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 remaining 

 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 thiilk, 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 simpfy 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. 



