Nostrils pervious, the opening linear or oval; wings long, strong,
and pointed; first primary longest; legs and feet moderate; hind toe
small and elevated; anterior toes fully webbed. Plumage of the adult
simple in color, being white, black, and pearl-gray, rarely brown,
usually in large areas. Young gray or mottled, very different in color
from the adult. Usually found in flocks and never far from water. Eggs
two to four, highly colored; nests usually on the ground or on cliffs;
young downy at birth and fed in the nest for some time. [11]
Family LARIDÆ.
Characters same as those given for the Order.
Subfamilies.
a1. Tail more or less forked (except in Anous); bill slender; terminal
portion of culmen straight or but slightly curved; angle of lower
mandible not prominent. ... Sterninæ (p. 86)
a2. Tail even; bill stouter; terminal portion of culmen decidedly
curved; angle of lower mandible distinct. ... Larinæ (p. 95)
Subfamily STERNINÆ.
The members of this subfamily afford no very tangible characters
to distinguish them from the gulls other than those already
mentioned. However, the terns are, as a rule, of more slender form
and more airy and graceful flight. The wings, bill, and tail are
proportionately longer and the body smaller than these parts in
the gulls.
Genera.
a1. Tail more or less forked.
b1. Tail but little more than one-third of wing, its outer feathers
broad and rounded. ... Hydrochelidon (p. 86)
b2. Tail much more than one-third of wing, its outer feathers narrow
and pointed. ... Sterna (p. 88)
a2. Tail graduated; plumage sooty brown. ... Anous (p. 94)
Genus HYDROCHELIDON Boie, 1822.
Bill short and slender; legs and feet small; webs between the toes
deeply emarginate; wings long, when closed, exceeding the tail;
tail short, nearly square.
Species.
a1. Black or dark gray below (adults in summer).
b1. Upper tail-coverts and tail white; under wing-coverts
black. ... leucoptera (p. 86)
b2. Upper tail-coverts and tail gray; under wing-coverts
white. ... hybrida (p. 87)
a2. White below (adults in winter and young).
b1. Tail white. ... leucoptera (p. 86)
b2. Tail gray.
c1. Rump gray like back. ... hybrida (p. 87)
c2. Rump white (young). ... leucoptera (p. 86)