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. 



•9 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>. Under parts black or blackish 77. Black Tern. 



a'. Under parts white ; bill black .... 63. Gull-billed Tekn. 

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



67. Cabot's Teen. 



b. Feet yellowish or orange. 



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



72. BosEATE Tern. 



J'. Inner web of outer tail-feather gray ; outer web of first priaiary 



gray 69. Foestee's Teen. 



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



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

 gray ; inner web white. 

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



70. Common Teen. 

 ffl2. Bill without a distinct black tip ; tarsus generally under -70. 



71. Aectio Teen. 



J. Under parts pure white ; inner web of (?utcr tail-feather gray ; outer 



web white 69. Foestee's Teen. 



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



A. Wing under 8-00 ; back pearl-gray 74. Least Teen. 



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



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



76. Bbidled Tekn. 



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



75. Sooty Teen. 



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

 lores not entirely black. 



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

 o. Outer tail-feather entirely pure white. 



oi. Bill over 1-75, tipped with yellowish ... 67. Cabot's Teen. 



(fl. Bill under 1'75, without a yellow tip . 72. Eoseate Teen (Im.). 

 i. Outer tail-feather not pure white. 



J». Inner web of outer tail-feather darker than outer web ; outer web 



