58 



KEY TO GULLS (Cont.) 



42 Back between wings "gull -gray"; wing coverts brown; bill pale at 



base but dark towards tip, lacking red or orange at gonydeal angle. 43 



42' Back between wings and wing coverts mostly "gull -gray"; bill 



yellowish, usually with a trace of orange at angle and dusky towards 

 tip; underparts nearly all white. 44 



43 Bill rather large and heavy (Plate 26a-4); primaries gray on both 



upper and under surfaces. GLAUCOUS-WINGED GULL, second year 



43' Bill more slender (less pronounced gonydeal angle; Plate 26b-2); 

 primaries usually dark gray-brown to black on upper surface with 

 distinct paler borders, pale gray on under surface. 



THAYER'S GULL, second year 



44 Bill rather large and heavy (Plate 26a-4); primaries gray on both 



upper and under surfaces. GLAUCOUS-WINGED GULL, third year 



44' Bill more slender (less pronounced gonydeal angle; Plate 26b-2); 

 primaries usually dark gray-brown to black on upper surface, 

 pale gray on under surface. THAYER'S GULL, third year 



45 Back between wings light to dark brown, mottled. 46 

 45' Back between wings light to dark "gull-gray", not mottled. 51 



46 Bill all black (maybe some pale areas basal ly in late spring). 47 

 46' Bill with pale area basally. 50 



47 Body plumage very dark brown; outer primaries not distinctly darker 

 than inner primaries and secondaries; tail nearly solid dark brown; 



bill large with a prominent gonydeal angle. 48 



47' Plumage generally paler; outer primaries distinctly darker than 



inner primaries and secondaries. 49 



48 Wing length >410 mm; body barred or finely speckled, the dusky 

 areas usually exceeding the white; unusual north of British Columbia. 



WESTERN GULL, first year 



