128 THE POPULAR SCIENCE MONTHLY 
that they would shortly succumb without that parental care and pro- 
tection which is so faithfully rendered. Growth and development are 
continued after hatching, but under new conditions, and at the age of 
two weeks, when the nest is commonly deserted, the young so far as 
instincts and intelligence are concerned are at about the same stage as 
many of the precoces at birth. 
Between these extreme types every intermediate stage is found. 
The American black and yellow-billed cuckoos have a place near the 
middle of the series, but as we have already seen, they are exceptional 
in many ways, not alone in the possession of great muscular strength, 
but in their equally remarkable muscular control, being able to grasp 
Nt in grams 

Fic. 27. GRowWTH-CURVES OF THH CEDARBIRD AND BLACK-BILLED CUCKOO, as repre- 
sented by the daily increase in body-weight from hatching to flight from nest, illus- 
trating an initial stage of relatively slow growth (in cedarbird first to third day), a 
period of maximum increase (third to ninth day), and a final stage of retarded growth 
or shrinkage in weight. See table. 
a twig, and with both feet pull themselves up when but four hours old, 
or possibly less. This ability is closely related to the climbing stage 
which is entered on the seventh day, when they leave the nest in succes- 
sion, and ascend into the branches, where they remain for a period of 
two weeks before ready for flight. 
In the cuckoo the curve of growth, as indicated by body-weight, 
appears to be quite even and regular after the beginning of the second 
day (Fig. 27%). In these particular birds the highest rate was regis- 
tered on the third day, and this proceeded without appreciable inter- 
ruption until the last day in the nest, when it was slightly checked. 
The power of muscular coordination, association and the instincts of 
fear and of preening seem to develop gradually after the first day. 
