BRITISH BIRDS. 143 



211. Cygnus olor (Gmel.). MUTE SWAN. 



Hab. Palaearctic region. 



Common everywhere in a semi-domesticated state while 

 in many localities numbers of birds which have reverted 

 to a wild state are found. It is distinguished from other 

 species by the protuberance at base of upper mandible. 



211a. C. olor immutabilis (Yarrell). POLISH SWAN. 

 As this form holds specific rank in the B. O. U. list, I 

 have allowed it to stand here, tentatively, as a sub-species 

 of the last. Many authorities consider it to be merely an 

 abnormal variety of C. olor, in which the cygnets are 

 usually dark grey, while in the Polish Swan they are white. 

 Birds referred to this variety are occasionally shot on our 

 east coast in winter. 



212. Cygnus musieus. Been. WHOOPER SWAN. 

 Hab. Northern Palasarctic region. 



Male : white ; basal three-fifths of bill pale yellow, this 

 colour extending below and beyond the nostrils ; rest of 

 bill and the feet black. Length 58*00. Female : slightly 

 smaller. Cygnet : greyish-brown ; bill flesh-coloured with 

 the edges and tip black ; feet flesh-coloured. 



A fairly common visitor during severe weather. 



213. Cygnus bewieki, Yarrell. BEWICK'S SWAN. 

 Hab. Eastern Arctic Europe and Arctic Asia. 



Male : white ; bill black, excepting an oval patch of 

 orange-yellow covering one-third of basal part of upper 

 mandible each side, but falling much short of the nostrils ; 

 feet black. Length 48*00. Female : slightly smaller. 



A common visitor to our coasts during severe winters. 



