Págalo Grande/Great Skua/Stercorarius skua 

James West (CC)

Nombre en español: Págalo Grande

Nombre en inglés: Great Skua

Nombre científico: Stercorarius skua

Familia: Stercorariidae

Categoria: H/MB (Hipotética/Migratoria Boreal)

Canto: Stanislas Wroza

El págalo grande o skúa (Catharacta skua o Stercorarius skua) es una especie de ave Charadriiforme de la familia Stercorariidae caracterizada por su gran tamaño y agresividad. Como todos los págalos, es un ave depredadora y oportunista.

El nombre común que recibe el págalo grande en los países nórdicos («skúa») deriva del feroés skügver («mechón de plumas»).

Foto: Dirk-Jan van Roest (CC)

Características

Es un págalo de gran tamaño. Alcanza los 58 cm de longitud, 1,4 m de envergadura y 1,7 kg de peso. Su parte superior es marrón oscura, bandeada, con un pico recio, ganchudo, de color gris oscuro. Las patas son del mismo color. En vuelo, posee bajo las alas una mancha blanquecina, cerca del álula. Dicho atributo es exhibido en las zonas de cría durante el cortejo.

En época de cría emiten un sonido similar a un ladrido profundo. En otros momentos, sin embargo, son sorprendentemente silenciosos.

Foto: Noel Reynolds (CC)

Alimentación

Captura peces, así como ejemplares jóvenes de otras especies de aves marinas. También persigue a gaviotas y otros pájaros (incluso alcatraces, considerablemente más grandes que él) y les obliga a soltar su presa o devolver su última comida. Su vuelo es normalmente lento y pesado, pero se torna rápido, hábil y tenaz cuando caza. Los skúas suelen acompañar a los barcos pesqueros que navegan por el Atlántico, aprovechando los desperdicios arrojados por la borda. También son carroñeros cuando se les presenta la oportunidad, alimentándose de los cadáveres de animales marinos muertos.

Hábitat

El skúa pasa la mayor parte del año en alta mar, asentándose en tierra sólo para criar. Nidifica en islas remotas, promontorios y marismas costeras.

Reproducción

Durante el cortejo, las parejas descienden en círculos sobre el punto de cría y, una vez en tierra, realizan una ceremonia de saludo. El nido es un hueco sin tapizar, con dos huevos puestos en una única nidada, de mayo a junio.

Su comportamiento ante aquellos que penetran en su zona de cría, inclusive seres humanos, es muy violento. En algunos casos llegan a ser peligrosos, golpeando fuertemente con su pico la cabeza del intruso.

Distribución

Cría en el norte de Escocia y otras áreas insulares aún más septentrionales (Islas Feroe e Islandia). Puede vérsele fácilmente en Europa occidental en primavera y otoño, generalmente en el mar, aunque a menudo las tempestades le conducen a tierra. En invierno emigra a regiones más templadas, llegando hasta el Atlántico meridional y Sudamérica.

En España, individuos de págalo grande son vistos con frecuencia durante las épocas invernales en los mares y costas del norte y el oeste peninsular. En el Mediterráneo es bastante más escaso y raro.

Foto: Nik Borrow (CC)

Great skua

The great skua (Stercorarius skua), sometimes known by the name bonxie in Britain, is a large seabird in the skua family Stercorariidae. It is roughly the size of a herring gull. It mainly eats fish caught at the sea surface or taken from other birds.

Taxonomy

The great skua was described from the Faroe Islands and Iceland by the Danish zoologist Morten Thrane Brünnich in 1764 under the binomial name Catharacta skua. It is now placed in the genus Stercorarius that was introduced by the French zoologist Mathurin Jacques Brisson in 1760. The English name and species name «skua» is believed to originate from the Faroese skúvur or skúgvur [ˈskɪkvʊər] and is the only known bird name to originate from the Faroes that has come into regular use elsewhere. In Britain, it is sometimes known by the name bonxie, a Shetland name of Norse origin. The genus name Stercorarius is Latin and means «of dung»; the food disgorged by other birds when pursued by skuas was once thought to be excrement. The species is monotypic: no subspecies are recognised.

Description

Great skuas measure 50–58 cm (20–23 in) long and have a 125–140 cm (49–55 in) wingspan. One study found that 112 males weighed an average of 1.27 kg (2.8 lb) and that 125 females weighed an average of 1.41 kg (3.1 lb). Adults are a streaked greyish brown, with a black cap, while juveniles are a warmer brown and unstreaked below. They have a short, blunt tail, and a powerful flight. The great skua’s call is a harsh hah-hah-hah-hah; quacking and croaking noises have also been heard. Distinguishing this skua from the other North Atlantic skuas (parasitic jaeger, pomarine jaeger and long-tailed jaeger) is relatively straightforward. The herring gull size, massive barrel chest and white wing flashes of this bird are distinctive even at a distance. It is sometimes said to give the impression of a common buzzard. Identification of this skua is only complicated when it is necessary to distinguish it from the closely related large southern-hemisphere skuas. Despite its name, the great skua is marginally smaller on average than the other 3 large southern-hemisphere skuas, although not by enough to distinguish them by size in the field. Some authorities still regard the great skua as conspecific with some of these southern skuas, and as a group they have sometimes been separated in the genus Catharacta, although currently this taxonomy is not commonly followed.

Origins

Genetic studies have found surprising similarities between the great skua and the pomarine skua, despite their dissimilar appearance. Many ornithologists now believe either that the great skua originated as a hybrid between the pomarine skua and one of the southern-hemisphere species, presumably as a result of vagrancy or migration across the equator by the southern species, or that the pomarine skua evolved from hybridization of the great skua and one of the small Arctic species (see pomarine jaeger for details).

Breeding

The great skua breeds in Iceland, Norway, the Faroe Islands, and on Scottish islands, with some individuals breeding on mainland Scotland and in the northwest of Ireland. They breed on coastal moorland and rocky islands, usually laying two spotted olive-brown eggs in grass-lined nests. Like other skuas, they will fly at the head of a human or other intruder approaching its nest. Although it cannot inflict serious damage, such an experience with a bird of this size is frightening. They are a migrant species, wintering at sea in the Atlantic Ocean and regularly reaching North American waters. Vagrant to Mediterranean countries (e.g. Turkey).

Diet

They eat mainly fish, birds, eggs, carrion, offal, rodents, rabbits, and occasionally berries.

They will often obtain fish by robbing gulls, terns and even northern gannets of their catches. They will also directly attack and kill other seabirds, up to the size of herring gulls. Like most other skua species, it continues this piratical behaviour throughout the year, showing less agility and more brute force than the smaller skuas when it harasses its victims. A common technique is to fly up to a gannet in mid-air and grab it by the wing, so that it stalls and falls into the sea, where the great skua then physically attacks it until it surrenders its catch. Due to its size, aggressive nature and fierce defence of its nest, the great skua has little to fear from other predators. While fledglings can fall prey to rats, cats or the Arctic fox, healthy adults are threatened only by greater raptors such as the golden eagle, the white-tailed eagle, and more rarely, by the orca.

Predation account

An aerial apex predator, the great skua is an aggressive pirate of the seas, deliberately harassing birds as large as gannets to steal a free meal. It also readily kills and eats smaller birds such as puffins. Great skuas show little fear of humans – anybody getting close to the nest will be repeatedly dive-bombed by the angry adult. Unusual behaviour by St Kilda’s skuas was recorded in 2007 during research into recent falls in the Leach’s storm petrel population. Using night vision gear, ecologists observed the skuas preying on the petrels at night, a remarkable strategy for a seabird.

Fuentes: Wikipedia/eBird/xeno-canto

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