Oystercatcher (genus)
| Oystercatcher | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Cliff Oystercatcher ( Haematopus bachmani ) |
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| Systematics | ||||||||||
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| Scientific name of the family | ||||||||||
| Haematopodidae | ||||||||||
| Bonaparte , 1838 | ||||||||||
| Scientific name of the genus | ||||||||||
| Haematopus | ||||||||||
| Linnaeus , 1758 |
The oystercatchers (Haematopodidae, Haematopus ) are a family with only one genus from the order of the plover-like (Charadriiformes). It comprises 12 species that are distributed along the coasts of all continents. Depending on the species, the oystercatchers are either black and white or completely black. Their food is mainly molluscs and annelids .
features
Oystercatchers are large, stocky wading birds . Their plumage is either black and white or completely black. Six species belong to the black and white group, five of the black, and one, the New Zealand oystercatcher, has both black and black and white morphs .
In black and white oystercatchers, the top, head, neck, front chest, and tail are black. The underside is white. There is a white wing band and a white tail band. The individual species are, if they occur in the same distribution area, difficult to distinguish from one another. The best option is to fly open when the shape of the wing band becomes visible. The eye color, which can be yellow or red, also provides a clue.
Black oystercatchers are always plain black without a differently colored plumage region. Since each species is strictly separated from the other geographically, there is no risk of confusion when observing the field. The leg and eye color differs from species to species.
Oystercatchers are 40 to 51 cm tall and weigh between 540 and 780 g. The Eurasian oystercatcher is the smallest and the New Zealand oystercatcher is the largest. As a rule, the black species are larger than the black and white ones. However, this rule is broken by the New Zealand oystercatcher, in which the black and white morph is particularly large.
There is no such thing as a sexual dimorphism that can be used in field ornithology . Females are heavier and larger than males on average and have slightly longer beaks.
Oystercatchers have medium-length, strong legs that allow them to run quickly. The feet are tridactyl . The wings allow a fast and sustained flight, which however does not allow any agile maneuvers. Oystercatchers have salt glands above their eyes , through which they can excrete any sea salt they have absorbed.
The striking beak is 6 to 9.5 cm long. Apart from the gender-specific size difference mentioned, there is also a discrepancy between the inhabitants of sandy beaches and rocky coasts. The oystercatchers that live on sandy beaches tend to have longer and slimmer beaks than those who live on rocky coasts.
distribution and habitat
The oystercatchers are widespread on the coast of the sea, only in the polar regions they are absent. Three species (brown coat, Tierra del Fuego and South American oystercatchers) inhabit the coasts of South America; the cliff oystercatcher is native to the Pacific and the brown-mantled oystercatcher is native to both coasts of North America. The rare black oystercatcher and the Eurasian oystercatcher live on Africa's coasts in northern winter. The Australian and soot oystercatchers occur in Australia, the New Zealand and South Island oystercatchers in New Zealand. The Chatham oystercatcher can only be found in the Chatham Islands south of New Zealand.
In the western Palearctic today, only one species is represented with the Eurasian oystercatcher. The endemic Canary Island oystercatcher , which used to breed in the eastern Canary Islands , has been considered extinct since 1968.
The northern populations of the Eurasian oyster fisherman migrate south or at least to the coasts in winter. There is a train movement from Iceland to the British Isles, from Scandinavia to the North Sea. Most of the other species are resident birds that only migrate briefly.
Sea coasts form the habitat. Some species also breed inland. This applies above all to the Eurasian oystercatcher, who has been breeding far away from the coast in Western Siberia for a long time and which gradually penetrated inland from the European coasts during the 20th century.
Some species are more adapted to sandy beaches, others to rocky coasts. However, there are no outspoken specialists, so that the species can also be found in the other habitat.
Way of life
nutrition
On the coasts, molluscs and worms are the main food for oystercatchers. The cliffs and snails predominate among the inhabitants of the rocky coast, while the many bristles among the inhabitants of the sandy beach . In addition, fleas , crabs and starfish are also captured, as well as very small fish. Earthworms and insect larvae provide food for the inland populations.
Due to the differences in the beak structure, there are often different food preferences between males and females. The beak of the males is usually shorter and more robust, so that it is suitable even for hard-shelled limpets.
In order to capture mussels, oystercatchers prefer to look for those whose shell is slightly open. Here the beak drives through the gap inside, so that the sphincter can be destroyed. Often the mussel shells are also destroyed from the outside with beak blows.
Reproduction
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Oystercatchers live in monogamy , only in the Eurasian species bigamy has occasionally been observed. They are extremely faithful to their location, so they return to the same breeding grounds every year. A hollow is scratched out in the ground as a nest. The male is responsible for the construction and creates several of these nesting hollows, from which the female then selects one.
The clutch comprises one to four, rarely five eggs. Oystercatchers in the northern hemisphere have larger nests than those in the southern hemisphere. The eggs are bluish-gray to beige-gray in color and are covered with irregular, dark spots. Only in the Tierra del Fuego oystercatcher are the eggs greenish, which provides better camouflage on the grass .
The eggs are incubated for 24 to 39 days. The Eurasian species have the shortest breeding period, the black oystercatchers the longest. It is incubated by both partners, but the proportion of the female is slightly larger. In this phase, the male is more concerned with defending the territory. The boys have a gray-brown down dress with dark spots that make them difficult to see in the gravel or sand. They flee the nest , but are still fed by their parents for several weeks - this combination is unique among birds. In total, young people stay with their parents for up to six months; they fledge after 33 to 49 days. A hierarchy is formed among the boys, which ensures that only the strongest boy gets through when there is a shortage of food. Under good conditions, however, several or all of the young can survive.
Systematics
What is striking is the existence of two color variants: the black and white and the black oystercatchers. However, this obvious distinction is not suitable for a classification. The black and white oystercatchers are likely the older variant, and blacks have evolved independently from these twice: once in America and once in the ancient world.
The following division into species is not without controversy. The South Island oystercatcher is sometimes classified as a subspecies of the Eurasian oystercatcher, and the Galapagos oystercatcher is separated from the brown-coat oystercatcher as a separate species.
- South American oystercatcher ( Haematopus ater ), black; Coasts of Peru, Chile and Argentina
- Cliff oystercatcher ( Haematopus bachmani ), black; North American Pacific coast from the Aleutian Islands to Baja California
- Chatham oystercatcher ( Haematopus chathamensis ), black and white; Chatham Islands
- South Island oystercatcher ( Haematopus finschi ), black and white; South Island of New Zealand, wintering areas also on the North Island
- Soot oystercatcher ( Haematopus fuliginosus ), black; Australia, Tasmania
- Tierra del Fuego oystercatcher ( Haematopus leucopodus ), black and white; Patagonia and Falkland Islands
- Australian oystercatcher ( Haematopus longirostris ), black and white; Australia, Tasmania, Moluccas
- Canary Island Oystercatcher ( Haematopus meadewaldoi ), black; Canary Islands, extinct
- Black oystercatcher ( Haematopus moquini ), black; Namibia and South Africa
- Oystercatcher ( Haematopus ostralegus ), black and white; Breeding areas in Europe, West Siberia and East Asia; Wintering areas also in Africa and South Asia
- Brown-mantled oystercatcher ( Haematopus palliatus ), black and white; South America, southern North America
- New Zealand oystercatcher ( Haematopus unicolor ), variable; New Zealand
Threat and protection
Most oystercatcher species are common. In the case of the Eurasian oystercatcher, there is even a steady increase in population with expansion of the range. The rarest living species is the Chatham oystercatcher, which the IUCN status endangered ( endangered lists). In its small area of distribution there is a population of only about 320 birds, which means a tripling of the population in the last twenty years.
The Canary Island oystercatcher is already extinct. This Canary Island bird was not scientifically described until 1888 and was last seen safely in 1913. Since then there have been reports that the bird was seen again - the last time in 1981. However, since coordinated searches in the well-developed area did not provide any evidence, the Canary Island oystercatcher is definitely considered extinct.
Mammals such as cats and rats are a particular threat to island populations if they were not previously native to the islands. Cats on the Chatham Islands are held responsible for the Chatham oyster fisherman's population collapse. The construction of a bridge to Marcus Island for the black oystercatcher had a similar effect .
Sources and further information
Sources cited
Most of the information in this article is taken from the source given under literature; the following sources are also cited:
- ↑ Haematopus chathamensis in the IUCN Red List of Threatened Species . Retrieved November 14, 2007.
- ^ Haematopus meadewaldoi in the IUCN Red List of Endangered Species . Retrieved November 14, 2007.
literature
- Josep del Hoyo et al .: Handbook of the Birds of the World. Volume 3: Hoatzins to Auks. Lynx Edicions, 1996, ISBN 84-87334-20-2 .
