Lechuza

La lechuza común ( Tyto alba ) es la especie de lechuza más ampliamente distribuida en el mundo y una de las más extendidas de todas las especies de aves, y se encuentra en casi todas partes del mundo excepto en las regiones polares y desérticas , Asia al norte del Himalaya. , la mayor parte de Indonesia y algunas islas del Pacífico . También se la conoce como lechuza común , para distinguirla de las otras especies de su familia , Tytonidae , que forma uno de los dos principales linajes de búhos vivos, siendo el otro los búhos típicos (Strigidae).

Lechuza
Rango temporal: Cuaternario-presente
Tyto alba -Centro Británico de Vida Silvestre, Surrey, Inglaterra-8a (1) .jpg
Lechuza en el British Wildlife Centre , Inglaterra
Gritos de lechuza grabados en Ceredigion, Gales
clasificación cientifica editar
Reino: Animalia
Filo: Chordata
Clase: Aves
Pedido: Strigiformes
Familia: Tytonidae
Género: Tyto
Especies:
T. alba
Nombre binomial
Tyto alba
( Scopoli , 1769)
Mapa de distribución combinado de Tyto alba, Tyto furcata, Tyto javanica.png
Gama global en verde
Sinónimos

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

La evidencia filogenética muestra que hay al menos tres linajes principales de lechuza común: uno en Europa, Asia occidental y África; uno en el sureste de Asia y Australasia; y uno en las Américas ; así como algunos taxones muy divergentes en varias islas. En consecuencia, algunas autoridades dividen a las lechuzas en la lechuza occidental , para el grupo en Europa , Asia occidental y África ; la lechuza oriental para el grupo del sureste de Asia y Australasia; y la lechuza común americana para el grupo en las Américas. Algunas autoridades taxonómicas clasifican a las lechuzas comunes de manera diferente, reconociendo hasta cinco especies distintas; y es necesario realizar más investigaciones para resolver las distintas taxonomías. Existe una variación considerable de tamaño y color entre las aproximadamente 28 subespecies, pero la mayoría tienen entre 33 y 39 cm (13 y 15 pulgadas) de longitud, con envergaduras que van desde 80 a 95 cm (31 a 37 pulgadas). El plumaje de la cabeza y el dorso es de un tono moteado de gris o marrón; que en las partes inferiores varía de blanco a marrón y, a veces, está moteado con marcas oscuras. La cara tiene la forma característica de un corazón y es blanca en la mayoría de las subespecies. Este búho no ulula, sino que emite un chillido inquietante y prolongado.

La lechuza común es nocturna en la mayor parte de su área de distribución; pero en Gran Bretaña y algunas islas del Pacífico, también caza de día. Las lechuzas comunes se especializan en la caza de animales en el suelo y casi toda su comida consiste en pequeños mamíferos, a los que localizan por el sonido, siendo su oído muy agudo. Los búhos generalmente se aparean de por vida a menos que uno de los dos muera, con lo cual se puede formar un nuevo vínculo de pareja. La cría se lleva a cabo en diferentes épocas del año, según la localidad, con una puesta de huevos, en promedio alrededor de cuatro, que se ponen en un nido en un árbol hueco, edificio antiguo o fisura en un acantilado. La hembra realiza toda la incubación, y ella y los polluelos dependen del macho para alimentarse. Cuando se dispone de un gran número de presas pequeñas, las poblaciones de lechuzas comunes pueden expandirse rápidamente; y, a nivel mundial, se considera que el ave tiene la menor preocupación para la conservación . Algunas subespecies con rangos restringidos están más amenazadas.

La lechuza común fue una de varias especies de aves descritas por primera vez en 1769 por el médico y naturalista tirolés Giovanni Antonio Scopoli en su Anni Historico-Naturales . Le dio el nombre científico Strix alba . [2] [3] A medida que se describieron más especies de búhos, el género Strix pasó a referirse únicamente a los búhos de madera de la familia de búhos típicos Strigidae ; y la lechuza común se convirtió en Tyto alba en la familia Tytonidae de la lechuza común . Tyto alba significa literalmente 'búho blanco', del griego antiguo onomatopéyico τυτώ tyto , 'búho' - compárese con el inglés "hooter" - y el latín alba , 'blanco'. [4] El pájaro es conocido por muchos nombres comunes que se refieren a su apariencia, llamada , hábitat o su vuelo misterioso y silencioso: búho blanco, [5] búho plateado, búho demonio, búho fantasma, búho de la muerte, búho nocturno, rata búho, búho de iglesia, búho de cueva, búho de piedra, búho de cara de mono, búho silbante, hobgoblin o búho aficionado, búho dobby, búho de pecho blanco, búho dorado, búho chillón, búho de paja, búho de corral y búho delicado. [4] [6] "Búho dorado" también podría referirse al búho enmascarado dorado relacionado ( T. aurantia ). "Búho silbante" y, particularmente en el Reino Unido y en la India, "búho chillón" se refieren a los cantos penetrantes de estas aves. [7] Este último nombre también se aplica a un grupo diferente de aves, los búhos chillones del género Megascops . [4]

Lechuza en vuelo

La lechuza común es una lechuza de tamaño mediano, de color pálido, con alas largas y una cola corta y cuadrada. Existe una variación de tamaño considerable entre las subespecies , con un espécimen típico que mide alrededor de 33 a 39 cm (13 a 15 pulgadas) de longitud total, la longitud varía de 29 a 44 cm (11 a 17 pulgadas). Las lechuzas comunes tienen una envergadura típica de unos 80 a 95 cm (31 a 37 pulgadas), con un rango extremo de 68 a 105 cm (27 a 41 pulgadas). [8] [9] La masa corporal adulta también es variable, con búhos machos de Galápagos ( T. a. Punctatissima ) que pesan aproximadamente 260 g (9.2 oz) en promedio, mientras que los machos de lechuza común oriental ( T. javanica ) promedian 555 g (19,6 oz), el peso de todas las lechuzas comunes varía de 224 a 710 g (7,9 a 25,0 oz). [10] Las lechuzas hembras son más grandes que los machos, con una T. alba fuerte hembra de una subespecie grande que pesa más de 550 gramos (19 oz). [11] En general, los búhos que viven en islas pequeñas son más pequeños y livianos, tal vez porque tienen una mayor dependencia de las presas de insectos y necesitan ser más maniobrables, [12] una excepción es la raza de lechuza común, T. una. furcata , de Cuba y Jamaica , que también es una raza isleña, aunque se encuentra en islas grandes con presas más grandes disponibles y pocos búhos más grandes compitiendo por los recursos dietéticos. [9] La forma de la cola es un medio para distinguir a la lechuza común de las lechuzas típicas cuando se ve en el aire. Otras características distintivas son el patrón de vuelo ondulado y las piernas colgantes y emplumadas. La cara pálida con forma de corazón y ojos negros le dan al ave voladora una apariencia distintiva, como una máscara plana con aberturas oblicuas negras oblicuas de gran tamaño, la cresta de plumas sobre el pico se asemeja un poco a una nariz. [13]

En la mayoría de las subespecies, la cabeza y la parte superior del cuerpo de las aves suelen variar entre marrón pálido y algo de gris (especialmente en la frente y la espalda). Algunos son de un marrón más puro y rico en cambio, y todos tienen motas finas en blanco y negro, excepto en las plumas del ala principal y las plumas de la cola , que son de color marrón claro con bandas más oscuras. La cara en forma de corazón suele ser de color blanco brillante, pero en algunas subespecies es marrón. [4] [14] La oreja izquierda está ligeramente por encima de los ojos, mientras que la derecha está ligeramente por debajo. Además, la orientación de las plumas encubiertas de una oreja difiere, en unos 15 °, de las de la otra. [15] Las partes inferiores, incluidas las plumas tarsometatarsianas (parte inferior de la pierna), varían de blanco a beige rojizo entre las subespecies, y en su mayoría no tienen patrones o tienen un número variable de pequeñas motas de color marrón negruzco. Se ha descubierto que, al menos en las poblaciones de Europa continental, las hembras con más manchas son más sanas que las aves más simples. Por el contrario, esto no es cierto para los machos europeos, donde las manchas varían según la subespecie. El pico varía de cuerno pálido a beige oscuro, correspondiente al tono general del plumaje, y el iris es marrón negruzco. Los pies, como el pico, varían en color, desde el rosa al gris rosado oscuro; y las garras son negras. [4] [14] Dentro de cualquier población, los machos, en promedio, tienden a tener menos manchas en la parte inferior y son de color más pálido que las hembras. Los polluelos están cubiertos de plumón blanco , pero el disco facial en forma de corazón se hace visible poco después de la eclosión. [11]

Contrariamente a la creencia popular, la lechuza común no ulula (tales llamadas las hacen los búhos típicos , como el cárabo u otros miembros del género Strix ). En su lugar, produce la característica Shree grito, un misterioso, a largo interminable grito que es doloroso para los seres humanos para escuchar a corta distancia. Los machos en el cortejo dan un gorjeo estridente. Tanto los animales jóvenes como los viejos producen un silbido defensivo parecido a una serpiente cuando se les molesta. Otros sonidos producidos incluyen un ronroneo que denota placer y un "kee-yak", que se asemeja a una de las vocalizaciones del cárabo. Cuando es capturada o acorralada, la lechuza común se arroja de espaldas y se agita con patas afiladas, lo que la convierte en una defensa eficaz. En tales situaciones, puede emitir ruidos rasposos o de chasquido, probablemente producidos por el pico pero posiblemente por la lengua. [13] [16]

Lechuza común, Canadá, con detalle de alas y plumas de cola

La lechuza común es la especie de ave terrestre más extendida en el mundo y se encuentra en todos los continentes excepto en la Antártida. [17] Su área de distribución incluye toda Europa (excepto Fennoscandia y Malta), la mayor parte de África excepto el Sahara, el subcontinente indio, el sudeste de Asia, Australia, muchas islas del Pacífico y América del Norte, Central y del Sur. [17] En general, se considera sedentario ; y, de hecho, muchas personas, que han establecido su residencia en un lugar en particular, permanecen allí incluso cuando se dispone de mejores áreas de alimentación cercanas. En las Islas Británicas, los jóvenes parecen dispersarse en gran medida a lo largo de los corredores fluviales; y la distancia recorrida desde su sitio natal promedia unos 9 km (5,6 millas). [18]

En Europa continental, la distancia de dispersión es mayor, comúnmente entre 50 y 100 kilómetros (31 y 62 millas) pero excepcionalmente 1,500 km (932 millas), con aves anilladas de los Países Bajos que terminan en España y Ucrania. En los Estados Unidos, la dispersión se produce típicamente en distancias de 80 y 320 km (50 y 199 mi), y los individuos más viajados terminan a unos 1.760 km (1.094 mi) de sus puntos de origen. Los movimientos de dispersión en el continente africano incluyen 1.000 km (621 millas) desde Senegambia a Sierra Leona y hasta 579 km (360 millas) dentro de Sudáfrica. En Australia hay cierta migración a medida que las aves se mueven hacia la costa norte en la estación seca y hacia el sur en la estación húmeda, así como movimientos nómadas asociados con plagas de roedores. De vez en cuando, algunas de estas aves aparecen en la isla Norfolk , la isla Lord Howe o Nueva Zelanda , lo que demuestra que cruzar el océano está dentro de sus posibilidades. [4] En 2008, las lechuzas comunes se registraron por primera vez reproduciéndose en Nueva Zelanda. [19] La lechuza común se ha introducido con éxito en la isla hawaiana de Kauai en un intento por controlar a los roedores; lamentablemente, se ha descubierto que también se alimenta de aves autóctonas. [20]

Macho Tyto alba alba (izquierda) y hembra T. a. lechuzas guttata en los Países Bajos, donde estas subespecies se intergran

El búho cariblanco ( T. glaucops ) estuvo incluido durante algún tiempo en T. alba . Basado en evidencia de ADN , König, Weick & Becking (2009) reconocieron a la lechuza común americana ( T. furcata ) y la lechuza común de Curazao ( T. bargei ) como especies separadas. [8] También propusieron que T. a. delicatula debe dividirse como una especie separada, que se conocerá como la lechuza común del este, que incluiría la subespecie T. d. delicatula , T. d. sumbaensis , T. d. meeki , T. d. crassirostris y T. d. interposita . [21] El Comité Ornitológico Internacional tiene sus dudas y ha declarado que la separación de Tyto delicatula de T. alba "puede necesitar ser revisada". [22]

Algunas subespecies de las islas se tratan ocasionalmente como especies distintas, un movimiento que debería esperar más investigaciones sobre la filogeografía de la lechuza común . Según Murray Bruce en Handbook of Birds of the World Volumen 5: Lechuzas a colibríes , "hace mucho tiempo que se necesita una revisión de todo el grupo". [4] El análisis molecular del ADN mitocondrial muestra una separación de la especie en dos clados , un alba del Viejo Mundo y un furcata del Nuevo Mundo , pero este estudio no incluyó a T. a. delicatula , que los autores parecen haber aceptado como una especie separada. También se encontró una amplia variación genética entre el T. a de Indonesia . stertens y otros miembros del clado alba , lo que llevó a la separación de stertens en Tyto javanica . [23]

Generalmente se reconocen de veinte a treinta subespecies, que varían principalmente en proporciones corporales, tamaño y color. Las lechuzas comunes varían en color desde la subespecie nominal alba , erlangeri y niveicauda , casi beige y blanca , hasta la contempta casi negra y marrón . Las formas de las islas son en su mayoría más pequeñas que las del continente, y las que habitan en los bosques tienen un plumaje más oscuro y alas más cortas que las que viven en pastizales abiertos. En general, se considera que varias subespecies están integradas entre poblaciones más distintas. [24] [4]

En Handbook of Birds of the World Volumen 5: Lechuzas comunes a colibríes , se enumeran las siguientes subespecies: [4]

SubespecieDescripciónDistanciaSinónimos
T. a. alba (Scopoli, 1769)
Adulto de color claro
Dorso gris y beige claro. Partes inferiores blancas, con pocas o ninguna mancha negra; los machos a menudo parecen completamente sin manchas. [14]Europa occidental desde las Islas Británicas al sur hasta el Magreb y al este a lo largo de las regiones costeras del Mediterráneo hasta el noroeste de Turquía en el norte y el Nilo en el sur, donde llega río arriba hasta el noreste de Sudán . También la Sierra de Aïr en el Sahara de Níger , las Islas Baleares y Sicilia en el Mediterráneo, y las Islas Canarias Occidentales ( El Hierro , La Gomera , La Palma Gran Canaria y Tenerife ). Se intercala con guttata de los Balcanes a través de Hungría y a lo largo de los ríos Rin y el Bajo Mosa , y con affinis alrededor de la frontera entre Egipto y Sudán. [4]lechuza común - incluye hostilis , kirchhoffi , kleinschmidti y pusillus .
Las poblaciones africanas pueden pertenecer a erlangeri .
T. a. furcata (Temminck, 1827)
En Cuba
Grande. Partes superiores de color naranja pálido ante y gris parduzco, partes inferiores blanquecinas con pocas motas. Cara blanca. [4]Cuba , Jamaica , las Islas Caimán (raras o posiblemente extirpadas en Gran Caimán ). [25]Lechuza común del Caribe - podría incluir niveicauda .
T. a. tuidara (JE Gray, 1829)
En Brasil
Dorso gris y anaranjado ante. Partes inferiores blanquecinas a beige claro con poco moteado. Cara blanca. Se asemeja pálido guttata . [4]Las tierras bajas de América del Sur al este de los Andes y al sur del río Amazonas hasta el sur hasta Tierra del Fuego ; también en las Islas Malvinas . [4]Incluye hauchecornei y posiblemente hellmayri .
T. a. guttata (CL Brehm, 1831)
En vuelo, Sandesneben (Alemania)
Más gris en las partes superiores que alba . Las partes inferiores se tornan rojizas con algunas manchas oscuras (más que en alba ). [14] Rostro blanquecino. Las hembras son en promedio más rojas por debajo que los machos. [4]Europa central al norte de los Alpes desde el Rin hasta Letonia , Lituania y Ucrania , y al sur hasta Rumanía , el noreste de Grecia y el sur de los Balcanes . Se intercala con alba en el límite occidental de su área de distribución. [4]Incluye rhenana .
T. a. pratincola (Bonaparte, 1838)
Adulto en vuelo
Grande. Dorso gris y anaranjado ante. Partes inferiores blanquecinas a beige claro con mucho moteado. Cara blanca. Se asemeja pálido guttata , pero por lo general más motas a continuación. [4]América del Norte desde el sur de Canadá hacia el sur hasta el centro de México; Bermudas , Bahamas , Hispaniola ; introducido en la isla Lord Howe (donde fue extirpado) y en 1958 en Hawai (donde aún vive). [4]Lechuza común norteamericana - Incluye lucayana ; también podría incluir bondi , guatemalae y subandeana .
T. a. punctatissima (GR Gray, 1838)
En la Isla Santa Cruz (las Islas Galápagos)
Pequeña. Marrón grisáceo oscuro en la parte superior, con la parte blanca de manchas prominentes. Partes inferiores de color blanco a beige dorado, con un patrón distintivo de vermiculaciones marrones o manchas finas y densas. [4]Endémica de las islas Galápagos . [4] Lechuza común de Galápagos : a veces se considera una especie separada.
T. a. poensis (Fraser, 1842)Partes superiores de color marrón dorado y gris con patrón muy atrevido. Partes inferiores de color beige claro con manchas extensas. Cara blanca. [4]Endémica de Bioko . [4]Puede incluir affinis .
T. a. thomensis (Hartlaub, 1852)Más bien pequeño. Partes superiores de color gris pardusco oscuro con un patrón llamativo, que incluye bandas de color marrón más claro en remiges y rectrices . Partes inferiores de color marrón dorado con extensas motas. Mejora de la cara. [4]Endémica de la isla de São Tomé . Un registro de Príncipe es erróneo. [4]Lechuza de Santo Tomé : a veces considerada una especie separada.
T. a. affinis (Blyth, 1862)
En tanzania
Similar a poensis , pero supuestamente más ligero en promedio. Partes superiores muy grises. Partes inferiores de color beige claro con manchas extensas. Cara blanca. [26]África subsahariana , incluidas las Comoras , Madagascar , las islas Pemba y Unguja ; introducido en las Seychelles . Se integra con alba alrededor de la frontera entre Egipto y Sudán. [4]Incluye hipermetra ; dudosamente distinto de poensis . [26]
T. a. guatemalae (Ridgway, 1874)Similar a la pratincola oscura ; menos gris arriba, motas más gruesas abajo. [4]Guatemala o el sur de México a través de Centroamérica hasta Panamá o el norte de Colombia ; las Islas de las Perlas . [4]Incluye subandeana ; dudosamente distinto de la pratincola .
T. a. bargei (Hartert, 1892)Similar a alba ; más pequeño y notablemente de alas cortas. [4]Endémica de Curazao y tal vez de Bonaire en las Indias Occidentales . [4] Lechuza común de Curazao : a veces se considera una especie separada.
T. a. contempta (Hartert, 1898)Casi negro con algo de gris oscuro en la parte superior, la parte blanca de las manchas se muestra de manera prominente. Marrón rojizo abajo. [4]Andes nororientales desde el oeste de Venezuela hasta el este de Colombia (poco común en la Cordillera Central y la Cordillera Occidental ) [27] al sur de Perú . [4]Incluye stictica .
T. a. schmitzi (Hartert, 1900)Pequeña. Similar a la guttata , pero la región de los senos tiene un ligero pulido. [4]Endémica de la isla de Madeira y Porto Santo en el Atlántico oriental . [4]
T. a. ernesti (Kleinschmidt, 1901)Similar a alba ; región del pecho siempre blanco puro sin manchas. [4]Endémica de Córcega y Cerdeña en el Mediterráneo. [4]
T. a. gracilirostris (Hartert, 1905)Small. Similar to schmitzi but breast darker, approaching guttata. Face light buff.[4]Endemic to the East Canary Islands (Chinijo Archipelago, Fuerteventura, Lanzarote; perhaps formerly also on Lobos).[4]Canary Islands barn owl
T. a. detorta (Hartert, 1913)Similar to guttata, but less reddish. Face buff.[4]Endemic to the Cape Verde Islands.[4]Cape Verde barn owl -sometimes considered a separate species.
T. a. erlangeri (W. L. Sclater, 1921)Similar to ernesti; upperparts lighter and yellower.[4]Crete and southern Aegean islands to Cyprus; the Near and Middle East including the Arabian Peninsula coastlands, south to Sinai and east to southwestern Iran.[4]Might include African populations assigned to alba.
T. a. hellmayri (Griscom & Greenway, 1937)Similar to tuidara, but larger.[4]Northeastern South American lowlands from eastern Venezuela south to the Amazon River.[4]Doubtfully distinct from tuidara.
T. a. bondi (Parks & Phillips, 1978)Similar to pratincola; smaller and paler on average.[4]Endemic to Roatán and Guanaja in the Bay Islands.[4]Doubtfully distinct from pratincola.
T. a. niveicauda (Parks & Phillips, 1978)Large. Similar to furcata; paler in general. Resembles alba.[4]Endemic to Isla de la Juventud.[4]Doubtfully distinct from furcata.

Like most owls, the barn owl is nocturnal, relying on its acute sense of hearing when hunting in complete darkness. It often becomes active shortly before dusk but can sometimes be seen during the day when relocating from one roosting site to another. In Britain, on various Pacific Islands, and perhaps elsewhere, it sometimes hunts by day. The owl's daylight hunting may depend on whether it can avoid being mobbed by other birds during that time.[4] In Britain, some birds continue to hunt by day—even when mobbed by such birds as magpies, rooks, and black-headed gulls—possibly because the previous night has been wet, making night hunting difficult. By contrast, in southern Europe and the tropics, the birds seem to be almost exclusively nocturnal, with the few birds that hunt by day being severely mobbed.[28]

A barn owl's talons

Barn owls are not particularly territorial but have a home range inside which they forage. For males in Scotland this home range has a radius of about 1 km (0.6 mi) from the nest site and an average area of about 300 hectares (740 acres). Female home ranges largely coincide with that of their mates. Outside the breeding season, males and females usually roost separately, each one having about three favoured sites in which to conceal themselves by day, and which are also visited for short periods during the night. Roosting sites include holes in trees, fissures in cliffs, disused buildings, chimneys, and hay sheds, and are often small in comparison to nesting sites. As the breeding season approaches, the birds move back to the vicinity of a chosen nest to roost.[29]

The barn owl is a bird of open country, such as farmland or grassland with some interspersed woodland, usually at altitudes below 2,000 metres (6,600 ft) but occasionally as high as 3,000 metres (9,800 ft) in the tropics, such as in Ethiopia's Degua Tembien mountain range.[30] This owl prefers to hunt along the edges of woods or in rough grass strips adjoining pasture. It has an effortless wavering flight as it quarters the ground, alert to the sounds made by potential prey. Like most owls, the barn owl flies silently; tiny serrations on the leading edges of its flight feathers and a hairlike fringe on 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.[31] Behavioural and environmental preferences may differ slightly even between neighbouring 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][32]

Hunting and feeding

Hunting in twilight or at night, the barn owl can target its prey and dive to the ground. Its legs and toes are long and slender, which improves its ability to forage among dense foliage or beneath the snow, and gives it a wide spread of talons when attacking prey. This bird hunts by flying slowly, quartering the ground and hovering over spots that may conceal prey. It has long, broad wings that enable it to manoeuvre and turn abruptly. It has acute hearing, with ears placed asymmetrically, which improves detection of sound position and distance; the bird does not require sight to hunt. The facial disc helps with the bird's hearing, as is shown by the fact that, with the ruff feathers removed, the bird can still determine a sound source's direction, although without the disc it can't determine the source's height.[33] It may perch on 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.[31][34]

Skull, showing the powerful beak

Rodents and other small mammals may constitute over ninety percent of the prey caught.[35][36][37] Birds are also taken, as well as lizards, amphibians, and insects. Even when they are plentiful, and other prey scarce, earthworms do not seem to be consumed.[38] In North America and most of Europe, voles predominate in the diet and shrews are the second most common food choice. In Ireland, the accidental introduction of the bank vole in the 1950s 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.[39] Mice and rats are the main foodstuffs in the Mediterranean region, the tropics, subtropics, and Australia. Barn owls are usually specialist feeders in productive areas and generalists in areas where prey is scarce.[38] On the Cape Verde Islands, geckos are the mainstay of the diet, supplemented by birds such as plovers, godwits, turnstones, weavers, and pratincoles.[40] On a rocky islet off the coast of California, a clutch of four young were being reared on a diet of Leach's storm petrel (Oceanodroma leucorhoa).[41] On bird-rich islands, a barn owl might include birds as some fifteen to twenty percent of 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). Smaller prey is usually torn into chunks and eaten completely, including bones and fur, while prey larger than about 100 grams (3.5 oz)—such as baby rabbits, Cryptomys blesmols, or Otomys vlei rats—is usually dismembered and the inedible parts discarded.[26][32][42]

Compared to other owls of similar size, the barn owl has a much higher metabolic rate, requiring relatively more food. Relative to its size, barn owls consume more rodents—often regarded as pests by humans—than possibly any other creature. Studies have shown that an individual barn owl may eat one or more voles (or their equivalent) per night, equivalent to about twenty-three percent of the bird's bodyweight. Excess food is often cached at roosting sites and can be used when food is scarce.[43] This makes the barn owl one of the most economically valuable wildlife animals for agriculture. Farmers often find these owls more effective than poison in keeping down rodent pests, and they can encourage barn owl habitation by providing nesting sites.[34]

Breeding

Egg, Collection Museum Wiesbaden, Germany

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, with the resultant temporary increase 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 habitat around the nest site.[44] An increase in rodent populations will usually stimulate the local barn owls to begin nesting; and, consequently, two broods are often raised in a good year, even in the cooler parts of the owl's range. [6]

Females are ready to breed at ten to eleven months of age. Barn owls are usually monogamous, sticking to one partner for life unless one of a pair dies. 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 selected nesting hole may be taken over by some other 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 attract a new spouse.[45]

Clutch of eggs

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. In 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. 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.[45]

Barn owls are cavity nesters. They choose holes in trees, fissures in cliff faces, the large nests of other birds such as the hamerkop (Scopus umbretta), 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. Tree nests 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 (Procyon lotor). 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 (Corvus monedula) nest in the same hollow tree or building and seem to live harmoniously with the owls.[46]

Brood prior to fledging, beginning to shed their nestling down

Before commencing laying, the female spends much 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 the clutch size averages about five eggs (the range being two to nine). The eggs are chalky white, somewhat elliptical, and about the size of bantam eggs. Incubation begins as soon as the first egg is laid. While the female 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 a plentiful supply 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.[45]

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, the chicks make a "chittering" sound but this soon changes into a food-demanding "snore". By two weeks old they are already half their adult weight and look naked, as the amount of down is insufficient to cover their growing bodies. By three weeks old, quills are starting to push through the skin and the chicks stand, making snoring noises with wings raised and tail stumps waggling, begging for food items which are now given whole. Atypically among birds, barn owl chicks can "negotiate" and allow weaker ones to eat first, possibly in exchange for grooming.[47] The male is the main provider of food until all the chicks are at least four weeks old, at which time the female begins to leave the nest and starts to 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.[45]

Moulting

Feathers become abraded over time and all birds need to replace them at intervals. Barn owls are particularly dependent on their ability to fly quietly and manoeuvre efficiently. In temperate areas the owls undergo a prolonged moult that lasts through three phases over a period of two years. The female starts to moult while incubating the eggs and brooding the chicks, a time when the male feeds her, so she does not need to fly much. The first primary feather to be shed is a central one, number 6, and it has regrown completely by the time the female resumes hunting. Feathers 4, 5, 7, and 8 are dropped at a similar time the following year and feathers 1, 2, 3, 9 and 10 in the bird's third year of adulthood. The secondary and tail feathers are lost and replaced over a similar timescale, again starting while incubation is taking place. In the case of the tail, the two outermost tail feathers are first shed, followed by the two central ones, the other tail feathers being shed the following year.[48]

The male owl moults rather later in the year than the female, at a time when there is an abundance of food, the female has recommenced hunting, and the demands of the chicks are lessening. Unmated males without family responsibilities often start losing feathers earlier in the year. Their moult follows a pattern similarly prolonged as that of the female. The first sign that the male is moulting is often when a tail feather has been dropped at the roost.[48] A consequence of moulting is the loss of thermal insulation. This is of little importance in the tropics, and barn owls there usually moult a complete complement of flight feathers annually. The hot-climate moult may still take place over a long period but is usually concentrated at a particular time of year outside the breeding season.[49]

Predators and parasites

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Three barn owl chicks threatening an intruder

Predators of the barn owl include large American opossums (Didelphis), the common raccoon, and similar carnivorous mammals, as well as eagles, larger hawks, and other owls. Among the latter, the great horned owl (Bubo virginianus), in the Americas, and the Eurasian eagle-owl (B. bubo) are noted predators of barn owls. Despite some sources claiming that there is little evidence of predation by great horned owls, one study from Washington found that 10.9% of the local great horned owl's diet was made up of barn owls.[50][51][52] In Africa, the principal predators of barn owls are Verreaux's eagle-owls and Cape eagle-owls.[53][54] In Europe, although less dangerous than the eagle-owls, the chief diurnal predators are the northern goshawk (Accipiter gentilis) and the common buzzard (Buteo buteo). About 12 other large diurnal raptors and owls have also been reported as predators of barn owls, ranging from the similar-sized Cooper's hawk and scarcely larger tawny owl to huge bald and golden eagles.[55] The goshawk and the eagle-owls are on the increase because of the greater protection these birds now receive.[28]

When disturbed at its roosting site, an angry barn owl lowers its head and sways it from side to side, or the head may be lowered and stretched forward and the wings outstretched and drooped while the bird emits hisses and makes snapping noises with its beak. Another defensive attitude involves lying flat on the ground or crouching with wings spread out.[16]

Barn owls are hosts to a wide range of parasites. Fleas are present at nesting sites, and externally the birds are attacked by feather lice and feather mites which chew the barbules of the feathers and which are transferred from bird to bird by direct contact. Blood-sucking flies, such as Ornithomyia avicularia, are often present, moving about among the plumage. Internal parasites include the fluke Strigea strigis, the tapeworm Paruternia candelabraria, several species of parasitic round worm, and spiny-headed worms in the genus Centrorhynchus. These gut parasites are acquired when the birds feed on infected prey.[56] There is some indication that female birds with more and larger spots have a greater resistance to external parasites. This is correlated with smaller bursa of Fabricius, glands associated with antibody production, and a lower fecundity of the blood-sucking fly Carnus hemapterus, which attacks nestlings.[57]

Lifespan

Landing on a handler's gloved hand. Captive birds often live longer than wild ones.

Unusually for a medium-sized carnivorous animal, the barn owl exhibits r-selection, producing a large number of offspring with a high growth rate, which have a low probability of surviving to adulthood.[58] While wild barn owls are thus on average short-lived, the potential lifespan, or longevity, of the species is much higher. Captive individuals may reach 20 years of age or more; a captive barn owl, in England, lived to be over 25 years old. Occasionally, a wild bird reaches an advanced age. The American record age for a wild barn owl is 11.5 years, while a Dutch bird was noted to have reached the age of 17 years, 10 months. Taking into account such extremely long-lived individuals, the average lifespan of the barn owl is about four years, and statistically 2/3 to 3/4 of all adults survive from one year to the next. This mortality is not evenly distributed throughout the bird's life, and only one-young-in-three manages to live to its first breeding attempt.[6]

The most significant cause of death in temperate areas is likely to be starvation, particularly during the autumn and winter, 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 death, 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. In some locations, road mortality rates can be particularly high, with collision rates being influenced by higher commercial traffic, roadside verges that are grass rather than shrubs, and where small mammals are abundant.[59] 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 being shot accounts for others, especially in Mediterranean regions.[60]

Barn owl on Lithuanian 5 litų silver coin (2002)

Barn owls are relatively common throughout most of their range and not considered globally threatened. If considered as a single global species, the barn owl is the second most widely distributed of all raptors, behind only the peregrine falcon. It is wider-ranging than the also somewhat cosmopolitan osprey. Furthermore, the barn owl is likely the most numerous of all raptors, with the International Union for Conservation of Nature (IUCN) estimating, for all barn owl individuals, a population possibly as large as nearly 10 million individuals (throughout the Americas, the American barn owl species may comprise nearly 2 million).[1][61] Severe local declines due to organochlorine (e.g., DDT) poisoning in the mid 20th century and rodenticides in the late 20th century have affected some populations, particularly in Europe and North America. Intensification of agricultural practices often means that the rough grassland that provides the best foraging habitat is lost.[62] While barn owls are prolific breeders and able to recover from short-term population decreases, they are not as common in some areas as they used to be. A 1995–1997 survey put their British population at between 3,000 and 5,000 breeding pairs, out of an average of about 150,000 pairs in the whole of Europe. In the US, barn owls are listed as endangered species in seven Midwestern states (Ohio, Michigan, Indiana, Illinois, Wisconsin, Iowa, and Missouri), and in the European Community they are considered a Species of European Concern.[4][6]

In Canada, barn owls are no longer common and are most likely to be found in coastal British Columbia south of Vancouver,[63] having become extremely rare in a previous habitat, southern Ontario. In spite of a Recovery Strategy, particularly in 2007–2010 in Ontario,[64] only a handful of wild, breeding barn owls existed in the province in 2018.[65] This is primarily because of disappearing grasslands where the bird hunted in the past, but according to a study, also because of "harsh winters, predation, road mortality and use of rodenticides".[66] The species is listed as endangered overall in Canada, due to loss of habitat and a lack of nesting sites.[67]

Captive barn owl near Lake Erie, in Ontario; the species has become extremely rare in this province

In the Canary Islands, a somewhat larger number of these birds still seem to exist on the island of Lanzarote, but altogether this particular subspecies (T. a. gracilirostris, the Canary barn owl) is precariously rare: perhaps fewer than two hundred individuals still remain. Similarly, the birds on the western Canary Islands, which are usually assigned to this subspecies, have severely declined; and wanton destruction of the birds seems to be significant. On Tenerife they seem relatively numerous; but on the other islands the situation looks about as bleak as on Fuerteventura. Due to the assignment to this subspecies of birds common in mainland Spain, the western Canary Islands population is not classified as threatened.[68][69][70]

Cultural aspects

Common names such as "demon owl", "death owl", "ghost owl", or "lich owl" (from lich, an old term for a corpse) show that rural populations in many places considered barn owls to be birds of evil omen. For example, the Tzeltal people in Mexico regard them as "disease givers".[71] These owls don't "hoot", instead emitting raspy screeches and hissing noises, and their white face and underbelly feathers, visible as they fly overhead, make them look "ghostly". Consequently, they were often killed by farmers who were unaware of the benefits these birds bring.[72] Negative perceptions can also be attributed to the false belief that they could eat large animals, such as chickens and cats.[73] In South Africa, barn owls are often associated with witchcraft and are persecuted. In some South African cultures, these owls are used in 'muthi' (traditional medicine) and are believed to give special powers when consumed.[74][75]

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

Nest boxes are used primarily when populations suffer declines.[76] Although such declines have many causes, among them are the lack of available natural nesting sites. Early successes among conservationists have led to the widespread provision of nest boxes, which has become the most used form of population management. The barn owl accepts the provided nest boxes and sometimes prefers them to natural sites.[77]

Conservationists encourage farmers and landowners to install nest boxes by pointing out that the resultant increased barn owl population would provide natural rodent control.[78] The nest boxes are placed under the eaves of buildings and in other locations. The upper bound of the number of barn owl pairs depends on the abundance of food at nesting sites.[79]

Surveillance

A nest box can also be regarded as an animal surveillance device, as they give direct access to the breeding location. While the diet of the barn owl has been studied, other behaviours–such as breeding–are not well known. Surveilling animals can lead to the discovery of new scientific and industrial fields. For example, biologists and engineers can work on barn owl surveillance techniques and devices, while social scientists document what cause humans to want to observe an animal.[80][81]

In Switzerland, a research group aims to install RFID tag readers on the entrances to the nest boxes, thus allowing tracking of barn owl movements from nest box to nest box. Information about the behaviour of the owls prior to breeding could be obtained using such surveillance.[82]

In the United Kingdom, the "Barn Owl Nest Box Scheme" is promoted by the World Owl Trust[83] and has many participants in local areas, such as Somerset, where a webcam was set up inside a nest box in which 7 young were reared in 2014.[84] Another barn owl nest box live-streaming webcam–located in California, United States–has proved popular online.[85] In May 2012, it was revealed that farmers in Israel and Jordan had, over a period of ten years, replaced pesticides with barn owls in a joint conservation venture called "Project Barn Owl".[86]

Other research tools include using GPS trackers fitted onto the barn owl, to allow precise location tracking of the owl. Tracks obtained enabled the identification of three types of movement: hunting, straight-lined flights, and roosting. By superimposing the track onto a map, the bird's foraging habits could be studied.[87]

Alternative rodent control technique

In some conservation projects, the use of rodenticides for pest control was replaced by the installation of nest boxes for barn owls, which has been shown to be a less costly method of rodent control.[88]

In Malaysia, large areas of rainforest were felled to make way for oil palm plantations; and with few tree cavities for breeding, the barn owl population, with its ability to control rodent pests, diminished. In a trial, the provision of two hundred nest boxes saw almost one hundred percent occupancy; and as the programme expanded, the plantations supported one of the densest barn owl populations in the world.[62] Similarly, providing nesting boxes has increased the number of barn owls in rice-growing areas of Malaysia, where the rodents do much damage to the crop. Although barn owl numbers have increased in both these instances, it is unclear as to how effective this biological control of the rats is, as compared to the baiting and trapping that occurred previously.[89]

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  • BrainMaps: Barn owl brain images
  • Barn owl videos, photos and sounds—Internet Bird Collection
  • Barn owl—USGS Patuxent Bird Identification InfoCenter
  • Barn owl species account—Cornell Lab of Ornithology
  • Ageing and sexing barn owls—Blasco-Zumeta, Javier; Heinze, Gerd-Michael
  • Barn owl feathers
  • Barn Owl sounds