Synthliboramphus
| Synthliboramphus | ||||||||
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Lummenalk ( Synthliboramphus hypoleucus ) |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Synthliboramphus | ||||||||
| Brandt , 1837 |
Synthliboramphus is a genus from the cauliflower family. This genus includes four recent species, all of which are native to the North Pacific. Three of the species are classified as endangered ( vulnerable )by the IUCN . Only the silver lime is considered safe. In Canada, however, the species is listed as potentially threatened, as the breeding success of this species is severely impaired by introduced mammals.
Appearance
The species of the genus Synthliboramphus are very small, rather slender alken birds with black-and-white to gray-brown-white plumage. The smallest species is the Craverialk with a body length of 21 centimeters. The largest alken bird from this genus is the silver alk , which reaches a body length of 25 centimeters. Both the sexual dimorphism and the seasonal difference are only slightly pronounced in the plumage of all four species. The biggest seasonal difference in plumage is found in the Japanese alk, which in its magnificent dress has noticeably elongated white head feathers that are largely absent in the plain dress.
Distribution area
The distribution area of the Synthliboramphus alks extends from Baja California along the North American west coast over the Gulf of Alaska to the coast of South Korea.
The Craverialk belongs to the species with a distribution area reaching far to the south. The only proven breeding sites of this species are on the coast of the Gulf of California , a 160,000 km² tributary sea to the Pacific between Mexico and the Baja California peninsula . Other breeding colonies may be found on the Pacific coast of Baja California. Outside of the breeding season, the Craverialk can be found in subtropical waters off the west coast of Mexico and the south of the US state of California. It then occurs as far as the coast of Monterey , where it can be observed regularly from mid-July to mid-October.
The breeding areas of the Lummenalk are only marginally further north and can be found on the Californian Channel Islands , on Guadalupe and on other islands off the coast of Lower California . Outside the breeding season it lives in the open sea, north to the British Columbia area .
The Silberalk has a very large distribution area. Its breeding colonies are located on islands between the 52nd and 60th degrees of north latitude in the eastern Pacific and between the 35th and 62nd degrees of north latitude on the Asian coast. Silver ox are common birds off the Aleutian Islands and in the Gulf of Alaska , among others . They can also be seen in large numbers in southeast Alaska and off Haida Gwaii . Even if some silver hawks remain in their breeding area during the winter months, they usually migrate further south during this time. They can be observed off the coast of the US state of Oregon, for example, between October and November and then again in March. Numerous silver owls overwinter off the California coast, where the birds arrive at the end of October. On the Asian side, silver hawks migrate to Taiwan. Most of them are off the Japanese and Korean coasts.
The Japanalk only breeds on some islands in the coastal waters of Japan, South Korea and possibly a bay near Vladivostok in the Sea of Japan . The species prefers to stay in marine regions with a warm current. This is especially true for the islands off Kyushu and the Izu Islands .
food
The feeding habits of the Synthliboramphus species have been studied to varying degrees. Well known are those of the silver hawks. These look for their food in schools of up to fifty individuals who dive more or less simultaneously. They are often associated with swarms of other bird species, typically are in swarm near Silberalken also kittiwakes , Nashornalken and other krill-eating seabird species. Silver hawks are usually found on the edge of such swarms. They attract seagulls because their dives drive sand eels and other schooling fish to the surface. The diving depth of silver hawks has not yet been explored. However, they are usually less than 45 seconds under water, which suggests a diving depth of ten to twenty meters. Their main diet is young sand eels and krill as well as young fish of other species. Young herrings are also among the fish that are fed to their nestlings by adult silver hawks. The feeding habits of the Japanese alken have so far been little researched, but they probably feed in a similar way to silver alks. In contrast to silver hawks, guillemots are seldom observed in schools; they too mostly eat very young fish. Craverialks prefer to eat fish with a body length of four to seven centimeters. Their preferred food are juvenile fish of the genus Sebastes , herring and Benthosema panamense .
Reproduction
All four species breed in burrows. These are located in crevices or niches in the rock or in caves, some of which you have dug yourself, under tufts of grass or bushes. All species are colony breeders, but their nests are somewhat further apart due to their requirements for the respective location. Similar to the Cepphus alks, which find their food near their breeding colonies, the Synthliboramphus species lay two eggs. The incubation period is 30 to 31 days, both parent birds are involved in the incubation of the eggs. The young birds only stay in the nesting cavity for a day or two and then leave the breeding colony with their parent birds. They are raised on the high seas. Guillemots raised in captivity show a clear change in behavior 48 hours after hatching. While they remain calm in their nest until about this point, they then show very agile behavior and run around excitedly in their nesting boxes. At this point in time in the wild, their parent birds take them out to sea. By then you are already very good swimmers and able to climb over obstacles on land. Their further development on the high seas has not yet been documented. Guillemot birds reared in captivity showed only very slow weight gain and a change in their plumage only on the 17th day of life.
Duration
The stock situation of the Synthliboramphus alken is inconsistent.
With a population of one to two million individuals, the silver alk is the most common Synthliboramphus species. The craverialk population in the Gulf of California is estimated to be 5,000 pairs. Together with the non-breeding birds, the total worldwide population is estimated at 15,000 to 20,000 individuals. The population of the hard-to-count Lummenalks is estimated to be similarly large. The Japanese alkali is the rarest species of the genus with a population of fewer than 10,000 individuals. Since the islands on which the breeding colonies of the Japanese alke are located are generally rocky and difficult to access, it cannot be ruled out that there are several other, previously unknown breeding colonies. However, the population has decreased significantly in the last few decades. The ornithologist Anthony Gaston estimates the number of endangering factors for this species to be so great and influential that he considers the Japanese alk to be the species whose extinction is most likely.
The factors that endanger the survival of the individual species are very similar. Introduced mammals - rats, raccoons, cats, and foxes - contribute significantly to populations of all four species. Introduced rats, for example, have reduced the number of breeding birds to ten individuals in the Japanalk on Koyashima Island, where several hundred birds were still breeding in 1987. Although attempts were made to prevent the spread of rats by using poisonous bait very soon after the first rats were discovered, the number of breeding birds had only marginally recovered by 1993. The disappearance of guillemotion on individual islands off Baja California and the significant decline in the number of breeding birds on other islands is attributed to the effects of cats. In the case of individual species of the genus Synthliboramphus , disturbances by humans are also among the factors threatening the population. In the Japanesealk, for example, several islands with breeding colonies are used by commercial fishermen as a temporary base of operations. Hobby anglers also use the islands to pursue their hobby. The litter that both groups leave behind attracts raven and raven-billed crows, as well as black kites , which also prey on Japanese falcons. The Japanese lalk is also one of the alken birds whose eggs are still collected by humans for consumption. Guillemots are also attracted to ship lights and therefore collide with ships more often. Anchoring ships near breeding colonies has resulted in significant disruptions in breeding activities. Like many other alkenbirds, Synthliboramphus species often drown in fishing nets.
species
The following species belong to the genus Synthliboramphus :
- Silberalk ( S. antiquus )
- Japanalk ( S. wumizusume )
- Craverialk ( S. craveri )
- Lummenalk ( S. hypoleucus )
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 et al. 1998, ISBN 0-19-854032-9 .
Single receipts
- ↑ BirdLife Factsheet on the Silberalk , accessed on October 19, 2010
- ↑ Alderfer, p. 289
- ↑ Gaston et al., P. 211
- ↑ BirdLife factsheet on the Craverialk , accessed on October 18, 2010
- ↑ Gaston et al., P. 216
- ↑ Gaston et al., P. 216
- ↑ Gaston et al., P. 218
- ↑ Gaston et al., S: 219
- ↑ BirdLife factsheet on the Craverialk , accessed on October 18, 2010
- ↑ Gaston et al. P. 210
- ↑ BirdLife Factsheet on the Silberalk , accessed on October 19, 2010
- ↑ BirdLife Factsheet on Japanalk , accessed on October 20, 2010
- ↑ Gaston et al., P. 225
- ↑ Gaston et al., P. 225
- ↑ Gaston et al., P. 225
- ↑ Gaston et al., P. 207 and p. 208
