Aethia
| Aethia | ||||||||
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Dwarf alc ( Aethia pusilla ) |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Aethia | ||||||||
| Merrem , 1788 |
Aethia is a genus of the alken family. The genus includes four recent species, all of which are found in the North Pacific. The genus includesthe smallest alken birds,the dwarf and bearded talks.
The IUCN currently classifies all four species as 
(= least concern - not endangered).
Appearance
The dwarf balk is the smallest species of the alkenbird. It 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 Bartalk reaches a body length of only 18 centimeters and is only slightly larger. Its weight averages 127 grams. The red-billed lalk and the crested lalk are the same size with 25 centimeters. The legs of all four species are bluish gray with darker webbed feet.
The adult birds of all four species of the genus Aethia have strikingly bright irises. Young birds, on the other hand, have a gray iris. All Aethia species have elongated white facial feathers, at least in their splendid dress . In each species a line runs from the eye towards the neck. In the Bartalk, the white facial markings are somewhat more pronounced than in the other species of the genus. A narrow, white line runs from the eye to the neck, two more white lines meet at a 90 ° angle just above the beak and thus form a lying V. In the plain dress, these white, elongated facial feathers have either completely disappeared or only hinted at. The red-billed lalk and the dwarf lalk are the two species that do not have a head of feathers. Bartalk and Schopfalk, on the other hand, in their splendid plumage, have elongated dark feathers on their foreheads that fall forward when the birds are at rest. In the Schopfalk, the feather bonnet consists of twelve to twenty, two to three millimeters wide and 15 to 50 millimeters long blackish feathers. Various studies have shown that crested falcons prefer partners with the largest possible spring hood. In the plain dress of the bearded and crested hawk, these forehead feathers are significantly shortened.
The beak shape of the individual species is very different. The red-billed lalk has a short, strong and orange-colored beak. The beak of the dwarf balk is also very small, the front half of the beak is reddish. Red-beaked lalk and crested lalk have striking orange-red beaks during the breeding season. There is a clear difference in the size of the beak between the splendid and the plain dress, especially with the crested lalk. In the mating season, the beak of this species is significantly enlarged by four to five horn-like plates. Males then have a noticeably stronger bill than the females. The plates are thrown off by breeding birds when they start rearing their young; non-breeding adult crested hawks keep them until the end of the breeding season. Crested hawks then have a significantly smaller and less conspicuous colored beak.
In all four species, the upper side of the body is dark and the underside is lightened. The dwarf balk has the lightest underside of the body. With him it 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. In the splendid plumage, the plumage exudes a citrus-like smell in both the crested and bearded talks.
distribution
The species of Aethia are limited in their distribution to the North Pacific, whereby their distribution areas partially overlap.
The Bartalke has a relatively small distribution area, the main distribution area of which is the Kuriles and Aleutians . The waters he prefers to stay on have a surface temperature of nine to twelve degrees Celsius in summer and two to four degrees Celsius in winter. Even outside of the breeding season, they rarely stay more than 10 miles from the coastline. In Asia, the Bartalk breed sporadically on islands in the north of the Sea of Okhotsk , on the Kuril Islands and the Commander Islands. On the Aleutian island chain, it occurs mainly in the east and breeds, for example, on the Islands of Four Mountains , the Andreanof Islands , the Rat Islands and the Buldir Island . Due to the very hidden way of life of the bearded salmon, the breeding colonies are very difficult to identify and it was not until 1994, for example, that a breeding colony of bearded salmon was discovered on Kanaga Island . The largest known breeding colony is on Buldir Island, but it is possible that the Krenitzin Islands are home to even larger breeding colonies.
The distribution areas of the red-billed, miniature and crested lalk partly overlap strongly. The main distribution of the crested falcon is the Bering Sea and the Sea of Okhotsk in the northwestern Pacific region. Crested hawks prefer waters with a surface temperature of two to ten degrees in summer and two to five degrees in winter. Breeding colonies of the crested hawk are also found on the Kuril Islands and islands of the Sea of Okhotsk such as Sakhalin and the Shantar Islands . In the western Bering Sea, crested hawks breed on the Commander Islands , on the southeastern coast of the Chukchi Peninsula and the 29 square kilometer Ratmanov Island , the easternmost point of Russia . On the Alaskan coast they breed on the remote islands of the Aleutian Islands , the Pribilof Islands , St. Matthew Island , St. Lawrence Island , King Island and the Shumagin Islands , an archipelago in the Gulf of Alaska .
The dwarf alkali breeds in the Aleutian Islands, Semidi Islands, Shumagin Islands and in the Bering Sea on Pribilof Islands, St. Matthew Island, St. Lawrence Island, King Island and Ratmanow Island. On the west coast of the Pacific, dwarf gallows 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 .
The red-billed lalk stays in the open sea more than other species of the genus Aethia . In Asia, its breeding area extends from the Kuriles and the Sea of Okhotsk to the commanders' islands and, in isolated cases, to the coast of the Kamchatka Peninsula and the Chukchi Peninsula. On the North American coast, the red-billed lalk breeds in the north of the Gulf of Alaska, including on the Shumagin Islands, the Semidi Islands , the Tschirikow Island and the Aleutian Islands and on islands of the Bering Strait. The northernmost breeding colony can be found on Ratmanow Island. The most southeastern breeding colony is probably on an island off the coast of Sitka in southeastern Alaska, and the southwesternmost near Sakhalin in the Sea of Okhotsk.
food
All four species prefer copepods , cephalopods and other animals of the marine plankton . Almost nothing is known about the depth and length of the dives of the four species. Both pygmy and red-beaked alks are believed to be poor divers. Some authors estimate that due to their low body mass, dwarf kalke 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. The red-beaked lalk finds its food mainly in shallow water, where small jellyfish play a special role in its diet, as do plankton, which are associated with jellyfish. Its specific beak shape is attributed to this food preference.
Reproduction
Social behavior and breeding colonies
All four species are colony breeders. In the red-beaked lalk, the activities in the breeding colonies are less synchronized than is the case with other Aethia species. The density of nest holes in the breeding colony is also lower. If they breed in the same breeding colonies as other Aethia species, they are usually absent from the alken birds that fly over the colony. Usually, small groups of ten to forty red-billed falcons gather in the coastal waters in front of the breeding colonies in the early hours of the morning and fly from there individually or in pairs to the breeding caves. The activities in the breeding colony are also relatively little aligned. Aggressive behavior towards other conspecifics is relatively rare, which clearly distinguishes them from the dwarf and crested lalk.
In contrast to the red-beaked lalk, the crested lalk is a very sociable bird that lives in large flocks with other species all year round. Individual crested falcons that lose their close proximity to their conspecifics immediately seek connection. This sometimes means that the crested hawks in the first row of a flock slow down, while birds at the end of the flock become faster and thus fly in a long swarm formation that condenses again and again and then breaks up into several individual flocks. Crested and dwarf falcons compete for suitable nesting sites within the colonies, and males in particular react aggressively in the breeding colonies when other males and young birds come too close. Fighting crested hawks chop with their beaks one after the other, regularly aiming for the eyes. They grab each other by the neck or beak and beat each other with their wings. Males often have plucked feather bonnets as a result of these fights. Basically, the hood size correlates with the dominance, the winner of such attacks usually has the larger spring hood. Aggressive interactions between males can also be observed on the high seas. This is especially true when a mated male defends his female against other males who approach it. Females are less likely to show aggressive behavior. Crested falcons show aggressive behavior towards other alken birds. The dwarf lalk, which has a similar intraspecific aggression behavior as the crested lalk, is regularly subject to the crested lalk in duels for nesting sites. It is even assumed that the dead dwarf galks, which can occasionally be found in breeding colonies, are victims of confrontations with the crested lalk.
In contrast to other species of the genus Aethia , the Bearded Talk stays in the breeding colonies mostly during the night. About an hour before dusk, bearded hawks gather in dense schools on the water near the breeding colony. They do not fly ashore until night falls. Noticeable flight maneuvers such as flying over the colony are missing. Bearded reeds usually leave the swimming school one at a time and usually fly straight to the entrance of their nesting cavity. As with many other nocturnal seabirds, activity in the breeding colony is noticeably reduced on moonlit nights. Presumably because of the then higher risk of predation, fewer calls can be heard and fewer birds can be observed on the earth's surface.
Nesting sites
The Aethia species breed in earthworks, in rock caves and between and under boulders. Of all the species in the genus, the red-beaked lalk shows the least specialization when choosing its nesting location. On islands where there are no mammals to chase the red-billed falcon, they often breed between boulders. They also dig nesting holes on gently sloping hills. On islands such as the Pribilof Islands , where foxes live, their nesting sites are limited to inaccessible cliffs. The distance between individual red-billed falcon nests is usually several hundred meters. In breeding colonies they are occasionally associated with dwarf galaxies and crested hawks. Here too, however, they avoid the immediate vicinity of nests of this type. The Bartalk, whose nesting holes are between three and 250 meters above sea level, is similarly adaptable. They are found in crevices, in mounds of rubble, on cliffs and in natural caves on steep grass slopes. The nests of the bartalk are also further apart than is the case with crested and dwarf galks.
The breeding colonies of the crested hawks are often found in scree slopes . Where these scree slopes are very thick, several breeding pairs occasionally use a large gap to get to their burrows, which are then occasionally up to ten meters below the surface. In such locations, the density of the nests can be very high. On Buldir Island , Alaska, 1,500 to 2,000 breeding pairs can be found on 100 square meters. The scree slopes here are ten meters deep, 1.5 to 2 breeding pairs breed per cubic meter of scree. The burrow is usually so deep that the breeding bird cannot be seen from the surface. In deep rubble heaps, burrows can be up to three feet below the surface, but they are usually closer to the surface.
Dwarf gallows breed in very large colonies along rocky coastlines and coastlines with scree slopes or lava fields. Most of the colonies are found on slopes that are directly on the coast. However, scree slopes 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.
Clutch and young bird
All species of the genus Aethia raise only one brood per year and only lay one egg, which distinguishes them, for example, from the genus Cepphus , which also belong to the alkene birds. If the clutch is lost, no additional clutch is usually laid. The peak of oviposition is internally correlated with the geographical latitude. In the dwarf alkali, the peak of egg-laying falls on the western Aleutian Islands, which are located around the 52nd degree of north latitude, at the end of March, on the Pribilif Islands (approx. 57 ° N) 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. Within the genus there are differences in the time of oviposition, even if the species breed in the same colony. On Buldir Island, for example, the peak of egg-laying falls in the first half of May and is one to three weeks earlier than in the dwarf and crested lalk, which also breed on this island.
The egg is oval to elongated oval in all species and has a smooth shell. It is white immediately after the eggs are laid, but is contaminated with soil by the environment, so that it is brownish towards the end of the breeding season. The parent birds each have two breeding spots , which are fledged again very soon after the young bird hatches. In the Bartalk, even non-breeding adults and even not yet sexually mature birds occasionally have the beginnings of breeding spots. Both parent birds breed equally and usually break away at 24 hour intervals. The breeding season is between 31 and 36 days. In the first days of the young bird is first almost continuously brooded , but then increasingly left alone during the day.
The nestling period varies depending on the species. Young birds of the red-billed falcon fledged for an average of 26 days, the dwarf falcon with 28.6 days and the crested falcon with 33 days. Basically, the young birds of the bearded reeds develop more slowly than is the case with other Aethia species, they only fly out when they have reached an age of 35 to 45 days. This comparatively delayed development is probably related to the restriction of daily food intake that is associated with the predominantly nocturnal feeding. Young birds gain a maximum of 3.5 grams per day. They fledge with an average weight of 106 grams, which is slightly less than the weight of an adult bird. It is unusual for alkenbirds that the young birds of the bearded salmon return to the colony and spend the night there. This behavior lasts for some time and is observed for up to six weeks after the point in time at which the breeding birds have largely left the colony. The young birds are not taken care of after they leave the Aethia species.
Reproduction rate and life expectancy
For the Bartalk it is estimated that every 100 breeding pairs between sixty and eighty young birds fledge. This would be the highest reproduction rate among the Aethia species. For the red-billed lalk, the reproduction rate is estimated at fifty young birds per hundred breeding pairs, that of the crested falcon is slightly higher with fifty to fifty-five young birds per hundred breeding pairs. The breeding success of dwarf galks, on the other hand, is estimated at fifty to seventy fledglings per hundred breeding pairs.
The predators of Aethia include mainly arctic foxes and red foxes, but also rats. All three not only kill young birds or eat eggs, but at least in the smaller Aethia species also the adult birds. Their introduction on most of the Aleutian Islands has contributed significantly to the fact that on some of the Aleutian islands, for example, the stocks of the bearded barn have declined or breeding colonies have been abandoned. The predators also include seagulls such as the bering gull , ice gull, and Kamchatka gull . Even bald eagles , giant eagles , gyrfalcon and peregrine regularly beat Aethia alkene.
The mortality rate of adult birds is around 18 percent per year for the Bartalk. Life expectancy is about five years. The average life expectancy of the dwarf galley is estimated to be slightly higher at around 5.5 years. Crested falcons, which are on average 9.6 years old, get significantly older. The life expectancy of the red-billed falcon, on the other hand, has not yet been very well researched.
Duration
None of the Aethia species are considered to be endangered in the population, but the population figures are very different. In 1993, the United States Fish and Wildlife Service estimated the hard-to-count bearded barn population in Alaska at 30,000 individuals. According to estimates by ornithologists Anthony Gaston and Ian Jones, however, the population was certainly much higher and amounted to at least 200,000 to 300,000 individuals in this region. Probably the same number breeds on the Kuril Islands and the Commander Island, but no systematic inventory has been carried out so far. An exact population estimate is also lacking for the red beak, as the red beaked falcons that breed on the Asian coasts have never been counted. However, the population is estimated to be around one million birds. At least two million birds live on the Russian coast and three million on the coast of North America. The pygmy lark is one of the most common alken birds, and in the 1990s the United States Fish and Wildlife Service estimated the population in Alaska alone at more than nine million birds.
As with other alkenbirds, the introduction of rats and foxes poses a significant threat to the Aethia species. Buldir Island is one of the few Aleutian species to which foxes have not yet been introduced, which may explain why it is one of the largest Breeding colonies are located on these islands. The increasing oil pollution of the oceans is one of the other risk factors, especially since some of the breeding colonies are close to busy shipping routes. The red-billed lalk is also particularly sensitive to small plastic particles floating in the sea. 94 percent of the red rots shot on the high seas had such plastic in their goiters. The influence on the health of the birds has not yet been conclusively investigated.
species
The following recent species belong to the genus Aethia :
- Red-billed lalk ( Aethia psittacula )
- Crested lalk ( Aethia cristatella )
- Bearded Talk ( Aethia pygmaea )
- Dwarf alc ( Aethia pusilla )
The previously common classification of the redhead falcon in the independent genus Cyclorhynchus is no longer common.
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
- ↑ a b BirdLife factsheet on the genus Aethia , accessed October 31, 2010
- ↑ Gaston et al., P. 254
- ↑ Gaston et al., P. 265
- ↑ Gaston et al., P. 249
- ↑ Gaston et al., P. 252
- ↑ Gaston et al., P. 262
- ↑ Gaston et al., P: 267
- ↑ Gaston et al., P. 264
- ↑ Gaston et al., P. 239
- ↑ Gaston et al., P. 236
- ↑ Gaston et al., P. 236
- ↑ Gaston et al., P. 256
- ↑ Gaston et al., P. 239
- ↑ Gaston et al., P. 248
- ↑ Gaston et al., P. 248 and p. 249
- ↑ Gaston et al., P. 258
- ↑ Gaston et al., P. 268
- ↑ Gaston et al., P. 240
- ↑ a b c Gaston et al., P. 250
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 259
- ↑ Gaston et al., P. 269
- ↑ Gaston et al., P. 269
- ↑ Gaston et al., P. 261
- ↑ Gaston et al., P. 251
- ↑ Gaston et al., P. 269
- ↑ Gaston et al., P. 269
- ↑ Gaston et al., P. 270
- ↑ Gaston et al., P. 270
- ↑ Gaston et al., P. 262
- ↑ Gaston et al., P. 252
- ↑ Gaston et al., P. 263
- ↑ Gaston et al., P. 255
- ↑ Gaston et al., P. 265
- ↑ Gaston et al., P. 238
- ↑ Rotschnabelalk on Avibase , accessed October 30, 2010
