Dwarf alk
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Dwarf alc ( Aethia pusilla ) |
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| Scientific name | ||||||||||
| Aethia pusilla | ||||||||||
| ( Pallas , 1811) |
The dwarf alken ( Aethia pusilla ) is the smallest species of the cauliflower family . In large parts of its range, the dwarf alk is the smallest seabird, after the Aleutian alk it is one of the best-studied alken birds.
With a population of 9 million individuals, it is the most common sea bird on the North American Pacific coast . No subspecies are distinguished for this species, but the plumage color differs in individual regions of the distribution area. For example, dwarf kalkes that breed on the Pribilof Islands have a lighter underside of the body than breeding birds on Buldir Island .
Appearance
The dwarf balk reaches a body length of 15 centimeters and is thus slightly smaller than a house sparrow . The weight varies between 70 and 101 grams and averages around 85 grams. The iris is white in all plumage, the feet and legs, as in all species of the genus Aethia, are blue-gray with darker webbed feet . The sexual dimorphism is only very weak. Males only have slightly stronger beaks. On land, the posture of the dwarf gal is upright. They usually only touch the ground with their feet, which distinguishes them, for example, from the silver ox , which usually lies on its stomach on land. Although the wings of the dwarf kalk are round and short, they are able to soar from the surface of the water very quickly. However, they are bad fliers and in flight they commute a little from one side to the other. They cannot approach against strong winds, but are regularly carried in hurricane gusts.
In their splendid plumage , dwarf galaxies have a dark gray or blackish body surface, whereby the wings can have whitish spots. Breeding birds have individual, narrow, somewhat elongated feathers on the forehead and behind the eye. The beak is dark at the base with a red beak part in front. The underside of the body is usually whitish with irregular darker spots and horizontal stripes. However, individual individuals can vary greatly and have, for example, a pure white or almost black underside of the body. Individuals with a very dark underside of the body usually have a whitish throat spot. Overall, individuals with a purely white or almost black underside make up about five percent of the population.
The plain dress is similar to the magnificent dress, but all dwarf galks then have a white underside of the body. The beak is black, on the face they have only a few longer white feathers. Not yet sexually mature dwarf falcons in the second year of life are predominantly brown on the forehead. They have only a few or no white facial feathers. The beak color is matt dark. They also have a variably colored underside of the body, but are usually darker in color than the sexually mature adult birds. Young birds in their first winter already resemble the adults in their simple dress. In your case, however, the iris is more pale gray than whitish.
voice
Little kalkes are very call-happy birds, for which a high chirping is characteristic. For example, courtship males call this way when they are in the breeding colonies. Neighboring birds react differently depending on their gender: Females are attracted by the chirping calls. In the case of competing males, on the other hand, the calling male triggers aggressive behavior. Courting couples also call in a duet. Dwarfalke also have shrill alarm calls, which can be heard mainly by birds flying up. Overall, the repertoire of calls differs significantly from that of other Aethia species and the Aleutian aalk .
Distribution area
Dwarfalke prefer to stay in bodies of water that have a surface temperature of two to eleven degrees during the summer and one to five degrees during the winter half-year.
On the North American coast, the dwarf alkali breeds in the Aleutian Islands, the Semidi Islands , the Shumagin Islands and in the Bering Sea on the Pribilof Islands, St. Matthew Island , St. Lawrence Island , King Island and Ratmanow Island . On the west coast of the Pacific, dwarf galks breed sporadically on the Kuril Islands, on islands in the Sea of Okhotsk , the commanders' islands and along the coast of the Kamchatka Peninsula to the southern coast of the Chukchi Peninsula . There are very large breeding colonies on Kiska Island and St. Lawrence Island and an island in the Sea of Japan . During the summer half of the year, dwarf galaxies are also observed significantly further north. Observations are available from Point Barrow , the northernmost headland of the US state of Alaska, and Wrangel Island .
During the winter months, dwarf alks prefer to stay near their breeding colonies, provided that the waters there remain ice-free. However, wintering birds can be found on the west coast of the North Pacific as far as the coast of northern Japan.
food
Dwarfalke find their food underwater, but little is known about their dives. Because of their low weight and small wings, they are only considered bad swimmers. Some authors estimate that due to their low body mass they can only dive to a limited extent and can reach water depths of a maximum of 15 meters. Other authors assume a maximum diving depth of up to 25 meters. Their diet consists mainly of copepods and other animals of the marine plankton . There, where their range overlaps with that of the Bartalk , the food composition of the two species is very similar.
Reproduction
Breeding colonies
Dwarf gallows breed in very large colonies along rocky stretches of coast as well as stretches of coast with rubble heaps or lava fields. Most of the colonies are found on slopes that are directly on the coast. However, rubble heaps are also used in the interior of the island up to a distance of 1.5 kilometers. Usually the area of the breeding colony shows no or only very little vegetation. On the Aleutian Islands, however, breeding colonies can also be found in older lava fields, which now have strong vegetation. Basically, however, the vegetation means that the area is increasingly unsuitable as a nesting site because humus and vegetation residues fill the crevices in the rock. The four largest colonies of the Aleutian Islands are also located in relatively young lava fields. Due to its location requirements, the species is fundamentally dependent on erosion and volcanic activity.
Social behavior
The breeding colonies can be made out from a distance during the breeding season because a large number of dwarf galks fly back and forth between the open sea and the breeding colony. Compared to the crested lalk , flying schools of dwarf galks are less dense and their flight speed is lower. What is striking is the difficulty of the dwarf kalke in approaching against the wind.
Breeding colonies usually have two peaks of activity, during which the greatest number of breeding birds are present. In the Aleutian Islands and the Pribilof Islands, at the beginning of the breeding season, the first peak of activity falls between around 9 a.m. and 2 p.m. and the second between 11 p.m. and 12 p.m., when dusk typically falls in these latitudes. In the course of the breeding season, the period of the first activity point shifts to the time from 11 a.m. to 4 p.m. In the far north of the breeding area, for example on Little Diomede Island , where there is almost continuous daylight during the breeding season, the activities are distributed more evenly over the day. Aggressive behavior between dwarf kalk can be observed very often in the breeding colonies. Usually males in particular react to approaching members of the same sex as well as young birds of both sexes with beaked hoes, which often pull the eyes. The aggressive behavior also includes grabbing the other bird by the neck or by the slightly elongated, white facial feathers. Dwarf falcons that win such fights usually have slightly lighter plumage. Experiments have shown that light-colored plumage has a status signal.
In the colonies, dwarf alks often breed together with other alken birds. On many islands they are associated with the Schopfalke. Typically, dwarf kalk returning from the sea end up before the crested falcon in the breeding colonies. In battles for suitable nesting sites, the small dwarf galaxies are regularly subject to the sometimes significantly larger Aethia species. Dead dwarf galaxies lying in crevices in the rock are believed to be the victims of aggressive crested hawks.
Clutch
Dwarf galks are basically monogamous birds, but copulations outside of the pair relationship are more common than with other Aethia species. In a study of twenty males, two raised a young bird that was not descended from them. Dwarf galaxies nest in crevices in the rock, with the brooding bird occasionally remaining visible. In breeding colonies with a very thick layer of rubble, the nest can be several meters below the surface, but the dwarf falcon generally does not nest as deep as the crested falcon.
The laying of eggs depends on the geographical latitude. In the western Aleutian Islands, which are about 52 degrees north of latitude, the peak of oviposition falls at the end of March, on the Pribilif Islands (approx. 57 ° N) it falls at the beginning of June, on St. Matthew Island (approx .60 ° N) in mid to late June and on St. Lawrence Island (approx. 63 ° N) in early July. In the more northern breeding colonies, the time when the snow melts influences the time at which the eggs are laid. In years with long snowfall, egg-laying can shift backwards by two weeks. Clutches are occasionally found in the snow. However, these clutches are not incubated. In mixed breeding colonies the young birds of the dwarf galaxies not only hatch before those of the crested hawks, but also fled earlier.
The clutch consists of only one egg that is either placed directly on the bare rock or on small pebbles. Additional clutches in the event of clutch loss are atypical for dwarf galleys. The egg is oval with a smooth surface. The shell is white after the eggs are laid, but then becomes increasingly dirty brown as the brood progresses. It weighs an average of 18.7 grams, which is about 22 percent of the female's body mass. It is incubated by both parent birds, each of which has two breeding spots . The breeding season averages 31.2 days. Both parent birds usually take turns at an interval of 24 hours. The egg is fundamentally insensitive to interrupted brood. This happens, for example, by people who are in the breeding colony or when there is a lack of food.
Young bird
Young birds of the dwarf gallows weigh an average of 11.9 grams at the time of hatching and can gain up to six grams per day during their nestling period. At the time of fledging, they weigh about 91.5 grams, making them about eight percent heavier than the average adult breeding bird.
Newly hatched chicks are almost continuously on the first day of life brooded , but then increasingly left alone during the day from parents birds. However, one or even both parent birds spend the night in the burrow for the first ten days after hatching. The parent birds bring feed two to four times during the day. This amount of food is estimated at around 5.4 grams. Here, too, both parent birds are almost equally involved. Dwarfalke are fledged with an average of 28.6 days, they then have a wing length that corresponds to the adult birds. Several days before they fly, the young birds climb out of their burrows and train their flight muscles by flapping their wings violently for 15 to 30 seconds. On the day the young birds leave the breeding colony, they usually climb a boulder near the burrow and then fly towards the sea. Many of the young birds land on the high seas after this first flight. Young birds, which are significantly below the average weight, try to reach the sea continuously or end up at the foot of the rubble hill. They are usually beaten by predators of the dwarf falcon. The parent birds do not take care of the young birds that have flown out.
Breeding success and life expectancy
The breeding success of dwarf galks is estimated at fifty to seventy fledgling young birds per hundred breeding pairs. The predators of the Zwergalk include both arctic and red foxes, which mainly beat adult birds in the colonies. Brown bears dig up burrows in the rubble to eat adults, nestlings and eggs. Voles mainly eat eggs and nestlings. Ermine and introduced rats beat adult dwarf galks, nestlings and eggs. The predators of the pygmy galks also include the Kamchatka , Bering and Ice gull , snowy owl , short- eared owl , bald eagle , giant sea eagle , gyrfalcon and peregrine falcon .
The adult dwarf kalke mortality rate is 21 percent. Their average life expectancy is around 5.5 years. Dwarf alkes reach sexual maturity at around three years of age.
Duration
The population in Russia was estimated at several million towards the end of the 20th century. The United States Fish and Wildlife Service estimated the number of North American dwarf galks at nine million in Alaska alone in 1993. It is possible, however, that these estimates are far too low and there are more than 20 million dwarf kalkes. Millions of other dwarf galks breed on the Russian coast, but their numbers are also not precisely recorded. Population trends are difficult to determine because the presence in the breeding colonies varies greatly during the day and over the year. On some islands of the Aleutian Islands the population has declined after arctic foxes were introduced there. Dwarf galks, unlike some other alken birds , also breed on islands where foxes, weasels and bears occur naturally.
supporting documents
literature
- Jonathan Alderfer (Ed.): Complete Birds of North America , 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
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 253
- ↑ Gaston et al., P. 254
- ↑ Gaston et al., P. 253
- ↑ Gaston et al., P. 252
- ↑ Gaston et al., P. 252
- ↑ Gaston et al., P. 253
- ↑ Gaston et al., P. 256
- ↑ Gaston et al., P. 256
- ↑ Gaston et al., P. 255
- ↑ Gaston et al., P. 256
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 257
- ↑ Gaston et al., P. 257
- ↑ Gaston et al., P. 258
- ↑ Gaston et al., P. 258
- ↑ Gaston et al., P. 260
- ↑ Gaston et al., P. 260
- ↑ Gaston et al., P. 260
- ↑ Gaston et al., P. 260
- ↑ Gaston et al., P: 261
- ↑ Gaston et al., P. 261
- ↑ Gaston et al., P. 262
- ↑ Gaston et al., P. 255
Web links
- Aethia pusilla in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed on January 1 of 2009.