208 
FRANCIS H. HEERICK 
when stirring about under the brooding parent as described above, 
are often interspersed with the responsive ker-ut-ut- ut, which then 
often sounds like kar-ach-dch, or when very hungry and excited 
they break into ar explosive squeal like kar-achit. 
When regularly fed, and otherwise undisturbed by the heat, 
their nest mates, or by loud sounds, the young lying flat, doze 
and sleep a good share of the time. The instinct to turn the head 
to one side and sleep with bill buried in the feathers of the 
back does not come until later, if at all. Up to the fifth or sixth 
day the chief exercise is derived from the grasping reflex, and the 
food response. Then with the preening or combing instinct, early 
in the seventh day, comes a new kind of exercise, associated with 
some pecking especially at crawling insects, the nest material, 
and occasionally at one another. The pecking is very indefinite 
at first, and I have never seen a case where a single insect was 
secured in this way either in these or other nestlings. Char- 
acteristic stretching of the wing and leg of one side is not seen in 
the nest-life of the cuckoo, because they leave the nest before 
prepared for flight, but they sometimes partly stretch one or both 
wings and duck the head before picking at the feather-tubes. 
Yawning has been noticed but very seldom, but the gaping and 
^'panting" reflex, due to excessive heat, are as characteristic of the 
young at an early age as of the adult. The vibratory throat- 
movements of rapid respiration have not been seen, however, until 
the sixth or seventh day. When taken in the hand on the sixth 
day, while the instinct of fear is beginning to rise, the young will 
sometimes peck rather feebly as if in defense. Association with 
the nest was shown by a bird which on the seventh day climbed 
to a point a foot or more away and returned again, but this was 
observed but once. 
The instinct of fear commonly matures at the beginning or close 
of the sixth day. When they are now closely or suddenly ap- 
proached, a frightened nestling will sometimes clear the nest with 
one bound, seize hold of a branch and cling to it, and if it drops to 
the ground, it will make off with surprising speed, (fig. 10) . When 
handled this young one utters a loud explosive squeal or danger- 
eall, like kar-r-r-r-r-eh, or more like the adult koor-uck-uck-uk, 
