Moth
to assume so peculiar an attitude when disturbed. When therefore I speak
of the origin, I do not refer to the mode of origin of variation; I take
for granted that variations somehow arise, and I seek to ascertain
whether there is anything in the phenomena which we have explored which
might reasonably be held to determine the survival of this one in
preference to that.

When we reflect upon the problem of song and consider the numerous and
diverse forms in which it is manifested, we are apt to draw a
comparison between the sounds we hear and those produced by musical
instruments, and hence to conclude that each bird is gifted with a
special instrument in virtue of which it produces its characteristic
melody. But there is a very remarkable phenomenon connected with the
singing of birds which shows that this is really not the case--I mean
the phenomenon of imitation. There are plenty of good imitators amongst
our native species, and the power of imitation is not the exclusive
property of those which have reached a high degree of vocal development,
nor, for the matter of that, of song-birds at all. Even the Jay, than
which few birds have a more raucous voice, that "hoots" like the
Wood-Owl, or copies the sounds produced by the tail feathers of the
Snipe, will occasionally imitate the most melodious strains of some
other species; and the Red-backed Shrike, whose sexual call is
principally a few harsh notes rapidly repeated, bursts at times into
perfect imitations of the song of the Swallow, Linnet, or Chaffinch.
Nevertheless it is amongst such typical songsters as the Warblers that
we find the greatest volume of imitation, and no limit seems to be
placed upon their capacity. The Marsh-Warbler can utter the call of the
Green Woodpecker, or sing as the Nightingale does, with as much facility
as it sings its own song; and the Blackcap is well-nigh as proficient in
copying the cries and melodies of surrounding species--and so, if it
were necessary, we might proceed to add to the list.

These examples demonstrate that different songs are not represented by
a corresponding number of different physiological contrivances; for if
the difference were really attributable to some structural peculiarity,
then the range of sounds embraced in the call-notes and the sexual call
of any given species, must be the measure of the capacity of its
instrument; and no matter how great its power of imitation may be, it
follows that it will on