ON THE INSTINCTS OF BIRDS. 119 
much surer criterion will be found in the uniformity 
so conspicuous in the manners and economy of birds 
of the same kind—a coincidence which can only be 
accounted for by supposing that their actions are 
instinctive. That this is actually the case I shall 
attempt to show, though it must be admitted that 
they are occasionally modified, in a considerable de- 
gree, by the exercise of the intellectual faculties. 
I will not occupy the time of the reader in examin- 
ing the many vague and contradictory opinions 
which have been entertained with regard to the 
nature of instinct by the various authors who have 
written on the subject, being convinced that they 
are purely speculative, and tend to retard rather 
than advance the progress of science. We must 
not, however, pass unnoticed the sophistical doctrine, 
so ingeniously maintained by Dr. Darwin, in ‘ Zoono- 
mia’ *, that what is usually termed instinct in animals 
has reference to the powers of intellect solely ; since 
the feathered tribes, notwithstanding the highly 
curious and unequivocal examples of instinctive ac- 
tions which they exhibit, have furnished him with 
some of his most plausible arguments in support 
of it. 
Depending on the assertion of Kircher, that young 
Nightingales, when hatched by other birds, never sing 
till they are instructed, and confiding in the remark 
* See the Section on Instinct, vol. i. 
+ ‘De Musurgia,’ Cap. de Lusciniis. 
