VOICES OF BIRDS. 
187 
separate voice assigned it, that each might continue as 
created, distinct and unmixed : and the very few devia- 
tions and admixtures that have taken place, considering 
the lapse of time, association, and opportunity, united 
with the prohibition of continuing accidental deviations, 
are very remarkable, and indicate a cause and original 
motive. That some of the notes of birds are as lan- 
guage designed to convey a meaning, is obvious from 
the very different sounds uttered by these creatures at 
particular periods : the spring voices become changed 
as summer advances, and the requirements of the early 
season have ceased ; the summer excitements, moni- 
tions, informations, are not needed in autumn, and the 
notes conveying such intelligences are no longer heard. 
The periodical calls of animals, croaking of frogs, &c., 
afford the same reasons for concluding that the sound 
of their voices by elevation, depression, or modulation, 
conveys intelligence equivalent to an uttered sentence. 
The voices of birds seem applicable in most instances 
to the immediate necessities of their condition ; such as 
the sexual call, the invitation to unite when dispersed, 
the moan of danger, the shriek of alarm, the notice of 
food. But there are other notes, the designs and mo- 
tives of which are not so obvious. One sex only is 
gifted with the power of singing, for the purpose, as 
Buffon supposed, of cheering his mate during the period 
of incubation ; but this idea, gallant as it is, has such 
slight foundation in probability, that it needs no confu- 
tation : and after all, perhaps, we must conclude, that 
listened to, admired, and pleasing, as the voices of many 
birds are, either for their intrinsic melody, or from as- 
sociation, we are uncertain what they express, or the 
object of their song. The singing of most birds seems 
entirely a spontaneous effusion produced by no exertion, 
or occasioning no lassitude in muscle, or relaxation of 
the parts of action. In certain seasons and weather, 
the nightingale sings all day, and most part of the night ; 
and we never observe that the powers of song are 
weaker, or that the notes become harsh and untunable, 
after all these hours of practice. The song-thrush, in 
a mild moist April, will commence his tune early in 
