138 THE UNIVERSITY OF THE STATE OF NEW YORK 



feathers" as they are rather incorrectly called, push out the 

 down feathers on their growing tips and begin to split open 

 shortly after they appear. The change from the almost naked 

 young to the fully feathered one is usually gradual. 



Red-winged blackbirds; four stages Nu BI38 



b Method of growth in cuckoos and kingfishers 



With the cuckoo, kingfisher, hummingbird and swift, how- 

 ever, the quills do not split open until the feathers are nearly full 

 grown inside. For a time the young birds are covered with 

 curious coats of mail and the change from this stage to the fully 

 feathered condition may take place in a few hours. 



Kingfishers in quills Nu KiB4 



Kingfishers in feathers Nu KiBS 



Yellow-billed cuckoo Nu CvY6 



4 Development of fear instinct 



At first the young of birds seem not to know fear and raise 

 their wobbly heads for food at any disturbance about the nest. 

 As soon as they have strength to respond to the calls of their 

 parents, however, the fear instinct develops. The old bird gives 

 a feeding call when it approaches the nest. Unless the young 

 hear this, any disturbance about the nest causes them to crouch 

 and try to hide. A study of the different calls of the old birds 

 and the responses of the young is very interesting. 



a In precocial young, at hatching — "play possum" 



Killdeer Nu KeS 



b In altricial young, when they develop feathers 



5 Appearance of fully fledged young 



See illustrations and notes under coloration, p. 148. 



