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Each species will offer its own problem, but in every instance the 
greatest interest will center about the life of the nest, where the com- 
plex relations of parent with parent and of both with offspring, supply 
occasions for the utterance of notes heard under no other conditions. 
Not the least interesting of these will be the warning calls by which the 
adult conveys to her inexperienced, or even blind, young, knowledge of 
a threatening danger, in the presence of which they must betray no 
sign of life. Perhaps no one case more strongly illustrates the impor- 
tance of a means of exact communication among birds, for failure to 
understand and obey may here be followed by death. 
Song . — As a rule, the songs of birds are uttered by the male alone 
and mainly or only during the nesting season. It is true that in rare 
cases the female sings; the female Cardinal and Rose-breasted Gros- 
beak, for example, sometimes sing to a limited extent, and the female 
of a certain tropical American Wren ( Pheugopedius rutilus) sings a 
delightful duet with her mate. It is also true that some birds sing more 
or less throughout the year, while many have a short, second song- 
season after the postnuptial molt. But song in its full development, and 
with its real significance, is restricted to the nesting-season. It is, 
therefore, a secondary sexual character, an irrepressible manifesta- 
tion of the greatly increased vitality of the bird during the period of 
reproduction. 
The systematist classifies as Oscines, or true singing birds, those 
species which have the “syrinx with four or five distinct pairs of intrinsic 
muscles, inserted at ends of three upper bronchial half-rings and thus 
constituting a highly complex and effective musical apparatus” (Coues) ; 
but while this group contains the most gifted singers, it does not by any 
means contain all our song birds, many species having a less highly 
developed syrinx with fewer muscles, which are inserted into the middle, 
not the ends, of the bronchial half -rings, still being able to produce both 
pleasing and complex vocal sounds. Note, for example, the songs of 
certain Snipe and Plover or of Goatsuckers. On the other hand, some 
true Oscines, like Crows, Magpies, and Jays, with a highly developed 
vocal apparatus, are practically songless, while the Cactus Wren, a 
member of a family of noted songsters utters only harsh squawks. 
Song, therefore, is not restricted solely to the Oscines, but in a 
broad sense is the attribute of every species of birds which gives expres- 
sion to the emotions inspired by the nesting-period. The whistling of 
Grebes, the ‘bleating’ of Snipe, the ‘booming’ of Bitterns, the ‘trumpet- 
ing’ of Cranes, the ‘whinny’ of Soras or 1 cooing’ of Doves, the hooting 
of the Owls, are, therefore, types of songs, and we may even include 
here such mechanical forms of bird music as the ‘drumming’ of Grouse, 
tapping of Woodpeckers or ‘booming’ of Nighthawks. 
Through the exercise of these vocal and instrumental gifts, which so 
delightfully voice the joys and hopes of spring, the male bird replies to 
the challenge in kind of a rival, and what is of far more importance, 
informs the female of his presence. 
