AUKS, MURRES, PUFFINS, ETC. 25 



swaying motion when flying thus differing 

 from other water birds and can wheel read- 

 ily in air. The horny outer covering of the 

 bill is moulted in some of the species, hence 

 the bill is of a different form in winter than 

 in summer. All assume a special winter plu- 

 mage. They nest in cavities on cliffs or 

 rocky islands, but some species often excavate 

 holes for themselves. The young are hatched 

 covered with down, but are comparatively 

 helpless and are fed by regurgitation. 



7. RAZOR-BILLED AUK. 



Size about that of the Ruddy Duck, 16 ; 

 like that species it often holds its tail up when 

 swimming. The Razor-bill ? however, has a 

 much shorter neck than that of any duck, 

 while its singular bill will always serve to 

 distinguish it when adult, fig. 16. This, and 

 its manner of carrying its tail, are the only 

 characters by which it may be known from 

 the Murres when at any distance, for like it 

 they also are black above and white beneath, 



