NON-INDIGENOUS BRITISH BIRDS. 283 



Range of egg colouration and measurement : 

 The egg-s of Buffon's Skua are usually two in number, 

 very rarely one or three. They are sometimes pyriform, 

 sometimes rotund in shape, and vary in ground colour 

 from olive to brown of various shades, spotted, speckled, 

 and streaked with dark brown, and with a few faint 

 underlying markings of grayish-brown. They cover the 

 same range of colour variation as those of Richardson's 

 Skua. Average measurement, 2'0 inches in length, by 

 1*4 inch in breadth, Incubation is performed by the 

 female, and is said to last about a month. 



Diagnostic characters : The eggs of Buffon's 

 Skua resemble those of Richardson's Skua, but are 

 much smaller, more constantly green in ground colour, 

 and the markings are, as a rule, a trifle more streaky. 

 The breeding area of Buffon's Skua is also much more 

 northerly. 



Family STERCORARIID^. Genus Stercorarius. 



P O M ATORHINE SKUA. 



Stercorarius pomatorhinus {Temminck). 



(British : Fairly common autumn and spring coasting migrant ; 

 few, winter.) 



Single Brooded. Laying season, July. 



Breeding area : Northern Nearctic and PaLnearctic 

 regions. The Pomatorhine Skua is not known to breed 

 anywhere on continental Europe, but may probably do 

 so on Franz-Josef Land, Spitzbergen, and Nova Zembla. 

 Eastwards it has been met with nesting on the Yalmal 

 and Taimyr peninsulas, and in the north-east of Siberia, 



