Page:Descent of Man 1875.djvu/394

378 The male alone of one of the Indian bustards (Sypheotides auritus) has its primary wing-feathers greatly acuminated; and the male of an allied species is known to make a humming noise

whilst courting the female. In a widely different group of birds, namely Humming-birds, the males alone of certain kinds have either the shafts of their primary wing-feathers broadly dilated, or the webs abruptly excised towards the extremity. The male, for instance, of Selasphorus platycercus, when adult, has the first primary wing-feather (fig. 44), thus excised. Whilst flying from flower to flower he makes "a shrill, almost whistling noise;" but it did not appear to Mr. Salvin that the noise was intentionally made.

Lastly, in several species of a sub-genus of Pipra or Manakin, the males, as described by Mr. Sclater, have their secondary wing-feathers modified in a still more remarkable manner. In the brilliantly-coloured P. deliciosa the first three secondaries are thick-stemmed and curved towards the body; in the fourth and fifth (fig. 45, a) the change is greater; and in the sixth and seventh (b, c) the shaft "is thickened to an extraordinary degree, forming a solid horny lump." The barbs also are greatly changed in shape, in comparison with the corresponding feathers (d, e, f) in the female. Even the bones of the wing, which support these singular feathers in the male, are said by Mr. Fraser to be much thickened. These little birds make an extraordinary noise, the first "sharp note being not unlike the crack of a whip."

The diversity of the sounds, both vocal and instrumental, made by the males of many birds during the breeding-season, and the diversity of the means for producing such sounds, are highly remarkable. We thus gain a high idea of their importance for sexual purposes, and are reminded of the conclusion arrived at as to insects. It is not difficult to imagine the steps by which the notes of a bird, primarily used as a mere call or for some other purpose, might have been improved