Page:Popular Science Monthly Volume 46.djvu/797

 gloomy caves to which it resorts, laying three or four white eggs in a shallow clay nest. The young are overlaid with quantities of fat, and are collected by the natives for the oil they afford therefrom. This is an extensive and interesting industry, upon which much has been written.

We have now passed into an extensive group of birds generally alluded to by ornithologists as the "picarian assemblage," that not only includes the goatsuckers, of which we have just been speaking, but also many other families. Some of the relationships of the representatives of these groups are by no means as yet understood fully; many of them are interrelated; others exhibit characters which link them with another great assemblage of birds that is, the passerine group, or the Passeres. This is the case with the woodpeckers, for example, and also with the swifts, which latter are related to the swallows (Hirundinidæ). All this with equal truth applies to the Passeres, of which we have just spoken, and to which the swallows belong. Quite a number of the families among the passerine birds, however, have been very carefully examined, and ornithologists the world over are agreed as to their affinities, while on the other hand we are at our wits' end in regard to the determination of the allies of some of the passerine outliers. A few of the more puzzling forms of these can now be briefly introduced. The little "American dipper" (Cinclus) of the Rocky Mountain region is one of these, a bird not much larger than a bluebird, which is completely aquatic, even to the extent of hunting for its food under water.