668 Mr. C, B. Ticelmrst on the 



moult was shown in one on Sept. 23; the latest date by 

 which no monlt had begun was Aug. 20, though one on 

 Sept. 19 had only jusc started, and the latest in uncom- 

 pleted moult was on Oct. 26; so that one may say that 

 September and a week or two on each side of it covers 

 most of the adult moulting. October birds, whether young 

 or old, are usually through the moult, 



Tiie meaning of this yellow plumage occurring in Crossbills 

 has long been the subject of speculation; it was formerly put 

 down to old age, but this theory has long been discarded. It 

 is, however, a well known fact that red Crossbills as well as 

 red males of Carpodacus^ Haniatosjnza, and Linota invariably 

 lose their red plumage after moulting in captivity, yellow 

 replacing the red. This has been attributed to lack of proper 

 food, air and exercise, or a combination of all three. Curious 

 and interesting as this coincidence is, it is very difficult to 

 see where it helps us in elucidation of this problem of 

 dichromatism in wild birds. Another theory put forward 

 to explain these yellow birds was that they were diseased 

 or weakly individuals. This theory has been rather widely 

 accepted, but will not, I think, bear investigation for a moment. 

 To begin with, these yellow birds are far too numerous for 

 them all to be diseased, weakly, or lacking in vigour; more- 

 over, many of them are in very good condition. Jf, too, this 

 change in colour is brought about by such conditions, why 

 is it to be seen often in Crossbills and very rarely in other 

 species ? Then, again, we have Newton's and Wheelwright's 

 assurance that these yellow birds breed in that dress, which 

 does not look as if they were less vigorous than the red birds. 



That the yellow i'eathers are not due to lack of pigment 

 I have satisfied myself ; microscopically, the red and the 

 yellow pigments are confined to and evenly distributed 

 throughout the rami except at the extreme tips, and it seems 

 to me that there is in each an equal amount of a different 

 pigment. There undoubtedly is, however, an interesting 

 relationship between red and yellow occurring in birds. 

 In the case of Loxia, Curpodaciis, and Piuicula, generally 



