INSTINCT AND INTELLIGENCE IN BIRDS 129 
Thus the initial attempt to preen, which involves the complicated act 
of drawing the mandibles over the feather-tubes, may be witnessed on 
the fifth day; thereafter it is repeated more and more frequently, until 
on the sixth day it is an established practise, and the movements have 
become very precise. Gradual also is the development of fear, an early 
premonition of which is crouching and hugging the floor of the nest, 
although its final manifestations, such as bristling and spreading, giv- 
ing a high-pitched alarm, or jumping out of the nest, may seem to 
mature suddenly, partly no doubt because the stimulus which provokes 
them is suddenly received. 
In the altricious cedarbirds, a single family of which was weighed 
and measured in 1901, there was (1) an initial period of relatively 
slow growth, lasting three days, followed by a second period (2) of 
L.wing inmm. 


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Day 
Fic. 28. GROWTH-CURVES OF THE BLACK-BILLED CUCKOO AND CEDARBIRD, based on 
daily increase in length of wing from hatching to climbing stage or flight. See table. 
maximum increase, of six days, and a final interval (3) of fluctuating 
or retarded growth, extending from three to six days before flight, the 
birds even losing weight either before or after this event. 
The growth-curve of the most vigorous member of this cedarbird 
family (Fig. 27), the first to hatch and to fly, is seen to start with a 
higher initial rate, and to maintain it from the third to the ninth day, 
at the age of flight. Fortunately this bifd, which was then lost, was 
recaptured on the fifteenth day, when it is seen to have shrunk very 
perceptibly. It had, in fact, lost nearly three grams, or seven per cent., 
in body-weight. The curves showing the rate of wing-growth in both 
cuckoo and cedarbird (Fig. 28) follow those of body-weight very closely, 
