KEY TO FAMILIES. WATEll UIKOS. 



13 



Xostrils, separaU' not tubular; bill, with cere (a horuy or skin-like covering on base of 

 upper iiiauilible) ; liind toe, sometimes very small; 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, usunllv very dark; middle tail feathers, longest, 



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Itut only very long in adult birds, sometimes only slightly longer than rest of tail feathers in 

 immature birds; in l)rowii plumages, the axillars (feathers extending from armpit) are 

 heavily l)arred, brown and white; in other plumages, tlie axillars and under wing coverts are 

 sooty brown or dark slaty brown Family STERCORARUD/E. Skuas and Jaegers. 



See page 34. 



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Nostrils, separate not tubular; bill, without cere; hind toe, sometimes very small; upper 

 niiiudible, curved; unguis (end of bill), not swollen; middle tail feathers, about equal in 

 length to the others ; tail, rarely dark, although sometimes tipped with black or brown ; 

 axillars and under wing coverts, white or gray, sometimes with narrow gray lines or faint 

 wavy bars. 



Family LARID^E. Subfamily LARIN^. Quils. 



See page 36. 



r^^ 



Nostrils, separate not tubular; hind toe, sometimes very small; upper mandible, nearly 

 straight, not hooked or decidedly rounded near tip: oute»tail feathers, usually longer tlian 

 middle feathers. Family LARID/E. Subfamily STERNIN^. Terns. 



See page 41. 



Bill, like blade of a knife, the under mandible the longer : plumage, black above, white 

 below . Family RHYNCHOPID/E. Skimmers. 



See page 45. 



