As all or most singing birds learn their songs from the adults of the
same species, it is not strange that there should be a good deal of what
we call mimicry in their performances: we may say, in fact, that pretty
well all the true singers are mimics, but that some mimic more than
others. Thus, the starling is more ready to borrow other birds' notes
than the thrush, while the marsh-warbler borrows so much that his
singing is mainly composed of borrowings. The nightingale is, perhaps,
an exception. His voice excels in power and purity of sound, and what we
may call his artistry is exceptionally perfect; this may account for the
fact that he does not borrow from other birds' songs. I should say, from
my own observation, that all songsters are interested in the singing of
other species, or at all events, in certain notes, especially the most
striking in power, beauty, and strangeness. Thus, when the cuckoo starts
calling, you will see other small birds fly straight to the tree and
perch near him, apparently to listen. And among the listeners you will
find the sparrow and tits of various species--birds which are never
victimized by the cuckoo, and do not take him for a hawk since they take
no notice of him until the calling begins. The reason that the double
fluting call of the cuckoo is not mimicked by other birds is that they
can't; because that peculiar sound is not in their register. The
bubbling cry is reproduced by both the marsh warbler and the starling.
Again, it is my experience that when a nightingale starts singing, the
small birds near immediately become attentive, often suspending their
own songs and some flying to perch near him, and listen, just as they
listen to the cuckoo. Birds imitate the note or phrase that strikes them
most, and is easiest to imitate, as when the thrush copies the piping
and trilling of the redshank and the easy song of the ring-ouzel, which,
when incorporated into his own music, harmonizes with it perfectly. But
he cannot flute, and so never mimics the blackbird's song, although he
can and does, as we have seen, imitate its chuckling cry.