THE AMERICAN NATURALIST 



[Vol. XLII 



None of these birds had been allowed to breed, and so, 

 although it was rather late in the year, they were still 

 in the height of vocal and physical condition. They were 

 all tame, and although during the period of experimenta- 

 tion they were confined in rather small cages, each bird 

 in a space 12 x 12 x 24 inches, yet their plumage remained 

 in almost perfect condition. 



I began gradually to cut off the supply of light and 

 slightly to increase the amount of food. This caused a 

 corresponding decrease in activity of the birds, and an 

 almost immediate increase of weight. The danger of 

 obesity in caged birds is that any excitement or sudden 

 fright may cause a blood vessel to break, or in some other 

 way bring about death from apoplexy. Consequently I 

 kept the tanagers in a room where they were never dis- 

 turbed and where no noise ever made possible the chance 

 of an untimely end. 



A month later when the time for the fall moult arrived, 

 the birds were living 4 4 the simple life" in a dim illumina- 

 tion and, although consuming a normal amount of food, 

 were exercising but little. The time for the fall moult 

 came and passed and not a single feather was shed. The 

 cages were made of mosquito-netting wire and wouldhave 

 confined any moulted feathers. In addition to this, the 

 birds were examined every third day, and nowhere on the 

 body was there any sign of moulted or of new, incoming 

 feathers. On blowing away the plumage from the breast, 

 the yellow sub-cutaneous layer of fat could be distinctly 

 seen. 



In brief, the birds skipped the fall moult entirely and 

 appeared to suffer no inconvenience whatever as a result. 

 As far as appearance went they were in perfect health, 

 showing only the symptoms of inactivity produced by an 

 excess of adipose tissue. Early in the experiment the 

 songs of the birds diminished and finally died away al- 

 together, and when a good layer of fat had been acquired 

 the birds seldom uttered even a chirp. 



From time to time a bird was gradually brought into 



