The SENSE OF HEARING in birds is remarkably acute, as might be readily inferred from the vocal capabilities conferred upon many of these gifted songsters. Their music is certainly not less appreciated by the performers than it is by their auditors. "Nobody can doubt," observes Bishop Stanley, "who sees a bird singing, clapping its little wings, turning from side to side, and glancing its bright eyes in all directions, as if courting attention and admiration, that it feels delight and satisfaction. Did we require further proof, we have but to recollect that the song-bird is most alert with the music of its voice when its affections and interests are awakened by its mate during the time of rearing its young." It is, indeed, principally during the breeding-season that the singing power of birds is in full activity; and seeing that in general it is only the male that possesses the musical faculty, we may naturally suppose that its exercise is intended for the solace and amusement of his mate during her confinement to her nest. The nightingale himself becomes voiceless so soon as the appearance of his nestlings calls him to more profitable employment. [Illustration: Fig. 8.--EXTERNAL EAR OF A YOUNG OWL. _a_, the Upper Part of the Head, partially denuded of feathers; _b_, the Beak; _d_, the Eye; _c_, _e_, _f_, Marginal Fold of Skin surrounding a cavity, the interior of which somewhat resembles the folds of the human ear; _g_, Auditory Passage leading to _h_, the Drum of the Ear (_membrana tympani_).] It is, however, among the nocturnal birds that the faculty of hearing is more specially developed. In the generality of birds there is no provision made externally for catching or concentrating sonorous impressions; but in the owls, the bustards, and a few others that venture forth at night, we find a different arrangement. In the owls, more especially, an external auditory apparatus is very conspicuous; not only does the integument exhibit a variety of folds, the disposition of which forcibly reminds us of the human ear, but the feathers upon the sides of the head are so disposed as to fulfil in some degree the purposes of a hearing trumpet. (See Fig. 8.) In such species the sense of hearing is exquisitely developed. In the generality of birds the SENSE OF TASTE can scarcely be said to exist. The manner in which they obtain and swallow their food precludes the possibility of enjoyment from this source, so that their tongue is in many cases appropriated to some totally different use. In by far the greater number the tongue is small, thin, and cartilaginous; the extremity is flat, and incapable of being protruded beyond the bill. (See Fig. 9.) There are, however, great varieties in the construction of this organ, a few of which will require our notice.