TERNS 55 



Subfamily. STERNIN^. Terns. 



Key to the species of STERNIN^. 



A. Wing over 14.00. Caspian Tern. 



B. Wing under 14.00. 



1. Wing under 9.00. 



a'. Wing over 7.80 and whole top of head black. Black Tern, 

 a*. Wing under 7.80 and forehead white. Least Tern. 



2. Wing over 9.00. 



a'. Top of head entirely black, 

 b'. Bill black, 

 r. Feet very dark or black. Gull-billed Tern, 

 rr. Feet orange or yellowish. Roseate Tern, 

 b''. Bill not black, mostly reddish, yellowish or brownish, 

 r. Bill distinctly black-tipped, tarsus over 0.65. 



Common Tern, 

 rr. Bill not distinctly black-tipped, tarsus under 0.65. 



Arctic Tern, 

 a*. Top of head not entirely black, some white or grayish on fore- 

 head or crown, 

 b'. Lores entirely black ; forehead white and crown jet 



black. Sooty Tern, 

 b''. Lores not entirely black ; forehead or crown white or gray- 

 ish, never jet black, but sometimes speckled with black, 

 c^ Wing black or very dark. Sooty Tern. (Im.) 

 c*. Wing pearl gray. 



d'. Outer tail feather pure white. Roseate Tern. (Im.) 

 d*. Outer tail feather not pure white. 



Tarsus not more than 0.65. Arctic Tern. (Im.) 

 Tarsus more than 0.65. Common Tern. (Im.) 



Genus GELOCHELIDON Brehm. 



63. Gelochelidon nilotica (Hasselq.). Gull-billed Tern; 



Marsh Tern. 



Plumage in summer adults : top of head, bill and feet black ; under parts 

 and tail white ; middle tail feathers grayish ; wings and back pale pearl gray. 

 Plumage in winter adults: differs in that the head and neck are white; 

 hind neck and ear coverts grayish. Immature plumage : similar to winter 

 adults but upper parts buffy washed and sometimes dusky streaked. Wing 

 11.60 to 12.30; culmen 1.40; depth of bill at base 0.48. 



