CHANGING TINTS OF BILL 327 



tion of the bill, while in the Red-crested Pochard 

 and Mandarin this change is variable, occurring in 

 some individuals and not in others. 



The colour of beak and feet, etc., also changes 

 according to age ; this is very noticeable in the 

 bill of the cygnet of the common Swan, which 

 changes from black, through grey and lilac, to pink, 

 and finally to orange-red ; but the change from black 

 to red can also occur by the gradual invasion of the 

 black by the red, as in the beak of the young Zebra- 

 Finch (T&niopygia castanotis). In the young Gan- 

 net the beak changes from black to white, and the 

 green lines down the black shank and toes only 

 appear as maturity approaches. The legs and bill 

 both change from black to white with age in 

 the Indian Pied Mynah (Sturnopastor contra). 

 Changes in the iris are quite numerous in birds. 

 Usually a dark eye changes into a light one ; thus 

 the grey Parrot, when young, has a dark grey iris, 

 and the Ring-necked Parrakeet (Pal&ornis tor- 

 quatus) a dark brown one, both having the iris 

 white ultimately. But the reverse change may 

 occur, for in the Pheasant-tailed Ja$an (Hydro- 

 phasianus sinensis), the young birds generally have 

 yellow eyes, and the old ones dark brown ones. In 

 the Gold Pheasant the young cocks can be known 

 by their yellow instead of brown eyes long before 

 coming into colour. Indeed, generally speaking, 

 the change, due to age, in the beak, feet, and iris, 

 tends to antedate the change in plumage ; but 

 there are exceptions, as in the case of the male 



