LIFE AND BEHAVIOR OF THE CUCKOO 
201 
mal environment. Indeed it becomes so completely linked to 
parent and nest, that after the seventh day, it can seldom be 
artificially evoked, in spite of hunger by any of the usual me- 
chanical stimuli whatsoever. So marked is this character that in 
early life at the nest when the variable a is known, the age of the 
young bird can be approximately gauged by the nature of the 
food-response alone. 
We should add here that shortly after birth muting begins to 
follow the taking of food quite regularly, and becomes as stereo- 
typed as any other phase of behavior. The nestling strives to 
Fig. a , 
Fig. a "Target'' of cuckoo at birth, showing symmetrical pattern of white 
spots or pads on palate and tongue, when mandibles are opened wide in food 
reaction. See fig. 5. 
raise the hinder end of its body, which is turned outward, so that 
the sac, when not taken direct by the parent the moment it 
leaves the cloaca, wall fall outside of the nest or upon its margin. 
During the first 24 hours the variable to be mainly considered 
in relation to the food-response is hunger, and when this element 
is known, the former can be predicted with precision, whatever 
the environment, within the limitations of bodily fatigue. From 
