American herring gull
| American herring gull | ||||||||||||
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American herring gull ( Larus smithsonianus ), adult bird in winter plumage and sub-adult bird (front) |
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| Larus smithsonianus | ||||||||||||
| Coues , 1862 |
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The American Herring or Kanadamöwe ( Larus smithsonianus ) is a bird art within the gulls (Larinae). It colonizes large parts of North America from the northeastern United States and the Great Lakes from northwest to Alaska and has long been considered an American subspecies of the herring gull . But genetic evidence showed that they more closely at the Gull and its subspecies and especially with the Ostsibirienmöwe ( Larus (argentatus) vegae is related). The latter could even form a species with the American herring gull, but it is also often given species status today.
The most important external difference between the American and the European herring gull is the expression of the youth clothes, which differ significantly in both species. The adult clothes , on the other hand, are very similar, as are the ecological demands, diet and reproduction. The American herring gull is also one of the most common shorebirds in its range.
description
With a body length of 53 to 65 cm and a wingspan of 120 to 150 cm, the American herring gull is between the two herring gull subspecies argentatus and argenteus . It is very similar to the herring gull in general.
Adult birds
In the brood plumage the head, neck, underside, upper tail-coverts and tail feathers are pure white. The iris is light, the orbital ring is orange-yellow, as is the beak. This one has a red gony spot . Remains of a black subterminal band on the front bill may be present until May . The color of the back, shoulders and the upper side of the wings is a lighter gray than that of the herring gull and shows a slightly bluish tinge. The trailing edge of the wing is white, the wing tip black except for the white tips of the wings. In addition, there is a white subterminal field on the outer and often also on the inner flag of the second outer wrist. The hand swing pattern is similar to that of the nominate form of European herring gulls. The gray of the upper side of the wing runs into the black of the wing tip in the form of several “tongues”. The legs are flesh-colored, but can have a yellowish tone in some individuals when brooding.
In the winter dress, the head is darkened. The dotted lines are often extended to the neck and form a dark "hood". This drawing is concentrated around the eyes, which clearly stand out from it with the bright iris. The beak is more dull in color and often has a dark mark in the area of the front bill, which partially covers the gony's spot.
Head portrait of an American herring gull in winter
Feet of an American herring gull
In flight, the pattern of the hand wings is easy to see.
Bird in very dark youthful dress, typical for eastern North America
Bird in the first winter
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Youth dress
The youth dress is very variable. It differs from that of the herring gull primarily in that the head and underside have an evenly brownish color, which can range from dark chocolate brown to gray-brown, but always looks a little velvety and not streaky like the herring gull. The beak and eyes are dark, the head on the vertex, forehead and chin are often slightly lightened and the neck is blurred and streaked. The top is dark brown and looks scaled due to narrow, light hems. The upper side of the wing is brownish scaly with black wings contrasting with it and a light field on the inner hand wings. The underside of the wing appears clearly two-colored due to the brown under wing coverts and light wings below. The rump and tail-coverts are broadly banded and stand out from the blackish control feathers, which only have a narrow, whitish lace hem. The legs and feet are flesh-colored.
Immature birds
The first winter dress is also very variable and is similar to the youth dress. Birds that are dark when they are young maintain this overall impression, but appear lighter due to the wear of their plumage. The shoulder and back plumage is gray with dark, subterminal markings. The base of the beak brightens up a bit. Some birds develop a very light head, which stands out clearly from the monotonous gray-brown body. The base of the beak in these individuals is often flesh-colored, light with a distinct black tip. Other birds become much brighter, especially in summer, and then resemble immature herring gulls, but show more blurred stripes on the flanks and underside.
In the second winter, some individuals are still quite gray-brown with a faded banded underside and head markings. Others already have a large proportion of light gray feathers on their shoulders and back. The large arm covers form an easily recognizable wing band with their dark feather centers. The rump is now white, the tail shows a broad dark band. The base of the beak has clearly lightened flesh-colored and the beak has a bright tip.
Birds in the third winter are similar to adult birds in winter plumage, but differ in the large arm covers drawn in brown, dark hand covers and the remains of a dark tail band. Another characteristic are the still very narrow white pointy spots on the wings of the hand. The black on the beak is much more extensive, the beak overall more flesh-colored.
Birds in their fourth winter still show remains of dark markings on hand covers, umbrella and rudder feathers. The pointy spots on the wings of the hand are still small and the dark markings on the now yellow beak are even more extensive than on adult animals.
voice
The vocal expressions are similar to those of the herring gull, but sound a bit bitter, deeper and faster overall. At least the calls differ in such a way that European herring gulls do not respond to a dummy sound with calls from the American herring gull. A frequent call is a si-auww , which is often followed by a deep, cackling gag-ag-ag-ag . In addition, a monosyllabic kluh and a hollow, deep kaaw can be heard.
Distribution and existence
The breeding distribution of the American herring gull extends from central Alaska eastward through the Northwest Territories , where it is only absent on the Beaufort Sea and in the extreme northwest north of the Arctic Circle. It breeds in the northeast on Southampton Island and in the south on Baffin Island . The southern border runs in the Rocky Mountains through the Cariboo Regional District in British Columbia , through Montana and northern Minnesota , Michigan and Illinois , northern Ohio and northern New York . On the east coast the species breeds south to North Carolina . In the west the area extends to New Brunswick , Nova Scotia and Newfoundland .
By 1900 the American black-backed gull had reached a low level due to the massive, commercial removal of eggs and young birds from the breeding colonies, but recovered after the species was placed under protection. Until the 1970s it doubled every 12–15 years. In New England , for example, the population rose from 4,000 to 8,000 pairs to 90,000 between 1901 and 1972. At the Great Lakes there have been local population declines again since 1980. The total worldwide population is now estimated at over 150,000 pairs. Since the species is still seen by the IUCN as conspecific with the herring gull, there is no separate endangerment status. But it is not endangered.
Geographical variation and hybrids
Since the American herring gull has long been considered a subspecies of the herring gull, little attention has been paid to a systematic study of geographic variation. This runs very gradually (clinically) from east to west. Adult birds are larger in the northeast and a bit darker on top. The hand wing shows more white and less black. In the winter plumage, a relatively dense head markings is common in northeastern birds. The same can be said for immature birds, which are generally darker in the northeast and in which the light field on the inner arm wings is often only very inconspicuous. On the west coast, a lighter type dominates, which is more reminiscent of the European herring gull.
In the area of the Arctic, hybrids with the ice gull are common in places . In their adult dress, these birds look like very bright American herring gulls with a very pale hand-wing pattern. Immature birds are quite light with brown outer and very light inner hand wings, pale brown arm covers and control feathers. The banding on the rump and under tail-coverts is often finer.
Hybrids with the Bering gull sometimes appear on the southern coast of Alaska .
hikes
Most American herring gulls are resident birds , but the northern populations migrate over the others to the wintering areas in the eastern and southern United States . Between December and January there are large concentrations such as 75,300 individuals in New York, 65,000 in Ontario, 50,000 in Pennsylvania and Virginia. On the Pacific coast, the species is widespread in winter, but not as numerically represented as on the east coast. The wintering areas extend partly to Central America and the West Indies . Here the species is only found in very small numbers.
food
The food spectrum is very broad, because the species feeds quite opportunistically. A rich supply of food is often used extensively and sometimes exclusively. The diet mostly consists of fish, worms, crabs and other marine animals such as mollusks and echinoderms , although certain species are sometimes preferred. In the mudflats off Maine it was observed that the green ringworm ( Nereis virens ) was given preference over smaller worms, the common sea crab , edible crabs and mussels . Furthermore, litter makes up a large part of the diet and the species is often found in large accumulations at dumps, fishing ports and sewers. Birds, bird eggs and nestlings are also captured. Sometimes some individuals or local populations specialize in it. In addition, insects and other arthropods , small mammals, fruits and arable crops are accepted as food. A study in Newfoundland found that during the breeding season, 75–80% specialized in one of three food sources - intertidal animals, rubbish dumps, or other seabirds. Only 20-25% maintained a diversified diet.
Reproduction
The American herring gull usually breeds in colonies that can contain up to several thousand breeding pairs. The nest spacing is between 60 cm and 10 m, but is mostly 2 m. Solitary pairs are less common and often breed on the edge of seabird colonies of other species.
The nest is built in locations that are safe from flooding and often under the protection of the vegetation. On the coast of New Jersey, only slightly elevated locations on islands in salt marshes were populated with vegetation from the silt grass Spartina patens . Places where the S. alterniflora silt grass grew and where there was a greater risk of flooding were avoided. Nest locations under bushes were preferred. In Newfoundland, the brood density was highest on rock terraces by the sea and the breeding success was significantly better here than on locations in coastal meadows, which were significantly more exposed to the risk of predation.
The nest is a voluminous structure made of grass, seaweed or other plant parts, which is preferably built in a hollow. The eggs are laid between the beginning of May and the beginning of June. The clutch usually consists of 2–3 eggs, which are incubated between 28 and 30 days. The boys become independent after 40–45 days.
Individual evidence
- ↑ Olsen / Larsson (2003), p. 244 and p. 254, see literature
- ↑ Glutz v. Blotzheim, p. 514, see literature
- ↑ Karole A. Haycock, William Threlfall: The Breeding Biology of the herring Gull in Newfoundland , The Auk 92 (Oct. 1975), pp. 678-697
- ↑ a b Olsen / Larsson (2003), p. 248, see literature
- ↑ Olsen / Larsson (2003), p. 247f, see literature
- ↑ a b Olsen / Larsson (2003), p. 248, see literature
- ↑ Karel A. Allard, André R. Breton, H. Grant Gilchrist, Antony W. Diamond: Adult Survival of Herring Gulls Breeding in the Canadian Arctic , Waterbirds, 29 (2), 2006, pp. 163-168
- ↑ a b c d Del Hoyo et al. (1996), pp. 609-610, p. literature
- ^ Raymond Pierotti, Cynthia A. Annett: Diet Choice in the Herring Gull: Constraints Imposed by Reproductive and Ecological Factors , Ecology Vol. 72, no. 1 (Feb. 1991), pp. 319-328
- ↑ Joanna Burger, Fred Lesser: Nest Site Selection in an Expanding Population of Herring Gulls , Journal of Field Ornithology 51 (3), 1980, pp. 270-280
literature
- Klaus Malling Olsen, Hans Larsson: Gulls of Europe, Asia and North America , Helm Identification Guides, Christopher Helm, London 2003 (corrected new edition from 2004), ISBN 978-0-7136-7087-5
- Urs N. Glutz von Blotzheim, KM Bauer : Handbook of the birds of Central Europe. Volume 8 / I: Charadriiformes. 3rd part: snipe, gull and alken birds. AULA-Verlag, ISBN 3-923527-00-4 .
- Josep del Hoyo , Andrew Elliott, Jordi Sargatal (eds.): Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions 1996, ISBN 978-84-87334-20-7 , pp. 604-605.
- 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
- JM Collinson, DT Parkin, AG Knox, G. Sangster, L. Svensson: Species boundaries in the Herring and Lesser Black-backed Gull complex . British Birds 101 (7), 2008, pp. 340-363
Web links
- Videos, photos and sound recordings of Larus smithsonianus in the Internet Bird Collection