Olrog's Gull
Adult Olrogmöwe (Larus atlanticus )
The Olrogmöwe (Larus atlanticus ) is a species of bird in the family of gulls ( Laridae ). It occurs on the Atlantic coast between Southeast Uruguay and Argentina, but breeds only in Argentina. It is one of the few globally threatened species of gulls. In her diet she has specialized largely to a few crab species.
The Olrogmöwe was first described as a subspecies of the very similar Simeonsmöwe from the west coast of South America, but is now generally recognized as a separate species. Both belong in the genus Larus to a fairly original group of four species that carry a dark tail band in all the dresses and show in the adult dress relatively simple beak drawings and almost completely black primaries.
The Olrogmöwe is named after its first describer the Swedish ornithologists Claës Christian Olrog named.
Description
The Olrogmöwe is 50-56 cm body length and a wingspan of 130-140 cm slightly smaller than a herring gull and greater langflügeliger and langschnäbeliger as the closely related Simeonsmöwe. The weight is 900-960 g
In breeding plumage the head, neck and underparts are white. The beak is yellow with black and red lace. The eye is enclosed in a dark red orbital ring. Shoulder and mantle feathers and the upper wing are blackish. It lacks, in contrast to Simeonsmöwe with a brownish tint and the transition between sheath and neck is sharper. The white tail shows a broad, black Subterminalband that does not extends to the outermost tail feathers. Feet and legs are yellow.
All other clothes are also similar to those of the Simeonsmöwe.
Voice
The calls are described as nasal or guttural.
Distribution and population
The Olrogmöwe is an endemic breeding bird of Argentina's Atlantic coast and breeds there only two 700 km between distant places. About 5 % of the stock breed in the Gulf San Jorge in Chubut province, more than 90 % in the southern part of the province of Buenos Aires. There are about 14 colonies in the mudflats at Bahía Blanca, Bahía Anegada, Bahía Melo and Caleta Malaspina. 70 % of the total stock breed in the estuary in Bahia Blanca.
The total population is estimated at about 4000-5000 different breeding pairs or with approximately 7000 adult and 3500 young individuals. Since the stock is slightly on the decline and the breeding sites are potentially threatened by human activities, the nature of the IUCN as endangered ( " vulnerable" ) is considered.
Hiking
After the breeding season Dismigrationsbewegungen take place, ranging northward to southward to Uruguay and the Argentine provinces of Río Negro and Chubut. As Irrgast the kind in Brazil and Tierra del Fuego was found.
Way of life
The Olrogmöwe is a coastal bird that feeds primarily during the breeding season of the three crab species Chasmagnathus granulata, Cyrtograpsus altimanus and Cyrtograpsus angulatus. Even in winter, make the most of these types of food it will get but also other species of crabs, mollusks, snails, small fish, and waste time. The food is usually sought in the vicinity of breeding colonies, where the birds in flight scan the mudflats and adjacent beaches or swimming peck the prey from the water surface. They often triggered from the Rüttelflug down. In contrast to Simeonsmöwe the kind rarely occurs as a predator on other species of birds. Perhaps the specialized diet of the species is due to the increased competition from the superior Kelp.
The Olrogmöwe broods of September in colonies whose size is about 10-350 nests. The Nistplatzdichte is often quite high, and the average distance between nests located partly at 66 cm. All colonies are located on sandy, muddy or rocky islands, the height may be less than above the sea level between 3 and 7 m. Most sites are free of vegetation or simply covered with a sparse herb layer of Queller, cordgrass, Frankenia beach or lilac. Not infrequently, the colonies in the vicinity of colonies of Kelp. The nest may be only a slight depression lined with plants, but also consist of a raised platform of twigs and samphire. The nest consists of 2-3 eggs.