SKUA, the name for a long while given to certain of the Laridae (see Gull), birds which sufficiently differ in structure, appearance and habits to justify their separation as a distinct genus, Stercorarius (Lestris of some writers), or even subfamily, Stercorariinae. Swift of flight, powerfully armed, but above all endowed with extraordinary courage, they pursue their weaker cousins, making the latter disgorge their already swallowed prey, which is nimbly caught before it reaches the water; and this habit, often observed by sailors and fishermen, has made these predatory, and parasitic birds locally known as “Teasers,” “Boatswains,” and, from a misconception of their
intent, “Dunghunters.” On land, however, whither they resort to breed, they seek food of their own taking, whether small mammals, little birds, insects or berries; but even here their uncommon courage is exhibited, and they will defend their homes and offspring with the utmost spirit against any intruder, repeatedly shooting down on man or dog that invades their haunts, while every bird almost, from an eagle downwards, is repelled by buffets or something worse.
The largest species known is the Stercorarius catarrhactes
of ornithologists — the “Skooi” or “Bonxie” of the Shetlanders, a bird in size equalling a herring-gull, Larus argentatus
. The sexes do not differ appreciably in colour, which is of a dark brown, somewhat lighter beneath; but the primaries have at the base a patch of white, visible even when the wings are closed, and forming, when they are spread, a conspicuous band. The bill and feet are black. This is a species of comparatively limited range, breeding only in some two or three localities in the Shetlands, about half a dozen in the Faeroes,
and hardly more in Iceland. Out of the breeding-season it shows itself in most parts of the North Atlantic, but never seems to stray farther south than Gibraltar or Morocco, and it is therefore a matter of much interest to find the Southern Ocean inhabited by a bird — the “Port Egmont Hen” of Cook's Voyages
— which so closely resembles the Skua as to have been for a long while regarded as specifically identical with it, but is now usually recognized as distinct under the name of S. antarcticus
. This bird, characterized by its stout deep bill and want of rufous tint on its lower plumage, has an extensive range, and would seem to exhibit a tendency to further differentiation, since Howard Saunders, in a monograph of the group (Proc. Zool. Society
, 1876, pp. 317-332), says that it presents three local forms — one occurring from New Zealand to Norfolk Island and past Kerguelen Land to the Cape of Good Hope, another restricted to the Falklands, and the third hitherto only met with near the south-polar ice. On the western coast of South America, making its way into the Straits of Magellan, and passing along the coast so far as Rio Janeiro, is found S. chilensis
, distinguished among other characters by the cinnamon tint of its lower plumage. Three other smaller species of the genus are known, and each is more widely distributed than those just mentioned, but the home of all is in the more northern parts of the earth, though in winter two of them go very far south, and, crossing the equator, show themselves on the seas that wash the Cape of Good Hope, Australia, New Zealand and Peru. The first of them is S. pomatorhinus
(often incorrectly spelt pomarinus
), about the size of a common gull, Larus canus
, and presenting, irrespective of sex, two very distinct phases of plumage, one almost wholly sooty-brown, the other parti-coloured — dark above and white on the breast, the sides of the neck being of a glossy straw-colour, and the lower part of the neck and the sides of the body barred with brown; but a singular feature in the adults of this species is that the two median tail-feathers, which are elongated, have their shaft twisted towards the tip, so that in flight the lower surfaces of their webs are pressed together vertically, giving the bird the appearance of having a disk attached to its tail. The second and third species so closely resemble each other, except in size, that their distinctness was for many years unperceived, and in consequence their nomenclature is an almost bewildering puzzle. H. Saunders (loc. cit.
) thinks that the larger of them, which is about the size of a black-headed gull, should stand as S. crepidatus
, and the smaller as S. parasiticus
, though the latter name has been generally used for the larger when that is not termed, as it often is, S. richardsoni
, a name that correctly applies only to whole-coloured examples, for this species too is dimorphic. Even its proper English name
is disputable, but it has been frequently called the Arctic gull or Arctic skua, and it is by far the commonest of the genus in Britain, and perhaps throughout the northern hemisphere. It breeds abundantly on many of the Scottish islands, and in most countries lying to the northward. The nest is generally in long heather, and contains two eggs of a dark olive-colour, suffused with still darker brown patches. Birds of either phase of plumage pair indiscriminately, and the young show by their earliest feathers whether they will prove whole or parti-coloured; but in their immature plumage the upper surface is barred with pale reddish brown. The smallest species, commonly known in English as the long-tailed or Button's
skua, is not known to exhibit the remarkable dimorphism to which the two preceding are subject. It breeds abundantly in some seasons on the fells of Lapland, its appearance depending chiefly on the presence of lemmings (Lemmus norvegicus), on which it mainly preys. All these three species occasionally visit the southern coasts of Europe in large flocks, but their visitations are highly irregular.