124 THE BIRDS OF BRITISH GUIANA. 
coloring. Cases of such birds, shown inthe British Guiana 
exhibit in the Columbian Exposition, have been a revelation 
and a marvel to visitors who, at the same time that they 
can hardly believe such brilliant tints to be natural, yet 
realize that they could not be produced by artificial means. 
In many cases this brilliance is only characteristic of the 
adult males, the young males and the females being both 
alike, and of quite sober plumage. Cases such as the Bell- 
birds (Chasmorhynchus), the Cotingas (Cotinga, Xipholena, 
etc.), the Firebirds (Phenicocercus), the Cock-of-the-rock 
(Rupicola), the Humming-birds (Zrochilide), etc., will at once 
occur to you. In other cases, the males and females are 
colored equally, or almost equally, brilliantly, such as the 
Scarlet Ibis (Zudocimus ruber) the Macaws (Ara), the 
Jacamars (Galbuiidaz), the Bill-birds (hamphastos), and 
others, though in many of these cases the young birds of 
both sexes are quite different in color from the adults. 
The peculiarity of tint in many of our species is well 
worthy of notice—the pure white of the males of the Bell- 
bird (Chasmorhynchus albus) ; the variegated grays of the 
Giant Goatsucker (/Vyctibius grandis) ; the intense green tints 
of the Parrots (Chrysotis) ; and the rainbow-colored Tanager 
(Calliste tatao). Sexual relations (as in the first case), and 
protective (as in the second and third), evidently serve to 
explain the advantages of such coloring. 
While on the subject of coloring, it is interesting to note 
that certain tints, in certain of our birds, can be entirely and 
permanently changed by the application of heat. Thus the 
purple tints on the throat, breast and body of Cotinga cayana, 
C. cerulea, and Xipholena pompadora, can be changed to a 
brilliant red by exposing them to heat in such a way as to 
affect those feathers without singeing—an indication of the 
possibilities in nature under changing thermal conditions! 
Here, too, must be recalled the change produced in so many 
of the Green Parrots by the native peoples of Guiana, who, 
by feeding these birds on a special diet, consisting largely 
