Larus leucopterus, White-Winged Silvery Gull, Swains. and Richards. Fauna Bor. Amer. part ii. p. 418.
Larus arcticus, Macgillivray, Wern. Trans, vol. v. p. 268.
White-winged Silvery Gull, Nuttall, Manual, vol. ii. p. 305.
Adult Male. Plate CCLXXXII. Fig. 1.
Bill shorter than the head, strong, nearly straight, compressed. Upper mandible with the dorsal line nearly straight at the base, arched and decimate towards the end, the ridge convex, the sides slightly convex, the edges sharp, nearly direct, the tip rather obtuse. Nasal groove rather long and narrow; nostril in its fore part, lateral, longitudinal, linear, wider anteriorly, open and pervious. Lower mandible with a prominence at the end of the angle, which is long and narrow, the dorsal line then nearly straight and ascending, the sides flat and slightly inclined, the edges sharp and inflected.
Head rather large. Neck of moderate length. Body rather full. Wings very long. Feet of moderate length, rather slender; tibia bare below; tarsus somewhat compressed, covered before with numerous broad scutella, laterally and behind with roundish scales, on the outer side also with a row of small scutella; toes of moderate length, rather slender, all covered above with scutella; the anterior connected by reticulated webs, the two lateral with an external thick margin; the first extremely small, the third longest, the fourth longer than second; claw of hind toe smallest, of third largest, with an inner thin edge, of second next in size, all more or less compressed and obtuse.
The plumage in general is close, elastic, very soft and blended, on the back rather compact. Wings very long, broad, pointed; primaries tapering, the first longest, the second slightly shorter, the rest rapidly graduated; secondaries broad and rounded, the inner elongated and rather narrow. Tail of moderate length, even, of twelve broad feathers.
Bill gamboge-yellow, with a spot of orange-red near the end of lower mandible; the angle of the mouth and the edges of the eyelids are also orange-red. Iris pale yellow. Feet pale flesh-colour; claws greyish-brown. The whole plumage is pure white, excepting the back and upper surface of wings; the tips of the secondaries, the terminal third or so of the primaries, their shafts, and the upper tail-coverts also white.
Length to end of tail 26 inches, to end of wings 28 1/4; extent of wings 50; bill along the back 1 3/4, along the edges 2 1/2; tarsus 2 1/2, middle toe 2 1/12, its claw 4 1/2/12; wing from flexure 17 1/2; tail 6 1/2.
Young in winter. Plate CCLXXXII. Fig. 2.