Figure H-4. After several tantalizing reports, a remarkable cluster of Slaty-backed Gulls documented in 2005 and 2006 at Half Moon Bay in San Mateo County, including this adult or near-adult, finally removed all reasonable doubt. Characteristic marks shown in this 21 March 2005 photo include the pale eye with dark “mascara,” bill shape less bulbous than that of the Western Gull in the foreground (but perhaps atypically dark for an adult), dark mantle color, and white “scapular crescent” broader than that of the Western Gull in the foreground. See also Figure H-23 on page H-14 (2005-048; Alvaro Jaramillo).

Figure H-5. The Committee has been unable to ascertain the identity of this pot-bellied, pale-eyed gull, which was molting into second alternate plumage when photographed on 5 February 1995 at Ventura Harbor in Ventura County. Perhaps most confounding in such cases is the potential for a hybrid involving the Glaucous-winged Gull, as the appearance of subadult hybrids may be highly variable. After failing to gain acceptance a decade ago, this record is currently undergoing re-review (1995-053; Don DesJardin).

Figure H-22. California’s second accepted Slaty-backed Gull was this sun-bleached second-winter bird photographed on 20 February 2005 at Half Moon Bay in San Mateo County. The characteristic pale eye with surrounding dark streaks and smudging tend to give the Slaty-backed a fierce or menacing visage. Note also this bird’s chunky body, parallel-sided bill, dark mantle and black wing-tips (2005-015; Alvaro Jaramillo).

 

Figure H-23. Another view of the dark-billed adult or near-adult Slaty-backed Gull photographed on 21 March 2005 at Half Moon Bay in San Mateo County (see Figure H-4 on page H-4). This helpful image shows the bird’s purple-pink legs, dark mantle, bold white trailing edge to the wing, and “string of pearls”—i.e., large white tongues proximal to the black segment of the primary tips, most evident on the sixth through eighth primaries (2005-048; Alvaro Jaramillo).

 

 

 

 

 

 

SLATY-BACKED GULL Larus schistisagus Stejneger, 1884

Accepted: 16 (76%)
Not accepted: 5	CBRC review: all records
Not submitted/reviewed: 0	Large color images: see Figures

This large gull breeds along the eastern coast of Siberia and south through Kamchatka to northern Japan. Most birds winter within the breeding range or disperse only as far south as southern Japan, with reduced numbers occurring southward to Taiwan and Hong Kong. The species has been recorded throughout the year in western Alaska and has nested there several times, including both pure and hybrid pairings (McCaffery et al. 1997, Winker et al. 2002). The species occurs rarely in northern Alaska and south along the Pacific coast to Vancouver, British Columbia. This gull is also a rare, regular visitor to the northwestern Hawaiian Islands (P. Pyle in litt.). Washington claims ten records and Oregon roughly 11 (NAB 60:428). Numerous records exist from elsewhere across North America, from extreme northern Nunavut and southern Quebec (records from both places listed by Cormier and Savard 1994) and Newfoundland (NAB 60:200) south to southern Florida (NAB 57:47, 193, 338) and extreme southern Texas.

After endorsing three records of Slaty-backed Gulls present between 13 January and 21 March 2005 at Half Moon Bay in San Mateo County (Figures H-4, H-22, H-23), the Committee later accepted an earlier report of a second-winter bird photographed at the same location on 1 March 2001. Almost inconceivably, the state total had mushroomed to at least 16 accepted records by the end of 2006! No less striking is the concentration of records from just one place, Half Moon Bay.

Each of the five previous reports of this species submitted to the CBRC received at least one accept vote, and the 1998 Salton City record (the only one in near-adult plumage) received 80% acceptance on its fourth circulation. Although most of the features evident on that bird appeared to fall within the Slaty-backed Gull’s known range of variation, a few points did not fit the CBRC’s expectations of a “classic” representative of the species, and some members believed that addition of this bird to the state list should not be based on such an individual. Consulted experts on Asian gulls reported that most Slaty-backed Gulls have completed their primary molt by December, but supporters of the record pointed out that some gull species can delay their molt considerably in unusual circumstances (cf. Howell and Corben 2000b). Several possibly later-molting Asian taxa, especially L. fuscus heuglini, caused concern, with particular regard to the limited knowledge of the extent of hybridization involving these forms. This bird’s leg color, somewhat paler than the dark pink normally associated with this species, and the intermediate width of the white trailing edge of the wings, which was variously regarded as supportive or damaging, were further considerations that left two members believing that the bird was best left unidentified. In light of recent events involving this species, however, the CBRC is reviewing this record again.

Goetz et al. (1986), Gustafson and Peterjohn (1994), King and Carey (1999), and various other authors have described and debated variation in this species.