Page:EB1911 - Volume 13.djvu/911

 Pliny, applied that name in a generic sense (Ornith. spec. novum, pp. 47, 48) to both. Taking the hint thus afforded, Linnaeus very soon after went farther, and, excluding the wrens, founded his genus Trochilus for the reception of such humming-birds as were known to him. The unfortunate act of the great nomenclator cannot be set aside; and, since his time, ornithologists, with but few exceptions, have followed his example, so that nowadays humming-birds are universally recognized as forming the family Trochilidae.

The relations of the Trochilidae to other birds were for a long while very imperfectly understood. Nitzsch first drew attention to their agreement in many essential characters with the swifts, Cypselidae, and placed the two families in one group, which he called Macrochires, from the great length of their manual bones, or those forming the extremity of the wing. The name was perhaps not very happily chosen, for it is not the distal portion that is so much out of ordinary proportion to the size of the bird, but the proximal and median portions, which in both families are curiously dwarfed. Still the manus, in comparison with the other parts of the wing, is so long that the term Macrochires is not wholly inaccurate. The affinity of the Trochilidae and Cypselidae once pointed out, became obvious to every careful and unprejudiced investigator, and there are probably few systematists now living who refuse to admit its validity. More than this, it is confirmed by an examination of other osteological characters. The “lines,” as a boat-builder would say, upon which the skeleton of each form is constructed are precisely similar, only that whereas the bill is very short and the head wide in the swifts, in the humming-birds the head is narrow and the bill long—the latter developed to an extraordinary degree in some of the Trochilidae, rendering them the longest-billed birds known. Huxley takes these two families, together with the goatsuckers (Caprimulgidae), to form the division Cypselomorphae—one of the two into which he separated his larger group Aegithognathae. However, the most noticeable portion of the humming-bird’s skeleton is the sternum, which in proportion to the size of the bird is enormously developed both longitudinally and vertically, its deep keel and posterior protraction affording abundant space for the powerful muscles which drive the wings in their rapid vibrations as the little creature poises itself over the flowers where it finds its food.

So far as is known, all humming-birds possess a protrusible tongue, in conformation peculiar among the class Aves, though to some extent similar to that member in the woodpeckers (Picidae) —the “horns” of the hyoid apparatus upon which it is seated being greatly elongated, passing round and over the back part of the head, near the top of which they meet, and thence proceed forward, lodged in a broad and deep groove, till they terminate in front of the eyes. But, unlike the tongue of the woodpeckers, that of the humming-birds consists of two cylindrical tubes, tapering towards the point, and forming two sheaths which contain the extensile portion, and are capable of separation, thereby facilitating the extraction of honey from the nectaries of flowers, and with it, what is of far greater importance for the bird’s sustenance, the small insects that have been attracted to feed upon the honey. These, on the tongue being withdrawn into the bill, are caught by the mandibles (furnished   in the males of many species with fine, horny, saw like teeth ), and swallowed in the usual way. The stomach is small, moderately muscular, and with the inner coat slightly hardened. There seem to be no caeca. The trachea is remarkably short, the bronchi beginning high up on the throat, and song-muscles are wholly wanting, as in all other Cypselomorphae.

Humming-birds comprehend the smallest members of the class Aves. The largest among them measures no more than 8 and the least 2 in. in length, for it is now admitted generally that Sloane must have been in error when he described (Voyage, ii. 308) the “least humming-bird of Jamaica” as “about 1 in. long from the end of the bill to that of the tail”—unless, indeed, he meant the proximal end of each. There are, however, several species in which the tail is very much elongated, such as the Aithurus polytmus (fig. 1) of Jamaica, and the remarkable Loddigesia mirabilis of Chachapoyas in Peru, which last was for some time only known from a unique specimen (Ibis, 1880, p. 152); but “trochilidists” in giving their measurements do not take these extraordinary developments into account. Next to their generally small size, the best-known characteristic of the Trochilidae is the wonderful brilliancy of the plumage of nearly all their forms, in which respect they are surpassed by no other birds, and are only equalled by a few, as, for instance, by the Nectariniidae, or sun-birds of the tropical parts of the Old World, in popular estimation so often confounded with them.

The number of species of humming-birds now known to exist considerably exceeds 400; and, though none departs very widely from what a morphologist would deem the typical structure of the family, the amount of modification, within certain limits, presented by the various forms is surprising and even bewildering to the uninitiated. But the features that are ordinarily chosen by systematic ornithologists in drawing up their schemes of classification are found by the “trochilidists,” or special students of the Trochilidae, insufficient for the purpose of arranging these birds in groups, and characters on which genera can be founded have to be sought in the style and coloration of plumage, as well as in the form and proportions of those parts which are most generally deemed sufficient to furnish them. Looking to the large number of species to be taken into account, convenience has demanded what science would withhold, and the genera established by the ornithologists of a preceding generation have been broken up by their successors into multitudinous sections—the more adventurous making from 150 to 180 of such groups, the modest being content with 120 or thereabouts, but the last dignifying each of them by the title of genus. It is of course obvious that these small divisions cannot be here considered in detail, nor would much advantage accrue by giving statistics from the works of recent trochilidists, such as Gould, Mulsant and Elliot. It would be as unprofitable here to trace the successive steps by which the original genus Trochilus of Linnaeus, or the two genera Polytmus and Mellisuga of Brisson, have been split into others, or have been added