MUTE SWAN. 77 



ferruginous matter would account for the vivid colouring 

 on the heads of some old swans, and the large size of 

 the head in an old cock swan, and the breadth of surface 

 coloured, would convey the impression, no doubt, that 

 the hen bird was always higher coloured in this respect 

 than the male. The feathers thus tinged, as before 

 remarked, are only tipped with red, the posterior por- 

 tions and the down remaining pure white, and only 

 those parts of the plumage which in feeding would come 

 in contact with the bed of the stream are thus affected. 

 The extent of this, both on the head and neck, varies 

 considerably. In Mr. Frere's whooper (ante, p. 53) 

 it extends far down the neck, and though deepest, 

 as usual, on the crown of the head, is generally dis- 

 tributed over the sides as well. Mr. Cremer's whooper, 

 killed at Blakeney, in November, 1871, which had the 

 head and neck strongly tinged with red (ante, p. 61), 

 was said to have been similarly stained on the under 

 parts of the plumage; but this I have never observed 

 myself in any swan, wild or otherwise. From such facts, 

 then, as I have here given, I had arrived at the conclu- 

 sion that the colouring in question is acquired and not 

 natural, due, in fact, merely to external causes; but it 

 remained to prove by some chemical test the actual 

 presence of iron in the red feathers themselves. The 

 idea of instituting some such experiment occurred to 

 me through reading a review, in the "Ibis'* for 1862 

 (1st series, vol. iv., p. 182), of a paper by Herr Conser- 

 vator F. W. Meves,* "On the red colouring in Gypaetus," 

 a raptorial genus between the vultures and eagles. By 



* This paper was communicated to the " Summary of the Trans- 

 actions of the Eoyal Academy of Sciences, at Stockholm, for 1860." 

 Herr Meves is the same naturalist whose ingenious theory as to 

 the drumming noise of the snipo is described in vol. ii. of this 

 work, p. 316. 



