NON-INDIGENOUS BRITISH BIRDS. 145 



Range of egg colouration and measurement: 

 The eggs of the Hooper Swan are from four to seven in 

 number. In Northern Russia two to four are described 

 as the usual clutch ; in Iceland five ; whilst the larger 

 clutches are probably laid by females in the prime of 

 life. They are creamy-white, rough in grain, and nearly 

 oval in shape. Average measurement, 4*5 inches in 

 length by 28 inches in breadth. Incubation, performed 

 largely if not entirely by the female, lasts from five to 

 six weeks. 



Diagnostic characters : The only eggs likely to 

 be confused with those of the present species are the 

 eggs of Bewick's Swan, but the latter are always smaller 

 in size (either in length or breadth or both), and the 

 empty shells much lighter in weight. 



Family ANATID.E. Genus Cygnus. 



Sub-family CYGNIN.^. 



BEWICK'S SWAN. 



Cygnus bewicki, Yarrell. 



(British : Fairly common autumn and winter migrant.) 



Single Brooded. Laying season, June. 



Breeding area : Northern Pala^arctic region. Be- 

 wick's Swan breeds on the tundras of Arctic Europe 

 and Asia, probably as far east as Bering Strait. It 

 appears to breed in the valleys of the Petchora (where 

 Messrs. Seebohm and Harvie-Brown obtained the first 

 authenticated eggs), the Obb, the Yencsay, and the 

 Lena, as well as on the islands of the Arctic Ocean 

 north of these areas. 



L 



