FAMILY STERCORARIID^l. SKUAS AND J.EGERS. 33 



FAfllLY STERCORARIID^E. 



Skuas and Jaegers. 



Nostrils, separate, and not tubular ; bill, with cere ; front toes, palmate 

 (full webbed); hind toe, small, but always present ; end of upper mandible 

 (unguis), swollen, and somewhat rounded; back and wings, 

 always dark, sometimes sooty, sometimes barred with brown ; 

 tail, never white or gray, usually very dark ; middle tail feath- 

 ers, longest. The cere (hard skin-like covering on base of upper 

 mandible) will distinguish these birds from Gulls. 



* Group 1. Wing, 11 to 15 inches long. 



Underparts, not entirely pure white; bill, over 1.35; tarsus, over 1.80; middle tail 

 feathers, not pointed ; plumage, sometimes dark brown; sometimes mixed gray, brown, and 

 white. Stercorarius pomarinus. Pomarine Jaeger. 



See No. 19. 



Bill, under 1.35; tarsus, under 1.80; middle tail feathers, pointed; base of unguis 

 to frontal feathers less than length of unguis ; shafts of primaries, yellow white. 



Stercorarius longicaudus. Long=tailed Jaeger. 



See No. 21. 



Bill, under 1.35; tarsus, under 1.80; middle tail feathers, pointed; base of unguis to 

 frontal feathers, greater than length of unguis; shafts of primaries, yellowish white. 



Stercorarius parasiticus. Parasitic Jaeger. 

 See No. 20. 



4 



* Group 2. Wing, over 15 inches long. 



Bill, with cere ; general color, dark brown, more or less streaked with light brown ; a 

 patch of white at base of primaries. Megalestris skua. Skua. 



See No. 18. 



* For directions for. measurement, see page 9. 



