142 



YELLOW-FOOTED WESTERN GULL (Larus oooidentalis livens; choices 29, 

 49' and 55, pp.56, 59 & 60 ) is a large gull essentially confined to the 

 Gulf of California. It is similar to the Western Gull except for the 

 bright yellow legs and feet of the adult, and in the sequence of immature 

 plumages. This form may be a separate species. Any specimens found out- 

 side the Gulf of California should be deposited in a museum. 



LESSER BLACK-BACKED GULL (Larus fuscusj not in key) has been recorded 

 only once on the west coast south of Alaska. Any specimen of this gull 

 should be saved. It is the only gull occurring in this region with a 

 black mantle. Its immature plumages and measurements are similar to the 

 Herring Gull and separation is difficult. The adult with yellow legs 

 might be confused with the Yellow- footed Western Gull but the Lesser 

 Black-backed Gull is smaller with a more slender bill and a darker mantle. 



HERRING GULL (Larus argentatus; choices 33', 50' ,54 and 58, pp.56, 59, 60) 

 may be found in coastal waters throughout the area treated by this manual. 

 It is often considered to be the typical "sea gull". The characters in the 

 key should identify most individuals. Herring Gulls are most likely to 

 be confused with Thayer's Gull or Western X Glaucous-winged hybrids. 

 Thayer's Gulls generally have more slender bills (Plate 26b, 1, 2) and 

 the underside of the outer primaries are pale, while the Herring Gull has 

 dark undenting tips. See the Glaucous-winged Gull account for hints 

 concerning the Western X Glaucous-winged intergrades. 



THAYER'S GULL (Larus thayeri; choices 33, 41 ', 43', 44', 49, 54' and 

 58', pp. 56-60 ) occurs along the Pacific coast in winter, from southern 

 British Columbia to southern California and less commonly in Alaska and 

 Baja California. It is a medium-sized gull closely related to the Herring 

 Gull. The combination of dark wing tips above and pale wing tips below is 

 common to most individuals of all plumages. Only some of the much larger 

 Western X Glaucous-winged intergrades share this characteristic. Adults 

 can be further separated from the Herring Gull by the brownish eye and 

 slender bill and from the California Gull by the pink legs. Immatures 

 are more difficult but with practice can be identified by the characters 

 used in the key. 



CALIFORNIA GULL (Larus oalifomious; choices 32, 50, 53 and 57, pp. 

 56, 59, 60), a medium-sized gull, is common along the coast from southern 

 Washington to Baja California. It is rare in British Columbia, and 

 coastal Alaskan specimens should probably be saved. This species is quite 

 similar to the Herring Gull but the gray of the mantle is distinctly 

 darker, the legs of 3rd year and adult birds are gray to greenish-yellow 

 and the eye is dark brown. First year birds are difficult to separate 

 from the Herring Gull but typically the sharp demarcation between the 

 pink base and black tip of the bill is distinctive. 



