Olroggull

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Olroggull
Adult Olroggull (Larus atlanticus)

Adult Olroggull ( Larus atlanticus )

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Laridae
Subfamily : Seagulls (larinae)
Genre : Larus
Type : Olroggull
Scientific name
Larus atlanticus
Olrog , 1958
Olroggull in youth dress. In the background a Dominican gull in the second plain dress and two gray-headed gulls in the plain dress.

The olrog's gull ( Larus atlanticus ) is a bird art within the gulls (Larinae). It occurs on the Atlantic coast between southeast Uruguay and Argentina , but only breeds in Argentina. It is one of the few species of gulls that are endangered worldwide. In her diet she has largely specialized in a few types of crab .

The Olroggull was first described as a subspecies of the very similar Simeonsgull from the west coast of South America, but is now generally recognized as a separate species. Both belong within the genus Larus to a rather original group of four species that wear a dark tail band in all clothes and show relatively simple beak drawings and almost completely black hand wings in adult dress.

description

With a body length of 50–56 cm and a wingspan of 130–140 cm, the Olroggull is somewhat smaller than a herring gull and larger, more long-winged and long-beaked than the closely related Simeon's gull. The weight is between 900 and 960 g.

In breeding plumage the head, neck and bottom are white. The beak is yellow with a black and red tip. The dark eye is enclosed by a red orbital ring . Shoulder and coat plumage as well as the upper side of the wing are blackish. In contrast to the Simeon's gull, it lacks a brownish tint and the transition between coat and neck is sharper. The white tail shows a wide, black sub-terminal band that does not extend to the outermost control feathers. Feet and legs are yellow.

All other dresses are also similar to those of the Simeon's gull.

voice

The calls are described as nasal or guttural.

Distribution and existence

The Olroggull is an endemic breeding bird of the Argentine Atlantic coast and only breeds there in two locations 700 km apart. About 5% of the population breed in the Gulf of San Jorge in the province of Chubut , over 90% in the southern part of the province of Buenos Aires . There are about 14 colonies in the mudflats near Bahía Blanca , Bahía Anegada , Bahía Melo and Caleta Malaspina . 70% of the total population breed in the estuary near Bahía Blanca.

The total population is given differently with about 4000-5000 breeding pairs or with about 7000 adult and 3500 young individuals. As the population is in decline and the breeding grounds are potentially endangered by human activities, the IUCN regards the species as endangered (“vulnerable”).

hikes

After the breeding season, dismigration movements take place that extend north to Uruguay and south to the Argentine provinces of Río Negro and Chubut. The species was found to be a stray visitor in Brazil and Tierra del Fuego .

Way of life

The olroggull is a coastal bird that feeds primarily on the three crab species Chasmagnathus granulata , Cyrtograpsus altimanus and Cyrtograpsus angulatus during the breeding season . Even in winter, these species provide most of the food, but then other types of crabs, mollusks , small fish and waste are added. The food is mostly sought in the vicinity of the breeding colonies, where the birds search the mudflats and adjacent beaches in flight or peck the prey from the surface of the water while swimming. Often they also come down from the shaking flight. In contrast to the Simeon's gull, the species hardly appears as a predator in other bird species. The specialized diet of the species may be due to increased competition from the superior Dominican gull.

The Olroggull breeds in colonies from September on, the size of which is between 10 and 350 nests. The nesting site density is often quite high and the average distance between the nests is sometimes 66 cm. All colonies are located on sandy, muddy or rocky islands, and the height above sea level can be between less than 3 and 7 m. Most locations are free of vegetation or only covered with a sparse herbaceous layer of samphire , silt grass , Frankenia or sea lavender. The colonies are not infrequently located in the vicinity of colonies of the Dominican gull. The nest can only be a hollow lightly lined with plants, but it can also consist of a raised platform made of twigs and samphire. The clutch consists of 2–3 eggs.

Etymology and history of research

The first description of the Olroggull was in 1958 by Claës Christian Olrog under the scientific name Larus belcheri atlanticus . As early as 1758, Carl von Linné introduced the new generic name Larus . This name comes from the Latin »larus}« or from the Greek »laros λαρος « for »predatory sea bird, probably a seagull«. together. The species name »atlanticus« stands for the Atlantic Ocean . The German trivial name was named after the person who first described it.

literature

  • Josep del Hoyo , Andrew Elliott, Jordi Sargatal (eds.): Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions 1996, ISBN 978-84-87334-20-7 , p. 601.
  • Pablo García Borboroglu, Pablo Yorio: Breeding habitat requirements and selection by Olrog's Gull (Larus atlanticus), a threatened species , The Auk , 124 (4), pp. 1201-1212, 2007. doi : 10.1642 / 0004-8038 (2007) 124 [1201: BHRASB] 2.0.CO; 2
  • Claës Christian Olrog: Notas ornitológicas sobre la colleción del Instituto Miguel Lillo Tucuman. III . In: Acta Zoologica Lilloana . tape 18 , 1958, p. 5-18 .
  • Carl von Linné: Systema Naturae per Regna Tria Naturae, Secundum Classes, Ordines, Genera, Species, Cum Characteribus, Differentiis, Synonymis, Locis . 10th edition. tape 1 . Imprensis Direct Laurentii Salvii, Stockholm 1758 ( biodiversitylibrary.org ).

Individual evidence

  1. ↑ a b c BirdLife Species Factsheet, s. Web links
  2. ↑ a b Borboroglu et al. (2007), p. 1202, see literature
  3. ↑ a b c Del Hoyo et al. (1996), p. 602, see literature
  4. ^ Claës Christian Olrog, p. 8.
  5. ↑ Carl von Linné, p. 136.
  6. ↑ James A. Jobling, p. 219.
  7. ↑ James A. Jobling, p. 58.

Web links

Commons : Olroggull ( Larus atlanticus )  - Collection of images, videos and audio files