One was perched quite still on a twig, singing merrily, while
the others were keeping time with wings and feet in a kind of dance, and
all twittering an accompaniment. He watched them for some time, and was
satisfied that they were having a ball and concert, and thoroughly
enjoying themselves; they then became alarmed, and the performance
abruptly terminated, the birds all going off in different directions.
The natives told him that these little creatures were known as the
"dancing birds."
This species was probably solitary, except when assembling for the
purpose of display; but in a majority of cases, especially in the
Passerine order, the solitary species performs its antics alone, or with
no witness but its mate. Azara, describing a small finch, which he aptly
named _Oscilador,_ says that early and late in the day it mounts up
vertically to a moderate height; then, flies off to a, distance of
twenty yards, describing a perfect curve in its passage; turning, it
flies back over the imaginary line it has traced, and so on repeatedly,
appearing like a pendulum swung in space by an invisible thread.
Those who seek to know the cause and origin of this kind of display and
of song in animals are referred to Darwin's _Descent of Man_ for an
explanation. The greater part of that work is occupied with a laborious
argument intended to prove that the love-feeling inspires the animals
engaged in these exhibitions, and that sexual selection, or the
voluntary selection of mates by the females, is the final cause of all
set musical and dancing performances, as well as of bright and
harmonious colouring, and of ornaments.
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