The color of the plumage of birds seems to bear less relation to their powers of song than to their habitats; and as the birds that live in trees are commonly less tuneful, they are more brilliantly arrayed.  The bird employs his song in wooing his mate, as well as in entertaining her after she is wedded; and it is not unlikely that Nature may have compensated those which are deficient in song by giving them a superior beauty of plumage.  As the offices of courtship devolve entirely upon the males, it is the more necessary that they should be possessed of conspicuous attractions; but as the task of sitting upon the nest devolves upon the female, she requires more of that protection which arises from the conformity of her plumage with the general hue of the objects that surround her nest.  While she is sitting, the plain hues of her dress protect her from observation; but when she leaves her nest to seek her companion, she is enabled by his brilliant colors the more easily to discover him.  The male is diligent in providing for the wants of the offspring, and hence it is important that his dress should render him conspicuous.  When the young birds have left the nest, upon seeing the flash of his plumage, they immediately utter their call, and by this note, which might not otherwise be sounded at the right moment, he detects them and supplies them with food.  Should a bird of prey suddenly come into their neighborhood, he overlooks the plainly-dressed mother and off-spring, and gives chase to the male parent, who not only escapes, but at the same time diverts the attention of the foe from his defenceless progeny.

But the birds that build low, either upon the ground or among the shrubbery, are exposed to a greater number and variety of enemies.  Hence it becomes necessary that the males as well as the females should have that protection which is afforded by sobriety of color.  Not being made conspicuous by their plumage, they are endowed with the gift of song, that they may make known their presence to their mate and their young by their voice.  I have often thought that the song of the bird was designed by Nature for the benefit of the young, no less than for the entertainment of his mate.  The sounds uttered by birds on account of their young always precede the period of incubation.  The common hen begins to cluck several days before she begins to sit upon her eggs.  In like manner the male singing-bird commences his song when the pair are making ready to build their nest.  While his mate is sitting, his song reminds her of his presence, and inspires her with a feeling of security and content, during the period of her confinement.  As soon as the young are hatched, they begin to learn his voice and grow accustomed to it, and when they fly from the nest they are prevented by the sound of it from wandering and getting bewildered.  If they happen to fly beyond certain bounds, the song of the male parent warns them of their distance, and causes them to turn and draw near the place from which it seems to issue.  Thus the song of the male bird, always uttered within a certain circumference, of which the nest is the centre, becomes a kind of sentinel voice, to keep the young birds within prudent limits.