57 



KEY TO GULLS (Cont.) 



35 Tail with distinct dark subterminal band (see Fig. 15). 36 



35' Tail not distinctly banded (usually with areas of dark and light 



mottling). 39 



36 Band along wing at base of secondaries (greater secondary coverts) 



gray; culmen usually >37 mm. 37 



36' Band along wing at base of secondaries (greater secondary coverts) 



brownish; culmen usually <37 mm. 38 



37 Upper wing (lesser and middle) coverts brownish, tipped with white; 

 primaries more or less pointed. RING-BILLED GULL, first year 



37' Upper wing (lesser and middle) coverts gray; primaries more or less 



rounded. ~ RING-BILLED GULL, second year 



38 Secondaries browner than mantle; primaries more or less pointed. 



MEW GULL, first year 



38' Secondaries gray like mantle; primaries more or less rounded. 



MEW GULL, second year 



39 Tail with gray or buffy, no dark brown. 40 



39' Tail with dark brown or black, sometimes largely white or largely 



brown. 45 



40 Back between wings brown or gray-brown, much mottled; underparts 

 clouded and flecked with gray-brown; bill black. 41 



40' Back between wings primarily "gull-gray"; underparts more or less 

 white; tail with much white basal ly; bill with some paleness 

 basally. 42 



41 Bill rather large and heavy, gonys prominent (Plate 26a-4); 

 primaries gray on both upper and under surfaces. 



GLAUCOUS-WINGED GULL, first year 



4T Bill more slender, gonys slight (Plate 26b-2); primaries usually 

 dark gray-brown to black on upper surface and light gray on under 

 surface with distinct paler borders at the tips. 



THAYER'S GULL, first year 



