Red-throated divers
| Red-throated divers | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Red-throated diver ( Gavia stellata ) |
||||||||||
| Systematics | ||||||||||
|
||||||||||
| Scientific name | ||||||||||
| Gavia stellata | ||||||||||
| ( Pontoppidan , 1763) |
The red-throated diver ( Gavia stellata ) is the smallest species within the genus of the loons ( Gavia ). It breeds in the tundra and taiga of the Holarctic and can be regularly observed on the migration, especially in autumn, in Central Europe. The red-throated diver differs from other loons in its small body size, its comparatively thin neck and small head, the slightly raised, thin beak and the top of the body, which appears uniformly gray in birds swimming on the water. It is more sociable than other loons and occasionally breeds at a short distance from one another in Western Europe. In the wintering areas and on the migration, large numbers of these birds occasionally gather in places that are particularly rich in food. In exceptional cases, these collections can be up to 500 individuals.
The German name refers to the dark red neck patch. A similar designation can be found e.g. B. in the white-starred bluethroat . The scientific species name stellata also means "with a star".
description
The red-throated diver is the smallest species of the genus. It reaches a body length of 55–67 cm and a wingspan of 91–110 cm. Males weigh an average of 1730 g in summer and are therefore slightly heavier than females, who reach an average of 1480 g in summer.
The species is unmistakable in the magnificent dress . The top of the back and wings are monochrome brown-gray. The head and the sides of the neck are light gray, the back of the neck and the nape of the neck are finely striped in black and white and the front neck is sharply defined rust-red over almost the entire length. The chest, abdomen and the under wing coverts are pure white. The beak is dark gray, the legs are black, and the feet are gray, with the webbed centers being flesh-colored. The iris is pink to red.
In the plain dress , the entire top is finely dashed in white. The neck is predominantly white, there is usually a white area in front of the eye. The beak is pale gray. The youth dress is very similar to the plain dress, but the upper side stripes are more matt and the white areas on the neck in the plain dress are covered in gray. The first downy dress is dark brown overall, but the underside of the body is slightly lighter than the upper side. The second downy dress is similar to the first, but the belly sides are brown-gray.
In simple and youthful dress, red-throated divers are easy to confuse with other loons, but especially with the only slightly larger black-throated diver . Clear defining features of the red-throated diver in comparison to the black-throated diver are the lower beak, which is slightly arched downwards and therefore slightly bent upwards, the head that is usually held slightly upwards, the sides of the neck that are predominantly white in the plain dress, the white area in front of the eye and the missing white flank mark.
Activity patterns and locomotion
Red-throated divers are active all day, especially during the breeding season. They show their territorial behavior especially during the night and in the early morning. The train mostly takes place during the day. Since the breeding waters usually have little or no food, they fish daily in larger lakes or at sea.
The red-throated diver is mostly on the water and is rarely seen in flight. He only goes ashore during the breeding season. He is an excellent swimmer and diver. On the water it holds up relatively high. In the event of danger, it sinks so deep that only a narrow strip of the back, neck and head protrude from the water. The typical movement patterns of the red-throated diver include standing up on the water accompanied by flapping wings.
Red-throated divers usually go completely silent. However, diving accompanied by loud splashing is part of the territory behavior and can also serve as a diversionary maneuver near the nest. You are able to stay underwater for up to 90 seconds. However, they usually reappear on the water surface after 40 to 50 seconds. The diving depth is usually between 2 and 9 meters. However, they can also reach depths of 21 meters. They sleep on the water with their head on their backs and their beak often stuck into their plumage.
Red-throated divers fly up from the water with a short approach. You can also start from land in an emergency. Unlike ducks, they don't land with their feet, but touch the surface of the water with their breasts first. In flight, red-throated divers stretch their feet back, the neck is stretched forward and slightly inclined. The flight is fast and straight, the wing beats fast and quite low. Red-throated divers generally fly individually, paired red-diver also keep some distance from each other in the air.
On land they move awkwardly due to their physique. They either crawl on the ground, pushing each other off with their feet and helping with their wings, or in a vertical posture with their heads lowered to the ground. The boys are able to hop on dry land for longer distances.
Vocalizations
In contrast to other divers, the area calls are usually made in pairs. The male calls arro-arro, the female also calls a longer version, aaarroo-aaarroo. Often times, the couple swims slowly forward while calling. The flight calls are similar to those of geese and can be described as "gak-gak-gak". Warning sound is a creak. Red-throated divers mostly do not make any sounds during winter.
distribution and habitat
The range of the species is circumpolar and includes the tundra and the taiga in Europe , Asia and North America . In Europe, the species occurs in Northern Ireland , Scotland , Iceland , Norway , central and northern Sweden , Finland and northern Russia . Their breeding areas are significantly further north than those of other loons and reach close to the arctic desert. During the breeding season, the species inhabits small still waters up to about 1 hectare in size and flies from there to search for food to neighboring larger lakes or to the seashore. These breeding waters are often only 10 to 15 meters long. Its smallest extent is probably determined by the approach distance required for the flight. The heavily swampy low tundra with a well-developed network of lakes and rivers and the tundra bordering the sea are ideal breeding areas for red-throated divers.
hikes
Red-throated divers are, depending on their geographical location , resident birds , barnacles or short-range migrants . The migration from the breeding area begins in August or September and coincides with the fledgling of the young. In Europe, the species overwinters mainly in the western Baltic Sea , in the North Sea and on the coast of the Atlantic from Norway to the Biscay . The populations of Asia overwinter predominantly on the Black Sea and the Caspian Sea . The species is regularly detected in Central European inland areas, especially in late autumn from mid-October, and more rarely when they migrate home from March to June. Most of the evidence is provided here on larger lakes, but also on rivers and in bays during migration.
nutrition
The red-throated diver hunts its food by diving. As a rule, it does not use the small bodies of water in which it breeds, but rather flies to larger lakes, rivers or the sea. The distance that he overcomes to the food grounds can be ten kilometers. When the young are close to fledging, such feeding flights can take place more than 50 times a day. It prefers shallower waters than other species of the genus and even looks for its food in rapids, where it dives against the current, similar to sawmills . Captured prey is killed by squeezing it with the beak.
The food mainly consists of small fish, frogs , crustaceans , molluscs and probably aquatic insects are also preyed on. The fish that are eaten mainly include young vendace and salmon fish . Char , roach , hazel , bleak , perch and bullhead play a particularly important role . The saltwater fish they eat include herring and other herring species , sandeel , flounder, and cod species .
Reproduction
Due to the temporal appearance of the definitive splendid dress, it is assumed that red-throated divers do not reach sexual maturity until the end of their second, but perhaps not until they are three. They are monogamous birds and since they are often found in pairs in the wintering areas, it can be assumed that the pair relationship lasts for more than one reproductive period.
Breeding grounds and nest
Red-throated divers reach their breeding sites relatively late in the year. Immediately upon arrival, the couple begins to copulate without any actual courtship. Copulation happens on the bank, often on the nest. The lakes that they use as feeding grounds then have sufficiently large ice-free areas and the smaller bodies of water are already completely ice-free. The time of arrival in the breeding area is largely determined by the latitude of the area. In Western Europe and in the north of the European part of Russia, the arrival takes place from the first decade of May until June. In the tundras of Eastern Siberia, however, they do not arrive until the first to second decade of June. Breeding pairs are generally very local and breed repeatedly in the same body of water. If there is a lack of suitable water, they even use previous nest locations.
In contrast to the other loons, red-throated divers usually only have a small area around the nest and look for food in the sea or in larger lakes. In more arctic areas, where suitable breeding sites are scarce, they occasionally breed in small colonies where the nests are a few meters apart. Swimming in pairs with a stretched neck and tilted head or with the front part of the body lifted almost vertically out of the water is part of the area marking. At the same time, people often call in pairs.
The nests are built on the banks of the water or on small islands and consist only of a hollow in the ground with plants. Both parent birds build it. The nest is built on the bank of the water and is often based on a pounded pile of moss, sedge stems or arctophila . Sometimes red-throated divers also process algae, which they fetch from the bottom of the water by diving. On shallow lakes, nests are built in the shallow water zone in the bank vegetation. The red- throated divers then lay the first nesting material between sedge or arctophila pods at a depth of 30 to 80 centimeters and build a nest in the form of a truncated cone that is held in the water by the stems. These nests are very massive, but only protrude five to eight centimeters above the surface of the water. Regardless of the nest location, the nest always has a nest cavity three to five centimeters deep and 18 to 20 centimeters in diameter. Should the water level rise, the birds can slowly move the eggs and nest.
Clutches and young birds
In Scotland and Scandinavia, eggs are laid from early May to early July, and in western Siberia from mid-June. The clutch usually consists of two, only very rarely one or three eggs, which are darkly spotted on an olive-brown to dark-brown background. The eggs are laid 24 to 36 hours apart. Red-throated divers raise a maximum of one brood per year. If the clutch is lost at the beginning of the incubation, red-throated divers are able to lay eggs a second time.
Incubation begins when the first egg is deposited. Both parent birds are involved, but the female has the greater share of the breeding business. The parent bird that is not sitting on the clutch stays nearby on the water or is on another body of water to forage. The incubation period lasts 25–30 days and the chicks do not hatch synchronously. Newly hatched chicks weigh an average of 65 grams. They do not flee from the nest, but are huddled in the nest by their parent birds in their first days of life. When there is insufficient food, the young fight intensely, and often only one young survives. Older chicks are also hoofed outside the nest in suitable places on the bank, where the parent birds sometimes carry them on their backs. During the first two weeks of life, one of the two parent birds is constantly with the chicks. Older chicks hide in the bank vegetation or under an overhanging stretch of bank when the parent birds are absent. In the event of disturbances, the parents can move away, e.g. B. to the neighboring lake, and then call intensely. The boys can then jump several hundred meters across the country, guided by the calls.
The chicks are initially unable to eat independently, although they can swim and dive from the first day of life. They are fed by both parent birds. They beg for food by swimming in front of the parent bird and pecking at the breast and beak. From the age of four to six weeks they can eat independently, although the small breeding lakes offer little food. The parents fetch the feed from larger lakes or the sea, up to 50 times a day. The family group leaves the hatchery as soon as the young can fly (see also above), but the young continue to be fed until the family dissolves after about eight to ten weeks.
Negative effects on the breeding process
Skuas and great gulls such as herring and ice gulls often destroy clutches of red-throated divers. This usually only happens when they find an abandoned clutch. The red-throated diver sitting on the nest is usually not bothered by these bird species. For this reason, it plays a major role in the breeding success of this species how much red-throated divers are disturbed, for example by being close to humans during the breeding process. Red-throated divers who are disturbed to leave their clutch do not return to the nest for a long time, which increases the risk that the clutch will be destroyed during this time.
Red-throated divers and humans
The red-throated diver is hunted as wild fowl in some regions of its range. As a rule, however, it is not hunted specifically; it is only occasionally shot together with other birds.
The neck and stomach part of star divers used to be processed in the fashion industry. It was used to work on women's hats or light collars and appliqués. This practice has now been completely discontinued.
Existence and endangerment
The world population was roughly estimated by the IUCN in 2002 at 490,000 to 1.5 million individuals and is considered safe. The European breeding population is about 32,000 to 92,000 pairs, of which more than 50% live in the territory of European Russia. There are between 5,000 and 30,000 breeding pairs in Greenland. The European winter population ranges from 51,000 to 115,000 individuals.
In Europe, there are currently only declines in parts of Fennoscandia. Otherwise the population is stable or, as in Great Britain, is even increasing slightly. Compared to the situation at the beginning of the 19th century, however, the breeding population is significantly lower today; the species has not recovered any more despite the reduction in hunting. The main causes of danger are the deterioration of habitat due to acidification, eutrophication and pollution, as well as the construction of water bodies and disturbances during the breeding season.
supporting documents
Individual evidence
- ↑ a b c d Il'ičev & Flint, 1985, p. 214.
- ↑ Viktor Wember: The names of the birds in Europe - meaning of the German and scientific names , Aula-Verlag, Wiebelsheim 2007, ISBN 978-3-89104-709-5 , p. 66.
- ↑ Il'ičev & Flint, 1985, pp 208th
- ↑ a b Il'ičev & Flint, 1985, p. 207.
- ↑ a b Il'ičev & Flint, 1985, p. 210.
- ↑ a b c d Il'ičev & Flint, 1985, p. 211.
- ↑ a b Il'ičev & Flint, 1985, p. 212.
- ↑ a b c d Il'ičev & Flint, 1985, p. 213.
- ↑ Bauer et al., P. 196.
literature
- Hans-Günther Bauer, Einhard Bezzel and Wolfgang Fiedler (eds.): The compendium of birds in Central Europe: Everything about biology, endangerment and protection. Volume 1: Nonpasseriformes - non-sparrow birds. Aula-Verlag Wiebelsheim, Wiesbaden 2005, ISBN 3-89104-647-2 .
- Einhard Bezzel: Compendium of the birds of Central Europe. Nonpasseriformes - non-singing birds . Aula, Wiesbaden, 1985: pp. 11-13. ISBN 3-89104-424-0
- VD Il'ičev & VE Flint (eds.): Handbook of birds of the Soviet Union - Volume 1: History of exploration, Gaviiformes, Podicipediformes, Procellariiformes . Aula Verlag, Wiesbaden 1985, ISBN 3-89104-414-3
- Lars Svensson , Peter J. Grant, Killian Mullarney, Dan Zetterström: The new cosmos bird guide. Kosmos, Stuttgart 1999, ISBN 3-440-07720-9 , p. 12 f.
Web links
- Gavia stellata in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed October 13 of 2008.
- Videos, photos and sound recordings of Gavia stellata in the Internet Bird Collection
- [1] Description on soortenbank.nl with call examples
- Red-throated diver's feathers