18 



KEY B. SIZE LARGE, WING .338-469 mm. 



1 Primary 10 longest wing feather. 2 

 1' Primary 10 shorter than 9 and usually shorter than 8. 7 



2 All 4 toes long and connected by webs (Plate 36-4); middle toenail 

 comb-like (Fig. 17). See BOOBIES (Page 31) 



2' Only 3 toes connected by webs, 4th toe reduced in size (Plate 35); 



middle toenail not comb-like. 3 



3 Tarsus flattened laterally in cross section (Plate 34); 16-20 tail 

 feathers. See LOONS (Page 24) 



3' Tarsus rounded in cross section; 12 tail feathers. 4 



4 Wings entirely black on upper surface. See TERNS (Page 62) 

 4' Wings not black on upper surface, wings white to gray or brown. 5 



5 Wings long and thin in proportion when extended, ratio of width to 

 total length 0.25 or less; tertials and scapulars very long - partic- 

 ularly evident in folded wing; distance from shoulder to wrist less 

 than wrist to wing tip; feet much longer than tarsi; tarsi short 



(<1/10 wing length); tail deeply forked. See TERNS (Page 62) 



5' Wings broader in proportion, ratio of width to total length 0.26 or 

 (usually much) more; tertials and scapulars not unusually long; 

 distance from shoulder to wrist about equal OR slightly more than 

 from wrist to wing tip; feet and tarsi about equal in length; tarsi 

 long (>1/10 wing length). 6 



6 Wings very dark brown all over except for white shafts and bases to 

 outer primaries; in some immatures, contour feathers may be spotted 

 with white, giving bird, especially near flanks and rump, a pro- 

 nounced checkered appearance; bill black (bill may be light near 

 nostrils); legs and feet black or legs blue and feet black; claws 

 very long and deeply curved (Plate 35-1). 



See SKUAS and JAEGERS (Page 50) 



