PDF - Wallace Online

HUMMING-BIRDSwe find them all pointing in the same direction. The sternumor breastbone is not notched behind ;and this agrees with theswifts, and not with the sun-birds, whose sternum has two deepnotches behind, as in all the families of the vast order ofPasseres to which the latter belong. The eggs of both swiftsand humming-birds are white, only two in number, andresembling each other in texture. And in the arrangementof the feather-tracts the humming-birds approach more nearlyto the swifts than they do to any other birds and; altogetherdiffer from the sun-birds, which in this respect, as in so manyothers, resemble the honey-suckers of Australia and other truepasserine birds.Resemblances of Swifts and Humming-birdsHaving this clue to their affinities, we shall find otherpeculiarities common to these two groups, the swifts and thehumming-birds. They have both ten tail-feathers, while thesun-birds have twelve. They have both only sixteen truequill-feathers, and they are the only birds which have sosmall a number. The humming-birds are remarkable forhaving, in almost all the species, the first quill the longest ofall, the only other birds resembling them in this respectbeing a few species of swifts ; and, lastly, in both groupsthe plumage is remarkably compact and closely pressed tothe body. Yet, with all these points of agreement, we findan extreme diversity in the bills and tongues of the twogroups. The swifts have a short, broad, flat bill, with a flathorny -tipped tongue of the usual character; while thehumming-birds have a very long, narrow, almost cylindricalbill, containing a tubular and highly extensible tongue. Theessential point, however, is, that whereas hardly any of theother characters we have adduced are adaptive, or strictlycorrelated with habits and economy, this character is preeminentlyso ;for the swifts are pure aerial insect-hunters,and their short, broad bills and wide gape are essential totheir mode of life. The humming-birds, on the other hand,are floral insect-hunters, and for this purpose their peculiarlylong bills and extensile tongues are especially adapted ;whilethey are at the same time honey-suckers, and for this purposehave acquired the tubular tongue. The formation of such a