Ear scar
| Ear scar | ||||||||
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Auritus ( Phalacrocorax auritus ) with outstretched wings to dry the plumage |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Phalacrocorax auritus | ||||||||
| ( Lesson , 1831) |
The double-crested cormorant ( Phalacrocorax auritus ) is a bird art from the family of cormorants . Ear shags are the only species of cormorant that can be found in large numbers in North America, both along the coast and inland , and are also the largest and most widespread species of cormorant in North America. A total of four subspecies are distinguished.
When looking for food, ear shags dive from the surface of the water into deeper water layers and pursue their prey underwater. During the dive they move forward with the help of their powerful webbed feet and use their tail as a rudder. They are extremely gregarious animals that form colonies of hundreds to more than a thousand individuals during the breeding season.
Fishermen traditionally see the shagfish as a competitor, which is why the total population fell sharply due to hunting, especially in the 19th century. In the 1960s and 1970s, the population continued to decline as a result of the use of pesticides. After the population had recovered, legal measures were introduced in the late 1990s to regulate the number of ear scars by shooting or by so-called "egg-oiling" (preventing successful hatching by sealing the eggs with oil).
In Europe the ear shag is a rare exceptional guest, with isolated evidence especially in Great Britain and less often in the Azores and the Canary Islands.
features
Build and color
Adult ear scars reach a body length of 76 to 91 centimeters and then have a body weight of around 1.5 to 2 kilograms. The plumage is black and shimmers slightly green. Ear shags have the torpedo-shaped body typical of cormorants. The neck is very flexible; the big feet are webbed. Similar to the cormorant native to Europe , they have a hook-shaped and powerful beak . The iris is greenish, the featherless skin on the chin and the base of the beak is orange and in some individuals also orange-yellow. The beak is dark.
Flight image and locomotion
Compared to other water birds, the ear shags have quite short wings, which leads to a high flight speed with a low carrying capacity. In contrast to other species of the cormorant family, the ear shags are better able to maneuver at low airspeed, for example when landing on branches or power lines. The animals slide very rarely and move forward with regular flaps of their wings. Above the water they fly close to the surface, while over land they fly at higher altitudes.
On land, scraps of ears move forward with a waddling and awkward-looking gait that is often interrupted by two-legged hops. Sometimes they use their hook-shaped beaks, especially when they are young, to climb rocks or branches.
Vocalizations
At nesting or sleeping places, the scarred ears emit deep, guttural grunts; otherwise they are rather quiet birds. Your alarm sound is a repeated "eh-hr". The vocalizations during the breeding season are described by Nelson as a deep, repeating and several seconds long loud "ok-ok-ok". In a master's thesis written in 1959, Van Tets distinguishes between a total of seven different vocalizations in a breeding colony.
Distribution area and habitat
The common area of the ear shag stretches from Alaska to the Gulf of California and in eastern North America from Newfoundland to Cape Cod.
The populations of this bird are very large. These birds pose a problem for the fish farms along the Mississippi River , as they also hunt the fish they move there.
The habitat are cool, subtropical coasts in protected estuaries or bays as well as mangrove swamps, rocky coasts and coastal islands. In the interior of the country, the species occurs on lakes, rivers, reservoirs and floodplains.
Way of life
Food acquisition and food
Ear shags feed almost exclusively on fish, occasionally also on insects, shellfish, eels and amphibians. When it comes to food choices, the ear shags proceed opportunistically and hunt the prey fish that are most readily available at the moment.
Foraging takes place during the day and is concentrated in shallow surface waters . Ear shags dive from the water surface into deeper water layers and pursue their prey underwater. During the dive they move forward with the help of their powerful webbed feet and use their tail as a rudder. Smaller prey is still eaten underwater, while larger or difficult-to-handle prey - such as eels or flatfish - is brought to the surface of the water. Occasionally, the ear shags shake such prey and hit them on the water to overwhelm them.
When hunting schools of fish, shags sometimes come together in groups. They then move towards the prey animals in a line or in a crescent-shaped formation, with individual birds repeatedly bringing themselves in front of their conspecifics diving through short flights.
Reproduction
Shags live gregariously all year round and breed in colonies. The birds are monogamous and have long-term relationships. Above all, they show great loyalty to the nest. In the breeding colonies, the males arrive first and defend the respective nest from competitors. Due to the loyalty to the nest and the annual nest building, the nests are very large and can reach a height of up to two meters. Both parent birds are involved in the annual construction and also defend the nest, as the theft of nesting material is common under the ear shags.
Clutches can contain between one and seven eggs. However, the common clutch size is four eggs. These are pale blue. They are incubated by both parent birds for a period of 25 to 30 days. The chicks are also fledged and fed by both parent birds. The young birds can fly at 20 to 30 days and can also fly after another 15 to 20 days. They are fertile at two to three years of age.
literature
- J. Bryan Nelson: Pelicans, Cormorants, and their Relatives , Oxford 2005, ISBN 978-1-4237-6812-8 , pp. 395-404, as well as Plate 6 No. 2 (cf. for example the review by EA Schreiber , in: The Auk 124, 4 (2007), pp. 1466-1468).
- Paul A. Johnsgard: Cormorants, Darters, and Pelicans of the World , Washington and London 1993, pp. 201-208.
- Jeremy J. Hatch / Datlaf Vaughn Weseloh / Brian S. Dorr: Double-crested Cormorant (Phalacrocorax auritus) , in: Birds of the World , ed. by A. Poole, Ithaca 1995 (access with costs; last accessed on May 22, 2020 with the status of the text on December 4, 2014)
- David N. Nettleship / David C. Duffy (Eds.): The Double-Crested Cormorant: Biology, Conservation and Management , Special Publication, Waterbird Society, also Colonial Waterbirds 18 (1995).
Web links
- Nannopterum auritus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings about Phalacrocorax auritus in the Internet Bird Collection
Remarks
- ↑ Hans-Günther Bauer, Einhard Bezzel and Wolfgang Fiedler (eds.): The compendium of birds in Central Europe: Everything about biology, endangerment and protection. Volume 1: Nonpasseriformes - non-sparrow birds , Wiesbaden 2005, ISBN 3-89104-647-2 , p. 241.
- ↑ a b For this and the following cf. Door / Hatch / Weseloh, Double-crested Cormorant , in: Birds of the World, section " Locomotion ".
- ^ A b Door / Hatch / Weseloh, Double-crested Cormorant , in: Birds of the World, section " Sounds and Vocal Behavior ".
- ↑ Nelson, Pelicans, Cormorants, and their Relatives , p. 396.
- ↑ GF Van Tets: A comparative study of the reproductive behavior and natural history of three sympatric species of cormorants, (Phalacrocorax auritus, P. penicillatus, & P. pelagicus) at Mandarte Island , Master's Thesis, University of British Columbia, Vancouver 1959, quoted here from Door / Hatch / Weseloh, Double-crested Cormorant , in: Birds of the World.
- ↑ On this and the following cf. Paul A. Johnsgard: Cormorants, Darters, and Pelicans of the World, Washington and London 1993, pp. 398–401, and Jeremy J. Hatch / Datlaf Vaughn Weseloh / Brian S. Dorr: Double-crested Cormorant (Phalacrocorax auritus) , Section " Diet and Foraging, " in: Birds of North America Online, ed. from A. Poole, Ithaca 1995, last accessed June 11, 2019.
- ^ Paul A. Johnsgard, Cormorants, Darters, and Pelicans of the World , Washington and London 1993, p. 66.
- ^ Sale, Complete Guide to Arctic Wildlife , p. 79.