CALL-NOTES 61 
and young Boobies scream; young Man-o’-war-birds squeal and rattle 
their bills; and all three species strike at one most viciously. Possibly 
the size and snowy plumage of these young birds renders them so con- 
spicuous that they cannot expect to escape observation by remainin 
motionless, and therefore adopt a more direct and aggressive means 
of self-preservation. 
As the young bird develops, its range of calls increases until finally 
we have the full vocabulary of maturity. This varies widely with differ- 
ent species, and it may, I think, be truly said that no exhaustive study 
has as yet been made of the calls of a single species of wild bird. 
When the young bird is old enough to care for itself, the language 
of the nursery is forgotten, and the recognition call, by which individuals 
of the same species are brought together in flocks or companies, is 
doubtless its most valuable and most frequently employed vocal asset. 
This is particularly true with migratory species, whose oft-repeated 
notes, while winging their way through the night, serve to mark the 
line of flight and keep stragglers in line. The pink of the Bobolink, the 
liquid purt of the Olive-backed Thrush, the fine but far-carrying cheep 
of Warblers, are familiar illustrations. 
Calls of this nature, by which a bird simply announces its presence, 
together with those of alarm, are uttered by most birds, and it is probable 
that they constitute a common language, the significance of which is 
generally understood. That is, a migrating bird may be guided by the 
notes of other species, without necessarily knowing to what species 
the call it follows belongs, just as it will recognize as an alarm call the 
warning note of a bird of a different species, which has been the first 
to see and give notice of the presence of a Hawk or Owl or other form 
of danger. 
Crows, however, immediately recognize the hoot of a Barred Owl 
as such, and on hearing it at once utter a certain caw-caw which may 
be termed their ‘rally call,’ and which is so quickly responded to by 
other Crows that within a few minutes a throng of them has surrounded 
the cause of the disturbance. This example serves well to illustrate 
the difference between the common or characteristic call.of a certain 
species, its simple “I am here” or “This is I,” and others possessing a 
special significance. That the rally call of the Crow is clearly under- 
stood by all the Crows that hear it, no one will doubt who-has observed 
its effect; while further attention to Crow caws will reveal a surprising 
variation in their character and the manner in which they are uttered; 
all of which doubtless possesses an exact significance to Crows and 
may some day be intelligible to man. 
The Robin also supplies a familiar illustration of a bird possessing 
a wide variety of calls, each one of which has its own meaning, and indeed 
one need go no further than the hen-yard to find opportunities for the 
study of bird language and to be convinced of the possibilities which 
may arise from close, sympathetic observation of this phase of the bird’s 
life. 
