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. The theory, with regard to birds is, that in the love-season, when the males are excited and engage in courtship, the females do not fall to the strongest and most active, nor to those that are first in the field; but that in a large number of species they are endowed with a faculty corresponding to the aesthetic feeling or taste in man, and deliberately select males for their superiority in some aesthetic quality, such as graceful or fantastic motions, melody of voice, brilliancy of colour, or perfection of ornaments. Doubtless all birds were originally plain-coloured, without ornaments and without melody, and it is assumed that so it would always have been in many cases but for the action of this principle, which, like natural selection, has gone on accumulating countless small variations, tending to give a greater lustre to the species in each case, and resulting in all that we most admire in the animal world--the Rupicola's flame-coloured mantle, the peacock's crest and starry train, the joyous melody of the lark, and the pretty or fantastic dancing performances of birds.