66 



KEY TO ALCIDS 



I Large: exposed culmen >25 mm; wing length >162 mm; tarsus 



usually >30 mm. 2 



I I Small: exposed culmen <25 mm; wing <160 mm; tarsus usually 



<30 mm. 16 



2 Underwing linings mostly white. 3 

 2' Underwing linings mostly dark. 8 



3 A great deal of white in wing coverts of upper surface of wing; 

 secondaries dark; feet may be pink to intense red. 4 



3' Upper surface of wing dark except that secondaries are broadly 



tipped with white; feet black or brown. (MURRE) 5 



4 Scapulars and back feathers checkered with black and white; upper 



wing coverts mottled black and white. BLACK GUILLEMOT, immature 



4' Scapulars and back black; upper wing coverts extensively white. 



BLACK GUILLEMOT, adult 



5 Throat and entire head dark. 6 

 5' Throat and lower cheeks white. 7 



6 Cutting edge of bill at base white or yellow (giving appearance of a 

 light mustache); depth of bill at gonydeal angle >l/3 the exposed 

 culmen. THICK-BILLED MURRE, breeding plumage 



6' Bill entirely dark; depth of bill at gonydeal angle <l/3 the exposed 



culmen. COMMON MURRE, breeding plumage 



7 White cheeks extending upward behind eye to cap, then posteriorly 

 to back of head (where black cap extends down neck), a distinct 

 dark line extending from eye back to intersect most of white on 

 side of head (as in Fig. 25); bill as in 6'. 



COMMON MURRE, winter adult and first year 



7' White of cheeks posterior to eye not extending above eye level, 

 dark line back from eye region indistinct; bill as in 6. 



THICK-BILLED MURRE, winter adult and first year 



