GULLS 153 



feed upon the eggs and young of the other birds among which they nest, 

 rarely, however, preying on their own species. 



Gulls are buoyant swimmers, and, unlike Terns, rest and roost on 

 the water, often gathering in close-massed "beds." They nest in colonies 

 on islands. The young are born covered with down of mottled pattern, 

 and though they may leave the nest in their natal dress, are dependent 

 on their parents until they acquire the power of flight. The voices 

 of Gulls possess a certain, indescribable human quality which adds 

 in no small degree to the impression created when storms rule and 

 these wild cries are heard above the tumult of wind and wave. 



KEY TO THE SPECIES 



I. Wing over 15'00. 



1. Back dark slaty black 47. BLACK-BACKED GULL. 



2. Back not dark slaty black. 



A. Back pearl-gray. 



a. Outer primaries marked with black .... 51. HERRING GULL. 



b. No black on primaries. 

 b 1 . Bill under 2'00. 



b z . Primaries light pearl-gray, fading gradually into white at 

 their tips 43. ICELAND GULL. 



/; 3 Primaries pearl gray, tipped with white, and with well-de- 

 fined gray spaces on the outer webs of the outer two 

 primaries and on both webs of the third and fourth 



primaries 45. KUMLIEN'S GULL. 



c 1 . Bill over 2'00 42. GLAUCOUS GULL. 



B. Back grayish, whitish, or brownish, or mottled or spotted with 



grayish or brownish. 



a. Tail black or blackish, with or without irregular white markings. 

 a 1 . Wing over 17' 50; depth of bill at nostril over '70. 



47. BLACK-BACKED GULL (Im.). 

 a 2 . Wing under 17*50; depth of bill at nostril under '70. 



51. HERRING GULL (Im.). 



b. Tail white or whitish or grayish brown, with or without black 



markings. 



ft 1 . Bill under 2'00 43. ICELAND GULL (Im.). 



b\ Bill over 2'00 , . 42. GLAUCOUS GULL (Im.). 



II. Wing under 15'GO. 

 1. Tail white. 



A. Head and throat slaty black. 



a. Outer primary black or mostly black. 



a 1 . Outer primary entirely black 58. LAUGHING GULL. 



a 2 . Inner half of inner web of first primary white. 



62. SABINE'S GULL. 



b. Outer primary mostly white. 



6 1 . Tip of first primary white 59. FRANKLIN'S GULL. 



6 2 . Tip of first primary black 60. BONAPARTE'S GULL. 



B. Head white, sometimes washed with pearl-gray. 



a. Wings white 39. IVORY GULL. 



6. Primaries with more or less black. 

 6 1 . Wing over ll'OO. 



6 2 . Hind- toe very small, without a nail .... 40. KITTIWAKE. 



6 3 . Hind-toe normal, with a nail . . . 54. RING-BILLED GULL. 

 c 1 - Wing under ll'OO ...... 61. Ross's GULI,. 



