Avocets (family)

from Wikipedia, the free encyclopedia
Avocets
Stilt (himantopus himantopus)

Stilt ( himantopus himantopus )

Systematics
Sub-stem : Vertebrates (vertebrata)
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Avocets
Scientific name
Recurvirostridae
Bonaparte , 1854

The avocets (Recurvirostridae) are a family from the order of the plover-like (Charadriiformes). They are common in almost all tropical and temperate zones in the world. They are characterized by a long neck, long legs and a long, slender beak. Depending on the genus, this is either straight or curved upwards. The three genera - the actual avocet, the stilt and the mud stilt - are outwardly quite different, but still closely related to each other.

features

All species have a long beak, a long neck and very long legs. The beak of the actual avocet is curved upwards and provided with lamellas to filter the food. In contrast, stilts have a straight or barely noticeably curved beak, which lacks the lamellae. The mud stilt, which mediates between the two genera in these and other characteristics, has a straight beak like the stilt, but has lamellae.

The legs of the real avocets are colored blue-gray, those of the other genera pink. Actual avocets have three front toes and one rear toe ( anisodactyl foot ). The front toes are through basal webbed connected. The stilt walkers have no back toe ( tridactylic foot ) and no webbed feet . Here, too, the mud stilts, who have a tridactyl foot with basal webs, mediate.

Typically the plumage is patterned in black and white. In three non-European species, the third color is red-brown. Only the black stilt is monochrome black. The juvenile plumage resembles or resembles the appearance of adult birds. Here, too, the black stilt is an exception, where juvenile birds can hardly be distinguished from the actual stilt.

distribution and habitat

Avocets are common on all continents except Antarctica. They live in temperate, subtropical and tropical climates. The preferred habitat is flat marshland in tree-poor landscapes. Actual avocets are mainly found at salt lakes and lagoons. The stilts are more flexible in their choice of habitat and can be found in rivers and lakes, as well as in fresh and brackish water. Breeding areas are usually inland, but outside the breeding season avocets can also be found on the coasts. The Andean avocet, which breeds in the Andes at heights of up to 5000 m, has a special habitat .

With the exception of the Andean avocet and the black stilt, at least partial populations of all species are migratory birds . Large parts of the populations of the northern and southern temperate zones move to warmer regions. The train usually takes place at night in small groups. The birds follow coasts or rivers.

Way of life

Avocets are primarily, but not exclusively, diurnal. In addition to the day-night rhythm, the tides also determine the times of activity of the avocets. With the exception of the solitary black stilt, the birds live in small to very large groups. The actual avocets and stilt-walkers breed between five and a hundred pairs. In contrast, the mudstilt colonies can comprise many thousands of pairs. Avocets also live in larger groups outside of the breeding season.

nutrition

The different anatomical structure of the beaks results in different diets: the actual avocets and mud stilts use the lamellae on their beak edges to search for food. With only a slightly open beak, they make sideways swiveling movements through shallow water or mud. Every two seconds the tongue thrusts forward and brushes off the small organisms that have stuck to the lamellae. In this way, crustaceans and worms living mainly in the plankton are ingested. In addition to this straining method, food is also consumed directly by picking it up. For the stilt this is almost the only way of eating. This mainly eats insects and their larvae as well as worms.

Mollusks, small fish and aquatic plants play a lesser role in the diet.

Reproduction

Two young birds that have just hatched and two eggs in a nest of the American stilt .

Avocets live in seasonal monogamy , the black stilt is monogamous for life. They breed in colonies with nests five to thirty meters apart; only in the mudstalk are the nests within a colony much more densely packed, here there can be up to eighteen nests on one square meter. Avocets often form mixed colonies with other wading birds.

Three to four eggs are almost always laid, although extremes of just one egg or eight eggs have also become known. The eggs are yellow or brown (white in the mudstalk) with dark spots. The size is 4.5 to 5.5 × 3 to 4 cm. Both partners breed and often take turns. The defense of the nest is also the task of both partners. Potential nest predators are either attacked or lured away from the nest, for example by simulating a wing injury.

The young birds of the actual avocets and the stilt are colored beige or red-brown with black spots. They hatch synchronously and leave the nest within the first twenty-four hours. They then stay with their parents for a few more months. The mud stilts are an exception here, too, whose young are monochrome white and come together in large “kindergartens” after hatching.

Tribal history

Avocets have been documented as an ancient family from the early Eocene . Fossil genera of this era are Coltonia (North America), Kashinia (Great Britain) and Fluviatilavis (Portugal).

Systematics

The avocets belong to the order of the plover-like . According to DNA analyzes, the closest relatives within this order are the oystercatchers , the ibis beak and parts of the paraphyletic plover family .

The family currently comprises 3 genera and 10 species:

The number of species within the genus Himantopus is controversial. Some authors see only the black stilt as an independent from the list shown above and view the others as subspecies of the same species. In addition to the above, some authors also use the Hawaiian stilt ( Himantopus knudseni ). Since the black stilt hybridizes with the white-faced stilt , even the splitting off of the black stilt is questionable.

The relationship between the three genera is unclear. Investigations brought contradicting results, according to which sometimes the genus Himantopus was found to be the sister group of the other two, then again the genus Cladorhynchus as a sister group of the others.

Humans and avocets

The actual avocet was once almost extinct in Central and Western Europe. Its reintroduction in Great Britain after a hundred years of absence was a success story for the Royal Society for the Protection of Birds in 1941 , which now has an avocet in its logo. Since the exploitation of avocets as food birds and for sport hunting no longer plays a major role, the destruction of wet habitats has become a greater threat.

At the species level, only one species is endangered: the black stilt is listed as critically endangered by the IUCN . After it was still common in the 19th century, there was a dramatic slump in the 20th century, which was mainly caused by the cats, weasels and rats introduced into New Zealand as well as by frequent hybridization with the white-faced wagtail. In 2001 there were only seven breeding pairs left. This number has meanwhile been increased again to twenty, but this requires constant release of animals raised in captivity.

literature

Josep del Hoyo et al .: Handbook of the Birds of the World (HBW). Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona 1996.

Individual evidence

  1. ↑ a b c del Hoyo et al .: HBW Volume 3, Morphological Aspects , p. 333, see literature
  2. ↑ del Hoyo et al .: HBW Volume 3, Habitat , pp. 333/334, see literature
  3. ↑ del Hoyo et al .: HBW Volume 3, Movements , p. 341, see literature
  4. ↑ del Hoyo et al .: HBW Volume 3, General Habits , p. 334, see literature
  5. ↑ a b del Hoyo et al .: HBW Volume 3, Food and Feeding , p. 336, see literature
  6. ↑ a b c del Hoyo et al .: HBW Volume 3, Breeding , pp. 338-340, see literature
  7. ↑ CJO Harrison: A new wader, Recurvirostridae (Charadriiformes), from the early Eocene of Portugal. In: Ciências da Terra , Vol. 7 (1983)
  8. Jump up ↑ Allan Baker, Sergio Pereira & Tara Paton: Phylogenetic relationships and divergence times of Charadriiformes genera: multigene evidence for the Cretaceous origin of at least 14 clades of shorebirds . In: Biology Letters 2007, Vol. 3, No. 2, pp. 205-210
  9. ↑ del Hoyo et al .: HBW Volume 3, Systematics , p. 332, see literature
  10. ^ Les Christidis, Walter Boles: Systematics and taxonomy of Australian birds . Csiro Publishing, 2008. ISBN 0-643-06511-3 . Pp. 131-132
  11. ↑ del Hoyo et al .: HBW Volume 3, Relationship with Man / Status and Conservation , pp. 341–342, see literature
  12. ↑ Himantopus novaezelandiae in the IUCN Red List of Threatened Species . Retrieved January 3, 2011.

Web links

Wiktionary: Avocets  - explanations of meanings, word origins, synonyms, translations
Commons : Avocets  - Collection of images, videos, and audio files