California Gull californicus

(last update: 22-12-2016 )

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Alex Abela
John Cant
Mars Muusse

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CALIFORNIA GULL Larus californicus Description in "Gulls of North America, Europe, and Asia", by Klaus Malling Olsen & Hans Larsson, Princeton University Press.

This is a copy of the chapter on California Gull, written by Klaus Malling Olsen. "I" in the text refer to the author. If you find any errors, please let me know at marsmuusse at gmail dot com.

CALIFORNIA GULL Larus californicus
(Lawrence, 1854, Stockton, California)

PART 1: IDENTIFICATION
PART 2: VOICE & DESCRIPTION
PART 3: GEOGRAPHICAL VARIATION & MEASUREMENTS (below)

GEOGRAPHICAL VARIATION Two taxa.

L. c. californicus (breeds Great Basin and adjacent areas from Washington and Montana S to California and E to Wyoming and Colorado; probably British Columbia) described above.

L. c. albertaensis (breeds N and E of nominate californicus; N Great Plains, from southern NW Territories S through Alberta into Montana, E to W Manitoba and North Dakota) larger than nominate with heavier, more parallel-edged bill and weaker gonys-angle. Generally bulkier with shorter projection of wings above tail, and on average shorter legs. Some (especially adult males) identifiable in the field but many characters overlap with nominate (mirroring situation between Common Gull races canus and heinei). Racial identification should always be based on direct comparison between several individuals. Note also that appearance of hybrids in areas of presumed contact, particularly Montana, remains to be studied (King 2001).

Adult Has paler upperparts (Kodak Grey Scale 5-6.5 (probably palest Canada)), sometimes approaching American Herring and Ring-billed Gull. Black on wingtip in full adult less extensive (and often comparable to Caspian Gull nominate race cachinnans). P10 often with complete white tip (29% versus 9% in nominate). Grey tongue on P10 continues 30-50% towards tip (max. 30% in nominate). P9 in full adult always with white mirror, generally broader and squarer than in nominate (rarely <10mm). In 10% black on outer web of P9 does not reach primary coverts. P6-8 with deeper pale grey tongues, often whiter at distal end, where sometimes forming ‘string of pearls’. Black on P7-8 normally does not reach primary coverts (in 15% on P8; grey base to P8 mainly >15mm) and is sharply divided from grey (in >90% of nominate, black reaches primary coverts; division between grey and black narrower and more diffuse, often as slight spotting). P7 with at least 50mm grey extension above primary coverts (<50mm in nominate); lacks diffuse black line along shaft almost to reach primary coverts of most nominate (but extension of black similar in fourth-year nominate). Distal edge of grey tongue on inner web of P7 longer than P5 (falls short of the tip in nominate); P5 grey, in 5-16% with black markings. P4 lack black markings. Black on wingtip often L-shaped versus fuller black of nominate. Underwing with indistinct darker secondaries, not forming extensive rectangle of nominate. Moult to winter generally 2-3 weeks later than in nominate, reaching P5-7 by late Jul, P9-10 Oct/Nov (Jehl  1987a & b, King 2001).

In winter, head-markings more extensive, sometimes similar to American Herring, with dark markings reaching chin and throat (rare in nominate).

First-years not subspecifically identifiable, although albertaensis is on average darker than the nominate. More research needed.

Note Separation of nominate and albertaensis based mainly on King (2001), who kindly submitted unpublished data for preparation of the text.

Aberrants

Fourth-year-type part-albino white with weak dark pattern to P6, scapulars and tail.

Hybrids

Hybridisation with American Herring Gull reported twice Colorado and one (probably) Wyoming
(Winkler 1996).

DISTRIBUTION AND MIGRATION

200,000 pairs in >100 colonies. Breeds in open, arid habitats, usually on low rocky islands in fresh and saline waters. Numbers reduced to 50,000 pairs in 1930, mainly by egg collecting, but increasing to 140,000 pairs in 1980 following protection (Conover 1983, del Hoyo et al. 1996). Extension of range linked with this increase. Largest colonies in Great Salt and Mono Lakes, Utah. Partly migratory, mainly moving north of breeding range following breeding season, gradually spreading S during winter. Common in all areas with sufficient food, such as towns, parks, estuaries, lakes and rivers.

At least 17,000 pairs of race albertaensis in Canada and 3,000 in Anaho Region, NW Territories.
Following the breeding season there is a strong westerly movement, with many younger L. c. californicus migrating N to Pacific NW, before moving S down Pacific coast to main winter areas in California and Mexico. L. c. albertaensis performs a leap-frog migration, wintering on average slightly more to the south than the nominate, mainly inland. However, nominate still dominates in whole area, accounting for >99% of birds in Sacramento and 90-95% at Salton Sea, California, and 70-80% on the Sonora coast, Mexico (King 2001).

In late Jul flocks >8,000 Washington. Max. 26,000 Vancouver Island Sep. Winters mainly Pacific coast S to Baja California, Colima and N Mexico. Winter flocks of max. 13,000 California (Sacramento, Santa Cruz, Monterey Bay, Orange County). Saskatchewan breeders migrate W to coastal British Columbia and disperse S to Sinaloa. Max. 600 winter Mountain West Region. Scarce N from Alaska and S from Baja California. Casual winter visitor to American Mid-west, Colorado and C South region (max. 21 winter). Vagrant Yukon, Quebec, Texas, Virginia, Delaware and Florida, Hawaii, Japan. Birds recorded E of Chicago probably belong to the race albertaensis (King 2001).

MEASUREMENTS

Lengths in mm; weights in g. Own data based on skins in LACM, MCZ, NHM, NRK, USNM, ZMO. Combined with Jehl (1987b). Note First-years all from California, not identified to subspecies.