Bartalk
| Bartalk | ||||||||||
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Bartalk |
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Aethia pygmaea | ||||||||||
| ( Gmelin , 1789) |
The bearded talc ( Aethia pygmaea ) is a small species from the cauliflower family . It lives in a small distribution area and only breeds on the Aleutian Islands and some Siberian islands, such as the Commander Islands . Its name refers to the long, white feathers that it wears on its head during the breeding season.
Appearance
The Bartalk reaches a body length of only 18 centimeters and is thus the second smallest alkenvogel; only the dwarf balk is smaller. The weight averages 127 grams. The sexual dimorphism is not very pronounced, males only have a slightly larger beak. On land, bearded barons are a little less agile than the other Aethia species. They typically sit on steep rocky cliffs, resting on their feet and legs, with their upper body leaning forward. Similar to the crested auklet the plumage of the Bartalks flows from a citrus-like odor during the mating season.
In the magnificent dress , the top and bottom of the body are almost uniformly black-gray. Basically, the plumage is darker and less bluish than that of the similar crested lalk. Only the under tail-coverts, the rump and the lower abdomen are light gray to whitish. The head and neck are slightly darker than the rest of the top of the body. The iris is white in adult birds and the eye is larger in proportion to body size than in other Aethia species. During the breeding season, the Bartalk has white, elongated facial feathers on its face, its short beak is strikingly reddish and on its forehead, elongated, dark feathers form a narrow head of feathers that falls slightly forward. The white facial markings are somewhat more pronounced than in the other species of the genus. A narrow white line runs from the eye to the neck, two more white lines meet at a 90 ° angle just above the beak and thus form a lying V.
The plain dress is similar to the magnificent dress, but the slim head of feathers is missing, the white facial feathers are significantly reduced and the beak is more dull. One- and two-year-old, not yet sexually mature dwarf galaxies resemble the adults in their splendid plumage during the summer, but they either have no or only a very short head of feathers. The elongated facial feathers are shorter and have a brownish tinge. The forehead and face are generally a bit brownish, the beak is dull red. Fledglings, on the other hand, resemble the adults in simple dress. However, their irises are still gray and the white, elongated facial feathers are only hinted at. The beak is still black.
There is a possibility of confusion with the Schopfalke. However, bearded barrels are much smaller and do not have an orange, but a red and much smaller beak. On land, the Bartalk is occasionally associated with other species of the genus Aethia . He is particularly noticeable by his meowing calls.
voice
The bearded talk is a very call-happy alkenvogel. It can be heard mostly at night when it is in the breeding colony, or in the early morning when the birds congregate on the high seas near the breeding colony. The most frequent call of the beard talk resembles the short and high and is reminiscent of the plaintive meow of a young cat. The call interval is only a few seconds. Above all, males let out a quick, staccato-like series of two-syllable calls, which can be onomatopically described as follows: bee-deer bee-deer bee-deer bee-deer bideer bideer bideer bidi bidi bidi bidi bidi bidee . During the courtship season, breeding pairs also let this call be heard together, but the call is then less musical. Bar bars that are exposed due to a disturbance emit a loud squeaking sound as an alarm call.
Distribution area
The Bartalk is a common bird in its range, but it lives very hidden. Its main distribution area are the Kuriles and the Aleutians. The waters he prefers to stay on have a surface temperature of nine to twelve degrees Celsius in summer and two to four degrees Celsius in winter. Even outside of the breeding season, they rarely stay more than 10 miles from the coastline.
In Asia, the Bartalk breed sporadically on islands in the north of the Sea of Okhotsk , on the Kuril Islands and the Commander Islands. On the Aleutian island chain, it occurs mainly in the east and breeds, for example, on the Islands of Four Mountains , the Andreanof Islands , the Rat Islands and the Buldir Island . Due to the way of life of the bearded salmon, however, the breeding colonies are very difficult to identify and it was not until 1994, for example, that a breeding colony of bearded salmon was discovered on Kanaga Island . The largest known breeding colony is on Buldir Island, however it is possible that the Krenitzin Islands are home to even larger breeding colonies.
food
The bearded talk usually finds its food in rough water with wave heights of up to ten meters. As a rule, the depth of the water at these points is no more than 100 meters. Usually there are large swarms that gather at these places. So far, no studies have been carried out on the diving depth.
According to current knowledge, the food composition is very similar to that of the dwarf galley. Dominating copepods , cephalopods and other small animals in the marine plankton .
Reproduction
Breeding colony
In contrast to other species of the genus Aethia , the Bearded Talk stays in the breeding colonies mostly during the night. About an hour before dusk, bearded hawks gather in dense schools on the water near the breeding colony. As soon as darkness falls, they fly ashore. There are no conspicuous flight maneuvers such as flying over the colony. Bearded hawks leave the swimming school one at a time and usually fly straight to the entrance of their nesting hole. As with many other nocturnal seabirds, activity in the breeding colony is noticeably reduced on moonlit nights. Presumably because of the then higher risk of predation, fewer calls can be heard and fewer birds can be observed on the earth's surface.
Due to the predominantly nocturnal way of life of the Bartalke, very little is known about its social behavior. Mating bearded hawks stay close together on the water and swim around the partner bird in a circle. Copulation takes place at sea in the early morning hours.
The nesting caves are between three and 250 meters above sea level and are located in crevices, in rubble hills, on cliffs and in natural burrows on steep grass slopes. Overall, the breeding colonies of the bearded barn are found in a wider range of terrain forms than is the case with other Aethia species. The nesting holes are also further apart than is the case with crested and dwarf balk. The nesting density on Buldir Island is only one to three breeding pairs per 100 square meters, even on terrain that offers a particularly large number of nesting opportunities. The burrow is usually so deep that the breeding bird cannot be seen from the surface. In deep rubble heaps, burrows can be up to three feet below the surface, but they are usually closer to the surface.
Egg and young bird
The clutch consists of only one egg. Additional clutches in the event of clutch loss have not yet been observed. The peak of oviposition on Buldir Island falls in the first half of May and is one to three weeks earlier than that of the dwarf and crested lalk, which also breed on this island. The egg is oval to oblong and has a smooth surface.
The parent birds each have two breeding spots , which are fledged again very soon after the young bird hatches. However, non-breeding adult birds and even not yet sexually mature birds occasionally show signs of breeding spots. The breeding season is 35 to 36 days, both parent birds breed equally and usually separate at intervals of 24 hours. In the first days of the young bird is first almost continuously brooded , but then increasingly left alone during the day. During the first ten days, one or even both parent birds spend the night together with the young bird in the breeding cave.
The young birds are also fed at night. The parent birds bring in food once or twice a night, the first time shortly after nightfall, the second time around an hour before dusk. In dense breeding colonies with dwarf and crested hawks, the parent birds also feed their offspring during the day. Basically, the young birds of the bearded reeds develop more slowly than is the case with other Aethia species. This comparatively delayed development is probably related to the restriction of daily food intake that is associated with the predominantly nocturnal feeding. Young birds gain a maximum of 3.5 grams per day. They fledge with an average weight of 106 grams, which is slightly less than the weight of an adult bird. The flies of the young birds have not yet been observed. It will probably take place during the night. It is unusual for alkenbirds that the young birds of the bearded salmon return to the colony and spend the night there. This behavior lasts for some time and is observed for up to six weeks after the point in time at which the breeding birds have largely left the colony.
Reproduction rate and life expectancy
It is estimated that every 100 breeding pairs between 60 and 80 young birds fledge. Arctic foxes and red foxes are among the predators of the bearded barn, but also rats. All three not only kill young birds or eat eggs, but also the adult birds. Their introduction to most of the Aleutian Islands has played a major role in the fact that some of the Aleutian Islands have lost populations or abandoned breeding colonies.
The predators also include the Bering gull and the Kamchatka gull . Peregrine falcons also regularly beat bearded hawks. The mortality rate of adult birds is around 18 percent per year. Life expectancy is about five years.
Duration
Due to their nocturnal way of life, it is very difficult to determine the population of barbeds. The best way to spot these species of breeding birds is to listen for their calls.
In 1993, the United States Fish and Wildlife Service estimated the stock of bearded barons in Alaska at 30,000 individuals. According to estimates by ornithologists Anthony Gaston and Ian Jones, however, the population was certainly much higher and was at least 200,000 to 300,000 individuals in this region. Probably the same number breeds on the Kuril Islands and the Commander Island, but no systematic inventory has been carried out so far.
The bearded barn population suffers greatly when predatory mammals are introduced on islands. The introduction of arctic foxes to some of the Aleutian islands had a significant impact on the population of the species and may also explain why one of the largest breeding colonies is located on Buldir Island. This island is one of the few where arctic foxes were not introduced. The most important population-threatening factor today is the accidental introduction of rats onto islands with breeding colonies of this species. Like many other nocturnal species, the bearded talc is also very strongly attracted to artificial light. Collisions with ships, such as fishing boats, are usually fatal for the Bartalk. Another hazard of this type is the increasing oil pollution of the seas. Buldir Island is close to an important Pacific shipping route and, accordingly, oil-polluted birds have been found here.
supporting documents
literature
- Jonathan Alderfer (Ed.): National Geographic complete Birds of Northamerica. National Geographic, Washington DC 2006, ISBN 0-7922-4175-4 .
- 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 .
Single receipts
- ↑ a b c Gaston et al., P. 262
- ↑ a b c Gaston et al., P. 265
- ↑ Gaston et al., P. 263
- ↑ a b c Gaston et al., P. 267
- ↑ Gaston et al., P. 264
- ↑ Gaston et al., P. 257
- ↑ a b Gaston et al., P. 268
- ↑ Gaston et al., P. 268 and p. 269
- ↑ a b c Gaston et al., P. 269
- ↑ a b Gaston et al., P. 270
Web links
- Aethia pygmaea in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed on December 20 of 2008.