LIFE AND BEHAVIOR OF THE CUCKOO 
205 
fold, the primaries from 5 to 25 millimeters in length (fig. 21, i-j), 
and the tubes of the dorsal tract from 8 to 20 mm. (including the 
flagellum of the primary down) . Each quill tapers rather abruptly 
to its tip which is generally closed. 
The feather-tubes of the linear abdominal tracts (B.g. 21, e-h) 
which are commonly the first to burst, have a length of about 8 
millimeters, and are yellowish white from the transparency of the 
tubular wall, and the color of the enclosed feathers. A few rudi- 
mentary down-hairs are still found on the back, and are later 
replaced by contour-feathers. The proper tail-quills which now 
appear as short thick, yellowish tubes, are not preceded by rudi- 
mentary down (fig. 21, o) ; the tail-coverts, however, are flagel- 
lated. 
Towards the close of the completed quill stage the behavior 
of the young cuckoo undergoes marked changes. It indulges 
in new attitudes, acquires new alarm and call notes, shows fear, 
and begins the preening or combing movements, which later affect 
an apparently sudden and wonderful change in its appearance. 
In watching these birds closely from the tent, the first striking 
change is seen in their general attitude. They begin to sit up 
and take notice. The nest is no longer the center and bound of 
their visual world. They attend to all kinds of sounds, and re- 
spond to many of them, and while thus in the nest one will oc- 
casionally give the feeding reaction, thereby starting the others, 
who always react to the first bird ; they will peck at crawling ants, 
or at mosquitoes, which have thitherto tormented them, unmolest- 
ed; they notice the leaves and branches about their nest, when 
stirred by the wind ; in short they begin to sit much like a brooding 
bird, with head upturned, and attend to everything. If the heat 
of the sun causes them discomfort, they move restlessly about the 
nest, gape, and pant with vibrating glottis, tongue and lower 
mandible, precisely like an old bird. 
The preening instinct, in the course of a few hours froni the 
first observed movement (in one case on the sixth day) , becomes 
very active; with its bill the little bird proceeds to comb every 
quill within reach, quickly drawing its mandibles over it from 
base to apex (fig. 19). With apparent suddenness at the close 
