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

Geographic Range

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)

Habitat

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)

  • Range elevation
    1500 (high) m
    4921.26 (high) ft

Physical Description

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)

  • Sexual Dimorphism
  • female larger
  • Average mass
    164.1 g
    5.78 oz
    AnAge
  • Range length
    16 to 25 cm
    6.30 to 9.84 in
  • Average basal metabolic rate
    0.586 W
    AnAge

Reproduction

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)

  • Breeding interval
    Breeding occurs once a year, usually, but a second clutch may be attempted in areas with dense resources.
  • Breeding season
    Breeding occurs from February through March and perhaps later.
  • Range eggs per season
    2 to 7
  • Average eggs per season
    3.5
  • Average eggs per season
    4
    AnAge
  • Range time to hatching
    26 to 34 days
  • Range time to independence
    8 to 10 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    365 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    1 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days
    AnAge

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.

Lifespan/Longevity

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)

Behavior

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)

Home Range

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

Communication and Perception

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)

Food Habits

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)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms

Predation

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)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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)

Mutualist Species

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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

Conservation Status

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)

Contributors

Tanya Dewey (author), Animal Diversity Web, Kari Kirschbaum (editor), Animal Diversity Web.

Stephen McDonald (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5? N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

Pearson, T.G. 1940. Birds of America. Third Edition. Garden City Publishing Company, New York.

http://www.eecs.tufts.edu/~cabotsch/bulloughs/vertebrates/birds/eastern-screech-owl.html

http://www.ai-design.com/stargig/raptor/global/content/report/Eastern Screech owl.html

Gehlbach, F. 1995. Eastern Screech Owl (Otus asio). The Birds of North America, 165: 1-24.