256 Zoologica : N. Y. Zoological Society. [I ; 14 



inactivity consequent upon an excess of adipose tissue. Early 

 in the experiment the songs of the birds became less frequent 

 and sustained, and finally died away altogether, and when a 

 good layer of fat had accumulated, seldom was even a chirp 

 uttered. 



From time to time a bird was brought gradually into a 

 brighter light and meal-worms added to its diet. This invaria- 

 bly resulted in a full resumption of song. Even in the middle 

 of winter a tanager or a bobolink, would, under these conditions 

 make a room ring with its spring notes, and with this was cor- 

 related a slight decrease in weight. This phase of the experi- 

 ment could not be prolonged indefinitely, however, for the song 

 period seemed limited, just as it would be under normal condi- 

 tions even in non-breeding birds, although the nuptial plumage 

 remained unchanged throughout the winter. As one of my 

 keepers pithily put it, "We have their calendar twisted back- 

 ward." 



A sudden alteration in temperature — either higher or lower 

 — wrought, I found, a radical change in the physical metabo- 

 lism of the birds. Under such conditions, they would cease feed- 

 ing almost altogether, and one tanager lost weight rapidly. A 

 few feathers on the neck fell out and in the course of about 

 two weeks this individual moulted every feather and came 

 strongly into his normal winter plumage of olive green. The 

 metaboli&m set up by the change in temperature, in its extent 

 and rapidity seemed comparable only to the growth of a deer's 

 antlers. 



Early in the following spring individual tanagers and bobo- 

 links were gradually brought under normal conditions and into 

 their seasonal activities, with quick result. Just as the wild birds 

 in their winter haunts in South America were at the same time 

 shedding their winter garb and assuming the more brilliant 

 hues of summer, so the birds under my observation also moulted 

 into the colors appropriate to the season. Herein lay the signifi- 

 cant fact of the whole experiment: The old scarlet and black 

 feathers fell from the tanagers and were replaced by others of 

 the same color; and from buff, cream and black, the bobolinks 

 moulted into buff, cream and black! There was no exception; 



