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Strix variabarred owl

By Stephanie Quimby

Geographic Range

Strix varia is found throughout southwestern Canada, Washington, Oregon and northern California. Its range extends throughout the eastern United States including Florida and Texas. Barred owls have expanded their range into western Canada and the United States during the twentieth century, probably as a result of human modifications of landscapes in those regions.

Habitat

Strix varia is arboreal, living in coniferous forests near water source, and wooded swamps. They require dense foliage for daytime roosting, and large trees with cavities for nesting. Their reliance on large tree cavities means that populations of barred owls are dependent on the presence of old growth forests throughout much of their range. However, in the Pacific Northwest, where they have been expanding their range in recent years, they readily accept second growth tree cavities. Their close relatives, spotted owls, rely on old growth forests in this region. This has had the effect, in recent years, of increasing the likelihood of interspecific competition in the Pacific Northwest between resident spotted owl populations and new barred owl populations. Some hybridization between the species has also occurred. The overall effect is to stress an already endangered species, spotted owls.

Physical Description

Strix varia is a large, round-headed woodland owl with a grey-white facial disc. Its plumage is grey-brown with buff-white edges and subterminal bars. Barred owls have brown eyes and lack ear tufts. The neck and upper breast have transverse barring and the belly contains vertical brown streaks. Strix varia is dimorphic in body size. Males are 48 cm in length and have a mean weight of 630 g, whereas females are 51cm in length and have an average weight of 800g. The wingspan of Strix varia is between 107 and 111 cm. Juveniles are a red-brown color with buff barring on the neck. Strix varia is a very vocal species with an easily recognizable 9 syllable call; "Who cooks for you? Who cooks for you-all?"

  • Sexual Dimorphism
  • female larger
  • Range mass
    630 to 800 g
    22.20 to 28.19 oz
  • Range length
    48 to 51 cm
    18.90 to 20.08 in
  • Range wingspan
    107 to 111 cm
    42.13 to 43.70 in

Reproduction

Strix varia is monogamous, pairing for life.

Barred owls form mated pairs that stay together for life.

Although barred owls prefer to nest in tree cavities, this species is known to use empty hawk nests, crows nests, or squirrel nests. A clutch of usually two to three eggs (range is from 1 to 5) will be laid in the nest; the female incubates the eggs for 28-33 days. Young do not all hatch at the same time, since egg laying occured over a period of days and incubation began immediately. While the female incubates eggs the male will hunt for her. Barred owls are capable of breeding at about 2 years of age.

  • Breeding interval
    Barred owls breed once yearly.
  • Breeding season
    Breeding season occurs from December to March.
  • Range eggs per season
    1 to 5
  • Average eggs per season
    2.5
  • Average eggs per season
    2
    AnAge
  • Range time to hatching
    28 to 33 days
  • Range time to independence
    6 (high) months
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

Nestlings are brooded by the female for three weeks, and fed by the male. Nestlings' eyes open after seven days, and at four to five weeks the young will leave the nest and venture to adjacent branches. At six weeks old the young will learn to fly. Parental care is exhibited for up to six months in Strix varia.

Lifespan/Longevity

The longest recorded age of a wild barred owl is 18 years and 2 months old. Mortality during the first year of life is probably highest.

Behavior

Strix varia is primarily a nocturnal hunter, although they have been reported active during the day. Barred owls live alone for most of the year, only living in family groups from the breeding season until the young leave the nest. Mated pairs typically live in adjoining home ranges, with the degree of overlap between home ranges increasing during the breeding season. They will call to other members of the species in the area if disturbed. Barred owls are territorial and do not range widely unless food scarcity causes them to move farther in search of prey. They do not migrate.

Home Range

Estimated home range sizes vary from 273 hectacres (Minnesota) to 1234 hectacres (Saskatchewan). Breeding home ranges tend to be smaller than non-breeding home ranges, from 149 ha (breeding) to 1234 ha (non-breeding) in Saskatchewan.

Communication and Perception

Barred owls are very vocal species with an easily recognizable 9 syllable call; "Who cooks for you? Who cooks for you-all?", called a two-phrase hoot. Barred owls also communicate with other calls, including the begging calls of nestlings, ascending hoots, and caterwauling, which is typically uttered by mating pairs during duets and occasionally when subduing large prey. Barred owls also probably communicate through some visual signals, through body language.

Barred owls use their keen senses of vision and hearing to detect prey from their perches.

Food Habits

Strix varia individuals are generalist carnivores, feeding on small mammals up to the size of rabbits, birds as large as grouse, reptiles, amphibians, and invertebrates. Barred owls have been observed capturing fish from perches and by wading in shallow water. Without exception Strix varia hunts prey that can be swallowed whole. Hunting is mainly done from a perch. Once prey is spotted, barred owls swoop down upon prey and grab it with sharp talons. Like most owls, barred owls cache prey in tree branches and nests.

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • insects
  • terrestrial non-insect arthropods

Predation

Barred owls are preyed on by raccoons and weasels as eggs and nestlings. Adults are sometimes killed by great horned owls, northern goshawks, hit by cars, and captured in traps set for mammals.

Ecosystem Roles

Barred owls are important predators of small animals in the ecosystems in which they live.

Economic Importance for Humans: Positive

Barred owls feed on small mammals, which helps keep the population of crop damaging rodents under control in rural areas.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no negative effects of barred owls on humans.

Conservation Status

Strix varia has been successfully expanding its range in past decades into the Pacific Northwest, where it comes into contact and competition with its close relative, Strix occidentalis, spotted owls. Competition and hybridization between these species stresses the already endangered populations of spotted owls.

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Stephanie Quimby (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

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.

arboreal

Referring to an animal that lives in trees; tree-climbing.

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

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

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.

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.

nocturnal

active during the night

oviparous

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

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"

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.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

Baicich, P., C. Harrison. 1997. A Guide to the Nests, Eggs, and Nestlings of North American Birds. Academic Press Natural World.

Dark, S., R. Gutierrez, G. Gould. Jan 1 1998. The Barred Owl (Strix Varia)Invasion in California. Auk: 50-56.

Del Hoyo, J., A. Elliott, J. Sargatal. 1999. Handbook of the Birds of the World. Barcelona: Lynx Edicions.

Farrand, J. 1983. The Audubon Society Master Guide to Birding. New York: Alferd A. Knopf.

Mathews, B. 1999. "Barred Owls" (On-line). Accessed Dec. 1, 1999 at http://www.owlpages.com.

Terres, J. 1980. The Audubon Society Encyclopedia of North American Birds. New York: Alfred A. Knopf.

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