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CYGNUS IMMUTABILIS. 



(POLISH SWAN.) 



I Anas clirccea, Hermann, Obs. Zool. p. 139 (1804). 

 Cygnus immutabilis, Yarrell, Proc. Zool. Soc. 1838, p. 19. 

 Cygnus olor immutabilis, Schlegel, Rev. Crit. p. 112 (1844). 



Figura unica. 

 Yarr. Brit. B. ed. 1, iii. p. 131. 



Ad. albus : rostro rubro-aurantiaco : pedibus griseo-plumbeis : gibbo rostri minore quam in Cygno olore. 



Juv. albus, dorso pallide ochraceo-isabellino lavatus : rostro pallide purpureo-incamato, pedibus pallide cinereo 

 plumbescentibus. 



Adult (Northrepps) . Plumage, as in Cygnus olor, pure white ; bill rather redder than in that species, and 

 the berry is smaller; legs rather more of a plumbeous grey tinge. Total length about 5 feet, bill 3 - 6 

 inches, wing 23*5, tail 6*8, tarsus 4*25. 



Young (Northrepps, 15th August). General colour white with a faint ochreous buff tinge on the back; bill 

 pale purplish pink, not plumbeous as in Cygnus olor ; legs greyish plumbeous. 



Young in down (Northrepps) . Covered with pure white silky down, without any trace of brownish grey. 



The article on the present species of Swan has been deferred as late as possible in the hope that 

 I might succeed in ascertaining something further respecting its true habitat ; but I have not 

 been able to do so, and it remains, as it hitherto has been, a mystery. Most of the continental 

 authors have not separated the Polish or Changeless Swan from the Mute Swan ; and it is 

 therefore almost impossible to trace its presence on the Continent ; but, so far as I can ascertain, 

 it has only been recorded in a wild state from the shores of Great Britain. For a long time I 

 was inclined to indorse the view taken by Mr. J. H. Gurney many years ago, that the true wild 

 Mute Swan belongs to this species ; but from the descriptions I have had of the young of wild 

 Cygnus olor, this view does not appear to be a correct one. That the Polish Swan is specifically 

 distinct from the Mute Swan there is, so far as I can see, no doubt ; for in the young plumage, 

 as well as in down, it is white, or white tinged but very slightly with pale buff; and besides this 

 there are considerable differences in various parts of the head between the two birds, which 

 enables one clearly to distinguish them. Mr. Pelerin, who made careful observations on these 

 differences, writes (Mag. Nat. Hist. 1839, p. 178): — "The measurement of an adult cranium of 

 each is as follows : — Length from the tip of the bill to the base of the occipital bone in Cygnus 

 immutabilis six inches and three eighths ; Cygnus olor six inches and seven eighths. Height, from 

 the bottom of the lower mandible when closed, to the top of the protuberance at the base of the 

 bill, in C. immutabilis, one inch and five eighths ; C. olor, two inches. Height from the base of 



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