Cormorán Orejudo/Double-crested Cormorant/Phalacrocorax auritus

Foto: Jorge Chinchilla

Nombre en español: Cormorán Orejudo

Nombre en inglés: Double-crested Cormorant

Nombre científico: Phalacrocorax auritus

Familia: Phalacrocoracidae

Canto: Paul Marvin

El cormorán orejudo (Phalacrocorax auritus) es una especie de ave suliforme de la familia Phalacrocoracidae​ que habita tanto zonas costeras como aguas dulces del interior de Norteamérica. Aunque estuvo en peligro debido al empleo masivo de DDT, su número se ha incrementado de nuevo en los últimos años.

Nombres comunes

Además de cormorán orejudo, también es conocido como cormorán de doble cresta, cuervo-pato, cormorán de Florida, cuervo marino y pavo marino.

Taxonomía

El cormorán orejudo fue descrito por René Primevère Lesson en 1831. Su nombre científico procede de los términos griegos phalakros/φαλακρος «calvo» and korax/κοραξ «cuervo», and the Latín auritus «orejudo», referido a sus crestas.

Subespecies

Se conocen cuatro subespecies de Phalacrocorax auritus:

  • Phalacrocorax auritus albociliatus – SW Columbia Británica a Golfo de California
  • Phalacrocorax auritus auritus – Golfo de San Lorenzo al Cabo Cod y localmente oeste de Utah
  • Phalacrocorax auritus cincinatus – islas Aleutianas, Golfo de Alaska hasta la península de Yakutat
  • Phalacrocorax auritus floridanus – costas de Carolina del Norte a Florida, Bahamas y Cuba

Descripción

El cormorán orejudo es un gran pájaro negro que alcanza hasta 91 cm de largo con una envergadura de 132 cm. Tiene una cola larga y una garganta amarilla. Su plumaje es negro con reflejos verdosos. La doble cresta blanca por la que recibe el nombre de «orejudo» solo aparece brevemente durante la estación de cría en los pájaros occidentales; es menos frecuente en los pájaros orientales. Los jóvenes son pardos con cabeza, cuello y pecho blancos.

Distribución y hábitat

Una especie muy extendida, inverna en cualquier lugar libre de hielo en la costa, llegando por el norte hasta el sur de Alaska en la costa oeste americana y al sur de Nueva Inglaterra en la costa este. Por el sur llega hasta México y las Bahamas. En ocasiones excepcionales ha cruzado el Atlántico, siendo avistado en Gran Bretaña, Irlanda y las Azores.

Conducta

Los cormoranes orejudos suelen nadar en la superficie del agua, dejando solo visibles su cabeza y cuello, pero bucean para alimentarse. Utilizan sus pies palmeados para propulsarse y son capaces de llegar hasta lo 7,5 m durante 30-70 segundos. Para secarse a menudo pasan mucho tiempo con las alas extendidas, ya que no son por completo impermeables. Suele volar a ras de la superficie.

Foto: Jorge Chinchilla

Dieta

Se alimenta en el mar, lagos de agua dulce y ríos. Como todos los cormoranes bucea para atrapar a sus presas. Se alimenta principalmente de peces, pero en ocasiones también de anfibios y crustáceos. Las presas más pequeñas son engullidas enteras, mientras que las más grandes son arrastradas hasta la superficie antes de ser devoradas. Los cormoranes regurgitan egagrópilas con los restos semidigeridos de sus comidas como espinas y raspas. Estos restos son utilizados para analizar su dieta.Jóvenes cormoranes orejudos en California California.

Reproducción

El apareamiento se produce en su hábitat habitual. Construyen nidos en árboles, acantilados o incluso en el suelo en lugares aislados y apropiados. Son pájaros gregarios y suelen formar colonias de cría, a menudo junto a otros pájaros acuáticos y para llamarse utilizando un profundo graznido gutural.

Recuperación

El número de cormoranes orejudos descendió alarmantemente en la década de 1960 debido a los efectos del DDT. De vez en cuando sus colonias también han sido afectadas por la acción humana ya que se cree que son una amenaza para la pesca.

En época reciente la población de cormoranes orejudos se ha incrementado. Se cree que se debe al descenso de contaminantes, debido al uso decreciente del DDT.

En 1894 Thomas McIlwraith escribió en su libro Aves de Ontario sobre el cormorán orejudo: «Cuando los jóvenes han crecido lo suficiente se reúnen en inmensas bandadas en parajes aislados, donde permanecen hasta que el agua se congela y entonces comienzan la migración y no regresan hasta la primavera.» Linda Wires y Francesca J. Cuthbert afirman que parece que los cormoranes eran mucho más comunes en Norteamérica que en la actualidad, pero que su número comenzó a decrecer en el siglo XIX hasta llegar al presente.

Las poblaciones que habitan en los Grandes Lagos parecen haberse beneficiado de la introducción de nuevas especies piscícolas. Los científicos no están de acuerdo de la influencia de la depredación de los cormoranes, pero parece que son especialmente determinantes en algunas localizaciones.

Por esta razón y debido a la petición de varias organizaciones de pescas el gobierno de los Estados Unidos ha extendido recientemente varias medidas de control para la reproducción y evitar la expansión excesiva de la especie.

Foto: Francisco Piedrahita

Double-crested cormorant

The double-crested cormorant (Phalacrocorax auritus) is a member of the cormorant family of seabirds. Its habitat is near rivers and lakes as well as in coastal areas, and is widely distributed across North America, from the Aleutian Islands in Alaska down to Florida and Mexico. Measuring 70–90 cm (28–35 in) in length, it is an all-black bird which gains a small double crest of black and white feathers in breeding season. It has a bare patch of orange-yellow facial skin. Five subspecies are recognized. It mainly eats fish and hunts by swimming and diving. Its feathers, like those of all cormorants, are not waterproof and it must spend time drying them out after spending time in the water. Once threatened by the use of DDT, the numbers of this bird have increased markedly in recent years.

Taxonomy

The double-crested cormorant was described by René Primevère Lesson in 1831. Its scientific genus name is derived from the Greek words φαλακρός : phalakrós, «bald» and κόραξ : kórax, «crow» or «raven». The species name is from the Latin auritus, «eared», referring to its nuptial crests. Its common name refers to the same nuptial crests.

Five subspecies are recognized:

  • P. a. albociliatus (Ridgway 1884), Farallon cormorant, breeds along the Pacific coast of North America from British Columbia to Bird Island in the state of Sinaloa, Mexico and possibly even further south. Significant colonies of these birds may also be found further inland including areas around the Salton Sea. According to currently available information, this subspecies is the third largest among the subspecies of the double-crested cormorant. Historical records indicate that this species was far more abundant in the past, but due to human persecution and development in their breeding range, the population of this subspecies has declined. The largest colony of cormorants in North America consisted of members of this subspecies at San Martin Island, Baja California Territory, Mexico, and was recorded in 1913. Physically, this subspecies is fairly large and has white to partially white nuptial crests.
  • P. a. auritus (Lesson, 1831), the nominate subspecies, has the largest and most widespread breeding population. It ranges from the Great Basin and Rocky Mountains east into central and eastern North America. This region includes the Canadian prairies and the Great Lakes. Historically, this subspecies has bred in abundance across most of this region, though there are questions as to whether this bird has always bred in the Great Lakes region. Some evidence indicates that the bird has only begun breeding in the region since the early 20th century while other evidence suggests that it has been breeding in the region much longer. Physically, this subspecies is moderately large and has black nuptial crests.[3][5]
  • P. a. cincinnatus (Brandt 1837), white-crested cormorant, currently this is the most geographically restricted subspecies with the smallest population. It is found along the southern coast of Alaska and on the Aleutian Islands, ranging west from Kodiak to Chuginidak in the Aleutians. Historically, the range extended west to the Near Islands, but possibly due to nest predation by introduced foxes, the birds were no longer breeding in the area by the mid-1930s. Physically, this subspecies is the largest and it bears straight, white nuptial crests.
  • P. a. floridanus (Audubon 1835), Florida cormorant, the smallest of the five subspecies, it is found from southern and central Texas east to the Atlantic and from North Carolina south to Florida. Records indicate that this subspecies was abundant throughout its range before the 20th century, but now is only abundant in Florida. This bird has dark nuptial crests.
  • P. a. heuretus This subspecies bears straight, white nuptial crests. Physically, it is the smallest. It has bare lores and a greenish gloss on the head and neck. It breeds only in the mangroves surrounding interior lakes of San Salvador in the Bahamas. It may also be resident on other Bahamian islands.

Description

The double-crested cormorant is a large waterbird with a stocky body, long neck, medium-sized tail, webbed feet, and a medium-sized hooked bill. It has a body length of between 70–90 cm (28–35 in) long, with a wingspan of between 114–123 cm (45–48 in). Double-crested cormorants weigh between 1.2–2.5 kg (2.6–5.5 lb). Males and females do not display sexual dimorphism.

This species has dark-colored plumage with bare supra-loreal skin and gular skin that is yellow or orange. An adult in breeding plumage will be mostly black with the back and coverts being a dark grayish towards the center. Nuptial crests, for which the species is named, are either white, black or a mix of the two. These are located just above the eyes with the bare skin on the face of a breeding adult being orange. A non-breeding adult will lack the crests and have more yellowish skin around the face. The bill of the adult is dark-colored. The double-crested cormorant is very similar in appearance to the larger great cormorant, which has a more restricted distribution in North America, mainly on the Canadian maritime provinces; it can, however, be separated by having more yellow on the throat and the bill.

The plumage of juvenile double-crested cormorants is more dark gray or brownish. The underparts of a juvenile are lighter than the back with a pale throat and breast that darkens towards the belly. As a bird ages, its plumage will grow darker. The bill of a juvenile will be mostly orange or yellowish.

Distribution and habitat

A very common and widespread species, it winters anywhere that is ice-free along both coasts, as far north as southern Alaska (on the west coast) and southern New England (on the east coast). It can be found as far south as Mexico and the Bahamas. It migrates from the coldest parts of its breeding range, such as eastern Canada, and has occurred in Europe as a very rare vagrant, for example in Great Britain, Ireland, and the Azores.

Behavior

The double-crested cormorant swims low in the water, often with just its neck and head visible, and dives from the surface. It uses its feet for propulsion and is able to dive to a depth of 1.5–7.5 m (4 ft 11 in–24 ft 7 in) for 30–70 seconds. After diving, it spends long periods standing with its wings outstretched to allow them to dry, since they are not fully waterproofed. This species flies low over the water, with its bill tilted slightly upward, sometimes leaving the colony in long, single-file lines.

Diet

Food can be found in the sea, freshwater lakes, and rivers. Like all cormorants, the double-crested dives to find its prey. It mainly eats fish, but will sometimes also eat amphibians and crustaceans. Fish are caught by diving under water. Smaller fish may be eaten while the bird is still beneath the surface but bigger prey is often brought to the surface before it is eaten. Double-crested cormorants are also considered pests to aquaculturists because of their intense predation on fish ponds which can cause thousands of dollars in losses to farmers. Cormorants regurgitate pellets containing undigested parts of their meals such as bones. These pellets can be dissected by biologists in order to discover what the birds ate.

Breeding

Breeding occurs in coastal areas as well as near inland rivers and lakes. They build stick nests in trees, on cliff edges, or on the ground on suitable islands. They are gregarious birds usually found in colonies, often with other aquatic birds, and have a deep, guttural grunt call.

Recovery

The double-crested cormorant’s numbers decreased in the 1960s due to the effects of DDT. Colonies have also been persecuted from time to time in areas where they are thought to compete with human fishing.

Recently the population of double-crested cormorants has increased. Some studies have concluded that the recovery was allowed by the decrease of contaminants, particularly the discontinued use of DDT.[8] The population may have also increased because of aquaculture ponds in its southern wintering grounds. The ponds favor good over-winter survival and growth.

In 1894, Thomas McIlwraith in his book, Birds of Ontario, concludes his section on double-crested cormorants by saying: “When the young are sufficiently grown, they gather into immense flocks in unfrequented sections, and remain until the ice-lid has closed over their food supply, when they go away, not to return till the cover is lifted up in the spring.”

For populations nesting in the Great Lakes region, it is believed that the colonization of the lakes by the non-native alewife (a small prey fish) has provided optimal feeding conditions and hence good breeding success. Double-crested cormorants eat other species of fish besides alewives and have been implicated in the decline of some sport-fish populations in the Great Lakes and other areas. Some anglers and commercial fishing outfits believe that double-crested cormorants may be a factor for some populations and in some locations.

In light of this belief, and because of calls for action by the public, the United States Fish and Wildlife Service (the U.S. federal government agency charged with their protection) has recently extended control options to some other government entities. This includes culling of populations and measures to thwart reproduction, in an effort to control their growing numbers. The U.S. Fish and Wildlife Service retains oversight and the control measures are not extended to the general public (no hunting season).

In May 2008, the Canadian government reduced significantly the number of nests of the birds on Middle Island, a small island in Lake Erie and part of Point Pelee National Park. This is an attempt to keep the small island in balance and preserve its vegetation but opponents to the plan have argued that it is based on faulty information, provided in part by anglers who view cormorants as competitors.

Fuentes: Wikipedia/eBird/xeno-canto

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