Tyto alba
barn owl (lechuza de granero)
By Kathleen Bachynski
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Aves
Order: Strigiformes
Family: Tytonidae
Genus: Tyto
Species: Tyto alba
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
Mass
430 to 620 g; avg. 525 g
(15.14 to 21.82 oz; avg. 18.48 oz)
Length
32 to 40 cm
(12.6 to 15.75 in)
Wingspan
107 to 110 cm
(42.13 to 43.31 in)
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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)
Reproduction
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.
Eggs per season
2 to 18; avg. 5.50
Time to hatching
29 to 34 days
Time to fledging
50 to 70 days; avg. 64.30 days
Time to independence
3 to 5 weeks
Age at sexual or reproductive maturity (female)
1 years (average)
Age at sexual or reproductive maturity (male)
1 years (average)
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.
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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)
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)
Lifespan/Longevity
Extreme lifespan (wild)
34 years (high)
Average lifespan (wild)
20.90 months
Average lifespan (captivity)
17.90 years
[External Source: AnAge]
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)
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)
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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 drawnout 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 lowlight 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 (1.5m4.5 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)
Predation
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Known predators
stoats (Mustela)
snakes (Serpentes)
golden eagles (Aquila chrysaetos)
red kites (Milvus milvus)
northern goshawks (Accipiter gentilis)
common buzzards (Buteo buteo)
peregrine falcons (Falco peregrinus)
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lanners (Falco biarmicus)
Eurasian eagle-owls (Bubo bubo)
tawny owls (Strix aluco)
great horned owls (Bubo virginianus)
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: Negative
There are no negative impacts of barn owls on humans.
Economic Importance for Humans: Positive
Barn owls limit rodent pest populations, benefiting farmers and others.
Ways that people benefit from these animals:
controls pest population.
Conservation Status
IUCN Red List:
Least Concern.
US Migratory Bird Act:
Protected.
US Federal List:
No special status.
CITES:
Appendix II.
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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.
Tanya Dewey (editor), Animal Diversity Web, University of Michigan Museum of
Zoology.
Kari Kirschbaum (editor), Animal Diversity Web Staff.
Marie S. Harris (author), University of Michigan.
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.
University of Michigan Museum of Zoology
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