Nearly white all over though most of them are, in the adult plumage, they are 

 yet obliteratively shaded, having " mantles" of darker or lighter bluish gray 

 on the back and wings — and in the case of many terns, crown-caps of black — 

 while all the remainder of their costume, with the exception of a few more 

 or less dark-marked quill feathers, is, in most cases, fleckless white. Black 

 markings aside (these we shall discuss later), this obliteratively disposed com- 

 bination of soft, water- and cloud-like pearly gray with bright, shadow-ab- 

 sorbing white is just such a coloration as insures its wearers, whether flying 

 or swimming, the greatest average inconspicuousness against the ocean. Often 

 they show light against dusky water, but just as often they show dark against 

 water brightly sky-lit; and hence in many intermediate cases they must pass 

 unseen, matching their 'background' as does the ptarmigan or grouse in its 

 appropriate domain, although so much less intricately. All this concerns the 

 aspect of the gulls as seen from above, against the ocean. But they have little 

 to dread from flying enemies, and the more vital service rendered by their col- 

 oration is doubtless concealment against the sky above, from the eyes of aquatic 

 animals below them. Like the Snowy Owl, the white herons and egrets, and, 

 in part, the skunks, deer, antelopes, etc., to be described in a later chapter 

 (Chapter XXII), these ocean-rangers are admirably equipped for incon- 

 spicuousness, in a great many views, against the sky itself. Thus, even to the 

 eyes of their aquatic enemies and aquatic prey, they wear the universal com- 

 plete obliterative coloration. Pure white or largely pure white though they are, 

 they must often relieve darkly against the sky, as always when seen directly 

 overhead. In many views, on the other hand, they ' melt away ' into their skyey 

 backgrounds, as do the white, masking rump-marks of many ruminants, and 

 the white back- and head-patterns of many grubbing carnivores (Chapter 

 XXII), etc. As the normal background of these sea birds is the unbroken sky, 

 varied only by unbroken, sky-reflecting ocean, so their prevalent coloration is 

 such as achieves pure and. simple sky- and ocean-picturing. On most of the 

 true gulls (Larince) the white of the rump, tail, and entire underside extends also 

 to the head and neck. The head's consequent lack of counter shading is 



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