Aleutian aalk

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Aleutian aalk
Aleutian alek (Ptychoramphus aleuticus)

Aleutian alek ( Ptychoramphus aleuticus )

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Alkenbirds (Alcidae)
Genre : Ptychoramphus
Type : Aleutian aalk
Scientific name of the  genus
Ptychoramphus
Brandt , 1837
Scientific name of the  species
Ptychoramphus aleuticus
( Pallas , 1811)

The Aleutian alek ( Ptychoramphus aleuticus ) is a small bird in the alken family that is widespread in the northeastern Pacific. It is the only recent representative of the genus Ptychoramphus . In contrast to other alken birds, it is able to raise two clutches a year.

The Aleutian alkali is rarely seen on land, as it only visits it at night. From research in California and British Columbia , more is known about this species than any other alkene.

Appearance

The Aleutian alkali reaches a body length of 25 centimeters. The weight averages 174 grams. They are small alkenbirds of plump build with short wings. The plumage shows no major seasonal changes. Due to the legs that are set far back on the body, they move awkwardly on land. Unlike the species of the genus Aethia , they usually do not assume a fully upright posture, but usually crouch on their legs. In contrast to a number of other alkenbirds, they are not particularly good fliers and need a long run-up at sea before they can fly up.

The plumage is almost uniformly dark brown-gray. Only the belly and the under tail-covers are whitish to greyish-white. The face and the top of the head are slightly darker than the top of the body, the lower chest and the belly have washed-out gray spots. The wings and the tail are black-gray, while the wing covers are dark brown-gray. The iris is light gray to whitish. There is a small, crescent-shaped white spot above the eye. The beak is black and compared to other alken birds of this size relatively large and strong. The feet and legs are blue-gray with darker webbed feet.

Fledglings are similar to their parent birds, but they have brown or brown-gray irises. The iris brightens up until the young birds reach sexual maturity.

voice

Aleutian alks are unusually call-happy birds. Especially during the night their calls are spectacularly loud. Since Aleutian alks respond to calls from conspecifics, the intensity of the calls in a colony varies greatly and can also be almost completely silent. They call most intensely on dark, foggy nights. On the other hand, they are relatively quiet on moonlit nights. There are individual ornithologists who suspect that the calls have, among other things, the function of synchronizing reproductive behavior.

Distribution area

Aleutian aks in the Farallon Islands

The breeding areas range from Baja California over the Aleutian Islands to Alaska . The largest colony with approx. 550,000 breeding pairs is located on the Vancouver Islands . Pronounced migratory behavior is not known, but northern populations move somewhat south in winter. Aleutian alks carve a deepening into the ground as a nesting place, or they use natural niches or man-made structures. The couples usually live together for several years and use the same nest. Both parents take turns breeding and the foraging bird returns at night as this provides better protection against birds of prey. The female only lays one white egg from which the chick hatches after about 40 days. The young animal is fed for about 35 days by the parents, who bring food in a special saddle bag every night. After the moult, the young animal finds its way to the sea on its own. In contrast to other marine birds in the northern hemisphere, it is possible that the parents breed again after a successful brood.

food

Aleutian alks seek their food in the open sea. They are based on submarine mountains and ocean currents. When foraging for food, they dive with the help of their wings. They are food generalists who eat krill and other zooplankton animals . Aleutian alks usually reach depths of 28, rarely 40 meters during their dives. During the breeding season, they prefer to look for food over the continental shelves , but are rarely seen in coastal waters. In winter they find their food on the high seas.

Reproduction

Breeding colonies and nesting holes

Aleutian chick

Aleutian alks are colony breeders. They leave their nesting sites before dawn in order to look for food on the sea all day and only return at night. Silver owls , which occasionally breed in the same colonies, break up before the Aleutian owls. In contrast to rhinoceros , crested , bearded , silver and red-billed alks , Aleutian alks do not already gather in front of the breeding colonies at dusk, but stay on the high seas until dark. This behavior appears to be an adaptation for the reenactment of bald eagles , peregrine falcons and large species of gulls. Within the colony, Aleutian alks show aggressive behavior towards their conspecifics, which can be attributed to the density of the nest.

Breeding colonies are usually found on hilly islands that lack mammals larger than small mice. Ideal islands have a soil that is soft enough for Aleutian alkes to dig their burrows. These burrows are usually found on thick grassy slopes within 500 meters of the shoreline. Usually the islands of the breeding colonies are not forested, but most of the breeding colonies on Haida Gwaii are in forests with a moss-covered subsoil. Aleutian alks also use cavities under tree roots to create their breeding caves. They even take nesting aids and breed in wooden boxes. In Baja California they also dig their burrows under cacti and thorn bushes. The entrances to the breeding caves stand out due to the whitish splashes of excrement. The breeding caves are on average 100 centimeters deep, the height of the entrance averages 13 centimeters. The nesting density can be very high on individual islands. On Triangle Island off the coast of British Columbia there are 1.36 burrows per square meter, while on the Queen Charlotte Islands the nesting density is 0.80 nests per square meter. The nesting density is not influenced by the size of the colonies.

Egg laying and incubation

The start of egg-laying varies depending on the geographical latitude. In Baja California, egg-laying begins as early as November and lasts until March. On the Farallon Islands off San Francisco, eggs are laid from March to May. In British Columbia, on the other hand, Aleutian alks lay their eggs between the end of March and the end of April. The young birds hatch there from the end of April to the end of May and the fledglings leave the breeding colony between the beginning of June and the beginning of July. The clutch consists of only one egg; where there are two eggs in a nest cavity, it is the clutch of two females. Additional clutches are usually, but on the Farallon Islands 10 percent of egg losses are replaced by additional clutches.

The eggs are elliptical to oval and have a smooth surface. They are initially white and then turn slightly bluish or greenish. A single, freshly laid egg weighs an average of 29.8 grams, which corresponds to 17 percent of the body mass of the female. The parent birds have two breeding spots running in parallel . These form one to two days before the egg is laid. However, this brood spot is absent in 60 percent of the Aleutian alks that raise a second clutch. According to current knowledge, both parent birds are equally involved in the breeding business. They alternate at 24 hour intervals.

Fledglings

The individual egg is incubated for an average of about 38 days. The chick makes audible noises one to three days before hatching. Newly hatched young birds weigh around 20 grams and gain up to 4.3 grams per day. For the first four days they are continuously fledged by the parent birds . The nestling period is 41 days on the Farallon Islands off San Francisco, and 45 days on Frederick Island. The speed of development of young birds varies greatly depending on the environmental conditions.

Breeding success and life expectancy

On average, an estimated 50–70% of the young reach the age of retirement, with second broods this value is significantly lower at 10%. The success of hatching and escaping increases with the experience of the breeding pairs.

The predators of the Aleutian alks include red and arctic foxes , which were introduced to some islands with breeding colonies of alken birds. The introduction of these predatory mammals has a drastic impact on colony size and breeding success. Rats and mice also eat eggs and young birds that have not yet fledged. On the Queen Charlotte Islands, the raccoons introduced there pose a serious threat to this species. The predators also include western and bering gulls , bald eagles, peregrine falcons and common ravens .

Of 100 adult Aleutian alks, 83 will live to the next year, so they have an average life expectancy of 7.6 years.

Duration

The Aleutian aalk is a widespread and common alken bird. By the late 20th century, its population was estimated at one million individuals in Alaska and 2.8 million individuals in British Columbia. Their number is significantly lower further south. During this period 43,800 breeding pairs were breeding on the coasts of the US state of Washington, 500 pairs each off Oregon and California. Baja California , on the other hand, has 10,000 to 20,000 breeding pairs. The largest breeding colony can be found on Triangle Island off the coast of British Columbia. 370,000 breeding pairs are counted there.

The Aleutian lalk is particularly threatened by mammals introduced on the islands where it breeds. In California and Baja California, a number of breeding colonies disappeared after cats, rats and foxes were introduced there. On Langara Island, one of the northernmost islands of the Queen Charlotte Islands , rats brought the breeding colony to extinction. The raccoons introduced there represent a growing danger on all Queen Charlotte Islands. In the Aleutian Islands, the Aleutian aalk was one of the most common prey of the arctic fox. This was introduced there because of its fur and brought the species to extinction on numerous Aleutian islands. Aleutian alks are also very sensitive to oil pollution in their waters.

Subspecies

There are two known subspecies:

Etymology and history of research

Peter Simon Pallas described the Aleutian aalk under the name Uria Aleutica . As the location of the type specimen that Carl Heinrich Merck had collected, he stated the Pacific Ocean in Alaska, which was then part of Russia. Johann Friedrich von Brandt introduced the new genus Ptychoramphus . This name is a combination of the Greek words "ptyx, ptychos, ptyssō, πτυξ, πτυχος, πτυσσω " for "fold, fold" and "rhamphos ραμφος " for "beak". The specific epithet »aleuticus« refers to the »Aleutians«. »Australis, austri« is the Latin word for »south, south«.

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 .
  • Peter Simon Pallas: Zoographia Rosso-Asiatica, sistens omnium animalium in extenso Imperio Rossico et adjacentibus maribus observatorum recensionem, domicilia, mores et descriptiones, anatomen atque icones plurimorum . tape 2 . Ex Officina Caes, Academie scientiarum, Saint Petersburg (Petropoli) 1811 ( online [accessed April 1, 2015]).
  • Adriaan Joseph van Rossem: Some new races of birds from Mexico . In: Annals and Magazine of Natural History (=  11 ). tape 4 , no. 22 , 1939, pp. 439-443 , doi : 10.1080 / 00222933908527006 .
  • James A. Jobling: Helm Dictionary of Scientific Bird Names . Christopher Helm, London 2010, ISBN 978-1-4081-2501-4 .
  • Johann Friedrich von Brandt: Report on a monograph de la famille des Alcadées . tape 2 , 1837, p. 344-349 ( online [accessed April 1, 2015]).

Web links

Commons : Aleutenalk  - album with pictures, videos and audio files

Single receipts

  1. ↑ a b Gaston et al., P. 232
  2. ↑ Gaston et al., P. 227
  3. ↑ a b c Gaston et al., P. 230
  4. ↑ a b Gaston et al., P. 231
  5. ↑ a b c Gaston et al., P. 233
  6. ↑ Gaston et al., P. 233 and p. 234
  7. ↑ a b Gaston et al., P. 234
  8. ↑ Gaston et al., P. 235
  9. ↑ Gaston et al., P. 228
  10. ^ IOC World Bird List Coursers, noddies, gulls, terns, auks & sandgrouse
  11. ↑ a b Peter Simon Pallas, p. 370.
  12. ^ Adriaan Joseph van Rossem, p. 443.
  13. ^ Johann Friedrich von Brandt, p. 347.
  14. ↑ James A. Jobling, p. 323.
  15. ↑ James A. Jobling, p. 41.
  16. ↑ James A. Jobling, pp. 62f.