476 Dr. A. G. Butler on the assumption of 



wind is to visit an eyrie and hurl the eggs or young to the 

 west into the sea, and for an east wind to go to the other side 

 of the island ; and this is surer than hammering a line of 

 holes in a granite boulder in the direction from which you 

 want the wind to come — also, if an eyrie is close by, it is 

 quicker. 



April 10 to May 1 is the usual time for eggs ; after that 

 young are very likely to be found. No young had been 

 hatched when the island was left on May 1, 1915. 



XXII. — The assumption of Summer Plumage in Pyroraelana 

 oryx. By A. G. Butler, Ph.D., F.L.S., F.Z.S., M.B.O.U. 



It has been definitely asserted by Mr. Jonathan Dwight, 

 Junr., and others, that a feather when once perfected is in- 

 capable of colour-change and that the apparent change which 

 takes place at the assumption of the summer plumage is 

 due to the falling off or abrasion of the tips or fringes of the 

 feathers. That this is the case in some species is certain ; 

 but it is equally certain that in many species there is an 

 actual change of colour in the feathers themselves, as I 

 pointed out in a short article which I sent to ' The Ibis ' in 

 1897, where I described changes of plumage in Quelea guelea 

 and Pyromelana fraud scana and P. afra. 



In Stark and Sclater's ^ Birds of South Africa,' vol. i. 

 p. 131, the authors confirm my statement as to the gradual 

 change of colour in the feathers themselves at the assump- 

 tion of the summer plumage in the case of Pyromelana 

 capensis. They say : — " Only the feathers of the lower back, 

 rump and flanks are entirely changed by a moult, the re- 

 maining plumage and bill becoming darker, owing to a 

 gradual absorption of colouring matter, the change first 

 appearing at the point of the lower mandible.^^ 



As I have elsewhere pointed out, if the plumage of birds 

 were incapable of change by absorption of colouring after it 

 h;id attained its full growth, it would be impossible for the 



