Polar gull

from Wikipedia, the free encyclopedia
Polar gull
Adult polar gull of the subspecies L. g. kumlieni in a simple dress

Adult polar gull of the subspecies L. g. kumlieni in a simple dress

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Laridae
Subfamily : Seagulls (larinae)
Genre : Larus
Type : Polar gull
Scientific name
Larus glaucoides
Meyer , 1822
Bird of the subspecies L. g. glaucoides in the first winter
Some birds in the first summer appear very light in their worn plumage. There are hardly any dark markings.
Hand wing pattern of adult birds of the two subspecies glaucoides and kumlieni and the Thayer gull ( thayeri ) in comparison. The third hand wing pattern from above shows the overlap area between the species - some of them are hybrids.
Bird of the subspecies L. g. kumlieni with visible hand wing pattern - here with a medium gray color.

The polar gull ( Larus glaucoides ) is a Lower Arctic, medium-sized species of gull from the genus Larus . It settles into two subspecies the coast of southern Greenland ( L. g. Glaucoides ) and the north-eastern Canada to Baffin Iceland ( L. g. Kumlieni ), wherein the latter form is highly variable, and possibly of a hybridization with the Thayer's Gull emerged. Often the Thayer gull is also viewed as a subspecies of the polar gull.

The polar gull breeds in cliffs by fjords and sounds . It feeds mainly on fish, but also on crustaceans , molluscs , carrion and other things. In winter it can be found on ice-free coasts and polynyas . The Greenlandic populations overwinter in the area of ​​the North Atlantic and in particular on Iceland , which earned the species the English name Iceland Gull , although it does not breed there. But birds of the American subspecies also regularly enter Europe. Their main wintering areas extend from Hudson Bay over the coasts of the eastern provinces of Canada.

description

With a body length of 52–60 cm and a wingspan of 125–145 cm, the polar gull is somewhat smaller than a herring gull and smaller than the very similar ice gull . The physique corresponds to that of a typical great gull; the relatively graceful, round head, on the other hand, is reminiscent of that of a common gull . In flight the species looks elegant with slender wings and relatively long hand wings . In contrast to the ice gull, the head and neck appear short and the wings more pointed. When the bird is sitting, the wing tips protrude quite far beyond the control feathers. A typical feature, even if it is not suitable for reliable identification of species, is that the wing tips are often not crossed, but rather placed on top of each other.

Adult dress

In their splendid plumage , adult birds of the nominate form have a yellow beak with a red gony spot ; it is not uncommon for the yellow color to tend towards the olive . The eye is surrounded by a red orbital ring, the iris is bright yellow. The head, neck, chest, underside, rump and rudder feathers are pure white. The top is light gray. The upper wing shows a white rear margin. In contrast to other species of the genus Larus, there is no black hand-wing drawing - as is the case with the ice gull. The feet and legs are pink to grayish flesh-colored. In the plain dress , the beak and orbital ring are more dull. The head is - partially reaching to the chest - brownish dashed.

Youth dresses

Like other large gulls, juvenile polar gulls are predominantly gray-brown in color. Similar to young ice gulls, however, they are overall very light to whitish gray. The wings, which are dark in color in other juvenile large gulls, are whitish or at least whitish lined. The rest of the wing, back and shoulder plumage show whitish feather centers and brown-gray subterminal drawings . In contrast to the ice gull, this drawing of the upper side is whiter and more open. Overall, the bird looks grayer and less yellow-brown. The head drawing is also richer in contrast. A fine dotted line condenses in the area of ​​the head and the ear covers, the neck often shows a lighter color. Whitish "lids" are usually missing. The eyes and beak are dark, the beak is often a little lighter at the base. The lower tail-coverts and the rump are banded brownish on a white background. The tail, which is usually finely banded with gray-brown, lacks the band. Feet and legs are flesh-colored.

In some birds of the nominate form, some feathers of the coat and shoulder plumage are molted towards the first winter, but this is hardly noticeable. This is clearer with the subspecies L. g. kumlieni , in which the back looks darkly scaled in youth clothing , but in the first winter the drawing is much more open. Towards the spring, some birds of both subspecies appear very light to almost pure white due to their worn plumage.

Birds in the second winter are similar to those in the first winter. The now predominantly flesh-colored beak shows a wide, black subterminal band, the underside is lighter and the markings are somewhat more irregular and lighter. The dotted lines on the head are often concentrated in an implied mask from which the eye, which is slowly lightening, clearly stands out. With some birds, the gray back of the adult dress is already indicated.

Birds in the third winter already strongly resemble adult birds. However, the yellow-olive beak still shows a black band and some upper wing-coverts still show a brownish pattern.

Geographic variation

Two subspecies are usually recognized - the nominate form native to Greenland and the nearctic gull , named after the Swedish-American ornithologist Thure Kumlien (1819–1888):

  • L. g. glaucoides Meyer 1822 - southern Greenland
  • L. g. kumlieni Brewster 1883 - northeastern Canada

However, some authors also consider the Thayer gull ( Larus thayeri ), whose distribution borders to the northwest and slightly overlaps in the northwest of Baffin Island, as a subspecies of the polar gull . Other authors consider the species to be a superspecies .

While a dark hand- wing pattern is completely absent in the nominate form, the subspecies kumlieni shows a very wide variability with regard to this characteristic. In very light birds, it is limited to a light gray striped pattern, which is formed by the dark colored outer flags of the four outer hand wings. In most birds, however, it extends over the outer four or five hand wings, is ice gray to dark gray and shows subterminal, dark bands in addition to the dark outer plumes. It is similar to that of the Thay gull and it is believed that this phenotype emerged from a hybridization with the latter. This is supported by the fact that there is a zone in the north-western part of the distribution in which Thayer gulls with a very reduced hand wing pattern often do not differ from L. g. Let the kumlieni be distinguished with very dark markings (see also fig. on the right). Presumably some of them are hybrids.

Another distinguishing feature of the subspecies is the orbital ring around the eye, which is yellow in Greenlandic birds and red in Canadian birds. The color of the iris is variable in kumlieni like the hand swing pattern . To the northwest, the proportion of birds with dark spotted irises (as in the Thayermöwe) increases.

voice

The vocal expressions of the polar gull are very similar in repertoire and quality to those of the herring gull and are sonically closer to them than the calls of other related great gulls such as the Mediterranean gull or the herring gull . Often, the utterances are described as strident than the, but the herring after observations Friedrich Goethe to the Greenland breeding grounds mainly on the " shouting " ( long call applicable). This is similar to that of the American herring gull , which is characterized by particularly shrill, high calls in the middle part. The main call of the polar gull is a very variable küa , which increases to a higher kia when excited . Goethe describes the “staccator call” uttered in danger as gägägäg . In general, he notes that many of the sequenced calls are made at a slower pace than the herring gull.

distribution

The breeding distribution of the polar gull extends in the area of ​​the Lower Arctic in scattered colonies over southern Greenland and parts of northeastern Canada.

In Greenland, the species is only found scattered on the east coast at the Kong Frederik VI Kyst , but more frequently from Tasiilaq north to the Kangerlussuaq fjord . On the west coast, the distribution ranges from the Sermersôq Island in the north of the Nanortalik district north to the Balgoni Islands (Balgoni Øer) in the Melville Bay at around 76 ° N. A breeding occurrence on Jan Mayen from 1882/83 has been since then not confirmed again.

In northeast Canada, the occurrences are limited to Baffin Island and the extreme north of Hudson Bay . The northernmost colonies are found in Home Bay on Baffin Island and on the offshore island of Broughton Island , where the area overlaps with the neighboring Thay gull to the northwest. Furthermore, the species occurs on Cumberland Sound and on the south coast of the island to Cape Dorset . Further south, the species breeds on Southampton Island and Coats Island as well as on Digges Sound in the extreme northwest of the Ungava Peninsula .

Arctic gulls regularly overwinter in small numbers in the north of the British Isles. Here is a bird in the first winter.

hikes

The polar gull is a resident bird in its southern range , the northern populations are short-range migrants. Young birds sometimes also cover longer distances.

The majority of the nominate form overwinters in southern Greenland. While the breeding birds of the west coast only clear the inland fjords, birds of the east coast mostly move on. They are then often found in the northern part of Iceland, where between 5,000 and 10,000 birds reside in winter. A small part also winters in the north of the British Isles. The species also makes its way to Norway, Northern and Western Europe more rarely and especially on larger, climate-related flights.

The breeding birds of Baffin Island overwinter in the area of ​​Hudson Bay and the maritime provinces of Eastern Canada, where flocks of over 9,000 birds sometimes form in the Gulf of St. Lawrence and in Newfoundland. The species is also sparsely found further south to the Great Lakes and as far as South Carolina as overwintering.

The breeding colonies are cleared from August and the birds spread over the surrounding coasts in the course of autumn or migrate along the inland fjords to finally reach the coast as well. The first winter guests arrive in Newfoundland and Iceland by the end of September. However, the peak of the hikes begins in October and is mainly in November. Winter populations peak anywhere between November and March. They move home between the end of March and the beginning of May.

The species also reaches the west coast of America as a stray visitor. In Europe L. g kumlieni is found very seldom but regularly as an errant , in America birds of the nominate form occasionally appear.

Breeding colonies of the polar gull are mostly located in cliffs on the Lower Arctic fjord coast, similar to this one in eastern Baffin Island
Some of the breeding sites are already occupied from mid-May, when the fjords are not yet free of ice. The ice cover usually only breaks up into clods between mid-June and July.

habitat

The breeding colonies of the polar gull are mostly located in cliffs on fjords or sounds . Breeding sites that are several kilometers inland are rarer. In very remote places where the species is not hunted, low islands or rock pinnacles are also used.

Young birds that have just fledged can be found on beaches or in the archipelago near the breeding grounds. In winter quarters the species can be found on ice-free coasts and polynyas. In the southern part of the wintering area, she seeks out similar places as other seagulls and socialises with them at mass wintering sites - including ports and rubbish dumps. Mostly you can find them in the area of ​​the coast, more rarely on inland lakes.

The polar gull often catches its food in flights from the surface of the water, where it often touches down briefly, but rarely submerges completely.

nutrition

Like many other gulls, the polar gull eats opportunistic and omnivorous . Most of the food, however, is made up of fish such as capelin and candle fish , which in summer reside in large schools just below the surface of the water. In seeschwalbenartiger manner they are shock-diving picked out of the water, where the gull but almost never completely submerged. She often touches down briefly on the water. The polar gull can be observed more frequently than other seagull species in low search flight above the water surface. It is typical that the prey is usually devoured in flight.

In addition to fish, invertebrates living in the intertidal zone such as barnacles , mussels or ringworms are collected at low tide . Eggs and juveniles from other rock breeders such as kittiwakes or thick-billed mums are also part of the diet - as are washed-up dead fish, other carcasses and crowberries .

Fish can also provide a significant proportion of the food in winter roosts. Here the species can sometimes also be found on the open sea in the wake of fishing boats. It is less common than other large gulls to be found at harbors or in landfills, rather it collects smaller pieces of waste from the surface of the water. Kleptoparasitism is rare.

Reproduction

Gelege, Museum Wiesbaden collection

The polar gull breeds in small colonies in cliffs near the coast, which are already occupied when the ice cover of the fjords is still closed and there is often still snow on the ledges and ledges. In Greenland this is between the end of April and mid-May, and on Baffin Island sometimes between the end of May and the beginning of July. The pairing usually takes place beforehand in the winter quarters on the ice-free coast.

The nesting sites in the steep walls are naturally mostly below 100 m above sea level. Where the species is hunted by humans, however, higher-lying places between 100 and 300 m, more rarely up to 800 m, are chosen. Places that can be reached by enemies such as the arctic fox are usually given up quickly. In mixed colonies the nests are always higher than those of the kittiwakes, but mostly below those of the ice gull, which occupy the highest places with some distance to the other cliff breeders.

Often the breeding sites and their immediate surroundings are overgrown by conspicuously orange-yellow, xerophilic species of lichen (genus Caloplaca and related species such as the delicate yellow lichen ) and therefore visible from afar, but mostly not to the same extent as the ice gull.

The nests can stand on narrow ledges, ledges and niches. In contrast to larger species of gulls, the polar gull needs little space with at least 0.2 m². In overgrown, rock-interspersed steep slopes, it often forms species-specific sub-colonies.

The nest is a sometimes rather misshapen heap of plant materials such as grass, branches of crowberry , herbaceous plants, peat and other mosses. The nesting trough is sometimes poorly lined with fine stalks and feathers.

In Greenland, eggs are laid between mid-May and mid-June, and on Cape Dorset during June. The clutch almost always consists of two or three eggs, which on a light brown to stone-gray background are moderately spotted with dark brown and are about 69 × 48 mm in size. They are incubated for about 24-26 days.

The young hatch in western Greenland around mid-June and fly out between July 20 and August 10. After leaving, the young stay on the archipelago or beaches near the breeding colony and are accompanied by their parents for a while.

Systematics

The systematics of the polar gull has always been controversial and was initially characterized by confusion with the ice gull. For a long time the species was listed as Larus leucopterus Faber in 1822, until it was found that Larus leucopterus Vieillot had priority as the older first description in 1820 . Jonathan Dwight considered the species under this name as a smaller but separate form of Larus hyperboreus . When it turned out that the type specimen described by Louis Pierre Vieillot had been an ice gull, the taxon was declared invalid and Bernhard Meyer's description of a wintering specimen from Iceland from 1822 that is no longer preserved was used as valid.

In the middle of the 20th century, many authors such as Boris Stegmann , Erwin Stresemann or Niko Tinbergen did not recognize the species status of this form, but regarded it as a particularly bright subspecies of the herring gull. However, genetic findings at the turn of the millennium showed that the polar gull is not closely related to the herring gull , but rather is to be assigned to a clade that developed from an ancestor close to the black-backed gull and spread across the Siberian region and the Bering Strait to North America. The polar gull is apparently more closely related to the Eastern Siberian gull ( Larus vegae ), the American herring gull and the Bering gull . There is a lack of clarity about a close relationship with the phenotypically similar ice gull. This genetically shows both haplotypes from the argentatus complex, which has its origin in the Atlantic area, and those from the Siberian lineage. Whether the similarity is related or based on a convergent development is therefore open.

The subject of much discussion and a hitherto unresolved problem is the relationship between the three taxa glaucoides , kumlieni and thayeri . Currently, the most recognized state is that the Thay gull - sometimes very similar to the American herring gull - forms its own species and glaucoides and kumlieni are subspecies of the polar gull . The high variability of kumlieni , which practically represents an unstable transition form leading from glaucoides to thayeri , and the - also controversially discussed - contact and hybridization zones between the taxa are interpreted differently by different authors. While some advocate merging the three forms into one species, others argue that this species would then practically not be assigned a clearly identifiable phenotype and that other species with similarly close relationships would also have to be grouped together. A final clarification of this question stands in the way of the fact that the origin of many museum hides collected as hibernators has not been precisely clarified and more detailed genetic studies are missing.

Existence and endangerment

There is a lack of reliable data on the total inventory. The rough estimates vary between 10,000–100,000 breeding pairs and 190,000–400,000 adult birds. According to the first estimate, there are more than 80,000 pairs in the Greenland population and around 10,000 in the Canadian population. Nothing is known about trends. The species is classified by the IUCN as Least Concern (not endangered).

In the second half of the 19th century, the species was hunted commercially for its feathers. Especially in Greenland it is still shot by Inuit today to use meat and feathers. After ring finds in West Greenland, 23% of this year's young birds fell victim to hunters, 94% of all ring finds were kills. Other hazards are environmental toxins in the breeding areas and oil pollution in the winter quarters.

literature

Individual evidence

  1. ↑ a b c Olsen / Larsson (2003), see literature
  2. ^ Lars Svensson, Peter J. Grant, Killian Mullarney, Dan Zetterström: Der neue Kosmos Vogelführer . Kosmos, Stuttgart; 1999: p. 181. ISBN 3-440-07720-9
  3. ↑ Glutz von Blotzheim, p. 501 and Goethe (1986), p. 120, see literature
  4. ↑ Glutz v. Blotzheim, p. 494f, see literature
  5. ↑ Olsen / Larsson (2003), p. 204f and Glutz v. Blotzheim, p. 494, see literature
  6. ↑ a b c Olsen / Larsson (2003), pp. 204f
  7. ↑ a b c Jürgen Haffer : Systematics and taxonomy of the Larus argentatus species group in Glutz von Blotzheim, p. 510f, see literature
  8. ↑ a b Olsen / Larson (2003), p. 214f ​​and p. 29/30, see literature
  9. ↑ Goethe (1986), pp. 124 and 130, see literature
  10. ↑ Goethe (1986), p. 129, see literature
  11. ↑ Goethe (1986), p. 130, see literature
  12. ↑ David Boertmann, Nicholas Per Huffeldt: Seabird Colonies in the Melville Bay, Northwest Greenland (PDF; 3.77 MB), Scientific Report from DCE no. 45 2013, ISBN 978-87-92825-82-7
  13. ↑ Glutz von Blotzheim, p. 495f, see literature
  14. ↑ Snell (2002), section Distribution , see literature
  15. ↑ a b Glutz von Blotzheim, p. 496f, see literature
  16. ↑ a b c d Olsen / Larson (2003), p. 216, see literature
  17. ↑ a b c Glutz von Blotzheim, p. 500, see literature
  18. ↑ a b Snell (2002), Habitat section , see literature
  19. ↑ a b c d e Snell (2002), section Food Habits , see literature
  20. ↑ a b Goethe (1986), p. 131, see literature
  21. ↑ a b c Del Hoyo et al. (1996), see literature
  22. ↑ a b c d e f g h Glutz von Blotzheim, p. 500f, see literature
  23. ↑ a b c d e Snell (2002), section Breeding , see literature
  24. ↑ a b c Goethe (1986), p. 116f, see literature
  25. ↑ Jonathan Dwight: The gulls (Laridae) of the world; their plumages, moults, variations, relationships and distribution , Bulletin of the American Museum of Natural History, Vol. 52, Art. 3 (pp. 63-401), New York 1925, PDF , pp. 250f
  26. ↑ a b Snell (2002), section Systematics , see literature
  27. ↑ Goethe (1986), p. 114, see literature
  28. ↑ Dorit Liebers, Peter de Knijff and Andreas J. Helbig : The herring gull complex is not a ring species , The Royal Society 271, London 2004, pp. 893-901
  29. ^ IOC World Bird List , accessed May 31, 2012
  30. ↑ a b Hans-Günther Bauer, Einhard Bezzel and Wolfgang Fiedler (eds.): The Compendium of the Birds of Central Europe , Volume 1: Nonpasseriformes - non-sparrow birds . Aula-Verlag Wiebelsheim, Wiesbaden 2005, ISBN 3-89104-647-2 , p. 618
  31. ↑ BirdLife Species Factsheet, see web links
  32. ↑ a b c Snell (2002), section Conservation and Management , see literature
  33. ^ F. Salomonsen: The birds of Greenland , Vol. 2., FE Bording, Copenhagen 1951, cited in Glutz von Blotzheim, Del Hoyo et al. and Snell (see literature)

Web links

Commons : Arctic Gull  - album with pictures, videos and audio files