(2058) Stercorarius parasiticus,
Larus parasiticus Linn., Syst. Nat., 10th ed., p. 136 (1758) (coast of Sweden). Stercorarius crepidatus. Blanf & Oates, iv, p. 329.
Vernacular names. None recorded.
Description. Dark ashy-brown, the crown still darker and generally showing indications of a paler collar on the hind-neck below rather paler ashy-brown; shafts of primaries white; tail darker brown, almost black on the ends of the central tail-feathers.
Another variety has the underparts from chin to posterior abdomen pure white, this white running up and round the hind-neck as a broad collar; there is generally also a narrow white forehead ; the white of the neck and sides of the head is glossed with golden-straw colour.
Most birds are definitely coloured according to one or the other of the two above descriptions but many are intermediate and I have seen one specimen in Foula with the whole head pure white just glossed with the golden-yellow. Some specimens agree with the second description but have the breast or some portion of it ashy-brown.
The variations are purely individual and the dimorphic coloration has nothing to do with age or sex.
Colours of soft parts. Iris hazel-brown; bill blackish- or horny-brown ; cere pale greenish-brown; legs and feet brownish-black to black.
Measurements. Wing, 304 to 326 mm., 300 to 321 mm; tail 170 to 212 mm ; tarsus 40 to 46 mm.; culmen 26 to 32 mm.
Young birds of the all-brown phase are a darker, almost blackish-brown all over, the feathers of the upper parts broadly edged with rufous, this colour occupying the whole of the feathers on the neck and head except on the bases and on a narrow central streak; below, the feathers are both tipped and barred with rufous. Young birds of the brown and white type have the edges to the feathers paler rufescent-white and the underparts barred throughout with white and brown, the breast darker and the chin, throat and fore-neck streaked rather than barred. The iris is grey-blue; the bill light horny; legs and toes pale grey-green or livid, the toes and terminal half of the webs black.
Nestling in down pale sooty-brown above, paler still below.
Distribution. Breeding in the circumpolar sub-arctic regions and in .winter wandering South as far as the Cape of Good Hope in Africa, the coast of Sind in India and to Australia, New Zealand and, in America, to Rio de Janeiro.
Nidification. Richard son's Skua breeds from the last week in May to the middle of June, a few birds earlier and still fewer after the' 15th of June, except iu the extreme North, where eggs may be laid up to the end of the month. It breeds in colonies, often of great size, that of Foula numbers nearly two hundred pairs, occasionally two or three pairs only, No nest is made, the two eggs being deposited in a depression in the moss in swampy land on hillsides. They are typical Gulls' eggs ; the ground-colour varies from pale olive, pale stone-yellow or buff to deep olive-green or dark brown, whilst they are spotted and blotched with dark brown. Two hundred eggs average 56.7 x 40.5 mm.: maxima 64.0 X 42.0 and 59.0 x 44.3 mm.; minima 48.7 x 39.0 and 59.6 x 37.2 mm.
Habits. The Skuas live almost entirely on fish etc. which they xob from Gulls and Terns, pursuing them in the air until they drop the desired morsel, which they then seize. They also feed on other birds' eggs and young and often take fish from the fishermen's nets, sometimes being caught in these. They are magnificent fliers, turning and twisting with the greatest elegance and speed, whilst their carriage on land is very haughty and Falcon-like. In defence of their young they are very bold and fierce, attacking intruders before they reach the spot where they are breeding and continuing their assaults until their foes are safely off the premises. Their call is a rather piercing scream but they have many hoarse and guttural notes also and their harsh " ga k, gack" is constantly uttered as they sail round in the air.
* Mathews, * Birds of Australia,' ii, p. 482 et seq. (Jan, 31st, 1913).