There is another thing to be considered. I believe that the bird, like
creatures in other classes, has his receptive period, his time to learn,
and that, like some mammals, he learns everything he needs to know in
his first year or two; and that, having acquired his proper song, he
adds little or nothing to it thereafter, although the song may increase
in power and brilliance when the bird comes to full maturity. This, I
think, holds true of all birds, like the nightingale, which have a
singing period of two or three months and are songless for the rest of
the year. That long, silent period cannot, so far as sounds go, be a
receptive one; the song early in life has become crystallized in the
form it will keep through life, and is like an intuitive act. This is
not the case with birds like the starling, that sing all the year
round--birds that are naturally loquacious and sing instead of screaming
and chirping like others. They are always borrowing new sounds and
always forgetting.

The most curious example of mimicry I have yet met with is that of a
true mocking-bird, Mimus patachonicus, a common resident species in
northern Patagonia, on the Atlantic side, very abundant in places. He is
a true mocking-bird because he belongs to the genus Mimus, a branch of
the thrush family, and not because he mocks or mimics the songs of other
species, like others of his kindred. He does not, in fact, mimic the set
songs of others, although he often introduces notes and phrases borrowed
from other species into his own performance. He sings in a sketchy way
all the year round, but in spring has a fuller unbroken song, emitted
with more power and passion. For the rest of the time he sings to amuse
himself, as it seems, in a peculiarly leisurely, and one may say,
indolent manner, perched on a bush, from time to time emitting a note or
two, then a phrase which, if it pleases him, he will repeat two or