Avocets
| Avocets | ||||||||||
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Avocet ( Recurvirostra avosetta ) |
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| Scientific name | ||||||||||
| Recurvirostra avosetta | ||||||||||
| Linnaeus , 1758 |
The avocet ( Recurvirostra avosetta ) is a species of bird from the family of the avocet (Recurvirostridae). With its black and white plumage, it is one of the most striking Limikolen . In the Wadden Sea of the North Sea , it is a bird that is often observed.
Despite the very large and disjoint distribution area, no subspecies of the avocet are distinguished.
Appearance
A full-grown avocet grows to 43 to 45 centimeters and weighs 290 to 400 grams. The wingspan is up to 80 centimeters. Avocets are unmistakable due to their plumage and the special, upwardly curved bill shape. In flight, however, they could be confused with herons ( Dromas ardeola ). In the bird's plumage, pure white contrasts with pure black. While the lower part of the head, neck, chest, back and belly are colored pure white, the upper part of the head, crown and neck, the side parts of the back and the upper and lower sides of the hand wings are black in the last third. The medium-length legs are gray with a slight bluish tinge. Striking and unique is the long, dark gray beak, which is clearly bent upwards towards the tip and which determined the name of the German generic name.
In flight, the bird looks pure white except for the black wing tips, seen from below, the black and white drawing of the wings is particularly clear when seen from above. While flying, the legs are straight and protrude considerably beyond the tip of the tail, but the neck is not fully extended.
The gender dimorphism is very low. Sometimes females show a slightly lighter fletching of the base of the beak and a white eye ring. In juvenile plumage, the plumage areas that are black in adult birds are rather dark brown, while the white areas are distinctly brown or isabel-colored .
voice
His call sounds something like plüüiit or clever . The call is clear, melodic and flowing. If the birds are startled, a high-pitched and quickly quik quik quik can be heard. Avocets react to disturbances at the nest, especially to intrusive seagulls, with high pii-jüli calls.
Distribution area
Breeding areas
The disjoint breeding area of the avocet extends over several climatic zones from the temperate Atlantic coasts of northwestern Europe and the continental steppes of Central Asia over the Mediterranean area southwards to the tropical and subtropical climates of East and South Africa .
In Europe , the avocet is a breeding bird on the coasts of Great Britain , southern Sweden , Estonia , Denmark , Germany , France and Portugal . In Spain it breeds both on the coast and inland . Avocets are also native to Sardinia in Italy , Greece , Romania and Hungary . In Austria they can be observed particularly well on Lake Neusiedl , where over five hundred adult birds were counted in 2004, but their breeding success was worryingly low. The Volga Delta is also one of the most important European breeding areas for the avocet.
Wintering areas
The migratory behavior of the species differs depending on the location of the respective breeding areas. Avocets are migratory birds, at least in the northern part of the range. In mild winters, many avocets that breed in Great Britain, France and the Netherlands remain in their breeding areas and are therefore to be regarded as resident birds . Also in the Heligoland Bay and in the Dutch Rhine Delta , where large flocks of Swedish, Danish, German and Dutch birds come to moult from mid-July , a small part remains over the winter.
The breeding birds of the coasts of northwestern Europe, which leave after the end of the breeding season and the subsequent moult in July and August, follow the Atlantic coast in a southwestern direction from October. Important winter areas are bays and river mouths rich in fine sediments on the French , Portuguese and Spanish Atlantic coasts . In addition to these areas, which are relatively near-natural despite numerous human interventions, anthropogenic habitats such as fish ponds and salt flats are also of great importance as wintering habitats. Some of the north-western European avocets overwinter even further south on the African Atlantic coast . The breeding birds of the Mediterranean area show no directional migration apart from dispersion movements and the search for suitable winter habitats . The breeding birds of Central and Southeastern Europe migrate to the Black Sea region , the Mediterranean area and North Africa in a south-east and south-westerly direction for wintering . Some of this population may cross the Sahara and overwinter in the eastern Sahel of Sudan and Chad . Little is known about the migrations of the Central Asian population; their wintering areas are in the Persian Gulf , in the northwest of the Indian subcontinent and in southeast China . The breeding birds of Africa spend the dry seasons as non-breeders in coastal habitats .
habitat
The most important habitat element Avocet are feinsedimentige, vegetated shallows and shore areas , where he its specialized form of foraging can pursue. He finds these conditions especially in shallow sea bays , estuaries , lagoons and shallow lakes. The preferred populated habitats are often brackish to saline in character. The breeding grounds are located on areas of the shore zone with little to no vegetation or on islands that offer protection from land-based predators . In north-western Europe, the avocet primarily inhabits the tidal flats of the Wadden Sea as well as brackish and freshwater lakes, the so-called kegs, created by dikes . In southern and southeastern Europe, salt flats and other anthropogenic bodies of water are among the most important habitats. Typical habitats in the Central Asian and African breeding areas are bodies of water and saline steppe lakes that arise briefly after rainfall.
nutrition
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The food of young and adult birds is heavily dependent on the local conditions of the respective habitat. It consists mainly of invertebrates from the fine silty sediments of the bank zone and the shallow water, but smaller fish are also occasionally caught. It is felt and swallowed by the typical saber, a mowing sideways movement of the beak in the sediment or shallow water. When looking for food in the sediment, about 30 square centimeters of mud are scanned with each mowing movement. The beak is about two to three centimeters deep in the sediment. Sometimes you can also observe that several birds go hunting together close together in shallow water. The mowing movements are usually faster because the beak is not pulled through mud, but only through water. The birds running next to each other whirl up prey, which they can then grab into the water. Avocets also peck visually located prey in clear water and from the surface of the ground .
Deeper water layers can be used by searching for food under the surface of the water. In large parts of the breeding area, very small (4–15 mm long) arthropods of salt and brackish water , especially aquatic insects and their larvae ( Coleoptera , Diptera ) and small crustaceans (Crustacea, e.g. Artemia spec., Daphnia spec .) the main food of young and adult birds. An important prey animal in the Wadden Sea is the sea annelid (Nereis spec.). In addition, other bristle worms (Polychaeta) and smaller mollusks such as mussels and snails are preyed on.
Reproduction
Pair formation
Pairing begins towards the end of winter. Many avocets arrive at the breeding site already paired . Shortly after arriving in the breeding area, courtship begins , which is usually a very short group courtship . About three to six, but occasionally up to 18 birds gather in shallow places in the water. With their heads turned inwards, they usually stand in a circular arrangement. Courtship rituals often include throwing up dry grass, pecking water, and violently shaking the head and beak. Not infrequently, this group courtship also includes threatening and aggressive gestures, which can lead to real fights. Mated birds stay as close as possible to their partner's side and express their affiliation by pressing against each other as much as possible.
The copulation takes place also in shallow water. Mating is preceded by ritualized water pecking and plumage cleaning until the female assumes a prompt position. The head is flat over the water and the legs are spread wide. Before the male jumps on the female, he often runs several times behind her back from side to side. Copulation is often followed by a short, shared spurt. Pressed closely together and with crossed beaks, the couples walk through the shallow water. In the male, the wings are often slightly open.
Avocets are colony breeders , even if they delimit their narrow feeding and breeding territories from one another. They often breed not only with their fellow species, but also with terns , smaller seagulls and other species of Limikolen .
Course of the breeding season and nest
The time course of the breeding season shows only minor geographical differences within Europe. It begins in the north-western European breeding areas with the occupation of the breeding colonies from late March to mid-April. In the southern European breeding areas, eggs can be laid as early as the beginning of April; on the Wadden Sea coast of northwestern Europe, it begins in the last decade of April. Avocets lead a monogamous seasonal marriage , both partners are involved in the incubation of the eggs and the rearing of the young. The nest is a hollow in the ground on the beach , which is covered with parts of plants and stones. Occasionally the nest is just a shallow scratch in the bare ground. The clutch , which usually consists of four eggs , is incubated for an average of 23 days. The eggs are pale cream to light green-brown. They are very variable with small black and gray polka dots and lines. Shortly after hatching, the breeding pairs leave the colonies and lead the young to rearing habitats that are up to several kilometers away, where they establish heavily defended territories.
Raising the young
The brood care for the young birds independently foraging for food is limited to the defense of the territory, the defense against predators and the warming of the young birds in the belly plumage, the so-called huddling . The length of the growing season to fledgling depends heavily on weather and nutritional conditions. It varies between 28 and 40 days and averages 35 days. In contrast to the adult birds, the chicks have a straight beak when they hatch. They can also swim quite well and follow the parent birds into the shallow water.
The young birds usually breed for the first time in their second year of life.
Stock situation
With around 11,000 breeding pairs, the Wadden Sea on the northern edge of the brood distribution is home to more than half of the north-western European population estimated at around 19,000 pairs .
The breeding population of the avocet in north-western Europe has increased continuously over the past decades and has only recently stagnated at a high level, although there are numerous indications that this population as a source population does not depend on immigration from breeding areas further south. This development is attributed to the establishment of extensive sea bird sanctuaries. The avocet is one of the few species that no longer has to be on the red list. Existence threats, however, come from extensive embankment plans at various points on the North Sea coast. Similar to the oystercatcher , it is predicted that the avocet will largely disappear as a result of global warming on Central European coasts. A research team that, on behalf of the British environmental authority and the RSPB, examined the future development of the distribution of European breeding birds on the basis of climate models, assumes that the avocet will suffer extensive loss of area by the end of the 21st century. It is predicted, among other things, that eighty percent of the current range will no longer offer suitable habitats.
Others
Avocets were extinct in Great Britain by the mid-19th century. This species was successfully reintroduced after 1940. A stylized avocet has since adorned the logo of the Royal Society for the Protection of Birds .
supporting documents
literature
- Peter Colston , Philip Burton: Limicolen - All European wader species, identifiers, flight images, biology, distribution. BLV Verlagsgesellschaft, Munich 1988, ISBN 3-405-13647-4 .
- Einhard Bezzel: birds. BLV Verlagsgesellschaft, Munich 1996, ISBN 3-405-14736-0 .
Individual evidence
- ^ Brian Huntley, Rhys E. Green, Yvonne C. Collingham, Stephen G. Willis: A Climatic Atlas of European Breeding Birds , Durham University, The RSPB and Lynx Editions, Barcelona 2007, ISBN 978-84-96553-14-9 , P. 166
Web links
- The avocet image documentation from Lake Neusiedl
- waarneming.nl also audio, you can change the language at the top right.
- Recurvirostra avosetta in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings for Recurvirostra avosetta in the Internet Bird Collection
- Avocet feathers
