247 
may infer that the utterance of sound was first occasioned by 
combat, in which it is, at the present time, most widely 
employed; and that it was used, if not as a defiance, at least 
as a plea for mercy—like the cry of a fowl or that of a dog 
defeated in fight. We may be certain that the perception of 
a threatened attack was only a mental anticipation of the 
combat which experience—personally acquired, or inherited— 
suggested to be a probable consequence of the approach of an 
enemy: thus a combat-cry might well be uttered before the 
fight was commenced, and it would then be a danger-cry, or 
alarm-note. The influence of mutual aid amongst gregarious 
species would have tended to a variation of the danger-cry, 
which would have been constantly employed for the protection 
of the community; and would thus have been varied in degrees 
of force co-extensive with the danger which called it forth. 
The call-notes, which I consider to have arisen partly from 
the retention of distress-cries uttered as calls for food by the 
young, would in the past have been, as they now are, similarly 
varied, especially for the purpose of expressing desire for the 
companionship of another bird. 
It is probable that the emotions have played an important 
part in the development of bird-voices. In solitary birds, fear, 
unless acute, always produces silence; and it may account for 
the lack of song amongst the larger kinds of birds, which are 
always so conspicuous that they are compelled to be vigilant. 
_ Love obviously has brought about the abundant use of call- 
notes; these, in the breeding-season, are uttered with great 
frequency by the males, sometimes continuously, and so as to 
constitute a phrase or song. They constitute the entire songs 
of some species. Call-notes are also uttered in the songs of 
_ several other birds. 
The influence of hate or anger is seen in the defiant cries 
of many rasorial birds. Many birds of this order are poly- 
_ gamous, and among such the selection of mates is greatly 
_ dependent upon combat. But vocal defiances are not confined 
_ to birds of this order: the songs of the robin, thrush, hedge- 
_ sparrow, and wren, at least, are occasionally of this character. 
K2 
