Central tail-feathers projecting three inches; gradually tapering from the base; the tips acute: tarsus one inch nine lines; slightly rugose posteriorly.
L. Richardsonii, Faun. Bor. Amer. part ii. p. 433. pl. 73. Cataractes parasiticus, Flem. in Edinb. Phil. Journ. vol. i. p. 101. Id. Brit. An. p. 138. Larus parasiticus, Edmondst. in Edinb. Phil. Journ. vol. v. p. 169, & vol. vii. p. 91. Arctic and Black-toed Gulls, Mont. Orn. Diet. § Supp. Bew. Brit. Birds, vol. ii. pp. 232, & 235. Arctic Skua, Selb. Illust. vol. ii. p. 520. pls. 101, & 101*. Richardson's Lestris, Gould, Europ. Birds, part iv.
Entire length twenty-one inches; the same, central tail-feathers excluded, eighteen inches: length of the bill (from the forehead) one inch two lines and a half, (from the gape) one inch nine lines and a half; of the tarsus one inch nine lines; of the middle toe, nail included, one inch eight lines and a half; of the central tail-feathers nine inches; from the carpus to the end of the wing thirteen inches.
(Adult male and female). Forehead, crown, occiput, wings and tail, deep black; the shafts of the quills and tail-feathers white to near their tips: rest of the upper plumage deep dusky brown tinged with cinereous: nape, and ear-coverts, straw-yellow: throat, breast, and belly, yellowish white: flanks, vent, and under tail-coverts, deep dusky gray: bill and legs black. (Young of the year). Extremely similar to those of the last species, from which they are scarcely to be distinguished except by their inferior size, less robust bill, shorter and smoother tarsi, and the sharp-pointed central tail-feathers, which in length, however, do not at this age exceed the others by more than half an inch: legs, and basal portion of the webs as well as toes, flesh-colour; the remaining portion of the membranes black, in which state it is the Black-toed Gull of English authors. Obs. In the adult state this species is subject to considerable variation of plumage; in some instances all the under parts being of a uniform dark brownish gray without any of the yellow and yellowish white tints, which are probably not assumed till after a certain number of years. This variety is common to both sexes, and individuals may be found shewing every intermediate shade of colouring. (Egg). Olive-brown, spotted with two shades of darker brown: long. diam. two inches four lines; trans, diam. one inch eight lines.
Of much more frequent occurrence than the next species, with which it appears to have been confounded by many authors. It is, however, principally confined to the Orkney and Shetland Islands, where it breeds in considerable abundance. Immature birds are occasionally met with on different parts of the English coast. Habits predatory, like those of the Common Skua. Nest constructed of dry grass, on unfrequented heaths. Eggs two in number. Is gregarious during the breeding season.