Japanalk
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Japanese alk ( Synthliboramphus wumizusume ) |
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| Synthliboramphus wumizusume | ||||||||||
| ( Temminck , 1836) |
The Japanese alkali ( Synthliboramphus wumizusume ) is a small, North Pacific species from the family of alken birds . It has a very small distribution area. No subspecies are distinguished for this species.
The IUCN classifies this species as endangered ( vulnerable ) because of its small population and the decline in population in recent years .
The type epithet comes from the Japanese term umisuzume (literally: "sea sparrow , sea sparrow ") for alken birds.
The species was named a Natural Monument of Japan on June 26, 1975.
Appearance
The Japanese lalk reaches a body length of 22 centimeters and weighs an average of 164 grams. It is therefore slightly larger than the Craverialk , the smallest alc of the genus Synthliboramphus , to which both species belong. There is no sexual dimorphism .
The Japanese lalk is very similar to the silver lalk . Like this one, he has a dove-gray body top and a black head in a magnificent dress . In contrast to the Silberalk, the black chin does not extend to the front breast, but ends in a straight line at chin level. The underside of the body is brilliant white. The beak is strong and horn-colored. The legs and feet are flesh colored with darker webbed feet. The iris is brown. The most striking feature of the Japanese alkali are the elongated white feathers on the head, which are much more pronounced than those of the silver alkali. They form a hood that extends from the eyes to the end of the neck. The parting, however, is black.
In the plain dress, the elongated white feathers on the head are missing. Instead, the head is consistently black-gray, the chin has an individually varying gray color. Young birds are similar to the adult birds in the plain dress, but have a shorter and slimmer beak.
Distribution area
The Japanese lalk breeds exclusively in the coastal waters of Japan, on some islands off the South Korean coast and possibly in a sea bay near Vladivostok in the Sea of Japan . The species prefers to stay in marine regions with a warm current. This is especially true of the waters around the islands off Kyūshū and the Izu Islands .
Breeding colonies are located on at least twelve islands off the coast of Honshūs and Kyūshūs. The most important breeding area are the Izu Islands, where there are breeding colonies on at least three islands in this chain of islands. It is also assumed that breeding colonies are also located on islands off the South Korean coast. Outside the breeding season, Japanese falcons migrate north and then also reach Sakhalin , the Kuril Islands and waters to the northeast of Hokkaidō .
food
The Japanese lalk only looks for its food in coastal waters during the breeding season. Outside of the breeding season, it stays on the open sea, whereby it can be found all year round in waters that have a surface temperature between 8 and 22 degrees Celsius. On the high seas, the Japanese alkali is usually observed in small groups. So far, very little is known about its food ecology, but it probably lives, similar to the silver alk, on juvenile fish and small sand eels as well as on krill.
Reproduction
The Japanese lalk prefers to breed on small, rocky islands, which naturally do not contain any mammals that could be dangerous to them. The nest holes are usually a few hundred meters from the coast. On some of the islands that serve as breeding colonies, white-faced shearwaters and swinhoe wave -walkers breed in close proximity to the Japanese falcon. It is not yet known whether and to what extent these species compete with one another for nesting sites.
The nest hole is located in crevices in the rock, occasionally in crevices of rock cliffs and in cavities under rocks. Japanese alks also dig burrows under tufts of grass. Compared to the silver alk, which also breeds in burrows, the nesting tubes of Japanese alks are shorter and easier to see. Breeding birds stay near their breeding colonies from February to May. Egg-laying begins in late February and ends in March. The small family groups leave the breeding colonies from April to early May.
The clutch almost always consists of two eggs. These are creamy yellow to reddish brown with brown spots and scribbles. Individual eggs are sometimes very strongly marked. Both parent birds are involved in the incubation of the eggs. They take turns with the hatchery after one to three days. Similar to the silver lalk, the eggs are insensitive to brood interruptions. Clutches have already been observed that were not incubated by the parent birds for five days and from which young birds hatched anyway. The incubation period is 31 days. The young birds usually spend one to two days in the burrow and then leave the breeding colony together with the parent birds. The rearing of young birds, which takes place on the high seas, has not yet been adequately investigated.
Existence and factors threatening the existence
The population of Japanese falcons is estimated to be less than 10,000 individuals. By the end of the 20th century, the Izu Islands had a breeding population of 1,000 birds. The largest colony off the coast of Honshū comprised 120 to 200 breeding birds, while the largest known colony is located off the coast of Kyūshū, where around 3,000 breeding birds occur. Since the islands on which the breeding colonies of the Japanese falcon are located are basically rocky and difficult to access for humans, it cannot be ruled out that there are other, previously unknown breeding colonies.
The stock of Japanese falcons has decreased significantly in the last few decades. Several factors contribute to this. Rats have been introduced onto a number of islands, which, like many other alken birds, has a direct impact on the breeding success of this species. The species is also sensitive to human interference. It also drowns a large number of individuals of this species in fishing nets. Several islands with breeding colonies are used by commercial fishermen as temporary bases of operations, and amateur anglers also use the islands to pursue their leisure activities. The litter that both groups leave behind attracts raven and raven-billed crows and black kites , all of which are predators of Japanese falcons. The people who visit the islands are also a major contributor to the introduction of rats to the islands. Introduced rats, for example, on Koyashima Island, where several hundred birds were still breeding in 1987, rapidly reduced the number of breeding birds to ten individuals. Although attempts were made to prevent rats from spreading by using poisonous bait very soon after the rats first appeared, the number of breeding birds had only marginally recovered by 1993. The Japanese lalk is also one of the alken birds whose eggs are still collected by humans for consumption. The ornithologist Anthony Gaston estimates the number of endangering factors as so large and influential that he considers the Japanese alken to be the species of alken, whose extinction is most likely.
supporting documents
literature
- 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 Japanalk , accessed on October 20, 2010
- ↑ カ ン ム リ ウ ミ ス ズ メ . In: 国 指定 文化 財 等 デ ー タ ベ ー ス (cultural monuments database). Bunka-chō , accessed October 19, 2013 (Japanese).
- ↑ Gaston et al., P. 223
- ↑ Gaston et al., P. 223
- ↑ Gaston et al., P. 225
- ↑ Gaston et al., P. 226
- ↑ Gaston et al., P. 226
- ↑ BirdLife Factsheet on Japanalk , accessed on October 20, 2010
- ↑ Gaston et al., P. 225
- ↑ Gaston et al., P. 225
Web links
- Synthliboramphus wumizusume inthe IUCN Red List of Threatened Species 2013.2. Listed by: BirdLife International, 2012. Retrieved January 14, 2014.