastern screech-owl females lay eggs over a period of days to more than a week and generally do not begin full-time incubation until the last egg is laid. As a result, eggs laid first also develop and hatch first. With larger broods, where newly hatched young may be developmentally up to 8 days behind their nestmates, younger nestlings tend to be killed accidentally or by their siblings. From 2 to 7 eggs, usually 3 or 4, are laid in a large nest cavity. They are incubated for 26 (eggs laid last) to 34 days (earlier eggs), with an average of 30 days of incubation. (Gehlbach, 1995)

Eastern screech-owl females incubate the eggs and brood the young. Males feed females and guard nest cavities during incubation and brooding. The young leave the nest at about 28 days old and remain with the parents until they are 8 to 10 weeks old. Both parents feed the young during this period.

An eastern screech-owl lived in the wild for 14 years and 2 months, though most probably live for much less than this. It is estimated that only 30 to 50% of young from one year survive into the next year. (Gehlbach, 1995)

Eastern screech-owls are not migratory and often times a pair may keep the same nest, in winter and summer. Females re-use successful nest sites. These owls are solitary, except during the mating season and during winters when mates share a winter nest. Males defend territories in which they maintain several nesting sites. These owls mainly fly but also hop and walk on the ground when chasing prey. (Gehlbach, 1995)

Estimates of home range size vary with region and season, from 6 to 16 hectares in size. (Gehlbach, 1995)

Eastern screech-owls have acute senses of hearing and vision which help them to locate prey in dim light. They use a variety of vocalizations. Nestlings and females call softly from within the nest cavity. Both males and females give the "trill" song, which may be used to advertise nest sites, in courting, when arriving at the nest with food, and to call nestlings out of the nest for fledging. Other calls are hoots, rasps, chuckle-rattles, barks, and screeches. These calls generally indicate some degree of alarm or anxiety. (Gehlbach, 1995)

Eastern screech-owls eat the most varied diet of any North American owl. Their diet includes large evening active insects, like moths and katydids, crayfish, earthworms, amphibians, reptiles, small mammals, like mice and bats, and small birds. These owls have symmetrical ears, which suggests that they hunt primarily using their vision. They do, however, have excellent hearing as they often capture prey hidden by leaf litter. They hunt by sitting on a tree branch and waiting to see or hear prey. Eastern screech-owls cache prey in their nests for later consumption by adults or nestlings. (Gehlbach, 1995; Gehlbach, 1995)

Eastern screech-owls are extremely vigilant near their nest holes, perhaps in order to assess predator movements. They are preyed on as adults and fledglings by larger owls, hawks, and other eastern screech-owls. Eggs and nestlings may be taken by black ratsnakes, Virginia opossums, raccoons, and ringtails. Eastern screech-owls use alarm calls and will physically attack potential predators that approach their nestlings and fledglings. Their coloration also makes them cryptic. (Gehlbach, 1995)

Eastern screech-owls are sometimes the most abundant and important small predator in urban and suburban forested areas. They also deliberately bring live animals, such as blind snakes into their nests. These animals feed on the ants, flies, and other insects that infest the nest cavity. Acrobat ants may inhabit the nest cavity of these owls and will repel intruders by spraying irritating secretions and biting. (Gehlbach, 1995)

Eastern screech-owls may help to control the populations of potential pests such as mice and some insects.

There are no negative effects of eastern screech-owls on humans.

Eastern screech-owls may suffer as a result of deforestation and the loss of appropriate nesting cavities and prey populations. They are relatively common throughout their range, though, and are not currently threatened. (Gehlbach, 1995)