Male gull

from Wikipedia, the free encyclopedia
Male gull
Male gull in breeding plumage

Male gull in breeding plumage

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Laridae
Subfamily : Seagulls (larinae)
Genre : Larus
Type : Male gull
Scientific name
Larus Heermanni
Cassin , 1852

The Heermann gull ( Larus heermanni ) is a species of bird within the seagulls (Larinae). The medium-sized gull breeds in a few colonies mainly on islands in the Gulf of California . The populations of the monotypic species are currently stable, but due to the small number of breeding colonies that appear endangered, the IUCN has classified it as NT (= Near Threatened, "warning list"). The species was named after the North American doctor and naturalist Adolphus Lewis Heermann .

Previously, it was believed due to several morphological similarities that the Herrmannmöwe close with some salt lakes of Altiplanos breeding Graumöwe ( Larus modestus was used). Genetic findings do not support this and suggest a convergent development. Accordingly, the male gull is still in the genus Larus , the gray gull, however, is placed in the genus Leucophaeus .

Appearance

With an average body length of around 50 centimeters, the male gull is slightly smaller than a herring gull . Due to its mostly gray plumage and the dark slate-gray legs, the species is unmistakable in its range. In the brood dress, between February and July, the head, neck and throat are colored pure white; Shoulder, chest and the entire underside are mostly slate gray, sometimes mixed with brownish tones; older birds can be almost white on the underside. The upper plumage is darker, especially the arm and hand wings are dark gray or dark gray-brown. The black control springs have a very fine white terminal band. The rather powerful beak is coral red and ends in a black tip. The legs are dark slate gray, the iris is dark brown. Outside the breeding season, the birds have an almost uniform gray plumage color, but the head and neck are clearly speckled white-gray.

Adult male gull in resting dress

The sexes do not differ in terms of coloration, but males are on average somewhat larger and, at up to 640 grams, a little heavier than females. The juvenile plumage is similar to the winter plumage, but has stronger brown components. The beak of juvenile male gulls is also two-colored, but the base is flesh-colored and not bright red.

Red points : breeding colonies
Orange : non-breeding season occurrences, young birds and non-breeders

distribution and habitat

The male gull breeds on some small islands in the Gulf of California, or on islands off Mexico and Baja California . By far the largest breeding colony is on Isla Rasa , a sparsely vegetated, arid island in the Gulf of California, only 56 hectares in size, where over 90 percent of the total world population of this seagull species breed. Outside the breeding season, the species migrates northward along the coast to about Vancouver Island and migrates south again in the course of winter, towards the breeding grounds. The seagulls spend most of their time in large flocks and often socialized with other sea birds such as pelicans , cormorants , other species of gulls and shearwaters , where they follow schools of herrings and other schooling fish. However, they also appear on the coast, mainly on rocky coastlines, and at river mouths and ports.

food

Male gulls, like most gull species, are food generalists, consuming a wide variety of marine animals, as well as human waste and carrion. In addition to herring, the main fish are Pacific sardines , anchovies and smelts . In addition, squid and other mollusks as well as insects and lizards on land are also preyed on. The prey is usually picked up while flying from the surface of the water, occasionally the seagull dips briefly, but without completely submerging. At the hatchery, eggs and chicks from other colony breeders, primarily those of the ornamental tern ( Thalasseus elegans ), are a not insignificant nutritional supplement. Like other gulls, male gulls pursue conspecifics or other sea birds that have just found food, attack them and can often force them to strangle their prey or to drop it. Especially brown pelicans and blue-footed boobies are often victims of this kleptoparasitism .

Pair formation and brood

Male gulls usually start brooding when they are 4 years old. The first breeding birds appear in the breeding colonies from late February to early March. During this time, new pairs are formed, and old bonds can be renewed. Both birds usually build a nest in a natural or excavated hollow in the ground, which is loosely laid out with various materials such as small twigs, blades of grass, seaweed, and sometimes feathers. The distances between the nests are very small, there can be 20 nests per 100 square meters. The clutch consists of one or two eggs; clutches of 3 are rarely found. If the clutch is lost early, there is always a new clutch. The 60 × 42 mm eggs, about the size of a hen's egg, are individually very different in color, but mostly speckled brown, purple or olive green on a gray or blue-gray background. The main laying time is in April, the first clutches are already found in the first ten days of March, fresh clutches can be found by the beginning of June. The clutch is incubated by both parents; the exact incubation period is not known, but should be around 28 days. Both parents provide the young with gagged food, but no information is available about its composition. The nestling period is approximately 46 days. To what extent and for how long fledgling young gulls continue to be cared for by their parents is not known.

Existence and endangerment

At the moment the stocks of the male gull are stable or even increasing, as breeding attempts far north of the actual breeding areas, so on Alkatraz might indicate. Nevertheless, the situation of this species is classified as NT (= "Near Threatened"), which is mainly due to the fact that over 90 percent of the total world population breeds on a small island, which makes the species appear endangered by unforeseeable environmental influences. The total population of breeding birds is estimated at around 150,000 to 200,000 pairs. The number of breeding birds on Isla Rasa varies greatly from year to year; it reached a low point in 1975 with only 55,000 breeding pairs, which is probably related to oceanic phenomena such as El Niño and the resulting restricted food availability. About 120,000 to 150,000 pairs are currently breeding on the small island, which has been a nature reserve since 1964 and only scientists and representatives of the Mexican Ministry of the Environment are allowed to enter during the breeding season. As a result, the traditional egg collection, which used to have a severe impact on stocks, was almost completely prevented. Today, the main threat to this species of seagulls appears to be overfishing of their feeding waters. Many birds also fall victim to longline fishing .

Adult male gulls have few natural predators. Occasionally they are preyed on by birds of prey, especially peregrine falcons . In the breeding colonies, rats and yellow-legged gulls pose the greatest danger to eggs and chicks.

swell

  • Kamal Islam: Heermann's Gull (Larus heermanni) The Birds of North America Online (A. Poole, Ed.). Ithaca 2002. Cornell Lab of Ornithology. Issue 643 (BNA)
  • J.-M. Pons, A. Hassanin, P.-A. Crochet: Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers . Molecular Phylogenetics and Evolution, Volume 37, Issue 3, December 2005, pages 686-699 doi : 10.1016 / j.ympev.2005.05.011
  • Factsheet Birdlife International
  1. ↑ Factsheet Birdlife International
  2. ↑ Pons et al. (2005), see literature
  3. ↑ BNA (2002) Habitat
  4. ↑ BNA (2002) Food Habits
  5. ↑ BNA (2002) Breeding

Web links

Commons : Heermannmöwe ( Larus heermanni )  - Collection of images, videos and audio files