KEY TO FAMILIES. — WATER BIRDS. 13} 
Nostrils, separate not tubular; bill, with cere (a2 horny or skin-like covering on base of 
upper mandible) ; hind 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, usually very dark; middle tail feathers, longest, 
but only very long in adult birds, sometimes only slightly longer than rest of tail feathers in 
immature birds; in brown plumages, the axillars (feathers extending from armpit) are 
heavily barred, brown and white; in other plumages, the axillais and under wing coverts are 
sooty brown or dark slaty brown. Family STERCORARIIDAE. Skuas and Jaegers. 
See page 34. 
Nostrils, separate not tubular; bill, without cere ; hind toe, sometimes very small; upper 
mandible, 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 LARIDAZ. Subfamily LARINAE. Gulls. 
See page 36. 
Nostrils, separate not tubular; hind toe, sometimes very small; upper mandible, nearly 
straight, not hooked or decidedly rounded near tip: outer tail feathers, usually longer than 
middle feathers. Family LARIDAE. Subfamily STERNINAE. Terns. 
See page 41. 
Bill, like blade of a knife, the under mandible the longer; plumage, black above, white 
below. Family RHYNCHOPIDA:. Skimmers. 
See page 45. 
