141 



GLAUCOUS-WINGED GULL (Larus glauaesoens; choices 26, 41, 43 and 44, PP- 

 55, 57, 58) is a large pale gull found commonly from Alaska to southern 

 California. This species characteristically has wing tips that are the 

 same color as the inner primaries and secondaries. Extensive hybridiza- 

 tion with the Western Gull in Oregon and Washington provides numerous 

 individuals whose specific identity is difficult or impossible to 

 determine. Most hybrids show darker outer primaries than typical 

 Glaucous-winged Gulls and have paler gray mantles than Western Gulls. 

 These individuals may be confused most readily with Herring and Thayer's 

 Gulls, although these species have smaller, more slender bills than the 

 hybrids. Also, Herring Gulls and most Thayer's Gulls have a distinct 

 demarcation between the dark wing tips and the mantle while the 

 Glaucous-winged X Western hybrids (as well as the northern race of the 

 Western Gull) show the black of the wing-tips merging gradually with the 

 gray or brown of the mantle area. Only familiarity with the variation in 

 these gulls will allow identification of many specimens. For more infor- 

 mation on these hybrids see Hoffman et al . (1978). 



SLATY-BACKED GULL (Larus sohistisagus> choices 28 and 48', pp. 55 and 58) 

 is a large dark-backed gull that occurs along the coast of the western 

 Pacific. This species is a straggler in western Alaskan waters and 

 accidental at best elsewhere along the North American coast. Any beached 

 birds thought to be this species should be saved for comparison with existing 

 specimens and for deposit in museum collections. Adults are similar to the 

 Western Gull but are larger with a darker mantle and more white in the wing 

 tips. First year birds are paler than other large dark-backed gulls, 

 have a distinctive drab wing bar at the base of the secondaries, and a white 

 chin. 



WESTERN GULL (Larus ocoidentaUs ; choices 29', 48, 52 and 56, pp.56, 58, 59 

 and 60 ) is another large dark-backed gull more or less resident from 

 Washington to the tip of Baja California. Specimens north of southern 

 British Columbia should be saved. The dark mantle and large bill should 

 separate this species from all but the preceding species. First year birds 

 are much darker than other large gulls in the same plumage. Hybridization 

 with the Glaucous-winged Gull in Oregon and Washington causes considerable 

 identification problems which are discussed in the Glaucous-winged Gull 

 account. This species occurs rarely in the Gulf of California where 

 separation from adult Yellow-footed Western Gulls requires fresh specimens 

 in which the leg color has not faded. Immature specimens can be impossible 

 to separate from the Yellow- footed Western Gull. Any suspected Western 

 Gulls from Gulf of California beaches should be saved. Specimens of the 

 paler northern populations of the Western Gull (north of northern 

 California) can be confused with Herring Gulls but the black of the wing 

 tip merges gradually with the gray of the mantle in the Western Gull and 

 is sharply demarcated in the Herring Gull. Usually the large thick bill 

 will identify the Western Gull. 



