Spatula skua
| Spatula skua | ||||||||
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Spatula sku (Helle Morphe in the summer of the second calendar year) |
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| Systematics | ||||||||
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| Scientific name | ||||||||
| Stercorarius pomarinus | ||||||||
| ( Temminck , 1815) |
The Pomarine ( Stercorarius pomarinus ) is a species of bird in the family of skuas (Stercorariidae). It breeds in the arctic tundra around the North Pole and is a highly specialized lemmings hunter there . Outside the breeding season, Spatula skuas live on the high seas, they overwinter on the seas of the tropics and subtropics . The species is a regular migrant on the North Sea coast, in inland Europe it is observed only very rarely.
description
anatomy
The Spatula Skua is the second largest Holarctic skua after the Skua . The body length is 42–50 cm, the wingspan 115–125 cm. The size of the species lies between the common gull and herring gull . Females are, on average, slightly larger and heavier than males. Adult male winter guests off Australia had a wing length of 341–368 mm, on average 352 mm; Females measured 339–373 mm, with an average of 360 mm. Male breeding birds that were hunted in northeastern Yakutia weighed 620–800 g (mean 660.0 g), females hunted there 680–830 g, mean 766.6 g.
Wing lengths of adult birds measured on museum bellows from the entire distribution area showed 343–377 mm for males, with an average of 360 mm; for females 341–382 mm, mean 366 mm.
This sku is strongly built, with a full chest, a large head and a rather powerful beak. As with all skuas, the upper beak shows a clear hook downwards. In gliding flight or slow rowing flight it looks very large and broad-winged, with a strong trunk and large head. The wings are very pointed, so at high airspeed the flight pattern looks more like that of a large falcon than that of a seagull.
Splendid dress
The spatula sku is quite variable in color and shows two color morphs in its splendid dress . In both morphs, the middle pair of control feathers is greatly elongated in the magnificent dress . These control feathers protrude from the rest of the tail by about 5.5 to 11.0 cm, are slightly twisted and have a spatula- shaped end (name!). In both morphs, the beak is pink with a sharp black tip, the legs are lead-gray.
In the light morph, the abdomen, chest and throat are bright white; the white of the neck and chest is separated by a dark chest band. The back of the skull is black, this black drawing extends forward and only ends there below the eye and below the beak. The head sides are light yellow. The rest of the underside and the entire upper side are almost monochrome, dark gray-brown. Only the base and the keels of the hand wings are white, as a result of which the hand wing shows a narrow white lightening on the upper side while in flight, a large whitish-gray field on the underside, which extends from the bases of the hand wings to about the middle.
The rarer dark morph is almost monochrome black-brown in its magnificent dress. The lower wing and the lower and upper tail-coverts are narrowly banded dark on a whitish-gray background. The wings are a little lighter gray on the underside than the under wing-coverts and the hand wings show the same bright fields as the bright morph.
The proportion of the dark morph in the breeding populations fluctuates with the geographical distribution between 1 and 15%. In the nearctic breeding areas, the proportion of dark birds seems to be slightly lower than in the Palearctic and rarely exceeds 10% in the individual populations.
Resting dress
The calm dress differs only slightly from the magnificent dress. The most striking difference in the light Morph is the lack of yellow on the sides of the head, which are instead darkly banded on a whitish background. In both morphs, part of the shoulder feathers and the feathers on the front back have a narrow, light border.
Youth dress
Birds in youthful dress can only be roughly assigned to the two color morphs. The lightest birds are medium gray-brown, but most birds are darker gray-brown; Swimming birds appear almost monochrome dark gray-brown in their youthful dress at a great distance. The beak is light blue-gray with a sharp black tip. The under-tail-coverts are strongly and sharply set off with a yellowish to almost white background and are cross-banded in dark brown. From a closer distance, the head and neck of swimming birds appear monochrome dark gray-brown, with the regions around the eyes being the darkest. The rest of the upper side is also dark gray-brown, but the cover feathers have a faint light brown border. These light edges are often barely noticeable on the large arm covers and the umbrella feathers. The tips of the hand swing arms do not show a light edge. The upper back, chest and flanks are a little lighter brown, the chest and flanks are finely banded in dark.
When gliding, birds in youthful dress appear almost monochrome dark brown on the upper side, the light-colored base of the hand wings is only recognizable on the outermost hand wings and is hardly noticeable. Only when the wings are spread out for landing are the light-colored bases and the white keels visible above on all the wings of the hand. The underside of the wings is significantly lighter and, compared to the upper side, strikingly rich in contrast. As in colored birds, the hand wings are monochrome whitish gray from the base up to about half the length; there is also another, often less noticeable and difficult to see, narrow, whitish band on the coverts of the lower hand towards the bend of the wing. The under wing-coverts are otherwise like the under-tail coverts on a whitish background strongly banded dark.
The tail is slightly wedge-shaped, the central control feathers protrude a maximum of only 1–2 cm above the rest of the tail and are rounded at the ends. The legs are light blue-gray; the toes and webbed feet are blackish-gray.
Spatula skuas are colored after 3 years. From the second calendar year, birds of the light morph show a strongly lightened belly, a dark upper head and diffuse yellowish head sides.
Possible confusion
Colored ( adult ) Spatula skuas in their splendid plumage can be easily distinguished from the other skuas by the spatulate ends of the central control feathers, the dark chest band and the black markings on the head that extend to below the beak.
The reliable identification of birds in their youthful dress is one of the difficult problems of field ornithology in Central Europe and is only possible under very good conditions or with a lot of experience with the other species of sku. Juvenile Spatula skuas differ from all other skuas in the combination of almost always monochrome, dark brown-gray head and neck, light blue-gray beak with a sharp black tip, finely light-dark banded breast and belly, strong and sharp banding of the under tail coverts and almost always missing or completely short tail skewers. In addition, only this species shows a white band on the bases of the lower hand covers in active flight. The species is also heavier and larger than the hawk and arctic skua ; however, this can hardly be used for the determination of a single bird at a greater distance.
Vocalizations
Like all skuas, this species is mostly silent outside of the breeding season. The courtship "song" is a monosyllabic shouting that is rendered with "jau (w) k". The standing bird stretches its wings and lifts its tail feathers. This call is also made during courtship flight, the wings are held slightly upwards so that a slightly V-shaped flight pattern is created. When attacking nest enemies, sharp, barking calls are emitted, which sound something like "kek kek kek". Alarm calls at the nest have two syllables like "witsch-jü".
distribution and habitat
The species inhabits large areas of the arctic tundra around the North Pole in summer . In Eurasia, the distribution area extends in the far north from the Kanin peninsula in northern Russia to northeast Siberia. In North America, the species occurs in the far north of Alaska and Canada . The brood distribution extends in Canada and Siberia to 76 ° N and in the Nearctic only falls below the Arctic Circle on the west coast of Alaska and in the Canadian Hudson Bay . In Siberia, the southernmost occurrences are on the Commander Islands at 55 ° N.
The spatula sku colonizes the more or less humid to wet tundra of the swampy lowlands, especially near the coast.
hikes
Outside the breeding season, the Spatula sku is an inhabitant of the oceans. The wintering areas are mainly in the tropical seas north of the equator in areas where cold deep water penetrates the surface through currents, as these areas are particularly rich in food. These are above all the Humboldt Current on the west coast of South America, the western Atlantic between Florida and Venezuela as well as the Benguela Current , the South Equatorial Current and its contact zone with the warm Guinea Current and the Canary Current off the west coast of Africa. Smaller numbers overwinter in the Indian Ocean north to the Gulf of Aden , the Arabian Sea and the Gulf of Oman as well as between New Guinea and the southeast coast of Australia.
At least occasional winter observations are also available from the other sea areas in the area of the continental shelf from the west coast of South America and the west and east coast of southern North America, all of Africa and Europe to southern Norway as well as all of Southeast Asia and Australia.
The migration of non-breeders begins in July, of breeding birds from August. The vast majority of the western Palearctic population evidently moves south along the European coasts of the North Atlantic or the North Sea to the winter quarters off the West African coast. On the Dutch North Sea coast, migration begins hesitantly at the end of July and then increases significantly from mid-August. The main passage takes place from the beginning of October to the middle of November; then the train ends quickly. Adult and sub-adult animals predominate until the end of October, later this year's individuals dominate. The migration takes place here mainly near the coast, on the open sea the species is hardly registered here, even at migration time.
On the Baltic coast, the species is rarely observed during migration, and very rarely in inland Central Europe, although part of the population at least in autumn regularly migrates across eastern Central Europe and Eastern Europe. For example, in Brandenburg and Berlin only 16 individuals were recorded up to 2004 (15 of them from July to November, one in March), in Switzerland from 1950–1996 49 individuals; here without exception on the move from August to December, with a significant increase in October and November. The small number of reliable records is, however, also due to the great difficulty of identification in the field, for example 845 skuas were observed in Switzerland in the above-mentioned period, which could not be identified at species level.
The home move begins in early to mid-April, the main move takes place in May. The breeding areas are reached in mid-May to early June. The migration home is evidently more concentrated than the migration over the sea, so inland observations in spring are extremely rare in Central Europe (see above). Great Britain is mainly passed on the west side, the further migration takes place along the coast of Norway to the North Cape and then east to the breeding areas.
nutrition
As with all skuas, the food spectrum of the spatula sku is very broad and includes small mammals, birds, fish, insects, crustaceans, molluscs and carrion. In most of the breeding areas, however, the species is dependent on lemmings - primarily Siberian lemmings ( Lemmus sibiricus ). In addition, also be in the breeding area collar Lemminge (genus Dicrostonyx ) field and Rötelmäuse , bird eggs and chicks as well as insect consumed. The Spatula sku has developed special hunting techniques for capturing lemmings; these are captured in spring when the ground is still completely frozen from the hide or from the shaking flight , later the flat tubes and burrows are dug up with the beak.
Non-breeding over-summerers also stay in the tundra in the lemming years and then also live there almost exclusively on lemmings. Otherwise they are mainly to be found near the coast and eat fish and carrion they have caught themselves or feed on a kleptoparasitic diet . The main victims are kittiwakes and arctic terns , but also large gulls up to the ice gull , which are attacked until they drop their prey or choke it back in flight.
On the migration and in winter quarters, the species often follows fishing trawlers in order to use the bycatch thrown overboard , or parasitizes other seabirds there. Here, however, she mostly catches fish herself, especially flying fish (family Exocoetidae) in the tropics , and therefore often accompanies dolphins or large predatory fish such as tuna that hunt in schools . Adult birds are also occasionally captured in the breeding area, especially small limikoles such as water treaders , but also larger birds on the move, especially black-headed gulls , which are usually drowned.
Reproduction
The nest is usually a simple hollow, about 5 cm deep scratched into the peat, with a diameter of about 25 cm. During incubation, this hollow is often covered with dry grass or leaves. The eggs are laid from early or mid-June to mid-July. The clutch usually consists of 2 eggs, more rarely only one egg is laid. In Alaska, for example, one egg was found 13 times (5.0%) in 261 nests, and two eggs in all other nests. Eggs from North America measured on average 62.0 × 44.0 mm, eggs from Siberia on average 63.8 × 44.7 mm. The basic color of the eggs varies from light brown or yellowish to dark olive green or dark brown. For this reason, the eggs are mottled gray to gray-violet, and often also show almost black lines or squiggles.
The breeding period is 25–27 days, in Alaska it was an average of 26 days. The down clothes of the nest young birds are plain dark brown or brown-gray. The young birds fledge after 28–34 days and are then guided by their parents for around 14 days.
The nest is vehemently defended against predators such as the ice fox by both partners. People are attacked head-on and at head height, but immediately before contact the birds turn away so that the head is usually only touched with the feet or the wing tips, if at all.
Settlement density
Due to their dependence on the frequency of the main prey lemmings, the settlement density of the Spatula sku varies enormously from year to year in individual areas. In several control areas in Alaska the density at the height of a lemming gradation was 7.9 breeding pairs / km², in lemming latency years only 0.05 BP / km², thus fluctuating more than a hundred times.
Life expectancy and mortality
So far, no information is available on the maximum age and mortality after fledging. Also, there are apparently no re-finds of ringed birds so far.
Systematics
The systematic position of the Spatula skua within the family of the skuas was at times controversial. The taxon of skuas was often divided into two genera: Stercorarius with the three types spatula, parasitic and Skua and Catharacta with the Skua and depending on the systematic conception of the author 1 to 5 Skua species of the Antarctic . Andersson pointed out as early as 1973, however, that the behavior of the Spatula skua is much more similar to that of the Skua than that of the Arctic and Hawk sku. Cohen et al. questioned the monophyly of the two genera again in 1997 on the basis of investigations of the mtDNA and certain ectoparasites , since according to their results the Spatula skua was much closer to the Skua than the other two species of the genus Stercorarius and the Skua itself closer to the Spatula skua than the other species Genus Catharacta . Braun & Brumfield analyzed the data from Cohen et al. again and came to the conclusion that the results of a monophyly of the genus Catharacta in the previous composition do not contradict, but the spatula sku is the sister taxon of the genus Catharacta . Andersson confirmed this position as sister taxon again on the basis of behavioral characteristics and pointed out that either, if the genus Catharacta was retained , the Spatula sku would have to be added to this genus or the genus Catharacta would have to be dissolved and reunited with Stercorarius .
In the more recent literature, Andersson's second proposal has prevailed (dissolution of the genus Catharacta and union with Stercorarius ), so that the sku family now only contains one genus Stercorarius . Glutz von Blotzheim & Bauer had already rejected the division of the family into two categories in 1982, with reference to Andersson's work from 1973 (see above).
So far, no subspecies have been described for the Spatula skua.
Population development and endangerment
Reliable information on the size and development of the population is not available; the IUCN gives a rough estimate for the population of 50,000 to 100,000 individuals. There are no indications of a threat, the species is therefore considered to be harmless (“least concern”).
swell
literature
- Klaus Malling Olsen & Hans Larsson: Skuas and Jaegers . Pica, East Sussex, 1997. ISBN 1-873403-46-1
- Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe. Volume 8 / I: Charadriiformes. 3rd part: snipe, gull and alken birds. Aula, Wiesbaden 1999, ISBN 3-923527-00-4 .
- R. Haven Wiley & David S. Lee: Pomarine Jaeger (Stercorarius pomarinus) . In: The Birds of North America, No. 483 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. Issue 483. (BNA)
- Lars Svensson , Peter J. Grant, Killian Mullarney, Dan Zetterström: The new cosmos bird guide. Kosmos, Stuttgart 1999, ISBN 3-440-07720-9 .
Web links
- Stercorarius pomarinus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed October 13 of 2008.
- Videos, photos and sound recordings of Stercorarius pomarinus in the Internet Bird Collection
- Spatula skua feathers
Individual evidence
- ^ Serventy, DL, VN Serventy & J. Warham: The handbook of Australian Seabirds. AH & AW Reed Ltd., Wellington, Auckland, Sydney & Melbourne, 1971. cit. in Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe , Volume 8 / I, Charadriiformes (3rd part) Snipe, gull and alken birds. 2nd ed., Aula, Wiesbaden, 1999: p. 53.
- ↑ Uspenskij, Böme, Priklonskij & Wechow, Ornitologija 4, 1962 (page number not given) cited. in: Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe , Volume 8 / I, Charadriiformes (3rd part) Snipe, gull and alken birds. 2nd ed., Aula, Wiesbaden, 1999: p. 53
- ^ Klaus Malling Olsen & Hans Larsson: Skuas and Jaegers . Pica, East Sussex, 1997: p. 119. ISBN 1-873403-46-1
- ↑ BNA (2000) Species (no page count)
- ^ RG Bijlsma, F. Hustings & K. (CJ) Camphuysen: Common and scarce birds of the Netherlands. (Avifauna van Nederland 2). GMB Uitgeverij / KKNNV Uitgeverij, Haarlem / Utrecht, 2001. ISBN 90-74345-21-2 : pp. 236-237.
- ↑ K. Witt & R. Beschow: Pomarine - Stercorarius pomarinus . In: Association of Berlin-Brandenburg Ornithologists (ABBO): The bird world of Brandenburg and Berlin . Natur & Text, Rangsdorf, 2001. ISBN 3-9807627-5-0 : pp. 314-315.
- ↑ H. Haupt, W. Mädlow & U. Tammler: Avifaunistischer annual report for Brandenburg and Berlin 2003. Otis 13, 2005: pp 1-43
- ^ R. Winkler: Avifauna of Switzerland. Der Ornithologische Beobachter, Supplement 10, 1999: pp. 106-107.
- ^ A b c W. J. Maher: Ecology of Pomarine, Parasitic, and Long-tailed Jaegers in Northern Alaska. Pacific Coast Avifauna 37, 1974, I-VIII, 1-148. quoted in: Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe , Volume 8 / I, Charadriiformes (3rd part) Snipe, gull and alken birds. 2nd edition, Aula, Wiesbaden, 1999
- ↑ M. Andersson: Behavior of the Pomarine Skua with comparative remarks on Stercorariinae. Ornis Scand. 4, 1973: pp. 1-16. quoted in: Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe , Volume 8 / I, Charadriiformes (3rd part) Snipe, gull and alken birds. 2nd edition, Aula, Wiesbaden, 1999: p. 15. ISBN 3-923527-00-4
- ↑ BL Cohen, AJ Baker, K. Blechschmidt, DL Dittmann, RW Furness, JA Gerwin, AJ Helbig, J. De Korte, HD Marshall, RL Palma, H.-U. Peter, R. Ramli, I. Siebold, MS Willcox, RH Wilson, RM Zinc: Enigmatic Phylogeny of Skuas (Aves: Stercorariidae). Proceedings of the Royal Society London: Biological Sciences 264, Issue 1379, 1997: pp. 181-190
- ↑ MJ Braun & RT Brumfield: Enigmatic Phylogeny of Skuas: An Alternative Hypothesis. Proceedings of the Royal Society London: Biological Sciences 265 Issue 1400, 1998: pp. 995-999
- ↑ M. Andersson: Phylogeny, Behavior, Plumage Evolution and Neoteny in Skuas Stercorariidae. Journal of Avian Biology 30, No. 2, 1999: pp. 205-215
- ^ American Ornithologists 'Union: Forty-second supplement to the American Ornithologists' Union Check-list of North American Birds. Auk 117, 2000: pp. 847–858 full text as pdf
- ^ PH Barthel & AJ Helbig: List of species of birds in Germany. Limicola 19; 2005: pp. 89-111.
- ↑ Urs N. Glutz von Blotzheim & Kurt M. Bauer: Handbook of the birds of Central Europe , Volume 8 / I, Charadriiformes (3rd part) Snipe, seagull and alken birds. 2nd edition, Aula, Wiesbaden, 1999: p. 15
