298 A HISTORY OF BIRDS 



by its absence, and this seems to be true also of birds from 

 the far north of Arctic America. In America below the 

 Arctic Circle both forms are met with as in Great Britain. The 

 Giant Petrel {Ossifraga gigantea) of the southern seas shows 

 a similar variation, inasmuch as normally dark brown in colour, 

 pure white birds are also met with, as well as every gradation 

 of coloration between these two extremes. So far it appears, 

 however, that the wholly white examples are only met with 

 just north of, and within, the Antarctic Circle. 



Another variable species is the little " Creeping Warbler " 

 {Parula americand) which shows a wonderful range of variation, 

 and one, moreover, which seems to present phases approaching 

 each of some five other allied species — P. superciliosa, P. pitia- 

 yumi, P. inornata, P. nigrilosa and P. insularis, as though these 

 were severally derived from P. ainericana. 



Less is known concerning the phenomena of discontinuous 

 variation than one would expect having regard to the number 

 of those who devote themselves to the study of Ornithology. 

 Nevertheless, some extremely interesting facts on this head 

 have been placed on record. 



Among British birds some good examples of this form of 

 variation are to be met with. And perhaps the best-known in- 

 stance is that furnished by the Guillemot {Lomvia troile) which 

 sporadically appears with a ring of white around the eye, and 

 a white streak extending from this ring backwards along the 

 side of the head. For a .long time birds so marked were 

 regarded as representing a distinct species — the Ringed or 

 Bridled Guillemot — but it is now generally admitted to be but 

 a variety of the typical species. " It inhabits," says Mr. Howard 

 Saunders, the same localities, and is always found in " company 

 with the common species, but in far inferior numbers." On 

 the Faroe Islands it appears not infrequently. On Handa, off 

 the coast of Sutherland, Mr. Harvie-Brown found this variety 

 to be abundant, as compared with other stations in Scotland, 

 being in the proportion of one in ten or twelve ; and he has 

 many times seen the common and ringed varieties paired. 

 And Colonel Fielden has noted the same in the Faroes and 

 Hebrides. In the north of Iceland it is commonly met with, 

 and there would appear to be some grounds for believing that 

 it occurs with greater frequency in more northern latitudes. 



