﻿32 ON THE CLASSIFICATION OF BIRDS. 



dication of this ornament is seen in those birds where 

 the head is very full of feather s, which are somewhat 

 longer than those of the nape and surrounding parts, 

 without assuming any particular shape : the appa- 

 rently large head of very many birds is caused by this 

 superabundance of feathers, rather than from the size 

 of the skull. The head of the Tamatias, or puff- 

 birds of Brazil, when they are quietly seated upon a 

 branch, appears to be nearly double the natural size, 

 from its thick clothing of feathers, which are then 

 somewhat raised*; but if the bird is suddenly disturbed, 

 instead of erecting these feathers still more, as the 

 woodpeckers do, the puff-bird immediately brings them 

 flat upon the skull ; and its head, although at all times 

 large, seems suddenly reduced to half its size.f The 

 thick-heads of New Holland (PachycephaZa Sw.), 

 which represent the last mentioned group in their own 

 circle, have the feathers equally thick, but we know 

 nothing of their manners. We can hardly call this 

 formation a crest, seeing that it assumes no form inde- 

 pendent of that common to the head, and it is certainly 

 no ornament. There can be no doubt, however, that 

 it is connected, in some way, with the economy of the 

 birds possessing it, otherwise we may feel assured it 

 would not be possessed only by certain races. Incipient 

 crests, in the same manner, are possessed by many birds, 

 which are generally de- 

 scribed, even by system- 

 atic writers, as having none. 

 We are not aware that any 

 of the describers of Bri- 

 tish birds have mentioned 

 the crest of the male chaf- 

 finch J (fig. 12.), which 

 is always erected when the 

 bird is disturbed, and retained in that position even after 



* As in Tamat'ut melanotis, Sw. Birds of Brazil, pi. 10. 

 + As in Tamatia maculata, ibid. pi. 11. 



} The head of the male yellow hammer is also decidedly crested. 



