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
264 The Naturalist in La Plata.
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.
My experience is that mammals and birds, with few exceptions--probably there are really no exceptions--possess the habit of indulging frequently in more or less regular or set performances, with or without sound, or composed of sound exclusively; and that these performances, which in many animals are only discordant cries and choruses, and uncouth, irregular motions, in the more aerial, graceful, and melodious kinds take immeasurably higher, more complex, and more beautiful forms. Among the mammalians the instinct appears almost universal; but their displays are, as a rule, less admirable than those seen in birds. There are some kinds, it is true, like the squirrels and monkeys, of arboreal habits, almost birdlike in their restless energy, and in the swiftness and certitude of their motions, in which the slightest impulse can be instantly expressed in graceful or fantastic action; others, like
Music and Dancing in Nature. 265
the Chinchillidae family, have greatly developed vocal organs, and resemble birds in loquacity; but mammals generally, compared with birds, are slow and heavy, and not so readily moved to exhibitions of the kind I am discussing.
The terrestrial dances, often very elaborate, of heavy birds, like those of the gallinaceous kind, are represented in the more volatile species by performances in the air, and these are very much more beautiful; while a very large number of birds--hawks, vultures, swifts, swallows, nightjars, storks, ibises, spoonbills, and gulls--circle about in the air, singly or in flocks. Sometimes, in serene weather, they rise to a vast altitude, and float about in one spot for an hour or longer at a stretch, showing a faint bird-cloud in the blue, that does not change its form, nor grow lighter and denser like a flock of starlings; but in the seeming confusion there is perfect order, and amidst many hundreds each swift- or slow-gliding figure keeps its proper distance with such exactitude that no two ever touch, even with the extremity of the long-wings, flapping or motionless:--such a multitude, and such miraculous precision in the endless curving motions of all the members of it, that the spectator can lie for an hour on his back without weariness watching this mystic cloud-dance in the empyrean.
The black-faced ibis of Patagonia, a bird nearly as large as a turkey, indulges in a curious mad performance, usually in the evening when feeding-time is over. The birds of a flock, while winging their way to the roosting-place, all at once seem possessed with frenzy, simultaneously dashing