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. Whig under 13-00. 



1. Entire top of the head jet-black. 

 ji. Bill black, or mostly black. 



a. Feet black or blackish. 



ai. Under parts black or blackish 77. Black Terist. 



a^. Under parts white ; bill black .... 63. Gull-billed Tern. 

 a3. Under parts white; bill black, broadly tipped with yellow. 



67. Cabot's Tern. 

 6. Feet yellowish or oran2:e. 



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



72. Eoseate Tern. 

 J2. 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 witli grayish; outer web of outer tail-feather 

 gray ; inner web white. 



ai. Bill broadly tipped with blackish ; tarsus generally over -70. 



70. Common Tern. 

 a2. 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. 



«!. Bill over 1'75, tipped with yellowish ... 67. Cabot's Tern. 

 a3. Bill under 1-75, without a yellow tip . 72. Roseate Tern (Im.). 



b. Outer tail-feather not pure white. 



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



