202 
FRANCIS H. HERRICK 
the second to the fifth day the response becomes more and more 
uncertain, when the bird is removed from its nest. Then at the 
sixth or seventh day, association has become so perfect that this 
bird will starve w^hile away from the nest, rather than open its 
mouth. 
I have taken a 7-day-old cuckoo from its nest, and kept it 25 
hours without being able to get a single food-reaction, w^hatever the 
nature of its treatment. In order to feed it at all it was necessary 
to pry open its mandibles, and force the food into the gullet, and 
then most of it would be regurgitated. But the very moment 
this same bird w^as returned to the nest, and its feet touched the 
familiar twigs, it expanded as if by magic into a new creature. 
Immediately erecting its feathers, sw^elling to almost double its 
former size, standing erect, with head and neck up-stretched, 
mouth open wide, wings spread and vibrating, the w^hole body 
trembling as with deep emotion, and giving its loudest guttural 
call, this bird not only presented a picture in striking contrast 
to what had gone before, but offered a unique example of the force 
of habit and the powder of association. In this respect, however, 
the cuckoo is by no means peculiar. 
The initial call note (3) is given practically as soon as the bird 
is hatched, and in precocious species like the gull and domestic 
fowl w^hile still in the shell, and either before or after this is pipped. 
In the cuckoo it is at first a feeble grating note or grunt, like kek, 
w^hich gradually increases in vigor until it develops into or is 
replaced by that peculiar w^heezing note, characteristic of the lat- 
ter part of nest-life, a sort of nasal w^hine, apparently made by ex- 
pelling the air through the nose, and often wdth the bill closed. 
This note is given repeatedly and in chorus, at every visit of the 
old birds, or in response to any stimulus w^hich arouses first one 
and then another nestling in quick succession, w^hen the whole 
performance suggests the seething of a boiling pot or the hiss of 
escaping steam. 
The powder of orientation (4) is quickly estabhshed the moment 
the bird entirely quits the shell and becomes exposed to the full 
influence of the air. If the cuckoo is turned on its back, it will 
