TERNS 163 
pendent on their parents until they acquire the power of flight. During 
this period, the young of some, possibly of all, species, enter the water 
of their own volition and swim freely, a habit in which the adult rarely, 
if ever, indulges. 
Subfamily Sternine. Terns 
KEY TO THE SPECIES 
I. Wing under 13°00. 
1. Entire top of the head jet-black. 
A. Bill black, or mostly black. 
a. Feet black or blackish. 
a}, Underparts black or blackish ........ 77. Buack TERN. 
a, Underparts white; bill black .... 63. GuLL-BILLED TERN. 
a’, Underparts white; bill black, broadly tipped with yellow. 
67. Cazpor’s TERN. 
b. Feet yellowish or orange. 
b!, Outer tail-feathers pure white; outer web of first primary black. 
Rosgats Tern. 
b?. Inner web of outer tail-feather gray; outer web of first primary 
OYAV 4.4 52h ed OA AE OE Se Forster’s TERN. 
B. Bill mostly or entirely yellowish, reddish, Rec or orange. 
a. Underparts tinged with grayish; outer web of outer tail-feather 
gray; inner web white. 
ai, Bill broadly tipped with blackish; tarsus generally over °70. 
Common TERN. 
a, Bill without a distinct black tip; tarsus generally under ‘70. 
Arctic TERN. 
b. Underparts pure white; inner web of outer tail-feather gray; 
outer web white ...........8. 69. Forster’s TERN. 
2. Entire top of head not jet-black. 
A. Forehead white; lores black; crown jet-black or silvery. 
a. Wing under 8°00; back pearl-gray ........ 74, Least TERN. 
b. Wing over 8°00; back grayish brown or blackish. 
bL ea grayish brown; a white stripe from the forehead over the 
a) Ce 6 RS GSA GL oat we 76. BripLep TERN. 
bo. Beek blackish; white of forehead not reaching over the eye. 
75. Soory TERN. 
63, Crown silvery, rest of plumage sooty....... 79. Noppy. 
B. Forehead or crown white or grayish, sometimes speckled with black; 
lores not entirely black. 
a. Wing pearl-gray. 
a, Outer tail-feather entirely pure white. 
a*, Bill over 1°75, tipped with yellowish. . 67. CagBot’s TERN. 
a’, Bill under 1°75, without a yellow tip. 
72. RoseaTte TERN (Im.). 
61, Outer tail-feather not pure white. 
62, Inner web of outer tail-feather darker than outer web; outer 
web mostly or entirely white; a black space generally on the 
side of the head inclosing the eye. 
69. ForsteR’s TERN (Im.). 
3, Outer web of outer tail-feather darker than inner web; tarsus 
Over “70% «ss wee a Raa 70. Common TERN (Im.). 
64. Outer web of outer tail-feather darker than inner web; tarsus 
der! 70) x. on a sees, Bw eek Oe 71. Arctic TERN (Im.). 
un 
65, Tail wholly gray, not deeply forked, wing under 9°00; belly 
white or mottled with black... . 77. Buack TERN (Im.). 
b. Wing blackish. 
b'. Underparts blackish .......... 75. Soory Tern (Im.). 
b?, Underparts white.......... 76. Briptep TERN (Im.). 
18 
