LIFE AND BEHAVIOR OF THE CUCKOO 
207 
objects, with but the first beginnings of the pin-feathers showing, 
and that the feathers remained sheathed until the day before the 
birds left the nest." '^Then in twenty-four hours every envelope 
burst, and the bird was completely feathered, with no trace of the 
sheathing except at the base of the tail." The blue pin-feathers" 
of the down have evidently been confused with the feather-tubes 
of the 'Quill stage, ^ which in the yellow-bill is preceded by a 
dusky gray instead of a white rudimentary down, as I am in- 
formed by Dr. Ned Dearborn, who has studied this species. 
The process of unsheathing is probably a mixed, and for most 
of the feathers a gradual one, as we have shown to be the case 
with its close relative, Coccygus erythrophthalmus. 
The power of association is far stronger in checking the feeding 
reaction than the influence of hunger in producing it. The effect 
of satiety, however, is seen when the stomach or gullet is full. 
Thus the last bird to be fed is frequently the only one not to re- 
spond upon the prompt return of a parent bearing food. Such 
a bird may be occupied in preening its feathers^ while the excite- 
ment of its fellows has reached to the highest pitch. Again, either 
when satisfied with food, or when the stimulus is not of the right 
sort or intensity, the nestling will not give the food-reaction, but 
responds with a simple monosyllabic cuck. 
During the last two days in nest, the young when undisturbed, 
give the food-response but seldom in the absence of the parents, 
when fed with the usual frequency. Thus on the fourth day of 
observation at nest No. 3, July 25, when all were in the quill 
stage, the feeding reaction was given spontaneously but once 
during a space of one and one-half hours, without the presence 
of the old birds. Meantime they would frequently respond to the 
call koor-uck-uck-uk of the distant parent in a note of similar 
quality. Ab out the fifth day the young have developed a rolling 
guttural call, like ker-r-r r-ek, and this a day or two later, at the 
close of the quill stage seems to pass into the responsive ker-ut-ut- 
ut, or koor-uck-uck-uk. Accordingly this note which originates 
as a responsive call is apparently modified later to serve as an 
alarm. Towards the close of nest-life the peculiar seething, pot- 
boiling sounds which these young utter when calling for food, or 
