Barn Owl

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Barn Owl
Tyto alba alba at British Wildlife Centre, Surrey, England
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Aves
Subclass:Neornithes
Infraclass:Neognathae
Superorder:Neoaves
Order:Strigiformes
Family:Tytonidae
Subfamily:Tytoninae
Genus:Tyto
Species:T. alba
Binomial name
Tyto alba
(Scopoli, 1769)
Global range in green
Synonyms

Strix alba Scopoli, 1769
Strix pratincola Bonaparte, 1838
Tyto delicatula Gould, 1837

 
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Barn Owl
Tyto alba alba at British Wildlife Centre, Surrey, England
Conservation status
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Aves
Subclass:Neornithes
Infraclass:Neognathae
Superorder:Neoaves
Order:Strigiformes
Family:Tytonidae
Subfamily:Tytoninae
Genus:Tyto
Species:T. alba
Binomial name
Tyto alba
(Scopoli, 1769)
Global range in green
Synonyms

Strix alba Scopoli, 1769
Strix pratincola Bonaparte, 1838
Tyto delicatula Gould, 1837

The Barn Owl (Tyto alba) is the most widely distributed species of owl, and one of the most widespread of all birds. It is also referred to as Common Barn Owl, to distinguish it from other species in the barn-owl family Tytonidae. These form one of two main lineages of living owls, the other being the typical owls (Strigidae). T. alba is found almost anywhere in the world except polar and desert regions, Asia north of the Alpide belt, most of Indonesia, and the Pacific islands.[1]

It is known by many other names, which may refer to the appearance, call, habitat or the eerie, silent flight: White Owl, Silver Owl, Demon Owl, Ghost Owl, Death Owl, Night Owl, Rat Owl, Church Owl, Cave Owl, Stone Owl, Monkey-faced Owl, Hissing Owl, Hobgoblin or Hobby Owl, Dobby Owl, White-breasted Owl, Golden Owl, Scritch Owl, Screech Owl, Straw Owl, Barnyard Owl and Delicate Owl. "Golden Owl" might also refer to the related Golden Masked Owl (T. aurantia). "Hissing Owl" and, particularly in the USA and in India, "screech owl", referring to the piercing calls of these birds.[2] The latter name, however, more correctly applies to a different group of birds, the screech-owls in the genus Megascops. The barn owl's scientific name, established by G.A. Scopoli in 1769, literally means "white owl", from the onomatopoetic Ancient Greek tyto (τυτο) for an owl – compare English "hooter" – and Latin alba, "white".[3]

The Ashy-faced Owl (T. glaucops) was for some time included in T. alba, and by some authors its Lesser Antilles populations insularis and nigrescens still are. The Barn Owls from the Indopacific region are sometimes separated as Eastern Barn-owl, Australian Barn-owl or Delicate Barn-owl (T. delicatula). While this may be warranted, it is not clear between which races to draw the line between the two species. Also, some island subspecies are occasionally treated as distinct species. While all this may be warranted, such a move is generally eschewed pending further information on Barn Owl phylogeography.[1]

Contents

Description

Adult T. a. alba in flight, Pyrenees (France)
Detail of talon
Barn Owl rushck.ogg
Australian subspecies T. a. delicatula giving shree calls; SE Queensland
A brood soon before fledging, moulting out of their nestling down

The Barn Owl is a pale, long-winged, long-legged owl with a short squarish tail. Generally a medium-sized owl, there is considerable size variation across the subspecies. The Barn Owl measures about 25–50 cm (9.8–20 in) in overall length, with a wingspan of some 75–110 cm (30–43 in).[4][5] Adult body mass is also variable, ranging from 187 to 800 g (6.6 to 28 oz), with the owls closer to the tropics being generally smaller.[6] Tail shape is a way of distinguishing the Barn Owl from true owls when seen in flight, as are the wavering motions and the open dangling feathered legs. The light face with its heart shape and the black eyes give the flying bird an odd and startling appearance, like a flat mask with oversized oblique black eyeslits, the ridge of feathers above the bill somewhat resembling a nose.[7]

Its head and upper body typically vary between a light brown and a light colored and dark grey (especially on the forehead and back) feathers in most subspecies. Some are purer, richer brown instead, and all have fine black-and-white speckles except on the remiges and rectrices, which are light brown with darker bands. The heart-shaped face is usually bright white, but in some subspecies it is browner. The underparts (including the tarsometatarsus feathers) vary from white to reddish buff among the subspecies, and are either mostly unpatterned or bear a varying amount of tiny blackish-brown speckles. It was found that at least in the continental European populations, females with more spotting are healthier on average. This does not hold true for European males by contrast, where the spotting varies according to subspecies. The bill varies from pale horn to dark buff, corresponding to the general plumage hue. The iris is blackish brown. The toes, as the bill, vary in color; their color ranges from pinkish to dark pinkish-grey. The talons are black.[8]

On average, within any one population males tend to be less spotted on the underside than females. The latter are also larger, as is common for owls. A strong female T. alba of a large subspecies may weigh over 550 g (19.4 oz), while males are typically about 10% lighter. Nestlings are covered in white down all over, but the heart-shaped facial disk is visible soon after hatching.[9]

Contrary to popular belief, it does not hoot (such calls are made by typical owls, like the Tawny Owl or other Strix). It instead produces the characteristic shree scream, ear-shattering at close range. Males in courtship give a shrill twitter. It can hiss like a snake to scare away intruders, and when captured or cornered, it throws itself on its back and flails with sharp-taloned feet, making for an effective defense. Also given in such situations is a rasp and a clicking snap, produced by the bill or possibly the tongue. It is most recognizable by its "mask-like" face.[7]

Subspecies

Light adult, representative of T. a. alba
Adult T. a. furcata in Cuba
Adult T. a. tuidara in Chile
Adult of T. a. guttata in flight, Sandesneben (Germany)
T. a. delicatula in flight
Adult T. a. pratincola in flight
Adult T. (a.) punctatissima on Santa Cruz Island (Galápagos)
T. a. stertens in India

Across its vast range, the Barn Owl has formed many subspecies, but several are considered to be intergrades between more distinct populations today. Still, some 20–30 seem to be worthy of recognition as long as the species is not split up. They vary mainly in size and color, sometimes according to Bergmann's and Gloger's Rules, sometimes more unpredictably. This species ranges in colour from the almost beige-and-white nominate subspecies, erlangeri and niveicauda to the nearly black-and-brown contempta:[1]

Upperparts grey and light buff. Underparts white, with few if any black spots; males often appear entirely unspotted.[10]
Large. Similar to alba but darker above, and with conspicuous speckling overall.
Large. Upperparts pale orange-buff and brownish-grey, underparts whitish with few speckles. Face white.
Upperparts grey and orange-buff. Underparts whitish to light buff with little speckling. Face white. Resembles pale Old World guttata.
More grey on upperparts than alba. Underparts buff to rufous with some dark speckles (more than in alba[10]). Face whitish. Females are on average redder below than males.
Similar to alba; slightly darker above, more speckles below. Tail with 4 bark brown bars.
Large. Upperparts grey and orange-buff. Underparts whitish to light buff with much speckling. Face white. Resembles pale Old World guttata, but usually more speckles below.
Small. Dark greyish brown above, with white part of spots prominent. Underparts white to golden buff, with distinct pattern of brown vermiculations or fine dense spots.
Upperparts golden-brown and grey with very bold pattern. Underparts light buff with extensive speckles. Face white.
Smallish. Upperparts dark brownish grey with bold pattern, including lighter brown bands on remiges and rectrices. Underparts golden brown with extensive speckles. Face buff.
Similar to poensis, but supposedly lighter on average. Upperparts very grey. Underparts light buff with extensive speckles. Face white.[12]
Similar to dark pratincola; less grey above, coarser speckles below.
Smallish. Almost uniformly dark reddish brown above. Reddish buff below, with some speckling. Face reddish buff.
Similar to alba; smaller and noticeably short-winged.
Large, particularly the bill. Similar to javanica; tail whitish with black bars.
Almost black with some dark grey above, the white part of the spotting showing prominently. Reddish brown below
Small. Similar to guttata, but breast region light buff.
Similar to alba; breast region always pure unspotted white.
Small. Similar to schmitzi but breast darker, approaching guttata. Face light buff.
Large. Similar to javanica; tail whitish with grey bars, underparts silvery-white with arrowhead-shaped speckles (larger than in javanica).
Similar to guttata, but less reddish. Face buff.
Similar to ernesti; upperparts lighter and yellower.
Similar to alba, but noticeably speckled below.
Similar to delicatula; darker, with stronger bill and feet.
Similar to delicatula; darker, with orange hue.
Similar to tuidara but larger.
Similar to pratincola; smaller and paler on average.
Large. Similar to furcata; paler in general. Resembles Old World alba.

Ecology

A (male) Tyto alba alba-type (left) and a (female) T. a. guttata-type Barn Owl in the Netherlands, where these subspecies intergrade

Tyto alba is nocturnal, as is usual for owls, but it often becomes active shortly before dusk already and can sometimes be seen during the day, when it relocates from a sleeping place it does not like.

This is a bird of open country such as farmland or grassland with some interspersed woodland, usually below 2,000 m ASL but occasionally as high as 3,000 m ASL in the tropics. This owl prefers to hunt along the edges of woods. It has an effortless wavering flight as it quarters pastures or similar hunting grounds. Like most owls, the Barn Owl flies silently; tiny serrations on the leading edges of its flight feathers help to break up the flow of air over its wings, thereby reducing turbulence and the noise that accompanies it. The behaviour and ecological preferences may differ slightly even among neighboring subspecies, as shown in the case of the European T. a. guttata and T. a. alba which probably evolved, respectively, in allopatric glacial refugia in southeastern Europe, and in Iberia or southern France.[14]

Diet and feeding

A Barn Owl skull, showing the rodent-killer beak

It hunts by flying low and slowly over an area of open ground, hovering over spots that conceal potential prey. They may also use fence posts or other lookouts to ambush prey. The Barn Owl feeds primarily on small vertebrates, particularly rodents. Studies have shown that an individual Barn Owl may eat one or more rodents per night; a nesting pair and their young can eat more than 1,000 rodents per year. Locally superabundant rodent species in the weight class of several grams per individual usually make up the single largest proportion of prey, no matter whether they are Muridae,[15] Cricetidae[16] or Geomyidae (pocket gophers). Such animals probably make up at least three-quarters of the biomass eaten by each and every T. alba, except in some island populations.[17] In Ireland, the accidental introduction of the Bank Vole in the 1950s has led to a major shift in the Barn Owl's diet: where their ranges overlap the vole is now by far the largest prey item.[18]

The diet is supplemented with local small vertebrate and large invertebrate life. A Barn Owl will eat anything it can subdue and that is more than a beakful, from small invertebrates weighing less than 0.05 grams to birds weighing as much as the owl itself, like the Spotted Nothura (Nothura maculosa). Small prey is usually torn into chunks and eaten completely with bones and all, while prey larger of about 100 g or more (such as baby rabbits, Cryptomys blesmols or Otomys vlei rats) is usually dismembered and the inedible parts discarded. Contrary to what is sometimes assumed, the Barn Owl does not eat domestic animals on any sort of regular basis; it might snatch a young chicken or guinea pig once or twice in its life, if at all. Regionally, different foods outside of rodents are utilized as per availability. On bird-rich islands, a Barn Owl might contain some 15-20% birds in its diet, while in grassland it will gorge itself on swarming termites, or on Orthoptera such as Copiphorinae katydids, Jerusalem crickets (Stenopelmatidae) or true crickets (Gryllidae). Bats and even toads and squamates may as well make up a minor but conspicuous part of the prey; small Soricomorpha like Suncus shrews (which to a hunting barn owl probably look much like mice) may be secondary prey of major importance.[19]

An Eulenloch ("owl-hole") in northern Germany lets Barn Owls access the attic for nesting

The Barn Owl has acute hearing, with ears placed asymmetrically for improved detection of sound position and distance, and it does not require sight to hunt. Hunting nocturnally or crepuscularly, it can target and dive down, penetrating its talons through snow, grass or brush to seize rodents with deadly accuracy. Compared to other owls of similar size, the Barn Owl has a much higher metabolic rate, requiring relatively more food. Pound for pound, Barn Owls consume more rodents – often regarded as pests by humans – than possibly any other creature. This makes the Barn Owl one of the most economically valuable wildlife animals to farmers. Farmers often find these owls more effective than poison in keeping down rodent pests, and they can encourage Barn Owl habitation by providing nest sites.[20]

Breeding

In temperate regions, the breeding season usually starts in late March to early April. Breeding can take place at any time prey is abundant, and in the warm parts of its range may occur at any time of the year. An increase in rodent populations will usually soon cause the local Barn Owls to begin nesting; thus, even in the cooler parts of its range two broods are often raised each year. The male entices as are often used. Occasionally, nesting takes place in mine shafts and caves.[21] The female typically lays four–seven eggs. The male brings food to the nest as the female incubates the eggs and cares for chicks.[22]

Lifespan and predators

Tyto alba -USA -three hissing and clicking-8.ogv
Three Barn Owls threatening an intruder.

Barn Owl threat displays usually include hissing and bill-snapping as shown in "Three Barn Owls threatening an intruder".

Unusual for such a good-sized and carnivorous animal, the Barn Owl emphasizes r-selection (as does their prey). Most individuals manage to breed only once in their life, falling victim to predators or accidents before being 2 years of age. While wild Barn Owls are thus decidedly short-lived, the actual longevity of the species is much higher – captive individuals may reach 20 years of age or more. But occasionally, a wild bird reaches an advanced age, such as about a dozen years or more. The American record age for a wild Barn Owl was 11 years and a half, while a Dutch bird was noted to have reached an age of 17 years, 10 months. Another captive barn owl, in England, lived to be over 25 years old. Taking into account such extremely long-lived individuals, the average lifespan of the Barn Owl is about 4 years, and statistically two-thirds to three-quarters of all adults survive from one year to the next. But as noted above, the mortality is not evenly distributed throughout the birds' life, and only one young in three manages to live to its first breeding attempt.[21]

Predators of the Barn Owl include large American opossums (Didelphis), the Common Raccoon (Procyon lotor), and similar carnivorous mammals, as well as large raptors such as hawks, eagles, and other owls. Among the latter, the Great Horned Owl (Bubo virginianus) and the Eurasian Eagle-owl (B. bubo) are noted predators of Barn Owls (though there is little evidence for predation on wild birds by Great Horned Owls).[23] Some also fall victim to large snakes, but the biggest threat are humans and their pets, in particular house or feral cats.

Status and conservation

Barn Owls are relatively common throughout most of their range and not considered globally threatened. However, locally severe declines from organochlorine (e.g. DDT) poisoning in the mid-20th century and rodenticides in the late 20th century have affected some populations. While the Barn Owl is prolific and able to recover from short-term population decreases, they are not as common in some places as they used to be. The most recent survey (1995-1997) put their British population at between 3,000 to 5,000 breeding pairs, out of an average of about 150,000 pairs (varying with rodent stocks) in the whole of Europe, for example. In the USA, Barn Owls are listed as endangered species in seven Midwestern states, and in the European Community they are considered a Species of European Concern.[24]

Barn owl on Lithuanian silver coin of 5 litas (2002)

Common names such as "Demon Owl", "Death Owl" or "Ghost Owl" show that for long, rural populations in many places considered Barn Owls to be birds of evil omen. Consequently, they were often persecuted by farmers, unaware of the benefit these birds bring. As late as 1975, hunting by fearful locals was limiting the population of T. a. gracilirostris on Fuerteventura. In current times, rodenticide poisoning is the main threat for the Canary Barn-owl, which in the Chinijo Archipelago is on the verge of disappearance while on Fuerteventura only a few dozen pairs remain overall. There, the abandonment of much agricultural land and the subsequent decline of rodent pests seem to have decreased the owl's numbers even further. Only on Lanzarote does a somewhat larger number of these birds still seem to exist, but altogether this particular subspecies is precariously rare: Probably less than 300 and perhaps less than 200 birds still exist, and it is classified as insuficientemente conocida ("data deficient") by the Spanish Ministry of Environment. Similarly, the birds on the western Canary Islands which are usually assigned to the nominate subspecies (though this seems suspect on grounds of biogeography) have declined much, and here wanton destruction seems still to be significant. On Tenerife they seem to be not uncommon, while on the other islands, the situation looks about as bleak as on Fuerteventura. Due to the assignment to the nominate subspecies, which is common in mainland Spain, the western Canary Islands population is not classified as threatened.[25]

A Barn Owl (probably of subspecies contempta) was the unofficial mascot of the Colombian football club Junior Barranquilla. The owl, living under the roof of Estadio Metropolitano Roberto Meléndez, had a habit of circling overhead when games were played. On February 27 2011, the owl landed on the field during a match between Junior and Deportivo Pereira and was hit by a passing ball, stunning it. Deportivo player Luis Moreno then kicked it out of the way, causing the owl to die on Tuesday March 1st at 2.57am, despite a veterinarian's attempts to save it. Fans were highly incited by the incident; Moreno eventually received a two-match ban, a high fine, and was sentenced to do community service in a zoo.[26]

See also

The Owl Box

Footnotes

  1. ^ a b c Bruce (1999)
  2. ^ Ali, S. (1993). The Book of Indian Birds. Bombay: Bombay Natural History Society. ISBN 0-149-563731-3. 
  3. ^ Bruce (1999), OwlPages (2006), BTO (2009)
  4. ^ [1]
  5. ^ [2]
  6. ^ CRC Handbook of Avian Body Masses by John B. Dunning Jr. (Editor). CRC Press (1992), ISBN 978-0-8493-4258-5.
  7. ^ a b Bruce (1999), Svensson et al. (1999): pp.212–213, OwlPages (2006)
  8. ^ Bruce (1999), Mátics & Hoffmann (2002)
  9. ^ a b OwlPages (2006)
  10. ^ a b Mátics & Hoffmann (2002)
  11. ^ Olson et al. (1981)
  12. ^ a b Traylor & Parelius (1967)
  13. ^ Krabbe et al. (2006)
  14. ^ Ehrlich et al. (1994): pp.250-254, Mátics & Hoffmann (2002), Cisneros-Heredia (2006)
  15. ^ E.g. multimammate mice (Mastomys), House Mouse (Mus musculus), Black Rat (Rattus rattus) or Indian Gerbil (Tatera indica): Laudet et al. (2002), Cisneros-Heredia (2006), Motta-Junior (2006)
  16. ^ E.g. Delicate Vesper Mouse (Calomys tener), Hairy-tailed Bolo Mouse (Bolomys lasiurus) or Black-footed Pygmy Rice Rat (Oligoryzomys nigripes): Motta-Junior (2006)
  17. ^ Ehrlich et al. (1994): pp.250-254, Ingles (1995), Laudet et al. (2002), Motta-Junior (2006), OwlPages (2006), PGC (2008)
  18. ^ Kelleher, Oliver and Sleeman Irish Birds Volume 9 (2011)
  19. ^ Traylor & Parelius (1967), Ehrlich et al. (1994): pp.250-254, Laudet et al. (2002), Motta-Junior (2006), OwlPages (2006)
  20. ^ UF (1999), Day (2001)
  21. ^ a b OwlPages (2006), BTO (2009)
  22. ^ "Barn Owl Fact Sheet, Lincoln Park Zoo"
  23. ^ Marti et al. (2005)
  24. ^ Bruce (1999), BLI (2008), BTO (2009)
  25. ^ Álamo Tavío (1975), Palacios (2004), MES (2006)
  26. ^ El Espectador (2011), n-tv (2011)

References

Further reading

External links