THE EVOLUTION OF BIRD-SONG. 235 



Warbler, Chiffchaff, Redbreast, and Tbrush, sing when about to 

 fight together, and often during a combat, upon which occasions 

 their songs are clearly intended as defiances. 



Increase of fear induces a proportionately rapid and vehement 

 repetition of the alarm-note. I have heard a Blackcap repeat his 

 alarm-note, " tack," so rapidly as to produce a shake, like the 

 shaking alarm-notes of the Magpie and Great Titmouse. The 

 Blackbird's rattling alarm is simply the quick reiteration of one 

 sharp note. The alarms of the Magpie, Missel Thrush, and male 

 House Sparrow were probably, with those of several other birds, 

 originated by single cries. The first alarms or danger-calls would 

 be uttered, not only when the birds themselves were in danger, 

 but also when their young were threatened. The first cry of the 

 nestling young marked the commencement of a new era in 

 bird-utterance. This cry was probably an imitation of that 

 of parent birds uttered near their nest, and, being induced by 

 hunger, was used as a demand for food from them. The cries of 

 the parents near the nest would generally be alarms. A bird 

 does not often sing in close proximity to its nest (though the 

 popular idea is to the contrary), but exclaims in alarm when its 

 nest is threatened. The most impatient and vehement of the 

 young probably obtained the most food, and consequently they 

 enjoyed the greatest chance of survival. The cries of the young 

 would be in effect call-notes, and as such would be useful to 

 them, and therefore would be retained after they had left the nest, 

 especially in gregarious species, which, in a greater degree than 

 solitary kinds, would develop these notes. In this case we should 

 find gregarious birds garrulous,* and solitary species generally 

 silent, and this is actually the case. Examples of the former kind 

 are the Mallard, Starling, Siskin, Linnet, Goldfinch, and the 

 Great, Blue, Coal, and Long-tailed Titmice ; and among the 

 latter are the Raptores and Picidce generally, and the Redbreast, 

 Hedge Accentor, and Wren. 



The call-note, being more or less the result of imitation, 

 would be influenced by other sounds familiar to the bird ; and 

 of these the most pleasant would be those resulting from or 



* Gregariousness was probably not induced by garrulity, but by the local 

 distribution of food, or by fear, and as a means to protection against enemies ; 

 or possibly, in birds that sleep in company, for the sake of mutual warmth. 



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