Western gull

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Western gull
Adult
Juvenile (1st Winter)

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Charadriiformes
Family: Laridae
Genus: Larus
Species:
L. occidentalis
Binomial name
Larus occidentalis
Audubon, 1839
Distribution
  Year-round
  Nonbreeding

The western gull (Larus occidentalis) is a large white-headed

west coast of North America and the Pacific Ocean. The western gull ranges from British Columbia, Canada, to Baja California, Mexico.[2]

It was previously considered

conspecific with the yellow-footed gull (Larus livens) of the Gulf of California
.

Physical description

Western Gull in flight over the cliffs of Bodega Head

The western gull is a large gull that can measure 55 to 68 cm (22 to 27 in) in total length, spans 130 to 144 cm (51 to 57 in) across the wings, and weighs 800 to 1,400 g (1.8 to 3.1 lb).

San Francisco Bay area. Western gulls also live in the Oregon Coast.[8]

Two subspecies are recognized, differentiated by the mantle and eye colouration.[9] The northern subspecies L. o. occidentalis is found between Central Washington and Central California, has dark grey upperparts. The southern subspecies L. o. wymani is found between central and southern California has a darker mantle (approaching that of the Great black-backed gull) and has paler eyes on average. wymani has more advanced plumage development than occidentalis, and generally attains adult plumage by the third year.[3]

Auditory description

Western gull calls
Western gull calls, recorded at the Golden Gate National Recreation Area

The call of the Western gull is bright, piercing, and repetitive.

Distribution and habitat

The western gull is a year-round resident in California, Oregon, Baja California, and southern Washington. It is migratory, moving to northern Washington, British Columbia, and Baja California Sur to spend the nonbreeding season.

Behavior

Pair-bonding behaviour

The western gull rarely ventures more than approximately 100 miles inland, almost never very far from the ocean;

Ano Nuevo Island, then Anacapa Island and Santa Barbara Island in Channel Islands National Park, and Alcatraz Island in San Francisco Bay. In the colonies, long term pairs aggressively defend territories whose borders may shift slightly from year to year, but are maintained for the life of the male.[citation needed
]

Feeding

Western gulls feed in

Oakland's Lake Merritt are known for killing and eating pigeons (rock doves). They will also snatch fish from a cormorant's or pelican's mouth before it is swallowed. The bird has also been observed directly pilfering milk from the elephant seal's teat.[10]

Reproduction

A nest of vegetation is constructed inside the parent's territory and 3 eggs are laid. These eggs are incubated for a month. The chicks, once hatched, remain inside the territory until they have fledged. Chicks straying into the territory of another gull are liable to be killed by that territory's pair. Chick mortality is high, with on average one chick surviving to fledging. On occasion, abandoned chicks will be adopted by other gulls.

Hybridization

Between Puget Sound in Washington and Northern Oregon, the western gull hybridizes frequently with the glaucous-winged gull, a cross referred to as the Olympic gull.[9] Hybrids between the two species are variable and may features of either parent species, they have paler mantles and wingtips paler than Western gulls but darker than Glaucous-winged gulls. Additionally, the nonbreeding plumage of hybrids typically has darker head markings than pure Western gulls, which have little to no streaking in their nonbreeding plumage.[3]

The prevalence of 'Olympic gull' hybrids is an example of bounded hybrid superiority, where natural selection favours hybrids in areas of intermediate habitat. One study found that females paired with hybrid males have higher breeding success than pairs of the same species.[11] In the central part of the hybrid zone, clutch size was larger among pairs with hybrid males, many of which established breeding grounds in more vegetative cover than pure western gull males, which preferred sand habitat resulting in heavier predation. In the northern section of the hybrid zone, there was no difference in clutch size, but breeding success is higher due to the hybrids being more similar to western gulls in foraging behaviour, feeding more on fish than glaucous-winged gulls. Little evidence of assortative mating was observed, except for weak assortative mating among hybrids in absence of mixed species pairs.

Western gulls and humans

Over San Francisco Bay

The western gull is currently not considered threatened. However, they have, for a gull, a restricted range. Numbers were greatly reduced in the 19th century by the taking of seabird eggs for the growing city of San Francisco. Western gull colonies also suffered from disturbance where they were turned into lighthouse stations, or, in the case of Alcatraz, a prison.

Western gulls are very aggressive when defending their territories and consequently were persecuted by some as a menace. The automation of lighthouses and the closing of Alcatraz Prison allowed the species to reclaim parts of its range. They are currently vulnerable to climatic events like

El Niño events and oil spills
.

Thousands of western gulls and chicks reside at the Anacapa Island in Channel Islands National Park.

Western gulls have become a serious nuisance to the

late innings of games. They swarm the field, defecate on fans, and after games eat leftovers of stadium food in the seats; how the birds know when games are about to end is unknown. The gulls left while a red-tailed hawk visited the park in late 2011, but returned after the hawk disappeared. Federal law prohibits shooting the birds, and hiring a falconer would cost the Giants $8000 a game.[8]

Western gull x Glaucous-winged gull hybrid nesting in Oregon. Note the grey (not black) wingtips and paler mantle compared to a pure Western gull.

In media

The western gull was one of the antagonists in Alfred Hitchcock's famous movie The Birds which was filmed in Bodega Bay, California.

Gallery

References

  1. doi:10.2305/IUCN.UK.2018-2.RLTS.T22694337A132543621.en
    . Retrieved 11 November 2021.
  2. ^ "Western Gull". U.S. National Audubon Society. Archived from the original on 24 October 2008. Retrieved 20 July 2010.
  3. ^
    ISBN 978-0691119977
    .
  4. ISBN 978-0-395-60291-1
    .
  5. ISBN 978-0-8493-4258-5
    .
  6. ^ a b "Western Gull". All About Birds. Cornell Lab of Ornithology. Retrieved 20 July 2010.
  7. ^
    JSTOR 4523362
    .
  8. ^ a b Rogers, Paul (20 July 2013). "AT&T Park gulls vex San Francisco Giants". San Jose Mercury News. Retrieved 20 July 2013.
  9. ^
    OCLC 1005861102.{{cite book}}: CS1 maint: location missing publisher (link
    )
  10. doi:10.12933/therya-10-14
    .
  11. PMID 11108604
    .

Additional sources

  • Pierotti, R.J.; Annett, C.A. (1995). "Western Gull (Larus occidentalis)". In Poole, A.; Gill, F. (eds.). The Birds of North America. The Academy of Natural Sciences, Philadelphia, and The American Ornithologists’ Union, Washington, D.C.

External links

Wikimedia Commons has media related to Larus occidentalis.
Wikispecies has information related to Larus occidentalis.
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