462 STEBCOBABIID^E 



gains the ascendancy (Saunders). In winter the Arctic 

 Skua wanders southward along the European coasts ; some 

 birds sojourn at the Mediterranean basin, others proceed 

 along the west coast of Africa, down to the Cape of Good 

 Hope, and beyond to Tasmania and New Zealand. West- 

 ward the migration-route extends to California on the 

 Pacific side, and the Barbadoes on the Atlantic side of 

 the American Continent. Eastward this bird reaches the 

 Persian Gulf. It is at once manifest that the geographical 

 distribution is very extensive. 



DESCRIPTIVE CHARACTERS 



PLUMAGE. It is generally admitted that this Skua shows 

 distinct dimorphism of plumage ; in other words, perfectly 

 mature individuals are not all alike. Two varieties are recog- 

 nised, the uniformly dark brown bird, which, strictly speak- 

 ing, is Richardson's Skua, and the white-breasted form, more 

 truly polar in its breeding-range, and hence called the Arctic 

 Skua (Plate XLIX., figs. 1 and 2). Between these, every 

 gradation of intermediate form exists, and is found breeding 

 in many of the Northern Islands of Europe. That there is 

 but one species is clearly borne out by the fact that, on 

 meeting, the birds pair readily, and without distinction of 

 choice of colour-markings ; indeed, with regard to the Ice- 

 landic birds, Mr. Coburn, who recently obtained an abundant 

 series of dark, light, and intermediate forms, from North 

 Iceland, is of the opinion that two types do not exist, but 

 that the white-breasted birds are simply adults, and take 

 several years to reach that stage (' Zoologist/ 1901, p. 416). 



Dark race. Adult male nuptial. Back, wings, tail, and 

 its coverts, umber-brown ; head, neck, breast, and abdomen, 

 sooty-brown. 



Light race. Adult male nuptial. Head, back, wings, 

 and tail, same as in the dark race ; hind-neck, dull white, 

 streaked with dark straw-colour ; abdomen, ash-brown ; 

 throat and breast, white. The lanceolate cheek-feathers 

 in both races are of a yellowish tinge. 



Adult female nuptial. Similar in the respective race to 

 the male nuptial plumage. 



Adult winter, male and female. Similar in the respec- 

 tive race to the nuptial plumages, but with a tendency to 

 striation on the flanks, and on the upper and under tail- 

 coverts, in birds not quite matured. 



