INSTINCTS OF BIRDS. 261 



combined with a suitable state of the vocal 

 organs. This latter condition deserves particular 

 attention, for it is a fact, which has been very 

 generally overlooked, that most of our songsters 

 are absolutely unable to continue their melodious 

 strauas beyond the latter end of July, or the 

 beginning of August; the strenuous but un- 

 availing exertions they make to prolong them, 

 sufficiently proving their silence not to be a 

 matter of choice, but of necessity. This cir- 

 cumstance, together with the extreme difficulty 

 they experience in recommencing their songs in 

 spring, clearly demonstrates, that their delightful 

 warblings depend upon the energy of those 

 muscles which contribute to form the voice ; an 

 energy which appears to be influenced chiefly 

 by food, temperature, and the exercise of the 

 reproductive functions; for by due attention to 

 the regulation of these particulars, the vocal 

 powers of caged birds may be called into action, 

 or circumscribed at pleasure. Of this, persons 

 who have the management of breeding canaries 

 may easily satisfy themselves; and female birds, 

 in a state of captivity, when brought into high 

 condition, are known, occasionally, to assume 

 the song of the male. That Jonston must have 

 been deceived in supposing he heard the night- 

 ingale in Scotland is evident, as it is well known, 

 that this warbler is never found north of the 



