TERNS. 77 



power of flight has deservedly won for them the name of Sea Swal- 

 lows. They capture their prey of small fish by plunging into the 

 water, frequently disappearing and swimming a few feet beneath the 

 surface. They nest in colonies. The nest is usually on the ground. 

 Generally it is simply a slight depression in the sand, shells, or pebbles 

 of a beach, or in the near-by seaweed, moss, or grasses. Sometimes it 

 is scantily lined with bits of grass, seaweed, moss, etc., but these are 

 frequently wanting. 



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 1 . Under parts black or blackish 77. BLACK TERN. 



a 8 . Under parts white ; bill black .... 63. GULL-BILLED TERN. 

 a 3 . Under parts white; bill black, broadly tipped with yellow. 



67. CABOT'S TERN. 



b. Feet yellowish or orange. 



b l . Outer tail-feathers pure white ; outer web of first primary black. 



72. EOSEATE TERN. 



J a . Inner web of outer tail-feather gray ; outer web of first primary 

 gray 69. FORSTER'S TERN. 



B. Bill mostly or entirely yellowish, reddish, brownish, or orange. 



a. Under parts tinged with grayish ; outer web of outer tail-feather 

 gray ; inner web white. 



a 1 . Bill broadly tipped with blackish; tarsus generally over '70. 



70. COMMON TERN. 

 a 2 . Bill without a distinct black tip; tarsus generally under "70. 



71. ARCTIC TERN. 



b. Under parts pure white ; inner web of outer tail-feather gray ; outer 

 web white 69. FORSTER'S TERN. 



2. Forehead white ; lores black ; crown jet-black. 



A, Wing under 8*00 ; back pearl-gray 74. LEAST TERN. 



B. Wing over 8-00 ; back grayish brown or blackish. 



a. Back grayish brown ; a white stripe from the forehead over the eye. 



76. BRIDLED TERN. 



b. Back blackish ; white of forehead not reaching over the eye. 



75. SOOTY TERN. 



3. Forehead or crown white or grayish, sometimes speckled with black; 

 lores not entirely black. 



A. Wing pearl-gray, over 9'00. 



a. Outer tail-feather entirely pure white. 



a 1 . Bill over 1-75, tipped with yellowish ... 67. CABOT'S TERN. 

 a. Bill under 1'75, without a yellow tip . 72. ROSEATE TERN (Im.). 



b. Outer tail-feather not pure white. 



b 1 . Inner web of outer tail-feather darker than outer web ; outer web 



