Barn owl

From Wikipedia, the free encyclopedia - View original article

Barn owl
Tyto alba -British Wildlife Centre, Surrey, England-8a (1).jpg
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)
Subspecies

many, see text

Schleiereule-Tyto alba-World.png
Global range in green
Synonyms

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

 
  (Redirected from Barn Owl)
Jump to: navigation, search
This article is about the common barn owl species. For the entire barn-owl family see Tytonidae
Barn owl
Tyto alba -British Wildlife Centre, Surrey, England-8a (1).jpg
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)
Subspecies

many, see text

Schleiereule-Tyto alba-World.png
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 the 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.[2] However, they have been introduced to control rodents in the Hawaiian island of Kauai.[3]

The barn owl is known by many other names which mostly refer to its pale colouring or silent flight. Barn owls specialise in hunting small mammals and nearly all of their food consists of small rodents. Breeding takes place at varying times of year according to locality with a clutch of about four eggs being laid in a nest in a hollow tree, old building, cliff fissure or cave.

Description[edit]

Plate 171 of the Birds of America by John James Audubon, depicting the barn owl
Adult T. a. alba in flight, Pyrenees (France)
Australian subspecies T. a. delicatula giving shree calls; SE Queensland

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 (9.8–19.7 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 28.2 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, an eerie, long-drawn-out shriek. Males in courtship give a shrill twitter. Both young and old can hiss like a snake to scare away intruders. Other sounds produced include a purring chirrup denoting pleasure, and a "kee-yak", which resembles one of the vocalisations of the tawny owl. When captured or cornered, it throws itself on its back and flails with sharp-taloned feet, making for an effective defence. Also given in such situations is a rasp and a clicking snap, produced by the bill or possibly the tongue.[7][10]

Taxonomy and etymology[edit]

The barn owl is known by many other names, which may refer to its appearance, call, habitat or its 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.[11] "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.[12] 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".[13]

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.[2]

Subspecies[edit]

Male Tyto alba alba (left) and female T. a. guttata barn owl in the Netherlands, where these subspecies intergrade

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:[2]

Distribution[edit]

The barn owl is considered to be the most widespread landbird species in the world, occurring in every continent except Antarctica. Its range includes all of Europe (except Fennoscandia and Malta), most of Africa apart from the Sahara, the Indian subcontinent, Southeast Asia, Australia, the Pacific Islands, North, Central and South America.[18] In general it is considered to be sedentary, and indeed many individuals, having taken up residence in a particular location, remain there even when better foraging areas nearby are vacant. In the British Isles, the young seem to largely disperse along river corridors and the distance travelled from their natal site averages about 9 km (5.6 mi).[19] In continental Europe the distance travelled is greater, commonly somewhere between 50 and 100 kilometres (31 and 62 mi) but exceptionally 1,500 km (932 mi), with ringed birds from the Netherlands ending up in Spain and in Ukraine. In the United States, dispersal is typically over distances of 80 and 320 km (50 and 199 mi), with the most travelled individuals ending up some 1,760 km (1,094 mi) from the point of departure. Movements in the African continent include 1,000 km (621 mi) from Senegambia to Sierra Leone and up to 579 km (360 mi) within South Africa. In Australia there is some migration as the birds move towards the northern coast in the dry season and southward in the wet, and also nomadic movements in association with rodent plagues. Occasionally, some of these birds turn up on Norfolk Island, Lord Howe Island or New Zealand, showing that crossing the ocean is not beyond their capabilities.[2]

Ecology[edit]

Detail of talon

The barn owl is nocturnal, as is usual for owls, but often becomes active shortly before dusk and can sometimes be seen during the day when relocating 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 and a hairlike fringe to the trailing edges help to break up the flow of air over the wings, thereby reducing turbulence and the noise that accompanies it. Hairlike extensions to the barbules of its feathers, which give the plumage a soft feel, also minimise noise produced during wingbeats.[20] 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 that probably evolved, respectively, in allopatric glacial refugia in southeastern Europe, and in Iberia or southern France.[21]

Diet and feeding[edit]

Skull, showing the rodent-killer beak

The diet of the barn owl has been much studied, and the items consumed can be ascertained from examining the regurgitated pellets of indigestible matter and identifying the prey fragments. Studies of diet have been made in most parts of its range, and in moist temperate areas, over 90% of the prey tends to be small mammals, whereas in hot, dry, unproductive areas, the proportion is lower. Most prey is terrestrial but bats and birds are also taken, as well as lizards, amphibians and insects. Earthworms, even when plentiful and other prey items scarce, do not seem to be taken.[22] Although the barn owl feeds primarily on small mammals, a great variety of other creatures are eaten depending on local abundance. In North America and most of Europe, voles predominate in the diet and shrews are the second most common food choice. Mice and rats form the main part of the diet in the Mediterranean region, the tropics, sub-tropics and Australia. Barn owls are usually more specialist feeders in productive areas and more generalists in drier areas.[22] In certain locations where mammals are scarce, exceptions occur; on the Cape Verde Islands, geckos are the mainstay of the diet, supplemented with birds such as plovers, godwits, turnstones, weavers and pratincoles;[23] on a rocky island off California, a clutch of four young was successfully reared on a diet of Leach's storm petrel.[24]

The barn owl hunts by flying low and slowly, quartering the ground and hovering over spots that may conceal prey. It may also use branches, fence posts or other lookouts to scan its surroundings, and this is the main means of prey location in the oil palm plantations of Malaysia. It has wide, broad wings, enabling it to manoeuvre and turn abruptly. Its legs and talons are long and slender which improves its ability to forage among long foliage or beneath the snow and gives it a wide spread of claws when attacking prey.[20] 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. Such animals probably make up at least three-quarters of the biomass eaten by each and every T. alba, except in some island populations.[25] 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.[26]

Small prey is usually torn into chunks and eaten completely including bones and fur, while prey larger than about 100 g (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. 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.[27]

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. The facial disc plays a part in this process, and with the ruff feathers removed, the bird can still locate the source in azimuth but fails to do so in elevation.[28] 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.[29]

Breeding[edit]

Barn owls living in tropical regions can breed at any time of year, but some seasonality in nesting is still evident. Where there are distinct wet and dry seasons, egg-laying usually takes place during the dry season, with increased rodent prey becoming available to the birds as the vegetation dies off. In arid regions, such as parts of Australia, breeding may be irregular and may happen in wet periods, triggered by temporary increases in the populations of small mammals. In temperate climates, nesting seasons become more distinct and there are some seasons of the year when no egg-laying takes place. In Europe and North America, most nesting takes place between March and June when temperatures are increasing. The actual dates of egg-laying vary by year and by location, being correlated with the amount of prey-rich foraging areas around the nest site and often with the phase of the rodent abundance cycle.[30] 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.[31]

Females are ready to breed at ten to eleven months of age although males sometimes wait till the following year. Barn owls are usually monogamous, sticking to one partner for life unless one of the pair is killed. During the non-breeding season they may roost separately, but as the breeding season approaches they return to their established nesting site, showing considerable site fidelity. In colder climates, in harsh weather and where winter food supplies may be scarce, they may roost in farm buildings and in barns between hay bales, but they then run the risk that their nesting hole may be taken over by some other, earlier-nesting species. Single males may establish feeding territories, patrolling the hunting areas, occasionally stopping to hover, and perching on lofty eminences where they screech to attract a mate. Where a female has lost her mate but maintained her breeding site, she usually seems to manage to attract a new spouse.[32]

Once a pair-bond has been formed, the male will make short flights at dusk around the nesting and roosting sites and then longer circuits to establish a home range. When he is later joined by the female, there is much chasing, turning and twisting in flight, and frequent screeches, the male's being high-pitched and tremulous and the female's lower and harsher. At later stages of courtship, the male emerges at dusk, climbs high into the sky and then swoops back to the vicinity of the female at speed. He then sets off to forage. The female meanwhile sits in an eminent position and preens, returning to the nest a minute or two before the male arrives with food for her. She apparently detects his imminent arrival in some way indiscernible to a human observer. Such feeding behaviour of the female by the male is common, helps build the pair-bond and increases the female's fitness before egg-laying commences.[32]

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

Barn owls are cavity nesters. They choose holes in trees, fissures in cliff faces, the nests of other birds such as the hamerkop and, particularly in Europe and North America, old buildings such as farm sheds and church towers. Buildings are preferred to trees in wetter climates in the British Isles and provide better protection for fledglings from inclement weather. Trees tend to be in open habitats rather than in the middle of woodland and nest holes tend to be higher in North America than in Europe because of possible predation by raccoons. No nesting material is used as such but, as the female sits incubating the eggs, she draws in the dry furry material of which her regurgitated pellets are composed, so that by the time the chicks are hatched, they are surrounded by a carpet of shredded pellets. Oftentimes other birds such as jackdaws nest in the same hollow tree or building and seem to live harmoniously with the owls.[33]

Before starting to lay eggs, the female spends her time near the nest and is entirely provisioned by the male. Meanwhile the male roosts nearby and may cache any prey that is surplus to their requirements. When the female has reached peak weight, the male provides a ritual presentation of food and copulation occurs at the nest. The female lays eggs on alternate days and clutch size averages about five, varying from about two to nine. The eggs are chalky white, somewhat elliptical and about the size of bantams' eggs, and incubation begins as soon as the first egg is laid. While she is sitting on the nest, the male is constantly bringing more provisions and they may pile up beside the female. The incubation period is about thirty days, hatching takes place over a prolonged period and the youngest chick may be several weeks younger than its oldest sibling. In years with plentiful supplies of food, there may be a hatching success rate of about 75%. The male continues to copulate with the female when he brings food which makes the newly hatched chicks vulnerable to injury.[32]

Brood soon before fledging, moulting out of their nestling down

The chicks are at first covered with greyish-white down and develop rapidly. Within a week they can hold their heads up and shuffle around in the nest. The female tears up the food brought by the male and distributes it to the chicks. Initially these make a "chittering" sound but this soon changes into a food-demanding "snore" sound. By two weeks old they are half their adult weight and look naked as the down is insufficient to cover their growing bodies. By three weeks old, quills are starting to push through and the chicks stand, making snoring noises with wings raised and tail stumps waggling, to receive food items whole. The male is the main provider of food until all the chicks are at least four weeks old when the female begins to leave the nest and roost elsewhere. By the sixth week the chicks are as big as the adults but have slimmed down somewhat by the ninth week when they are fully fledged and start leaving the nest briefly themselves. They are still dependent on the parent birds until about thirteen weeks and receive training from the female in finding and eventually catching prey.[32]

Lifespan and predators[edit]

Three barn owl chicks threatening an intruder

Barn owl threat displays usually include hissing and bill-snapping.

Unusually for such a medium-sized carnivorous animal, the barn owl exhibits r-selection, producing large number of offspring with a high growth rate, many of which have a relatively low probability of surviving to adulthood.[34] While wild barn owls are thus decidedly short-lived, the actual longevity of the species is much higher – captive individuals may reach twenty years of age or more. But occasionally, a wild bird reaches an advanced age. The American record age for a wild barn owl is eleven and a half years, while a Dutch bird was noted to have reached an age of seventeen years, ten months. Another captive barn owl, in England, lived to be over twenty-five years old. Taking into account such extremely long-lived individuals, the average lifespan of the barn owl is about four 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 bird's life, and only one young in three manages to live to its first breeding attempt.[31] Causes of death are variable but the most significant one in temperate areas is likely to be starvation, particularly over the autumn and winter period when first year birds are still perfecting their hunting skills. In northern and upland areas, there is some correlation between mortality in older birds and adverse weather, deep lying snow and prolonged low temperatures. Collision with road vehicles is another cause of mortality, and may result when birds forage on mown verges. Some of these birds are in poor condition and may have been less able to evade oncoming vehicles than fit individuals would have been. Historically, many deaths were caused by the use of pesticides, and this may still be the case in some parts of the world. Collisions with power-lines kill some birds and shooting accounts for others, especially in Mediterranean regions.[35]

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).[36] 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[edit]

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.[37]

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.[38] 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.[39]

In the UK, the Barn Owl Nest Box Scheme is promoted by the World Owl Trust[40] and has many participants in local areas, including Somerset[41] and Falkirk.[42]

In May 2012, it was revealed that farmers in Israel and Jordan had been using barn owls, instead of pesticides, to deal with mice and rats for the previous ten years as part of a joint conservation venture called Project Barn Owl.[43]

See also[edit]

The Owl Box

References[edit]

  1. ^ BirdLife International (2012). "Tyto alba". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 2013-11-26. 
  2. ^ a b c d Bruce (1999)
  3. ^ Birds of Kauai – Barn owl. Kauaibirds.com. Retrieved on 2014-01-04.
  4. ^ Birds. Seaworld.org. Retrieved on 2014-01-04.
  5. ^ Barn owl videos, photos and facts – Tyto alba. ARKive. Retrieved on 2014-01-04.
  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. ^ Witherby, H. F. (ed.) (1943). Handbook of British Birds, Volume 2: Warblers to Owls. H. F. and G. Witherby Ltd. pp. 343–346. 
  11. ^ Bruce (1999), OwlPages (2006), BTO (2009)
  12. ^ Ali, S. (1993). The Book of Indian Birds. Bombay: Bombay Natural History Society. ISBN 0-19-563731-3. 
  13. ^ Bruce (1999), OwlPages (2006), BTO (2009)
  14. ^ a b Mátics & Hoffmann (2002)
  15. ^ Olson et al. (1981)
  16. ^ a b Traylor & Parelius (1967)
  17. ^ Krabbe, Niels; Flórez, Pablo; Suárez, Gustavo; Castaño, José; Arango, Juan David; Duque, Arley (2006). "The birds of Páramo de Frontino, western Andes of Colombia". Ornitología Colombiana 4: 39–50. 
  18. ^ Shawyer (1994) p. 10
  19. ^ Shawyer (1994) p. 91
  20. ^ a b Taylor (1994) pp. 47–61
  21. ^ Ehrlich et al. (1994): pp. 250–254, Mátics & Hoffmann (2002), Cisneros-Heredia (2006)
  22. ^ a b Taylor (1994) pp. 29–46
  23. ^ de Naurois, R. (1982). "Le statut de la Chouette effraie de l'archipel du Cape Verte". Rivista italiana di Ornitologia 52: 154–166. 
  24. ^ Bonnet, P. (1932). "An outlaw barn owl". Condor 30: 320. 
  25. ^ Ehrlich et al. (1994): 250–254, Ingles (1995), Laudet et al. (2002), Motta-Junior (2006), OwlPages (2006), PGC (2008)
  26. ^ Kelleher, Oliver and Sleeman Irish Birds Volume 9 (2011)
  27. ^ Traylor & Parelius (1967), Ehrlich et al. (1994): pp. 250–254, Laudet et al. (2002), Motta-Junior (2006), OwlPages (2006)
  28. ^ Knudsen, Eric I.; Konishi, Masakazu (1979). "Mechanisms of sound localization in the barn owl (Tyto alba)". Journal of Comparative Physiology 133 (1): 13–21. doi:10.1007/BF00663106. 
  29. ^ UF (1999), Day (2001)
  30. ^ Taylor (1994) pp. 121–135
  31. ^ a b OwlPages (2006), BTO (2009)
  32. ^ a b c d Shawyer (1994) pp. 67–87
  33. ^ Taylor (1994) pp. 136–148
  34. ^ Altwegg, Res; Schaub, Michael; Roulin, Alexandre (2007). "Age‐specific fitness components and their temporal variation in the barn owl". The American Naturalist 169 (1): 47–61. doi:10.1086/510215. 
  35. ^ Taylor (1994) pp. 203–215
  36. ^ Marti et al. (2005)
  37. ^ Bruce (1999), BLI (2008), BTO (2009)
  38. ^ UF (1999)
  39. ^ Álamo Tavío (1975), Palacios (2004), MES (2006)
  40. ^ "Nest-boxes for Barn Owls". Owls.org (2005-03-25). Retrieved on 2014-01-04.
  41. ^ "Barn Owl Project". Somersetwildlife.org. Retrieved on 2014-01-04.
  42. ^ "Barn Owl nest box scheme". falkirk.gov.uk
  43. ^ "The Israeli-Jordan Barn Owl love that knows no borders". Bbc.co.uk (2012-05-18). Retrieved on 2014-01-04.

Bibliography[edit]

External links[edit]