Nombre en español: Búho Campestre

Nombre en ingles: Short-eared Owl

Nombre científico: Asio flammeus

Familia: Strigidae

Foto: Cesar Chillon

Canto: Lauri Hallikainen

El búho campestre, lechuza campestre, lechuzón de pajonal³ o nuco⁴ (Asio flammeus) es una de las rapacesnocturnas con mayor actividad diurna. Habita en áreas abiertas, zonas herbáceas sin trabajar, marismas, cultivos, brezales y, sobre todo, en marjales costeros. Su población en una zona en concreto depende sobre todo de la disponibilidad de presas. Es frecuente verlo parado en el aire, aunque sin llegar a cernirse, buscando roedores por entre las hierbas altas.

Es similar al búho chico, pero el búho campestre tiene los mechones de la parte superior de la cabeza muy pequeños y normalmente ocultos, un anillo negro que enmarca cada ojo (de iris amarillo,) y es más esbelto que éste. Las alas están surcadas por una franja de color crema que parte del tronco del animal (por la cara dorsal), y tienen la punta negra. El vientre es blanco, con menos rayas oscuras que en otros búhos afines.

Habita en todos los continentes excepto en la Antártida y Australia, aunque es una especie rara en gran parte de su área de distribución. Es migradora, desplazándose hacia áreas más templadas en invierno.

Su voz es un ladrido nasal y áspero, tipo latigazo. También puede producir un sonido suave con pitido rápido y zumbante, u-u-u-u. En las zonas de invernada suelen permanecer silenciosos.

Caza volando lentamente sobre el suelo u observando desde una percha. Come pequeños roedores y pájaros.

Longitud: de 34 a 42 cm
Envergadura: de 90 a 105 cm
Peso: 250-450 g
Longevidad: de 10 a 15 años

Nido y reproducción

Nidifica directamente sobre el suelo, en herbazales y marismas, entre la hierba. El nido es una zona aplanada sin revestir, aunque ocasionalmente aporta semillas, hierbas o plumas. Pone de 4 a 8 huevos en una única nidada, aunque en algunas regiones hasta dos. En los años de abundancia de roedores puede llegar a poner 12 e incluso 14 huevos en una temporada. El huevo mide 35 ~ 45 X 29 ~33 mm y es blanco puro, mate.

La incubación es realizada por la hembra y se prolonga entre 21 y 37 días. Pone cada 48 horas, y empieza a incubar desde que pone el primer huevo, de modo que puede haber bastante diferencia de edad entre los nacidos en la misma nidada. Los volantones pueden abandonar el nido con solo cuatro semanas y vuelan a las cinco semanas. El macho monta guardia en las proximidades del nido y aporta el alimento. Como otras aves que crían en el suelo, los adultos tienden a burlar a los depredadores que se acercan al nido simulando lesiones en las alas que les impiden volar.

Alcanza la madurez sexual al año de edad. En el Hemisferio Norte la reproducción tiene lugar entre marzo y junio, con un máximo en abril. Tienden a formar colonias lasas. El cortejo nupcial es muy llamativo, ya que los machos realizan espectaculares vuelos de exhibición. Es una especie generalmente monógama.

Alimentación

Aunque como se ha señalado es más diurno que el resto de las estrigiformes, caza sobre todo de noche. La técnica más frecuente es en vuelo lento y muy bajo, dejándose caer frecuentemente sobre las presas. Otras veces aguarda desde un posadero. Su horario de caza parece coincidir con la actividad de los topillos(Arvicolinae), su presa preferida. En general suele volar muy bajo, con peculiar aleteo. Es frecuente que coincidan varios ejemplares en el mismo cazadero. Su alimentación consiste principalmente en roedores (más del 90%), pero también otros pequeños mamíferos, reptiles y algunos grandes insectos. A veces captura pequeñas aves.

Otros aspectos de comportamiento

Es muy característico de esta especie su comportamiento nómada, errático, solo fija a un área concreta durante el período de reproducción.
En invierno duermen en dormideros comunales.
Aunque no es rara su actividad diurna, normalmente comienza su actividad 30-60 minutos antes de la puesta del sol.

Subespecies

Actualmente se aceptan diez subespecies de Asio flammeus.⁵

Asio flammeus bogotensis (Chapman, 1915)
Asio flammeus domingensis (Statius Müller, 1776)
Asio flammeus flammeus (Pontoppidan, 1763)
Asio flammeus galapagoensis (Gould, 1837) – Islas Galápagos⁶
Asio flammeus pallidicaudus (Friedmann, 1949)
Asio flammeus ponapensis (Mayr, 1933)
Asio flammeus portoricensis (Ridgway, 1882)
Asio flammeus sandwichensis (A. Bloxam, 1827): De Hawaii, donde se conoce como Pueo y es sagrado en su mitología⁷
Asio flammeus sanfordi (Bangs, 1919)
Asio flammeus suinda (Vieillot, 1817)

Short-eared owl

The short-eared owl (Asio flammeus) is a species of typical owl (family Strigidae). Owls belonging to genus Asio are known as the eared owls, as they have tufts of feathers resembling mammalian ears. These «ear» tufts may or may not be visible. Asio flammeus will display its tufts when in a defensive pose, although its very short tufts are usually not visible. The short-eared owl is found in open country and grasslands. The scientific name is from Latin. The genus name Asio is a type of eared owl, and flammeus means «flame-coloured».^[1

Description

The short-eared owl is a medium-sized owl measuring 34–43 cm (13–17 in) in length and weighing 206–475 g (7.3–16.8 oz). It has large eyes, a big head, a short neck, and broad wings. Its bill is short, strong, hooked and black. Its plumage is mottled tawny to brown with a barred tail and wings. The upper breast is significantly streaked. Its flight is characteristically floppy due to its irregular wingbeats. The short-eared owl may also be described as «moth or bat-like» in flight. Wingspans range from 85 to 110 cm (33 to 43 in).^[ Females are slightly larger than males. The yellow-orange eyes of A. flammeus are exaggerated by black rings encircling each eye, giving the appearance of them wearing mascara, and large, whitish disks of plumage surrounding the eyes like a mask.

Separation from long-eared owl

Over much of its range, short-eared owls occurs with the similar-looking long-eared owl. At rest, the ear-tufts of long-eared owl serve to easily distinguish the two (although long-eared owls can sometimes hold its ear-tufts flat). The iris-colour differs: yellow in short-eared, and orange in long-eared, and the black surrounding the eyes is vertical on long-eared, and horizontal on short-eared. Overall the short-eared tends to be a paler, sandier bird than the long-eared. There are a number of other ways in which the two species the differ which are best seen when they are flying: a) short-eared often has a broad white band along the rear edge of the wing, which is not shown by long-eared; b) on the upperwing, short-eared owls’ primary-patches are usually paler and more obvious; c) the band on the upper side of short-eared owl’s tail are usually bolder than those of long-eared; d) short-eared’s innermost secondaries are often dark-marked, contrasting with the rest of the underwing; e) the long-eared owl has streaking throughout its underparts whereas on short-eared the streaking ends at the breast; f) the dark markings on the underside of the tips of the longest primaries are bolder on short-eared owl; g) the upper parts are coarsely blotched, whereas on long-eared they are more finely marked. The short-eared owl also differs structurally from the long-eared, having longer, slimmer wings: the long-eared owl has wings shaped more like those of a tawny owl.^[ The long-eared owl generally has different habitat preferences from the short-eared, most often being found concealed in areas with dense wooded thickets. The short-eared owl is often most regularly seen flying about in early morning or late day as it hunts over open habitats.

Subspecies

As of 2009, there are ten recognized subspecies of the short-eared owl:^[

A. f. bogotensis – Chapman, 1915: found in Colombia, Ecuador and northwestern Peru
A. f. domingensis – (Statius Müller, 1776): found on Hispaniola
A. f. flammeus – (Pontoppidan, 1763): nominate, found in North America, Europe, northern Africa and northern Asia
A. f. galapagoensis – (Gould, 1837): Galápagos Islands^[10]
A. f. pallidicaudus – Friedmann, 1949: found in Venezuela, Guyana and Suriname
A. f. ponapensis – Mayr, 1933: found on east Caroline Island
A. f. portoricensis – Ridgway, 1882: found in Puerto Rico
A. f. sandwichensis – (A. Bloxam, 1827): Pueo or Hawaiian short-eared owl – found in the Hawaiian Islands^[11]
A. f. sanfordi – Bangs, 1919: found on the Falkland Islands
A. f. suinda – (Vieillot, 1817): found from southern Peru and southern Brazil to Tierra del Fuego

Some authorities recognize a further subspecies:^[

A. f. cubensis – Garrido, 2007: found in Cuba

Range

The short-eared owl occurs on all continents except Antarctica and Australia; thus it has one of the most widespread distributions of any bird. A. flammeus breeds in Europe, Asia, North and South America, the Caribbean, Hawaii and the Galápagos Islands. It is partially migratory, moving south in winter from the northern parts of its range. The short-eared owl is known to relocate to areas of higher rodent populations.^[ It will also wander nomadically in search of better food supplies during years when volepopulations are low. (See a map of the short-eared owl’s distribution across the New World.)

Behaviour

Short Eared Owl in its habitat. Notice how it chooses short shady trees to roost under, in a grassland/ desert habitat.

Nesting and reproduction

Egg, Collection Museum Wiesbaden

Sexual maturity is attained at one year. Breeding season in the northern hemisphere lasts from March to June, peaking in April. During this time these owls may gather in flocks. During breeding season, the males make great spectacles of themselves in flight to attract females. The male swoops down over the nest flapping its wings in a courtship display.^[ These owls are generally monogamous.

The short-eared owl nests on the ground in prairie, tundra, savanna, or meadow habitats. Nests are concealed by low vegetation, and may be lightly lined by weeds, grass, or feathers. Approximately 4 to 7 white eggs are found in a typical clutch, but clutch size can reach up to a dozen eggs in years when voles are abundant. There is one brood per year. The eggs are incubated mostly by the female for 21–37 days. Offspring fledge at a little over four weeks. This owl is known to lure predators away from its nest by appearing to have a crippled wing.^[

Diet and foraging habits

Hunting occurs mostly at night, but this owl is known to be diurnal and crepuscular as well. Its daylight hunting seems to coincide with the high-activity periods of voles, its preferred prey. It tends to fly only feet above the ground in open fields and grasslands until swooping down upon its prey feet-first. Several owls may hunt over the same open area. Its food consists mainly of rodents, especially voles, but it will eat other small mammals such as mice, ground squirrels, shrews, rats, bats, muskrats and moles. It will also occasionally predate smaller birds, especially when near sea-coasts and adjacent wetlands at which time they attack shorebirds, terns and small gulls and seabirds with semi-regularity. Avian prey is more infrequently preyed on inland and centers on passerines such as larks, icterids, starlings, tyrant flycatchers and pipits. Insects supplement the diet and short-eared owls may prey on roaches, grasshoppers, beetles, katydids and caterpillars. Competition can be fierce in North America with the northern harrier, with which the owl shares similar habitat and prey preferences. Both species will readily harass the other when prey is caught.^[

Pellets

Because of the high pH in the stomach of owls they have a reduced ability to digest bone and other hard parts, they eject pellets containing the remains of their prey.^[

Calls

Short-eared owls have a scratchy bark-like call. Raspy waowk, waowk, waowk or toot-toot-toot-toot-toot sounds are common. A loud eeee-yerp is also heard on breeding grounds. However, short-eared owls are silent on the wintering grounds.^[

Conservation status

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It is listed as declining in the southern portion of its US range. It is common in the northern portion of its breeding range.^[

It is listed as endangered in New Mexico. Its appearance at the Calverton Executive Airpark on Long Island has prompted the New York State Department of Environmental Conservation to take the lead on ruling whether a massive redevelopment of the airport will receive the necessary environmental permits.^[