Larus marinus, Linn. Syst. Nat. vol. i. p. 225.—Lath. Ind. Ornith. vol. ii. p. 813.—Ch. Bonaparte, Synopsis of Birds of the United States, p. 362.
Black-backed Gull, or Cobb, Nuttall, Manual, vol. ii. p. 308.
Adult Male in Summer. Plate CCXLI.
Bill shorter than the head, robust, compressed, higher near the end than at the base. Upper mandible with the dorsal line nearly straight at the base, declinate and arched towards the end, the ridge convex, the sides slightly convex, the edges sharp, inflected, arcuate-declinate towards the end, the tip rather obtuse. Nasal groove rather long and narrow; nostril in its fore part, lateral, longitudinal, linear, wider anteriorly, pervious. Lower mandible with the angle long and narrow, the outline of the crura rather concave, as is that of the remaining part of the mandible, a prominent angle being formed at their meeting, the sides nearly flat, the edges sharp and inflected.
Head rather large, oblong, narrowed anteriorly. Neck of moderate length, strong. Body full. Wings long. Feet of moderate length, rather slender; tibia bare below; tarsus somewhat compressed, covered anteriorly with numerous scutella, laterally with angular scales, behind with numerous small oblong scales; hind toe very small and elevated, the fore toes of moderate length, rather slender, the fourth longer than the second, the third longest, all scutellate above, and connected by reticulated entire membranes, the lateral toes margined externally with a narrow membrane. Claws small, slightly arched, depressed, rounded, that of middle toe with an expanded inner margin.
The plumage in general is close, full, elastic, very soft and blended, on the back rather compact. Wings very long, broad, acute, the first quill longest, the second scarcely shorter, the rest of the primaries rather rapidly graduated; secondaries broad and rounded, the inner narrower. Tail of moderate length, even, of twelve rounded feathers.
Bill gamboge-yellow, the lower mandible bright carmine towards the end. Edges of eyelids bright carmine, iris silvery. Feet yellow, claws black. The head, neck, and all the lower parts, pure white; back and wings deep blackish-grey tinged with purple, or dark slate-colour; the rump and tail white, as are the edges of the wing, and a large portion of the extremities of all the quills; the second, third, fourth, and fifth primaries have a broad band of black across their ends, the inner web only of the second being so marked, in some specimens however both webs. The œsophagus is very large, the gizzard small, the intestine four feet long, and about the thickness of a goose quill.
Length to end of tail 29 3/4 inches, to end of wings 31 1/2, to end of claws 29 1/4; extent of wings 67; wing from flexure 20; tail 9; bill along the ridge 2 10/12, along the edge of lower mandible 3 9/12; its depth at the angle 1, at the base 11/12; tarsus 3 2/12; middle toe 2 1/2, its claw 1/2. Weight 3 lb.
The Female is similar to the Male, but considerably less.
The Young when fledged have the bill brownish-black, the iris dark brown, the feet as in the adult. The head and neck are greyish-white, streaked with pale brownish-grey; the upper parts mottled with brownish-black, brownish-grey, and dull white, the rump paler. The primary quills blackish-brown, slightly tipped with brownish-white; the tail-feathers white, with a large brownish-black patch towards the end, larger on the middle feathers, which are also barred towards the base with dusky. The lower parts are greyish-white, the sides and lower tail-coverts obscurely mottled with greyish-brown.