59 



KEY TO GULLS (Cont.) 



48' Wing <410 mm; body coarsely spotted, the white areas usually ex- 

 ceeding the dark; not to be expected outside of the Bering Sea and 

 Aleutian area in the eastern Pacific Ocean. 



SLATY-BACKED GULL, first year 



49 Bill rather slender (less pronounced gonydeal angle; Plate 26b-2); 

 primaries dark brown to black on upper surface, usually with 

 distinct pale edgings, pale gray to brown on under surface. 



THAYER'S GULL, first year 



49' Bill large with prominent gonydeal angle (Plate 26a); primaries 

 very dark brown on both upper and under surfaces. 



YELLOW-FOOTED WESTERN GULL, first year 



50 Bill pink in basal half with clearly defined blackish tip. 



CALIFORNIA GULL, first year 



50' Bill with pink base gradually fusing into blackish tip. 



HERRING GULL, first year 



51 Back between wings "gull-gray"; wing coverts and secondaries brown; 



tail usually largely dark brown. 52 



51' Back between wings, wing coverts and secondaries more or less 



uniform "gull -gray", sometimes with a brownish cast; tail usually 



with some white at the base and at very tip of the feathers. 55 



52 Back between wings dark gray; outer three primaries not distinctly 

 darker than inner primaries and secondaries. WESTERN GULL, second year 



52' Back between wings light gray; outer three primaries distinctly 



darker than inner primaries. 53 



53 Legs dull bluish; eye dark brown; primaries very dark brown without 

 conspicuous edgings. CALIFORNIA GULL, second year 



53' Legs pink; eye pale brown or yellow. 54 



54 Primaries dark brown on both upper and under surfaces, without 

 conspicuous pale edgings; eye pale yellow. HERRING GULL, second year 



