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, giving 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
Fig. 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 bird, 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,
