292 The Bird 
New York Zoological Park, I have had opportunity to 
record many cases of the effect of food upon colour. An 
experiment very commonly known is that of feeding 
canaries on red pepper, thus causing their plumage, after 
Fig. 232.—Variation due to climate, ete., in races of North American Song Sparrows 
(From a photograph provided by the American Museum of Natural History.) 
successive moults, to become of an intense orange colour. 
This is the more remarkable since the actual red pigment, 
or capsicin, of red pepper is not the direct cause of the 
canaries’ changed hue, but a fatty substance known as 
triolein, which is a constituent of the pepper. 
