LAEIDJE — LABIN^: GULLS. 739 



dusky, its nail almost black. Tarsi deep leaden-blue; tibiae, phalanges, interdigital mem- 

 branes, and claws black. Occiput subcrested, more decidedly than in any other species, form- 

 ing ii calotte of brownish-black, which color extends downward on the cheeks, the feathers 

 before and below the eye and on the sides of the bill being of this color. Neck all round, but 

 especially the sides of the head and tlie peculiarly-formed feathers on the latero-nuchal region, 

 light straw-yellow. Whole upper parts, with upper wing and tail-coverts, deep slate, which, 

 on the primaries, secondaries, lateral tail-feathers, and distal half of central pair, deepens into 

 a lustrous brownish-black. Under surface of wings and taU deeper slate than the black, but 

 not so deep as the upper surfaces. Chin, throat, and upper breast while, gradually becoming 

 obscured with dusky-plumbeous, which deepens posteriorly, so that the abdomen and under 

 tail-coverts are nearly as dark as the back. Rhachides of first two or three primaries pure 

 white, deepening into brownish-black at their tips ; of the other primaries, and of the tail- 

 feathers (including the central pair), brown, except just at the base, blackening terminally. 

 Under surfeces of all the rhachides white for nearly their whole length. Length of culmen 

 1.15 inches; gape 1.70; cere 0.60; unguis about the same; gonys 0.30; from feathers on 

 sides of bill to tip 0.90; wing 12.50; tail 6.25; central pair 14.00 to 16.00 ; the projection 

 S.OO to 10.00 inches; tibife bare 0.75; tarsus 1.60; middle toe without claw 1.40. All 

 changes and states of plumage identical with those of No. 766. N. Am., northerly ; breeds 

 in Arctic regions. Eggs not distinguishable from those of No. 766, averaging smaller but 

 dimensions overlapping; a fair specimen is 2.10 X 1-50 ; from this down to 1.90 X 1-40. 



71. Subfamily LARIN>E: Culls. 



Covering of bill continuous, horny throughout ; bill more or less strongly epignathous, 

 compressed, with more or less protuberant gonys ; nostrils linear-oblong, median or sub-basal, 

 pervious. Tail even or nearly so, rarely forked or cuneate, without projecting middle feathers. 

 Certain of the smaller slenderer-biUed species alone resemble terns, but may be known by the 

 not forked tail (except Xema) ; in all the larger species, the hook of the bill is distinctive. 

 GuUs average much larger than terns, with stouter build ; the feet are larger and more 

 ambulatorial, the wings are shorter and not so thin ; the birds winnow the air in a steady 

 course unlike the buoyant dashing flight of their relatives. They are cosmopolitan ; species 

 occur in abundance on all sea-coasts, and over large inland waters ; iu general, large numbei'S 

 are seen together, not only at the breeding-places, but during the migrations, and in winter, 

 when their association depends upon community of interest in the matter of food. This is 

 almost entirely of an animal nature, and consists principally of fish ; the birds seem to be 

 always hungry, always feeding or trying to do so. Many kinds procure food by plunging 

 for it, like tenis; others pick up floating substances; some of the smaller kinds are adroit 

 parasites of the pelicans, snatching food from their very mouths. They all swim lightly — 

 a circumstance explained by the .smaUness of the body compared with its apparent dimensions 

 with the feathers on. The voice of the larger species is hoarse, that of the smaller shrill ; 

 they have an ordinary note of several abrupt syllables during the breeding season, and a 

 harsh cry of anger or impatience ; the young emit a querulous whine. The nest is connnonly 

 built on the ground ; the eggs, 2-3 in number, are variegated in color. 



Several circumstances conspire to render the study of these birds difficult. With some 

 exceptions, they are ahnost identical in form ; while in size they show an unbroken series. 

 Individual variability in size is high ; northerly birds are usually appreciably larger than 

 those of the same species hatched further south ; the ^ exceeds the 9 a little (usually) ; 

 very old birds are likely to be larger, with especially stouter bill, than young or middle-aged 

 ones. There is, besides, a certain plasticity of organization, or ready susceptibility to modify- 

 ing influences, so marked that the individuals hatched at a particular spot may be appreciably 

 different in some slight points from others reared but a few miles away. One pattern of color- 



