14 LONGIPENNES: Long-winged Swimmers 



PLUMAGE CHANGES OR MOULTS OF GULLS 



In studying Gulls it must be remembered that the plumage of 

 immatures, except the Heermann, is progressively lightening in 

 color through wear and fading, irrespective of moults, until the 

 adult stage is reached. The annual, or post-nuptial moult, in 

 which the entire plumage is replaced, begins in May, and is 

 usually completed in late August or September. A partial 

 moult in which head and neck feathers, and to some extent 

 those of the breast, are renewed, occurs in winter and early 

 spring, the time varying with different species. 



The small white marks, or apical spots, on extreme tips of 

 primaries of adult black-winged Gulls, are conspicuous in fresh 

 fall plumage, but are soon reduced and finally lost through wear. 

 The larger white spots near tips of outer primaries are called 

 "mirrors," and are useful field marks. 



KEY TO SPECIES 



(Length) 



No black in plumage. Coastwise 44. GLAUCOUS-WINGED 24-27 



Body dark. Head white; bill red; coastwise 57. HEERMANN 16-18 



Body white; black in plumage. 



A. Head black in spring. Ocean, chiefly 60. BONAPARTE 14 



B. Head white in spring. 



a. Mantle dark. Extensive black in wing -tips; heavy angle lower 

 mandible; coastwise .49. WESTERN 23-25 



b. Mantle light. 



a'. Large. Black of wing-tips not extensive; comparatively 



rare; coastwise 51. HERRING 23-26 



b'. Medium size. 



1. Wing-tips solid black; smallest of this group; coast- 

 wise 40a. PACIFIC KITTIWAKE 16 



2. Very large white mirrors; coast and inland 



53. CALIFORNIA 18-21 



3. Black ring on bill near tip; coast and inland; southern 



California 54. RING-BILL 17-19 



4. Very large white mirrors; short, slender bill; coastwise 



55. SHORT-BILL 16-18 



