A scarlet-breasted troupial of La Plata perches conspicuously on a tall plant in afield, and at intervals soars up vertically, singing, and, at the highest ascending point, flight and song end in a kind of aerial somersault and vocal flourish at the same
284 The Naturalist in La Plata.
moment. Meanwhile, the dull-plumaged female is not seen and not heard: for not even a skulking
crake lives in closer seclusion under the herbage--so widely have the sexes diverged in this species. Is the female, then, without an instinct so common r --has she no sudden fits of irrepressible gladness? Doubtless she has them, and manifests them down in her place of concealment in lively chirpings and quick motions--the simple, primitive form in which gladness is expressed in the class of birds. In the various species of the genus Cnipolegus, already mentioned, the difference in the sexes is just as great as in the case of the troupial: the solitary, intensely black, statuesque male has, we have seen, a set and highly fantastic performance; but on more than one occasion I have seen four or five females of one species meet together and have a little simple performance all to themselves--in form a kind of lively mock fight.
It might be objected that when a bird takes its stand and repeats a set finished song at intervals for an hour at a stretch, remaining quietly perched, such a performance appears to be different in character from the irregular and simple displays which are unmistakably caused by a sudden glad impulse. But we are familiar with the truth that in organic nature great things result from small beginnings--a common flower, and our own bony skulls, to say nothing of the matter contained within them, are proofs of it. Only a limited number of species sing in a highly finished manner. Looking at many species, we find every gradation, every shade, from the simple joyous chirp and cry to the
Music and Dancing in Nature. 285
most perfect melody. Even in a single branch of the true vocalists we may see it--from the chirping bunting, and noisy but tuneless sparrow, to linnet and goldfinch and canary. Not only do a large majority of species show the singing instinct, or form of display, in a primitive, undeveloped state, but in that state it continues to show itself in the young of many birds in which melody is most highly developed in the adult. And where the development has been solely in the male the female never rises above that early stage; in her lively chirpings and little mock fights and chases, and other simple forms which gladness takes in birds, as well as in her plainer plumage, and absence of ornament, she represents the species at some remote period. And as with song so with antics and all set performances aerial or terrestrial, from those of the whale and the elephant to those of the smallest insect.
Another point remains to be noticed, and that is the greater frequency and fulness in displays of all kinds, including song, during the love season. And here Dr. Wallace's colour and ornament theory helps us to an explanation. At the season of courtship, when the conditions of life are most favourable vitality is at its maximum, and naturally it is then that the proficiency in all kinds of dancing-antics, aerial and terrestrial, appears greatest, and that melody attains its highest perfection. This applies chiefly to birds, but even among birds there are exceptions, as we have seen in the case of the field-finch, Sycalis luteola. The love-excitement is doubtless pleasurable to them, and it takes the form in which keenly pleasurable emotions are