Short-beaked lalk
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Short-beaked lalk ( Brachyramphus brevirostris ) |
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| Brachyramphus brevirostris | ||||||||||
| ( Vigors , 1829) |
The short-beaked lalk ( Brachyramphus brevirostris ) is a small alkenbird of the northern Pacific . Unlike other alks, the species does not breed in colonies by the sea, but on isolated mountain tops above the tree line. Not much is known about the short-beaked lalk. Since it is so rare, an intensive examination is not carried out for reasons of protection. The English name, Kittlitz's Murrelet , refers to the German zoologist Heinrich von Kittlitz , who was the first to catch an animal of this type.
The short-beaked lalk was classified as critically endangered by the IUCN in 2012 , but in 2014 it was assigned to the significantly lower category near threatened , which corresponds to the "warning list" in Germany. The information on dramatic population declines in the last few decades has been seriously questioned by recent studies.
Appearance
The Kurzschnabelalk reaches a length of 25 centimeters and weighs an average of 241 grams. This makes it one of the very small alken birds. It differs from other alkenbirds in its small size, relatively slim build and relatively long, pointed wings. However, during the moult it can easily be mistaken for the Marmelalk . Just like the Marmelalk, it has extremely short legs that start very far back on the body. Because of this, short-billed eagles move very clumsily on land. Swimming animals have their heads pointing upwards, their tails sticking out of the water and pointing upwards as well.
During the breeding season it wears gray-brown plumage that camouflages it well. This magnificent dress is spotted gray-brown and white on the top. The throat and chest also show a pattern of spots, which gradually merges on the underbust into the white of the abdomen and the underside of the tail. The plain dress is black and white and is reminiscent of the plain dress of Lummen , but the short-beaked is a bit gray on the upper side of the body. The black of the parting extends to the nape of the neck. The sides of the neck are white. Similar to the Marmelalk, some birds keep their plain dress during the summer. These are probably not yet sexually mature birds.
The beak is smaller than that of the Marmelalke from the same genus. Overall, it is slightly more curved and, due to the forward-facing springs, looks even smaller than it actually is.
The plumage of young birds is similar to the plain dress of adult birds, but shows a fine gray transverse markings on the underside of the body during autumn. Later in winter they can hardly be distinguished from adult birds in simple dress.
The call repertoire of the short-beaked talk includes a gentle, grunting urr and a sharp quack reminiscent of ducks .
distribution
The short-beaked lalk occurs on the North American and East Asian coasts of the northern Pacific, subspecies are not described. In its area of distribution, the surface water reaches a temperature of two to ten degrees in summer and one to eight degrees in winter. Similar to the Marmelalk, the short-beaked lalk stays near the coast and looks for food mainly in bays and fjords. The two types are often associated.
The North American distribution area extends from LeConte Bay in southeast Alaska over Prince William Sound , the Kenai Peninsula , Kodiak Island and Afognak Island to the Bering Strait and the Aleutian Islands . Short-billed falcons that breed on the coast of the Bering Strait have to migrate south after the breeding season because these waters freeze over. Otherwise, however, only a few southward migratory movements of North American birds can be observed. Individual wanderers, however, have been observed as far as southern British Columbia and the coasts of the US states of Washington and California.
In Siberia, the short-beaked lalk occurs mainly in the north of the Sea of Okhotsk . However, breeding birds can also be found on the coasts of the Chukchi Peninsula and on Karaginsky . Occasionally, however, short-billed falcons are also observed significantly further south, for example on the Kuriles and Hokkaido . Short-billed falcons have also been observed significantly further north. It is possible that the species breeds on Wrangel Island as well .
food
The diet of the short-billed falcon has not yet been studied in detail. Due to the very small beak, it is assumed that the short-beaked lalk only lives on very small fish and zooplankton. The chicks are also fed small fish such as sand eels . These fish are usually carried across the beak by the parent birds.
Reproduction
Like the marmelalk and the Kamchatka marmelalk , the short-beaked falcon show a breeding behavior that differs significantly from that of other alken birds. They do not nest in colonies, but individually. Their nest is on average 20.5 kilometers from the coast. Extreme nesting sites are found at a distance of 75 kilometers from the nearest ocean.
The nest location is often above the tree line. The nest is nothing more than a simple, unpadded depression in the ground and is usually on a slope sloping southwards, often closely adjacent to a snow surface. The first nests were found by people from the indigenous peoples of the breeding area. Their description that short-beaked falcons usually breed in the immediate vicinity of mountain peaks initially met with skepticism among ornithologists.
Short-billed falcons, like most alken birds, only lay one egg. The eggs are elliptical in shape and pale olive green, bluish green or yellowish in color. Regardless of the basic color, they have irregular brown spots. Egg-laying takes place in southeast Alaska from mid-May to mid-June. On the other hand, on the Alëuts and on the coasts of the Bering Sea, oviposition occurs in the period from early to mid-June. The time at which the eggs are laid seems to be influenced by the time at which the ice breaks up and the snowmelt starts even at those altitudes where short-beaked falcons breed.
Both parent birds are involved in the brood. The length of the breeding season is not known. The nestling period is 25 days. As an adaptation to the extreme northern location of the breeding area, the chicks only lose their down feathers 12 hours before the actual moult. It has not yet been sufficiently clarified whether chicks fly on their way to the sea or swim to the help of rivers. In any case, parental care ends with the moult. No young animal has been seen at sea together with an adult.
Duration
The short-billed lalk only occurs in large numbers in a few, widely spaced places. The most famous are Glacier Bay National Park and Prince William Sound . The population of short-billed falcons is probably only between 20,000 and 50,000 individuals. 70 percent occur in Alaska. The IUCN classifies the species as critically endangered because populations have declined by 80 to 90 percent, especially in the last 15 years. Above all, the loss of breeding areas due to melting glaciers and marine pollution from ships and oil production facilities have a negative impact. The Exxon Valdez may have killed up to 10 percent of the world's population.
supporting documents
literature
- Anthony J. Gaston, Ian L. Jones: The Auks (= Bird Families of the World. Vol. 4 (recte 5)). Oxford University Press, Oxford u. a. 1998, ISBN 0-19-854032-9 .
- Richard Sale: A Complete Guide to Arctic Wildlife. Christopher Helm, London 2006, ISBN 0-7136-7039-8 .
Web links
- Brachyramphus brevirostris in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 30 of 2009.
Single receipts
- ↑ BirdLife Factsheet , accessed October 15, 2010
- ↑ Gaston et al., P. 200
- ↑ Gaston et al., P. 201
- ↑ Sale, p. 270
- ↑ Gaston et al., P. 201
- ↑ Gaston et al., P. 201
- ↑ Gaston et al., P. 203
- ↑ Gaston et al., P. 203
- ↑ Gaston et al., P. 204
- ↑ Gaston et al., P. 204
- ↑ BirdLife Factsheet , accessed October 15, 2010
- ↑ Gaston et al., P. 201