1914] Beebe: Postponed Moult in Passerine Birds. 255 



In mid-summer I placed several Scarlet Tanagers and Bobo- 

 links under careful observation. None of these birds had been 

 allowed to breed, and so, although it was rather late in the sea- 

 son, they were still in the height of vocal and physical condition. 

 They were all tame, so that, although during the period of ex- 

 perimentation they were confined in rather small cages, each 

 bird in a space of about 12 x 12 x 24 inches, yet their plumage 

 Vv-as not damaged by violent struggles caused by fear or a desire 

 to escape, and remained throughout in almost perfect condition. 



Little by little I began to cut off the supply of light and 

 slightly to increase the amount of food. This caused a corre- 

 sponding decrease in activity on the part of the birds, and an 

 almost immediate increase of weight. The great danger from 

 obesity in caged birds is that fright or sudden excitement of 

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

 way bring about death from apoplexy. Consequently I kept the 

 birds in a room where they were never disturbed, and where 

 the absence of noise and other distractions reduced the possibil- 

 ity of an untimely end. 



In about a month, when the time for the normal autumn 

 moult arrived, the tanagers and bobolinks were living the "sim- 

 ple life" in a dim illumination, and although consuming a fair 

 amount of food, were exercising but little. The time for the 

 autumn moult came and passed and not a single feather was 

 shed. The cages were made intentionally of wire mosquito net- 

 ting, the fine mesh of which would have caught and revealed 

 any feathers had any been moulted. In addition to this, the 

 birds were examined twice a week, and nowhere on body or head 

 was there any evidence of ^oulted, or of new, incoming feathers. 

 On blowing away the breast feathers the yellow sub-cutaneous 

 layer of fat could be seen, which in a bird caged under normal 

 conditions, would have been a danger symptom not to be disre- 

 garded. 



As the winter gradually passed, it was evident that the 

 birds had skipped the autumn moult entirely, and appeared to 

 suffer no inconvenience as a result. As far as appearance went 

 they were in perfect health, showing only the symptoms of 



