52 SEA-BIRDS 



of it W. Templeman (1945) collected twelve common guillemots 

 (? at random) of which six (50 per cent.) were bridled. When Horring 

 and Salomonsen (1941) compiled a list of all the common guillemots 

 that had been then collected on the west coast of Greenland they 

 recorded six out of thirty-two (18.7 per cent.) as bridled, but knew of 

 no breeding-colony. Soon afterwards Salomonsen (1944) became aware 

 of the colony in the Sukkertoppen district; but no count has apparently 

 yet been made there. 



All the four skuas appear to vary in plumage; the bonxie (great 

 skua) particularly in the amount of rufous colour, especially among 

 some of its southern forms; the three smaller skuas have a 'normal' 

 pale phase of plumage with light breast and underparts, and yellowish 

 or buff on the sides of their necks ; and a 'dark' phase which is almost 

 uniformly, or uniformly, dusky; and intermediates. The dark phase 

 of the long-tailed skua is so rare that it has hardly ever been seen. 

 Among the population of pomarine skuas, wherever they may breed, 

 from five to twenty per cent, are dark; the distribution of dark birds 

 is even, in the sense that there is no detectable gradient. Southern's 

 detailed analysis (1944) shows that no geographical area contains 

 significantly more dark pomarine skuas than any other. Among the 

 arctic skuas (Southern, 1943), however, the situation is quite different. 

 In the southern parts of this bird's breeding-range about three- 

 quarters of the birds are dark; in the middle parts about half, in 

 the Low Arctic less than half, and in the High Arctic a quarter or less. 

 In north-east Greenland, indeed, the dark form is unknown. There are 

 a few, rare, birds intermediate in colour between the pale and dark 

 forms. This looks like a quivering balance between two 'stable' types. 

 The proportion of the colour-forms in the British colonies is (Southern 

 points out) subject to rather special considerations, since the colonies 

 are generally small and scattered, and thus liable to random fluctu- 

 ations — in fact between the limits of 50 and 86 per cent. dark. The 

 mean probably lies at about 75 per cent. 



Southern has attempted to correlate the distribution of the dark 

 arctic skuas (Fig. 10) with temperature, relative humidity and various 

 ecological factors. His material carries darkness with humidity over 

 a considerable part of the bird's total range; but the correlation breaks 

 down in Norwegian Lapland — also, good meteorological figures are 

 not available for all the arctic regions. 



We found the same difficulty in correlating the distribution of the 

 colour phases of the fulmar, Fulmarus glacialis, with climate and other 



