352 



BRITISH BIRDS. 



rine Skua. The adult has the general colour of the upper parts dark brown. 

 The colour of the underparts varies in a somewhat exceptional manner. 

 There are two forms of this species : in one the entire underparts are 

 as dark a brown as the upper parts ; in the other the underparts are 

 white barred on the sides of the breast, the flanks^ and the under tail- 

 coverts with dark brown ; the white on the throat extends to the sides of 

 the neck, meeting below the nape, and is more or less suflFused with yel- 

 low. Bill slate-grey, black at the tip ; legs and feet black ; irides hazel. 

 Young in first plumage of the light form have the upper parts dark brown, 

 each feather with a narrow pale buffish-brown margin, and the underparts 

 a paler brown, each feather with abroad pale buffish-brown margin. Young 

 in first plumage of the dark form have both the upper and under parts 

 dark brown, each feather with an obscure pale margin, most conspicuous 

 on the under tail-coverts. In both forms each successive autumn moult 

 advances the colours of the plumage to that of the adult, which, in Booth's 

 opinion, is not assumed until the fifth moult. Young in down are uniform 

 sooty brown, slightly paler on the underparts. 



