22 Mr. J. Blackwall’s Ornithological Notes. 
an instinctive impulse, liable to be brought into operation by the 
agency of various stimuli, combined with a suitable state of the 
vocal organs* ; and this latter condition deserves especial atten- 
tion, for most of our songsters manifestly become mute in autumn 
from inability to continue their melodious strains; their perse- 
vering but ineffectual efforts to prolong them, and the difficulty 
they experience in recommencing them in spring, proving to 
demonstration that their pleasing lays depend upon the energy 
of those muscles which contribute to form the voice; an energy 
which is influenced chiefly by food, temperature, health, and the 
exercise of the reproductive function. 
The moulting of birds speedily follows the exhaustion conse- 
quent on the propagation of their species, and an attendant re- 
laxation of the vocal organs, which renders them incapable of 
obeying the dictates of the will, is, I conceive, the true cause of 
the periodical silence of singing birds. To this state of things 
succeeds a gradual reduction in the temperature of the atmo- 
sphere and in the supply of animal food, so that, with a few ex- 
ceptions already noticed, and those dependent in all probability 
upon some constitutional peculiarity, the enfeebled organs of 
voice do not recover their tone till the ensuing spring, when in- 
numerable animated beings, excited to activity by the genial 
warmth of the season, afford abundance of stimulating nutriment 
_ to the feathered songsters, which, with the concurrent restora- 
tion of their physical energies, enliven every copse with their 
sweet and unsophisticated music. Such I apprehend is the real 
nature of the connexion which subsists between atmospheric tem- 
perature and the singing of birds. 
Many birds are endowed with an extraordinary capacity for 
imitating sounds, and under the careful tuition of skilful imstruct- 
ors readily learn to pipe long and difficult tunes, to articulate 
words, and even to repeat short sentences with surprising pre- 
cision. Among our native species, the jay, magpie, starling and 
bullfinch afford familiar instances of the truth of this assertion ; 
but I am impressed with the belief that the spontaneous employ- 
ment of this faculty by individuals which have never been re- 
moved from their natural haunts is much more limited than is 
commonly supposed. If the term “mimic” be strictly applicable 
to any British bird im the wild state, the sedge warbler may be 
thought pre-eminently to merit that appellation, and, indeed, its 
song is usually described in ornithological works as being com- 
posed, in a great measure, of passages borrowed from the lays of 
other songsters ; yet I feel thoroughly satisfied that this reiterated 
* For particulars consult an essay on the notes of birds published in the 
Memoirs of the Literary and Philosophical Society of Manchester, second 
series, vol. iv. p. 289. 
