Water treaders (birds)
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Thor's chickens in breeding dress |
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The water treaders ( Phalaropus ) are a genus of arctic snipe birds . The genus consists of two species, the Thor's chicken and the Odin's chicken . Both species can occasionally be observed during their migration on the German North Sea coast , rarely inland.
Compared to most other bird species, the role of the sexes is reversed in the water treaders. The plumage of the females is more colorful than that of the males, the females defend the territory and courtship, the males raise the chicks.
Systematics
The Wassertreter were formerly placed together with the Wilson Wassertreter as a separate family Phalaropodidae (or Phalaropidae) to the plover-like . Here it was assumed that they were related to the family of the avocets . Today, based on morphological and molecular genetic analyzes, there is no doubt that water treaders belong to the family of snipe birds . Due to their different characteristics, however, they are often listed as a separate subfamily Phalaropodinae within the snipe birds. The Odin's chickens used to be separated as a separate genus ( Lobipes ).
For the Wilson water treadmill or American Odinshickchen ( Steganopus tricolor ), which is sometimes assigned to this genus, the assignment to the genus Steganopus is common. In this article, the meanwhile common classification is followed, in which only Odin's chickens and Thor's chickens belong to the genus of water treaders.
features
The common characteristics of the two species
In terms of shape, water treaders resemble sandpipers . But they are not built so clumsily and look more delicate overall. With a body length between 18 and 25 cm, they are also slightly larger than this.
In contrast to many other Limikolen you rarely see treaders wading, but mostly swimming. Especially in winter they are even pronounced deep sea birds that do not need any contact with the land. When swimming you lie very high in the water and move with rhythmic movements of your feet; every movement of the legs is accompanied by a nodding movement of the head. In adaptation to the swimming lifestyle, the feet have formed flaps of skin on the sides of the front toes, as can also be found in the white rail . This similarity led to the scientific name Phalaropus (from the Greek phalaris = coot and pous = foot). The English name phalarope is derived from this.
In the case of water treaders, gorgeous and simple dress differ greatly from one another. In the simple winter dress, females and males look identical and can only be distinguished by the slight differences in size. Towards summer the appearance changes, both sexes get a beautiful colored dress. The coloring of males and females is basically identical or at least very similar, but the females have a significantly more luminous plumage, while it appears dull and pale in the males.
The distinction between the Odin's and Thor's chickens
The two types of water treaders can easily be distinguished from one another in their respective splendid dress. The basic color of the plumage of the chicken is red. The color of the female is somewhat brighter than that of the male. The head sides are white. The female wears a black-brown head cap, the male a light brown head cap. The beak is yellow with a black tip, although the proportion of yellow is greater in the female. The basic color of the plumage of the Odin's chickens in their splendid plumage is gray, whereby this is a slate gray in the female and gray-brown in the male. The underside and throat are white. Noticeable is a spot on the fore neck that reaches up to the cheeks and is orange-red in the female and orange-brown in the male and is smaller.
In the plain dress, however, the two species are very similar. In both species the plumage is then white on the underside of the body and light gray on the top. However, a distinction between the two types is possible through the following features:
- The chick's beak is shorter and significantly stronger than that of the chick's Odin.
- The upper side of the Thor's chickens is a solid gray, and the Odin's chickens are gray with white stripes.
- A wing stripe that is visible in flight is much more pronounced in the Odin chick than in the Thor's chick.
Breeding areas
The breeding areas of the Thoroughbred are on the northern edges of Canada , Alaska and Siberia as well as on Greenland , Iceland and Svalbard . The breeding areas of the Odin's chickens are by no means as high Arctic as the Thor's chickens. Breeding occurrences can also be found on the Faroe Islands , the Shetland Islands , the Orkneys and the Hebrides as well as on the mainland of Norway , Sweden and Finland . The Odin's chick breeds far inland and not always as close to the coast as the Thor's chick.
Reproduction
When the birds return from their winter quarters to their arctic breeding grounds, the females usually arrive earlier. This happens in late May or early June. If the inland waters have not yet thawed at this point, the birds wait a few days at the edge of the ice. Then they look for the banks of the lake, ponds or river valleys. The Thor's chickens always stay close to the coast, while the Odin's chickens can breed a few kilometers inland along the river valleys.
While the Thor's chick only tries to keep competing females away with threatening gestures, the active defense of a territory was found in the Odin's chick . This area comprises an approximately 15 m long shore zone. If the boundaries are exceeded by other females, they are driven away with beak blows. In courtship , the females are also the more active partners. They undertake long courtship flights, to which they rise from the water, shaking, standing in place, shouting with their heads outstretched and then settling down again on the water. This behavior can take hours. If a male is attracted by these efforts, the female sits down on the water in front of him and stretches out flat, almost sinking. If the male does not accept this invitation to mate, the female lifts her neck and head vertically upwards before it assumes the mating position again, until the mating is finally completed.
The nest is initially a simple hollow that is created when a bird presses its breast to the ground and turns in a circle. Only when the eggs are laid does the male pad the hollow with leaves and twigs. Such a nest has a diameter of 6 to 10 cm in the Odin's chick and 8 to 14 cm in the Thor's chick. Usually four eggs are laid, occasionally three. The Thor's chickens lay their eggs between mid-May and mid-July, although the exact time varies from region to region. The earliest oviposition in May takes place in Alaska , the latest in July in Canada , Greenland and Siberia . The Odin's chickens lay their eggs between the beginning of May and the beginning of July; here the breeding populations in Greenland and the British Isles begin, while those in Siberia are the latest.
The chicken's egg is 3.1 x 2.2 cm in size and has an olive-green base color, on which irregular, black-brown spots spread, which become larger towards the poles of the egg. It has a weight of 10.2 g. The chicken egg is slightly smaller (3 x 2.1 cm) and looks very similar; the basic color is more olive brown. The spots are usually also present, but in exceptional cases they may be missing.
Soon after hatching, the females leave their young and further rearing is the responsibility of the males.
Zug and winter quarters
The females often leave the breeding grounds ten days after laying their eggs and are only rarely there when the young are hatched. Correspondingly, the men and women withdraw to winter quarters with a time lag. Males and females also seem to retreat to the breeding areas mostly separately, albeit not with as great a time lag as on their departure.
Although both Thor's and Odin's chickens are found on German North Sea coasts during migration , this is obviously only a fraction of the populations. The chance to see the rare birds is from August to October and in April and May. Most of the water treaders are likely to move across the sea and have no contact with the mainland. But there are also populations that mainly migrate over land: The Canada's Odinshowl rest on the train by tens of thousands on the Great Salt Lake and Mono Lake . The Siberian populations also migrate over land and, for example, stop at the Caspian Sea .
After storms, treaders moving across the sea often end up on the coasts, and in very rare cases also inland.
Outside the breeding season, water treaders are pronounced deep sea birds. Their winter quarters are located off the coasts of South and Central America, Africa and Asia (see distribution maps) and are characterized by a pronounced abundance of plankton, the main food for treaders in winter. Huge distances are covered during the train. The winter quarters of the Thor's chickens are in the plankton-rich seas off the coasts of South America , West Africa and South Africa . The Alaskan Thor's chickens, some of which migrate to Cape Horn , cover a distance of 15,000 km. In contrast, the winter quarters of the Chicken Odin's are scattered over tropical and subtropical seas, but also on the coasts of Patagonia and southern Japan .
In the winter quarters, the birds sometimes swim in huge flocks on the open sea.
food
The diet differs between breeding areas and winter quarters. At sea, water treaders feed almost exclusively on krill and only occasionally on very small fish. They often settle over large schools of fish in order to benefit like them from the abundance of plankton . Thoroughbreds have also been observed to sit on the backs of emerging whales to pick off parasites. Whalers are said to have made use of this in the past and specifically searched for water treaders in order to find whales. Most of the time food is reached by swimming, only immersing the head; You almost never see treaders completely submerged.
In summer, treaders have a different food spectrum because of their inland connection. Here they try to catch water beetles , mosquito larvae , caddis fly larvae , annelid worms and crustaceans living in pools, lakes and rivers . In very shallow waters you can often see treaders turning counterclockwise quickly around their own axis and churning up the bottom sludge in order to then pick up the small animals that have been whirled up. Likewise, they often go through shallow waters in association with other wading birds, for example avocets , in order to benefit from the food that has been startled together.
In addition, water treaders eat flying insects and rarely plant materials in their summer quarters. Plants seem to make up a large part of the food spectrum, especially in young birds.
Enemies
In the arctic breeding areas, gyrfalcons , peregrine falcons , snowy owls and skuas hunt water treaders. Clutches and young birds are mainly eaten by arctic foxes . In order not to make the clutches easy prey, treaders sometimes seek the company of other bird species that are able to aggressively defend their eggs against intruders, for example arctic terns .
In the wintering areas, sharks and other predatory fish try to capture the birds swimming on the surface of the water.
Man uses the great confidence of the treaders for his own purposes. In Canada, some Inuit can easily approach breeding birds in order to kill and eat them. The entire population of Treaders is not endangered by this minor hunt. Both species have a huge range and are considered to be very common overall. A worldwide population of between 1 and 1.9 million individuals is assumed for the Thor's chickens, and even around 3.5 million for the Odin's chickens.
literature
- Stanley Cramp (Ed.): The complete birds of the western palearctic on CD-ROM. Oxford University Press, Oxford 1998, ISBN 0-19-268579-1 (3 CD-ROMs and 1 booklet).
- Bernhard Grzimek (Ed.): Grzimeks Tierleben Volume 8. The Birds 2. dtv, Munich 1980, ISBN 3-423-03205-7 .
- Otto Höhn: The water treaders (Phalaropodidae). Westarp, Hohenwarsleben 2003, ISBN 3-89432-753-7 (Die neue Brehm-Bücherei 349).
- Josep del Hoyo et al. a. (Ed.): Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona 1996, ISBN 84-87334-20-2 .
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