Western gull

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Western gull
Gull ca usa.jpg

Western gull ( Larus occidentalis )

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Laridae
Subfamily : Seagulls (larinae)
Genre : Larus
Type : Western gull
Scientific name
Larus occidentalis
Audubon , 1839

The western gull ( Larus occidentalis ) is a species of bird found on the west coast of North America among the gulls (Larinae). It is the only seagull species that breeds along the entire stretch of the Pacific coast from Vancouver Island in the north to the Mexican Baja California peninsula in the south.

The western gull is one of the large gulls and differs from the common bering gull ( Larus glaucescens ) by its darker back, its black instead of gray markings on the wing tips and its amber-yellow iris with an orange-yellow to pale pink orbital ring instead of a brown iris with a reddish- purple orbital ring. In the northern part of the distribution area of ​​the western gull there is an intensive hybridization with the bering gull, which makes the identification more difficult.

In contrast to other species of gull, the western gull is extremely rare inland. It prefers to breed not far from the Pacific coast on rocky islands such as Southeast Farallon Island , where more than 30% of the total population is native.

The western gull, like most seagulls, is omnivorous , but feeds primarily on fish and invertebrates . When the opportunity arises, it also feeds on carrion and human waste.

Due to its extensive distribution area and the large total population, the species is classified as not endangered by the IUCN . Since the western gull mainly finds its food in the sea, it is potentially threatened by weather phenomena such as El Niño and human influences such as oil spills , plastic waste and pollution from pesticides .

features

Build and color

West gulls at Bodega Head (1 minute 22 seconds, 20.6 MB). The February 2016 footage shows western gulls on the rocky coast of Sonoma County, California.

With a length of 62 to 66 cm and a wingspan of 135 to 140 cm, the western gull is one of the larger gull species. In adults , the head, neck, underside and tail are white; The head and neck of the nominate form can be interspersed with gray dashes in winter. The upper and upper wing covers are lead gray, the wings are gray and have black hand wings . The tips of the rearmost arm wings are light gray to white. The yellow beak has a red spot on the gonyseck , the angle on the underside of the beak. The feet are flesh-colored. Adult specimens of the two subspecies L. o. Occidentalis and L. o. Wymani are easiest to distinguish by the color of their coat. In the occidentalis subspecies , this is slate-colored, while that of the wymani subspecies is darker.

Western gulls take four years to develop into adults, like most of the larger gulls. During this time, the young seagulls go through different stages of coloring, which makes it difficult to determine the exact age. The development of the coloring is individually very variable and depends, among other things, on the time of the moult . Some broad ideal characteristics include:

  • Youth dress: fairly uniform dark brown head and body. Back and wings dark with light feather edges. Tail dark brown. The wing feathers on the top of the wings are blackish, on the underside they are shiny gray. Black beak. Legs dark gray and light pink. Iris dark brown.
  • First winter: The first plain dress is similar to the youth dress, but has gray feathers on the head, neck, chest and shoulder feathers to a very different extent. Black beak with pale coloring below. Iris dark brown.
  • Second winter: head and underside more white, but still gray stripes on the nape. Back piebald and dark gray. White underside, striped neck. White wing tips. Dark tail. Bill pale flesh-colored, with a blackish stripe behind the nostrils. White beak tip. Irises pale straw-colored or brown.
  • Third winter: neck and head with some brown feathers, otherwise white. Dark gray back with only a few brown feathers. Underside white. Tail mostly white with some dark sprinkles. Wings black with white tips. Arm wings dark gray with broad white tips. Bill yellowish with a blackish stripe behind the nostrils. Iris yellow or yellow-brown.

  • Western gull in the first winter

  • Western gull in the second winter

Flight image and locomotion

Aerial image of a pre-adult western gull

On land, western gulls usually move by walking or running. In order to reach higher places, the animals push their legs off the ground and at the same time ensure an upward movement by flapping their wings. When fighting with adversaries, western gulls walk with wings partially raised. Hopping is not used for locomotion.

In flight, western gulls move very often gliding. The wings are angled for a dive. When approaching groups of seabirds swimming on the water for food, western gulls often fly in ever smaller circles while flapping their wings quickly. Invaders into their territory drive western gulls swooping away, attacking their enemies with flaps of their wings and with their feet.

When swimming on the water, western gulls use their legs to move. Diving for food takes place either from the surface of the water or from a low altitude. When diving, however, the animals can only reach depths of no more than one to two meters.

Vocalizations

Cheering of a western gull at Bodega Head (27 seconds, 7.3 MB)

Western gulls have a complex repertoire of 12 to 15 calls. Two of these calls only occur with young birds and three others only during the breeding season.

The cheering of the western gull ( long call ) is a loud series of calls of more than six tones generated in quick succession. Male animals use the exultation towards rivals in the course of the formation of the territory as well as before the brood. Compared to related gulls, the cheering of the western gull is shorter, deeper and less clear.

The "Katzenruf" (English mew call ) sounds like the drawn out meow of a house cat. It can be heard above all in breeding colonies and is uttered by western gulls mostly during recruitment, interaction with their young and in conflicts with neighboring breeding pairs.

The “ choking call ” is a series of guttural huo-huo-huo sounds that occur when the animals are aggressive towards other conspecifics and when choosing a nesting site.

Western gulls use their alarm call ( Eh-Eh , HaHaHa , or Kek-Kek ) as soon as they spot an intruder but this is not yet an immediate threat.

Habitat, Distribution, and Migration

Distribution of the western gull. Orange: only in winter, green: all year round

The range of the western gull extends from Vancouver Island to the southern tip of the Mexican Baja California peninsula . The outer sections of the distribution area in the north and south serve the animals only as winter quarters.

The western gull is found almost exclusively near the coast and - unlike other gull species - is extremely rarely found inland. An exception is the salmon spawning season in the Pacific Northwest , during which the western gulls follow the salmon for a few kilometers upriver. In winter, the animals seek shelter from storms in large bays such as Puget Sound and San Francisco Bay .

When breeding, the western gull prefers islands and rocks off the coast, often near colonies of the California sea lion ( Zalophus californianus ). The largest breeding colony with more than 13,000 pairs is located on Southeast Farallon Island , a volcanic rock island around 43 kilometers west of the Golden Gate .

Animals of the subspecies L. o. Occidentalis move only to a limited extent from their colony. Studies of birds ringed on South East Farallon Island in the 1970s and 80s showed that few individuals left the island permanently. Older birds stay in their breeding area almost all year round, while younger individuals migrate north to more nutrient-rich areas in summer and then return south again in winter.

A few western gulls of the L. o. Wymani subspecies migrate to the coast of the Mexican state of Sonora on the eastern side of the Gulf of California . About 20,000 to 30,000 individuals overwinter near the California city of Santa Cruz .

Way of life

Food acquisition and food

Western gulls devour smaller prey in one piece (here a starfish ).

Like most gulls , western gulls are omnivores . They feed primarily on fish such as the American anchovy ( Engraulis mordax ) and invertebrates such as krill , octopus , jellyfish , starfish , clams and snails . In addition, they feed on eggs and juveniles from other western gulls and related birds. When the opportunity arises, they also feed on carrion and search human waste for usable remains.

Research on Alcatraz Island has shown that the choice of food depends not only on the availability of the different food sources, but also on other factors. Western gulls on the islet in San Francisco Bay switched their diets from human waste to small fish as soon as the breeding season began in June. This is attributed to the fact that the nutritional value - measured in terms of protein, fat and calories - per gram of food for fish is higher than for the waste on Alcatraz Island, which mainly consisted of chicken meat. A long-term study of the breeding success in relation to the choice of food showed that particularly successful western gulls and their young fed on fish for more than 60%.

It is not uncommon for western gulls to feed on a kleptoparasite . Here a western gull chasing an ornamental tern ( Thalasseus elegans ).

When looking for food on the open sea, scattered groups of western gulls quickly unite to form large flocks as soon as they spot groups of prey. Often they follow foraging California ( Zalophus californianus ) and Steller sea lions ( Eumetopias jubatus ), southern fur seals ( Arctocephalus ) and dolphins . In addition, they join groups of birds that prey on their food by diving (especially pelicans , cormorants , guillemots and alken birds ). Western gulls also often act as catalysts by being the first to spot schools of fish and by their activity attracting other species.

Western gulls prey on their food either by swimming on the water and grabbing prey below the surface with their beak, by shallow diving or by landing and grasping with their toes. Near the coast they also prey on their food continuously at low tide.

Reproduction

Colonies and territorial behavior

Western gulls usually breed in colonies, with the nest spacing between 1.5 and 2.0 meters on Bird Rock (a tiny island near Santa Catalina Island ) and between 1.75 and 21.0 meters (ø 10.9 ± 4.9 Meters) on Santa Barbara Island . The size of the respective territory depends on both the subsoil and the heterogeneity of the habitat , with more heterogeneous habitats resulting in smaller territories. The territory behavior varies depending on the breeding phase. Aggressive behavior is weakest during the incubation of the eggs and strongest during the rearing of the young.

Pairing and copulation

Copulation of two western gulls

When pairs are formed between January and June, the female approaches the male in a humble "humpback position", throws her head back and lets out a begging call. The males react to this either with an upright posture or with the "cat call" posture and the cat call. The female then circles the male and increases her efforts when the male answers with the cat call. The copulation occurs as soon as the female accepts high gewürgtes feed by the male.

Nest building, incubation and rearing of young

Two western gulls with their recently hatched chick in San Luis Obispo
Chick about three weeks old in San Luis Obispo

The nesting of the western gulls begins in the last weeks of April and regularly ends in May, rarely until June. During this time, both the male and the female dig up to three hollows in a sheltered position, which they fill with nesting material. When creating the nest hollows with an average of 15 cm inside diameter, the animals emit a guttural sound, the " choking call" . If both sexes sound the pestle sound together on a hollow, this is a sign that the nesting site has been chosen. The decision is final as soon as the female starts laying eggs.

The female usually lays three eggs in the nesting trough every two days. During this time, the female, who rarely moves from the nest, is provided with food by the male. The eggs are incubated by both parent animals for about a month, with the animals taking turns every two to four hours. The eggs weigh between 85 and 105 grams, 67–75 mm long, 47–52 mm wide and are light olive, yellow-brown or greenish in color with black, dark brown or dark olive spots.

From the moment the chick first breaks through the egg shell with its beak, hatching takes a total of two to three days. During this time, the chick makes beeping noises, which are answered by the parent animals with a cat call. After hatching, the chicks are flocked intensely for seven to ten days .

The young birds stay in the nest or in its immediate vicinity until they have fledged after about 40 to 50 days. They keep returning to the nest over the next three months. Often roaming young animals are killed by seagulls in the neighboring breeding grounds. Parentless chicks, on the other hand, are sometimes adopted by other couples.

Mortality and Age

A long-term study of western gull mortality conducted on South East Farallon Island between 1978 and 1986 found that 50% of chicks died of malnutrition in June, 54% of chicks were killed by adults in July, and 91% of chicks in August and September starved to death. As a result of the food shortage in the El Niño year 1983, the importance of attacks by adult Western gulls on young animals as a cause of mortality increased. During the entire study period, 59% of the examined annual western gulls died due to inadequate nutrition. In adult animals, the researchers found a variable distribution of the causes of death, depending on the season, of starvation, illness and accidents. Western gulls can reach a maximum age of 20 to 25 years with a typical life expectancy of 10 to 15 years.

Taxonomy

Research history

The type specimen of the species comes from Cape Disappointment, the tip of a headland at the mouth of the Columbia River.

First described the Western Gull by the American ornithologists was John James Audubon in 1839 in the fifth volume of the work Ornithological biography dedicated to the birds of North America. His colleague John Kirk Townsend (1809-1851) had sent him a subadult and an adult bird. Townsend gave Cape Disappointment at the mouth of the Columbia River in today's state of Washington as the location of these type specimens . Townsend had taken part in an expedition over the Rocky Mountains to the coast of the Pacific Ocean organized by the American entrepreneur Nathaniel Jarvis Wyeth (1802-1856) in the 1830s and not only traveled the until then largely unknown Pacific Northwest , but - together with the British botanist and zoologist Thomas Nuttall - also researched his flora and fauna. In his first description, Audubon pointed out that the two specimens found at Cape Disappointment were similar in color to the herring gull ( Larus argentatus ), but differed from it in a number of characteristics, from which he concluded that it was a new and previously undescribed Kind of acted.

The large breeding population of the western gulls on Southeast Farallon Island makes it easy to collect data on the species.

Of the 21 species of seagulls breeding in America, the western gull is among the six most widely studied. The reason for this lies in the fact that statistically relevant data can generally be collected more easily and quickly from colony breeders and that the breeding colonies of the western gulls are relatively easy to reach for humans. Especially in the 1980s, at a time when seagulls were increasingly seen as competition for fishing, a number of studies were carried out that looked at the western gull. The research focus was on the breeding biology extensively researched by George L. Hunt, Jr. and Molly W. Hunt, Malcolm C. Coulter, Raymond Pierotti and others, as well as on the population development and migration of the species, of which Larry B. Spear is one Has contributed to a number of studies. Research into the western gull was further facilitated by the fact that a significant part of the total population lives on South East Farallon Island all year round, making long-term studies possible that have contributed significantly to today's understanding of the species.

External system

Phylogenetic position of the western gull
  Seagulls  

 Numerous species of Larus

   

 Common Gull ( Larus canus )


   

 Ring- billed gull ( Larus delawarensis )


   

 Western gull ( Larus occidentalis )


   

 Yellow-legged gull ( Larus livens )


   

Lesser black-backed gull complex (including Bering gull ( Larus glaucescens ))







Template: Klade / Maintenance / Style

For a long time, the western gull was assigned to a group of white-headed great gulls, whose complex family relationships could only be discovered through genetic studies at the beginning of the 21st century. In the course of a comparison of the mitochondrial DNA of gulls of the argentatus fuscus shape circle , Dorit Liebers , Peter de Knijff and Andreas Helbig found in 2003 that the haploid genotype of western gulls differs significantly from all other species of white-headed great gulls. They concluded that the western gulls - like their close relatives, the yellow-legged gulls ( Larus livens ) - lived on the North American continent for at least a million years before other species of white-headed great gulls reached it. Although the western gulls clearly differ in their genetic makeup from the bering gull ( Larus glaucescens ) and have no younger common relatives, they are still able to hybridize with them.

Internal system

There are two subspecies, whereby the subspecies L. o. Wymani , which is widespread south of Monterey , differs from the nominate form mainly through its darker upper side and its lighter iris. In winter, L. o. Occidentalis also has faint dark markings on the head, while the head of the southern subspecies is white all year round. The specific epithet "occidentalis" is of Latin origin and means "western". “Wymani” is dedicated to the ornithologist Luther Everet Wyman (1870–1928).

Until it was reclassified by the American Ornithologists' Union in 1982, the yellow-legged gull ( Larus livens ) was listed as a subspecies of the western gull. This can be traced back to the American ornithologist Jonathan Dwight , who in 1919 differentiated L. o. Livens from L. o. Occidentalis based on a specimen from the island of San José in the Gulf of California . In 1925 Donald Ryder Dickey and Adriaan Joseph van Rossem added a third subspecies L. o. Wymani , already stating that the western gulls classified as L. o. Livens in the Gulf of California have yellow instead of pink legs. Through the work of biologist Judith Hand since 1981 clear is that the earlier subspecies L. o. Livens not differ only by the color of their legs, but also by their vocalizations by the Western gulls, which is why they now as a separate species Larus livens run .

Existence and endangerment

Western gull on the former prison island of Alcatraz in San Francisco Bay

In the wake of the California gold rush , the population of western gulls on the Farallon Islands was severely decimated by egg collectors. Food was scarce in San Francisco, and companies like the Pacific Egg Company competed with the lighthouse keepers at Farallon Island Light Station , who were also trying to make a profit from selling bird eggs. The staff of other California lighthouses also participated in the intensive hunt for sea birds. Raymond Pierotti and Cynthia Annett suspect that the automation of the station on Southwest Farallon and in particular the lighthouses of Anacapa Island and Año Nuevo Island in connection with the closure of the federal prison on Alcatraz had a positive influence on the population development of the western gulls in the 20th century.

For the northern part of the distribution area, population figures are available for the years between 1975 and 1980. Speicher and Wahl estimated the population on the coast of Washington state to be around 3,000 to 4,000 pairs, although these numbers should be used with great caution due to the hybridization with Larus glaucescens . Spendelow and Patton identified around 5,000 breeding pairs for Oregon and around 2,500 breeding pairs for California north of Point Reyes .

The population residing in central California between Point Reyes and Point Conception comprised around 17,000 breeding pairs in the late 1970s and decreased to around 14,000 pairs by the 1990s - presumably as a result of ENSO phenomena. The population in southern California - that is, south of Point Conception - increased in the same period from around 5,500 to around 14,000 breeding pairs.

In the IUCN's red list , the western gull is now classified as least concern (“not endangered”). The species is potentially threatened by weather phenomena such as El Niño and human influences such as oil spills and environmental pollution from pesticides . Pierotti and Annett also point out that institutions such as the Point Reyes Bird Observatory in Point Reyes National Seashore and the National Park Service still see the western gull as a potential troublemaker to other seabirds in California and therefore regard their protection as secondary.

Humans and western gulls

Western gull in flight in front of the San Francisco skyline

In San Francisco , West Gulls are known, among other things, for appearing at the end of the games of the San Francisco Giants baseball team in their AT&T Park stadium to look for food. During the final innings, they circled the field in large swarms and, after the end of the game, settled on the bleachers to steal leftover food such as hot dogs and French fries . How the animals know that a game is nearing its end is still unclear. In an interview with the San Jose Mercury News newspaper in 2013, the biologist Russ Bradley suspected that the West Gulls could orientate themselves on the fans who left the stadium during the last innings. It is also possible to recognize the melody of the song Take Me Out to the Ball Game , which is traditionally played during the seventh-inning stretch . In 2011, the appearance of a red-tailed buzzard ( Buteo jamaicensis ) in the AT&T Park provided a short-term solution to the problem. After this bird of prey, dubbed “Bruce Lee” by the stadium staff, disappeared, the western gulls returned to AT&T Park.

literature

  • Raymond J. Pierotti / Cynthia A. Annett: Western Gull (Larus occidentalis) , in: Birds of the World , ed. by A. Poole, Ithaca 1995 (paid access; last accessed on May 23, 2020 with the status of the text on January 1, 1995)
  • Western Gull. Larus occidentalis , in: Klaus Malling Olsen / Hans Larsson, Gulls of Europe, Asia and North America , London 2004, pp. 165–177 (the first edition from 2003 was heavily error-prone and was withdrawn by the publisher).

Web links

Commons : Westmöwe  - Album with pictures, videos and audio files
Wiktionary: Westmöwe  - explanations of meanings, word origins, synonyms, translations

Remarks

  1. ↑ "Western Gull. Larus occidentalis ", in: Klaus Malling Olsen / Hans Larsson, Gulls of Europe, Asia and North America, London 2004, pp. 165–177, here p. 165.
  2. ↑ Information from Western Gull, Identification , All About Birds, Bird Guide, The Cornell Lab of Ornithology, accessed on February 3, 2016, and Malling Olsen / Larsson, Gulls of Europe, Asia and North America , pp. 166f.
  3. ↑ On this and the following cf. Pierotti / Annett, Western Gull , in: Birds of North America, section “ Behavior ”.
  4. ^ Pierotti / Annett, Western Gull , in: Birds of North America, section " Behavior ".
  5. ↑ On this and the following cf. Pierotti / Annett, Western Gull , in: Birds of North America, section " Sounds ", and Judith L. Hand, A comparison of vocalizations of Western Gulls (Larus occidentalis occidentalis and L. o. Livens) , in: The Condor 83 ( 1981), pp. 289-301, here: p. 291. Relevant is Hands' dissertation, published in 1979 with the title Vocal communication of the Western Gull (Larus occidentalis) .
  6. ^ Arnold Small, California birds: their status and distribution , Vista 1994, p. 116.
  7. ↑ Teresa M. Penniman / Malcolm C. Coulter / Larry B. Spear / Robert J. Boekelheide, Western Gull , in: David G. Ainley / Robert J. Boelkelheide (eds.), Seabirds of the Farallon Islands: ecology, dynamics, and structure of an upwelling system community, Palo Alto 1990, pp. 218-244, here p. 219.
  8. ↑ Larry B. Spear / Peter Pyle / Nadav Nur, Natal Dispersal in the Western Gull: Proximal Factors and Fitness , in: Journal of Animal Ecology 67, 2 (1998), pp. 165-179, here p. 166.
  9. ↑ Burger / Gochfeld / Garcia, Western Gull (Larus occidentalis) , in: Handbook of the Birds of the World Alive, section "Movements"
  10. ↑ Malling Olsen / Larsson, Gulls of Europe, Asia and North America , p. 172.
  11. ↑ Cynthia Annett / Raymond Pierotti, Chick Hatching as a Trigger for Dietary Switching in the Western Gull , in: Colonial Waterbirds, 12, 1 (1989), pp. 4-11.
  12. ↑ Cynthia A. Annett / Raymond Pierotti, Long-Term Reproductive Output in Western Gulls: Consequences of Alternate Tactics in Diet Choice , in: Ecology 80, 1 (1999), pp. 288-297.
  13. ↑ a b For this and the following cf. Pierotti / Annett, Western Gull , in: Birds of North America, section “ Food habits ”.
  14. ↑ Wayne Hoffman / Dennis Heinemann / John A. Wiens, The Ecology of Seabird Feeding Flocks in Alaska , in: The Auk 98, 3 (1981), pp. 437-456, here p. 444.
  15. ^ Charles A. Harper, Breeding Biology of a Small Colony of Western Gulls (Larus occidentalis wymani) in California , in: The Condor 73, 3 (1971), pp. 337-341, p. 339.
  16. ↑ George L. Hunt, Jr. / Molly W. Hunt, Reproductive Ecology of the Western Gull: The Importance of Nest Spacing , in: The Auk 92, 2 (1975), pp. 270-279, here: p. 273.
  17. ^ Raymond Pierotti / Cynthia A. Annett, Patterns of aggression in gulls: asymmetries and tactics in different roles , in: The Condor 96 (1994), pp. 590-599, here p. 591.
  18. ↑ On this and the following Burger / Gochfeld / Garcia, Western Gull (Larus occidentalis) , in: Handbook of the Birds of the World Alive, section "Breeding"
  19. ↑ Pierotti / Annett, Western Gull , in: Birds of North America, section " Breeding "
  20. ↑ LB Spear / TM Penniman / JF Penniman / HR Carter / DG Ainley, Survivorship and mortality factors in a population of Western Gulls , in: Studies in Avian Biology 10 (1987), pp. 44-56.
  21. ↑ a b c Spear [u. a.], Survivorship and mortality factors , p. 49.
  22. ↑ Spear [u. a.], Survivorship and mortality factors , p. 50.
  23. ^ Pierotti / Annett, Western Gull , in: Birds of North America, section " Demography ".
  24. ^ A b John James Audubon: " Western Gull. Larus occidentalis “, in: John James Audubon / William Macgillivray, Ornithological biography, or: An account of the habits of the birds of the United States of America , Vol. 5, Edinburgh 1839, pp. 320–322.
  25. ↑ John James Audubon, Western Gull. Larus occidentalis , p. 320.
  26. ↑ John James Audubon, Western Gull. Larus occidentalis , p. 321.
  27. ^ William E. Southern, Gull Research in the 1980s: Symposium Overview , in: Studies in Avian Biology 10 (1987), pp. 1-7, here pp. 1f.
  28. ^ Southern, Gull Research in the 1980s , p. 2.
  29. ↑ On George L. Hunt, Jr. cf. its homepage on the website of the University of Washington.
  30. ↑ On Coulter cf. David Duffy, In Memorium [sic!]. Malcolm C. Coulter, 1947-2013 , The Waterbird Society, accessed February 6, 2016.
  31. ↑ On Pierotti cf. its homepage on the pages of the University of Kansas.
  32. ↑ See for example Penniman / Coulter / Spear / Boekelheide, Western Gull , in: Seabirds of the Farallon Islands, Stanford 1990, pp. 218-244.
  33. ↑ J.-M. Pons / A. Hassanin / P.-A. Crochet, Phylogenetic relationships within the Laridae (Charadriiformes: Aves) inferred from mitochondrial markers , in: Molecular Phylogenetics and Evolution 37 (2005), pp. 686-699, here p. 691.
  34. ↑ Dorit Liebers / Peter de Knijff / Andreas Helbig, The Herring Gull Complex Is Not a Ring Species , in: Proceedings: Biological Sciences 271 (2004), pp. 893-901, here p. 895.
  35. ↑ Peter de Knijff / Andreas Helbig / Dorit Liebers, The Beringian Connection: Speciation in the Herring Gull Assemblage of North America , in: Birding 8 (2005), pp. 402-411, here p. 409.
  36. ↑ de Knijff / Helbig / Liebers, The Beringian Connection , p. 406.
  37. ↑ Malling Olsen / Larsson, Gulls of Europe, Asia and North America , p. 165.
  38. ↑ James A. Jobling: "occidentalis, occidens, occidentis", in: Helm Dictionary of Scientific Bird Names, London 2010, p. 278.
  39. ↑ a b Donald Ryder Dickey / Adriaan Joseph van Rossem, A Revisionary Study of the Western Gull , in: The Condor 27, 4 (1925), pp. 162-164, here p. 163.
  40. ↑ On this and the following Guy McCaskie, Another look at the Western and Yellow-footed gulls , in: Western Birds 14 (1983), pp. 85-107, here p. 96.
  41. ↑ Jonathan Dwight, Description of a new race of the western gull , in: Proceedings of the Biological Society of Washington 32 (1919), pp. 11-13.
  42. ^ Dickey and van Rossem, A Revisionary Study of the Western Gull
  43. ^ Hand, A comparison of vocalizations of Western Gulls
  44. ↑ Peter White, The Farralones , in: The Keeper's Log, Fall 1988, pp. 2–13, here p. 4, and Arthur Cleveland Bent, Life Histories of North American Gulls and Terns , section “Larus occidentalis”, p. 89 -101, here p. 90.
  45. ↑ a b Pierotti / Annett, Western Gull , in: Birds of North America, section " Conservation and Management "
  46. ↑ Steven M. Speich / Terence R. Wahl, Catalog of Washington seabird colonies , Washington DC 1989, pp. 46–48 and maps and tables from p. 91.
  47. ↑ JA Spendelow / SR Patton, section " Western Gull (Larus occidentalis) ", in: National atlas of coastal waterbird colonies in the contiguous United States, 1976-82 , Washington DC 1988, pp. 153-157.
  48. ↑ Arthur L. Sowls / Anthony R. DeGange / Jay W. Nelson / Gary S. Lester, Catalog of California seabird colonies , Washington DC 1980, p. 38.
  49. ↑ a b Pierotti / Annett, Western Gull , in: Birds of North America, section " Demography and Populations "
  50. ↑ On this and the following Paul Rogers, AT&T Park gulls vex San Francisco Giants , in: San Jose Mercury News of July 20, 2013, accessed on February 2, 2016.
  51. ↑ "[...] perhaps by fans leaving the park toward the end of the game. Or maybe even by the organ playing "Take Me Out to the Ball Game" every seventh inning. ", Paul Rogers, AT&T Park gulls vex San Francisco Giants .
This article was added to the list of excellent articles on April 18, 2016 in this version .