Rhinoceros lalk
| Rhinoceros lalk | ||||||||||
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Rhinoceros lalk ( Cerorhinca monocerata ) |
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| Systematics | ||||||||||
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| Scientific name of the genus | ||||||||||
| Cerorhinca | ||||||||||
| Bonaparte , 1828 | ||||||||||
| Scientific name of the species | ||||||||||
| Cerorhinca monocerata | ||||||||||
| ( Pallas , 1811) |
The rhinoceros auklet ( Cerorhinca monocerata ) is a kind from the family of Auks that breeds along with other sea birds in large colonies. The name rhinoceros lalk is derived from a horn-like bulge on the beak that is only visible during the breeding season.
The rhinoceros balk is the only recent member of the genus Cerorhinca . No subspecies are recognized for this species.
In 2016, the population of the rhino alke was classified in the IUCN Red List of Threatened Species as “ Least Concern (LC) ” = “not endangered”.
Appearance
The rhinoceros lalk is a medium-sized alken bird and reaches a body length of 35 centimeters. At an average of 510 grams, the males are slightly heavier than the females, who weigh an average of 457 grams. Their shape is somewhat reminiscent of puffins , but this species has a more rounded head and, above all, a more powerful beak. Rhinoceros rarely adopt an upright posture on land, but rather rest on their legs with their upper body almost horizontal. Occasionally they also touch the ground with the sternum . The iris is bright yellow, the legs and toes are yellow with more brown webbed feet and black toenails.
In the splendid dress , the rhinoceros aalk is sooty brown-gray on the upper side of the body, the throat, sides of the neck and brood are slightly lightened. The belly is whitish. Similar to the Aethia species, the rhinoceros lalk also has elongated white facial feathers. They run in one line from the eye to the nape of the neck, a second line of elongated facial feathers runs from the base of the beak towards the mantle. The beak is orange. The horn-like bulge lies over the nostrils and can be up to 25 millimeters long. The plain dress is similar to the magnificent dress, but it lacks the beak bulge and the elongated white facial feathers. The beak is a dull brown, the belly is darker in color than in the magnificent dress.
Young birds resemble adult rhinoceros in a plain dress, but their beak is a little shorter and slimmer. The top of the body is dark black-brown with dark gray head sides, the throat is slightly lightened and a sharp line separates the darker upper chest from the white chest and the white belly. The latter has individual gray feathers that form an indistinct transverse drawing.
voice
Rhinoceros have a very extensive repertoire of calls. During the breeding season, calls can be heard in the colonies at night that are vaguely reminiscent of the mooing of cows. The repertoire also includes short, barking calls and individual sounds that can be heard from the nesting structures. A harsh, squeaky call is emitted by birds on the high seas who feel threatened.
The call frequency in the breeding colonies is very high. It is believed that there is also the pairing of birds that are not yet breeding and that this is why so many calls can be heard.
Distribution area
The distribution area of the rhinoceros is the North Pacific. It breeds on islands from the Aleutian Islands to the north of Honshū and on the east coast of the Pacific to the coast of California . However , the species is only found sporadically between the Alaska Peninsula and northern Japan.
During the breeding season, rhinoceros falcons are mainly observed in waters with a surface temperature between five and 16 degrees Celsius. In Asia there is one of the large breeding colony on the Teuri Island (天 売 島), which lies off the west coast of Hokkaidō . More than 350,000 individuals breed there. The other colonies on the Asian coast of the Pacific are much smaller and comprise only a few thousand breeding birds. They are located on islands off the Korean Peninsula , off the Primorye , Sakhalin and southern Kuril Islands . On the North American coast, most of the breeding colonies are located off the coastline of the US state of Washington, British Columbia and southeastern Alaska. The southernmost breeding colonies include those on Farallon Islands , which are 43 kilometers west of Golden Gate , and those on Año Nuevo Island .
After the breeding season, rhinoceros falcons usually leave the region of their breeding colonies and move further south. Rhinoceros falcons can be seen off the west coast of Vancouver Island , mainly from August to September. Much of the Northeast Pacific Rhinoceros hibernates off the California coastline. On the west coast of the Pacific, the migratory movement of the rhino falcon is not quite as pronounced. In the winter months, rhinoceros falcons are observed off the coast of Tokyo and they occasionally reach Kyushu and the coast of northeast China.
food
Rhinoceros mainly eat fish such as sand eels or young herrings , but also crustaceans and squids . During their foraging, they mainly stay in the region of continental shelves . Generally they look for their food far away from the coast and only during the breeding season can they be seen near the coast. Exceptions are bays or sounds like Puget Sound or Monterey Bay , where they can also be seen outside of the breeding season. They prefer waters with a depth of less than 15 meters and find their food more in the middle water depth and not on the bottom of the water. The diving depth can be up to 60 meters, but they usually find their food at a depth of ten meters. The dive length in shallow waters is 45 seconds, with an average of almost 11 seconds between dives. They only look for food during the day and at dusk. While foraging, they are often associated with schools of other seabirds, including silver hawks , guillemots , kittiwakes , Pacific divers and cormorants . There is no evidence that rhino hawks cooperate in foraging for food, for example by specifically rounding up schools of fish.
Reproduction
Colonies
Rhinoceros prefer to breed on islands that cover several thousand hectares and that are forested or have thick grass cover. The birds return to the breeding colonies off the California and Japanese coasts as early as February, on the coast of Washington and British Columbia, however, not until March and in Alaska in April. As soon as the young birds have fledged, the number of rhinoceros in the breeding colonies decreases significantly. However, individual birds return to their burrows several weeks after the last young birds have fled.
Rhinoceros return to the large breeding colonies mostly during the night. In some areas, however, they are also active at twilight and there are isolated breeding colonies that the rhino hawks visit during the day. In the breeding colonies, which are only visited by the rhinoceros at night, they gather four hours before they land there in dense swarms on the waters near the colony. With the onset of sunset, the first rhino hawks begin to circle over the colonies and land there about 60 to 90 minutes after sunset. In the morning, the first breeding birds leave the colony two hours before sunrise, with most birds using the last hour before sunrise. On foggy days, however, individual birds remain in the colonies even after dusk.
Aggressive behavior between the rhinoceros is more common in the colonies. A narrow path to the burrow is defended, and usually a slightly elevated place near the burrow, which the rhino hawks use for take-off. Aggressive behavior includes chasing after another bird with its wings raised. Occasionally they grab each other by the beaks and try to scratch the other bird's belly with their feet. Young birds are occasionally killed by other rhinoceros when they take refuge in the wrong burrow. Occasionally they nest in the same colonies as the Aleutian aalk or yellow cappole . Occasionally, rhinoceros deliberately break the eggs of Aleutian alks or even kill their young birds. On the Farallon Islands, on the other hand, they are driven away by the yellow poppies. On the Japanese island of Teuri, rhinoceros are also ousting Japanese gulls .
Nesting tube
Rhinoceros breed in burrows that are between one and five meters deep and lie under grass, low shrubbery or tree roots. On Protection Island, an island off the coast of Washington, the burrows are usually more than ten meters above sea level. There is a building on two square meters. In the breeding colonies, which are located on islands off British Columbia and southeastern Alaska, burrows can be found up to two hundred meters above sea level. There they lie in the woods, the ground is only sparsely vegetated. Rhinoceros use bills and claws to dig their burrows, and both parent birds are involved in the digging. For every night they dig, they lengthen the nest tube by up to eighteen centimeters.
Clutch and young bird
The time of oviposition depends on the geographical latitude. In the breeding colonies off the coast of California, the peak of oviposition falls in mid-April, off Alaska, however, between late May and early June. However, the prevailing weather conditions affect how eggs are laid. The peak of oviposition on the Japanese island of Teuri differed in two observation years from May 25th to June 8th. The cause of this shift was a persistent snow cover. As is typical for many alkenbirds, rhinoceros only lay one egg. This is elliptical, whitish and has faint lilac or purple spots. A freshly laid egg weighs an average of 77 grams, which is around 16 percent of the body mass of an adult rhinoceros balk. The brood begins immediately after oviposition, but is occasionally interrupted for up to four days. This has no effect on the hatching rate. Both parent birds are involved in the brood, and they usually separate at intervals of 24 hours. Both parent birds each have two breeding spots . The average incubation period is 45 days.
Newly hatched rhinoceros are covered with thick down and can walk immediately. They weigh an average of 54.5 grams. They can regulate their body temperature themselves from the second day of life. They already show hints of the beak bulge on the beak. They are fed by both parent birds during the night, which each provide an average of 36.3 grams of food. Due to the fact that rhinoceros only look for food during the day and only return to the breeding colony at night, they usually only receive food twice during the night. The daily weight gain between the tenth and fortieth day of life is between 5.2 and 7.1 grams per day. At the time of fledgling they usually weigh between 266 and 384 grams. The young birds occasionally come to the entrance of the nest tube during the night, but remain in the actual nesting chamber during the day. They usually leave the breeding colony around their 50th day of life. They reach the high seas when the young birds either run to the sea or flutter. Their plumage is completely present at this point, but they usually still have a few down feathers on the neck and torso. The wing length corresponds to about 83 to 86 percent of the adult birds at the time.
Reproductive success and life expectancy
The breeding success of rhinoceros is impaired in some cases considerably when humans are in the breeding colonies. Therefore, only very limited data are available. On Protection Island, in the parts of the breeding colony where observers were present, there were only 28 to 30 fledglings for every 100 clutches. The breeding success in the undisturbed parts of the breeding colony is estimated at 81 to 91 fledgling young birds per 100 clutches. Similar estimates are also available for other islands. Contrary to this, on Triangle Island, an island off the coast of British Columbia, the reproductive success was significantly lower and is estimated at only 32 to 62 percent.
The predators of the rhinoceros hawks include bald eagles , great horned owls, and peregrine falcons . On the North American coasts, bald eagles gather regularly at dusk to hunt alken birds, including hornbills. Peregrine falcons are also regularly successful in hunting alkenbirds. On an island off the coast of the US state of Washington, at least 69 of 300 breeding alken birds died from peregrine falcons. Also Kleptoparasitism can be observed in Nashornalkenkolonien regularly. On the Japanese island of Teuri, both Japanese gulls and Kamchatka gulls show an activity peak after dusk during the breeding season of the rhinoceros. They then hunt the returning rhinoceros for food. The risk of kleptoparasitism decreases as it gets darker. However, the risk of injury to the returning rhinoceros is significantly higher because they can no longer see obstacles. According to ornithologists Anthony J. Gaston and Ian L. Jones, both kleptoparasitism and predator hazard are the reasons why rhinoceros only return to their breeding colonies at night.
The mortality rate of rhinoceros has so far only inadequately been determined. However, ringed birds that were at least fifteen years old were caught.
Duration
The IUCN estimates the population to be at least 1.3 million individuals. The ornithologists Anthony Gaston and Ian Jones point out in their monograph on the alkenbirds, however, that with this type of population estimation there is a great risk of estimation, since rhino horns are very difficult to count even in their breeding colonies. Accordingly, population trends for this species are difficult to determine. On the Japanese island of Teuri, however, the populations increased significantly between 1950 and 1970, several smaller breeding colonies on other Japanese islands showed significant increases between the 1970s and 1980s. On the North American coast, populations observed off the coast of Oregon, California, and British Columbia have also shown increases since the 1970s. The removal of sheep and rabbits from some islands off the US coast has contributed to the fact that populations here have also risen sharply. One of the islands in the southeast of the Farallon Islands was repopulated in the 1970s after rabbits were removed from rhinoceros. The rabbit burrows there were used by the rhino as breeding caves, which led to a doubling of the population between 1973 and 1977. Only in the 1980s did the population stabilize at a high level. On Destruction Island, a small island off the coast of the US state of Washington, the population increased from 3,500 breeding pairs in 1969 to 28,000 breeding pairs in 1974 after the removal of sheep. However, the trend is different on Haida Gwaii , the only island group on which there is a proven negative population trend. Introduced raccoons reproduce the rhino hawks there, and rats also contribute to the decline in the population on at least one island. In the Aleutian Islands and on islands in the Gulf of Alaska , introduced foxes are believed to have had negative effects on the population, but this is not precisely documented.
Fossil history
The genus Cerorhinca developed in the North Pacific, probably in the middle to late Miocene . Although only one species is found today, the genus was originally more species-rich and more widespread. Fossil findings are available from Baja California , among other places , which is significantly more southern than today's southern limit of distribution on the North American coast. There are three prehistoric species:
- Cerorhinca dubia , (Late Miocene, found in San Barbara County, USA)
- Cerorhinca minor (Late Miocene / Early Pliocene, found on Cedros Island, Mexico)
- Cerorhinca reai (Late Miocene, find near San Diego, USA)
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 .
Individual evidence
- ↑ Cerorhinca monocerata in the endangered Red List species the IUCN 2016 Posted by: BirdLife International, 2016. Accessed January 29, 2018th
- ↑ BirdLife Factsheet on the Rhinoceros Walk , accessed October 30, 2010
- ↑ Gaston et al., P. 271
- ↑ Gaston et al., P. 270
- ↑ Gaston et al., P. 275
- ↑ Gaston et al., P. 279
- ↑ Gaston et al., P. 271 and p. 272
- ↑ Gaston et al., P. 275
- ↑ Gaston et al., P. 272
- ↑ Gaston et al., P. 274
- ↑ Gaston et al., P. 272
- ↑ Gaston et al., P. 275
- ↑ Gaston et al., P. 275
- ↑ Gaston et al., Pp. 275 to 277
- ↑ Gaston et al., P. 279
- ↑ Gaston et al., P. 277
- ↑ Gaston et al., P. 278 and p. 279
- ↑ Gaston et al., P. 279
- ↑ Gaston et al., P. 280
- ↑ Gaston et al., P. 280
- ↑ Gaston et al., P. 280
- ↑ Gaston et al., P. 280
- ↑ Gaston et al., P. 280 and p. 281
- ↑ Gaston et al., P. 281
- ↑ Gaston et al., P. 281
- ↑ Gaston et al., P. 281
- ↑ Gaston et al., P. 282
- ↑ Gaston et al., P. 282
- ↑ BirdLife Factsheet on the Rhinoceros Walk , accessed October 30, 2010
- ↑ Gaston et al., P. 274
- ↑ Gaston et al., P. 274
Web links
- Cerorhinca monocerata in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings of Cerorhinca monocerata in the Internet Bird Collection