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Tyto albabarn owl

By Kathleen Bachynski and Marie S. Harris

Geographic Range

Barn owls are the most widespread of all owl species, and are found on every continent except Antarctica. In the Americas, barn owls occur in suitable habitat throughout South and Central America, and in North America as far north as the northern United States and southwestern British Columbia. In Europe, barn owls range from southern Spain to southern Sweden and east to Russia. They are also found throughout Africa, across central and southern Asia, and throughout Australia. Barn owls have been introduced to some oceanic islands to control rodent pests.

Habitat

Barn owls occupy a vast range of habitats from rural to urban. They are generally found at low elevations in open habitats, such as grasslands, deserts, marshes and agricultural fields. They require cavities for nesting, such as hollow trees, cavities in cliffs and riverbanks, nest boxes, caves, church steeples, barn lofts, and hay stacks. The availability of appropriate nesting cavities often limits use of suitable foraging habitat. (Marti, 1992)

Physical Description

Barn owls are medium-sized owls with long legs that are sparsely feathered down to their grey toes. The head is large and rounded without ear tufts. Barn owls have rounded wings and a short tail that is covered with white or light brown, downy feathers. The back and head of the bird are a light brown with variable black and white spots, while the underside is a grayish white. Barn owls are very striking in appearance. Females tend to be larger, weighing around 570 grams, while males weigh around 470 grams. Females also have a slightly longer body length (34 to 40 cm for females, 32 to 38 cm for males) and wingspan. Wingspan of males and females ranges from 107 to 110 cm.

Up to 35 subspecies of Tyto alba are recognized based on differences in body size and coloration. ("The Owl Pages", 2003; Marti, 1992)

  • Sexual Dimorphism
  • female larger
  • Range mass
    430 to 620 g
    15.15 to 21.85 oz
  • Range length
    32 to 40 cm
    12.60 to 15.75 in
  • Range wingspan
    107 to 110 cm
    42.13 to 43.31 in

Reproduction

Barn owls are most commonly monogamous, although several reports of polygyny exist. Pairs typically remain together as long as both individuals live.

Courtship begins with display flights by males which are accompanied by advertising calls and chasing the female. During the chase, both the male and the female screech. The male will also hover with feet dangling in front of the perched female for several seconds; these are known as moth flights.

Copulation occurs every few minutes during the nest site search. Both sexes crouch down in front of each other to solicit copulation. The male mounts the female, grasps her neck, and balances with spread wings. Copulation continues with decreasing frequency throughout incubation and chick rearing.

Barn owls breed once per year. They can breed almost any time of the year, depending upon food supply. Most individuals begin breeding at 1 year old. Due to the short life span of barn owls (2 years on average), most individuals breed only once or twice. Barn owls usually raise one brood per year, though some pairs have been observed raising up to three broods in one year

Barn owl pairs often use an old nest that has been occupied for decades rather than building a new one. The female usually lines the nest with shredded pellets. She lays 2 to 18 eggs (usually 4 to 7) at a rate of one egg every 2 to 3 days. The female incubates the eggs for 29 to 34 days. The altricial chicks are brooded and fed by the female for about 25 days after hatching. They leave the nest on their first flight 50 to 70 days after hatching, but return to the nest to roost for 7 to 8 weeks. The chicks usually become independent from the parents 3 to 5 weeks after they begin flying. ("The Owl Pages", 2003; Marti, 1992)

  • Breeding interval
    Barn owls breed once yearly; somtimes two or even three broods per year are produced.
  • Breeding season
    Barn owls breed essentially any time of the year, depending upon food supply.
  • Range eggs per season
    2 to 18
  • Average eggs per season
    5.5
  • Average eggs per season
    6
    AnAge
  • Range time to hatching
    29 to 34 days
  • Range fledging age
    50 to 70 days
  • Average fledging age
    64.3 days
  • Range time to independence
    3 to 5 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Female barn owls leave the nest during incubation only briefly and at long intervals. During this time, the male feeds the incubating female. All brooding is done by the female, beginning immediately after hatching and lasting until the oldest young is about 25 days old. Males bring food to the nest for the female and chicks, but only the female feeds the young, initially tearing the food into small pieces. The female also eats the feces of the chicks for the first few weeks after hatching in order to sanitize the nest. The parents continue to feed the chicks for up to 5 weeks after fledging. (Marti, 1992)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

Most barn owls have a relatively short life span. Many only survive one breeding season and the mortality rate may be as high as 75% in the first year of life. in one study, the mean age at death for 572 banded birds was 20.9 months. However, the longest recorded lifespan of a wild barn owl is 34 years. (Marti, 1992)

  • Range lifespan
    Status: wild
    34 (high) years
  • Average lifespan
    Status: wild
    20.9 months
  • Average lifespan
    Status: wild
    185 months
    Bird Banding Laboratory

Behavior

Barn owls are solitary, or found in pairs. They are nocturnal, and roost during the day in tree cavities, cliff crevices, riverbanks, barns, nest boxes, churches steeples, and other man-made structures.

Barn owls are very efficient hunters. It is suspected that they spend much of their time loafing. Most barn owls are sedentary, though some individuals in the northern part of the range are migratory. (Marti, 1992)

Home Range

In a study of barn owls in New Jersey, the average home range was 7.17 square kilometers. (Marti, 1992)

Communication and Perception

Barn owls communicate with vocalizations and physical displays. Owlets still in the nest utter several distinct vocalizations, including a twitter used to express discomfort, attention-seeking, and when quarreling with nestmates. Young also give a raspy snoring food call. Adults use a variety of vocalizations, including the advertising call, a drawn-out gargling scream that is probably the best known call. The distress call is a series of drawn-out screams. Other vocalizations include a defensive hissing sound, a fast, often prolonged, twitter for feeding, and an explosive yell that is usually directed at a mammalian predator. Also, greeting and conversational twitters seem to convey recognition of mate and accompany various courtship activities. Barn owls are much less vocal when not breeding.

The ability of barn owls to locate prey by sound is the most accurate of any animal tested. This very acute sense of hearing allows barn owls to capture prey hidden by vegetation or snow. Their amazing ability to locate prey using sound is aided by their asymmetrically placed ears. This asymmetry allows these owls to better localize sounds generated by prey. Their ears are extremely sensitive and can be closed by small feathered flaps if the noise level is too disturbing. Barn owls also have excellent low-light vision.

Food Habits

Barn owls are nocturnal predators that prefer small mammals such as mice, voles, shrews, rats, muskrats, hares and rabbits. They may also prey on small birds. Barn owls begin hunting alone after sunset. As an aid for detecting movement in grassland, they have developed highly sensitive low-light vision. When hunting in complete darkness, however, the owl relies on its acute hearing to capture prey. Barn owls are the most accurate birds at locating prey by sound. Another trait that adds to their hunting success is their downy feathers, which help to muffle the sound of their movement. An owl can approach its prey virtually undetected. Barn owls attack their prey in low flights (1.5m-4.5 meters above the ground), capture the prey with their feet, and nip through the back of the skull with the bill. They then swallow the prey whole. Barn owls do cache extra food, especially during the breeding season. (Marti, 1992)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals

Predation

Barn owls have few predators. Nestlings are occasionally taken by stoats and snakes. There is also some evidence that great horned owls occasionally prey upon adult barn owls. Barn owl subspecies in the western Palearctic are much smaller than those in North America. These subspecies are sometimes preyed upon by golden eagles, red kites, goshawks, buzzards, peregrine falcons, lanners, eagle owls and tawny owls.

When facing an intruder, barn owls spread their wings and tilt them so that their dorsal surface is towards the intruder. They then sway their head back and forth. This threat display is accompanied with hissing and billsnaps that are given with the eyes squinted. If the intruder persists, the owl falls on its back and strikes with its feet. (Marti, 1992)

Ecosystem Roles

Barn owls limit populations of the mammal and bird species that they prey upon. They also serve as food for those species that prey upon them. Barn owls are host to several parasites. Nestlings are commonly infested with the dipteran Carnus hemapterus. They also host several protozoan blood and intestinal parasites and two species of lice (Kirodaia subpachygaster and Strigiphilus aitkeir). (Marti, 1992)

Economic Importance for Humans: Positive

Barn owls limit rodent pest populations, benefiting farmers and others.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no negative impacts of barn owls on humans.

Conservation Status

Barn owls are protected under the U.S. Migratory Bird Treaty Act and under CITES Appendix II. They are not federally threatened or endangered in the United States, but they are protected in some individual U.S. states--including Michigan, where they are considered endangered.

Threats to barn owl population include climatic changes, pesticides, and changing agricultural techniques. A change of the climate in northern regions is causing snow to last for longer periods, making winter survival difficult for the species. Unlike other birds, barn owls do not store extra fat in their body as a reserve for harsh winter weather. As a result, many owls die during freezing weather or are too weak to breed in the following spring. Pesticides have also contributed to declines in this species. For unknown reasons, barn owls suffer more severe effects from consuming pesticides than other species of owls. These pesticides are often responsible for eggshell thinning in females. Another major factor limiting population growth is modern agricultural methods. Traditional farms with many small structures favored barn owl populations. In modern farms, there is no longer an adequate amount of farm structures for nesting, and farm land can no longer support a sufficient population of rodents to feed a barn owl pair. The barn owl population, however, is declining only in some localities, not throughout the range. (Marti, 1992)

Contributors

Kathleen Bachynski (author), University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Kari Kirschbaum (editor), Animal Diversity Web.

Marie S. Harris (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

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

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

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.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

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.

forest

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

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

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

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

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

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

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

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

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

year-round breeding

breeding takes place throughout the year

References

Perrins, Christopher, M.. et. al., The Encyclopedia of Birds. Facts on File Publications, 1985.

2003. "The Owl Pages" (On-line). Accessed January 26, 2004 at http://www.owlpages.com/species/tyto/alba/Default.htm.

Marti, C. 1992. Barn Owl. Pp. 1-15 in A Poole, P Stettenheim, F Gill, eds. The Birds of North America, Vol. 1. Philadelphia: The Academy of Natural Sciences; Washington DC: The American Ornithologists' Union.

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