"These different strains are interspersed with pauses which in all styles of melody concur in producing great effects. We dwell on the beautiful notes we have just heard, and which still resound in our ears; we enjoy them the more because the pleasure is more limited, more exclusive, and undisturbed by new sensations. Soon we expect, we desire another strain; we hope it may be pleasing; if we are mistaken, the beauty of what we hear will not leave us room to regret that which is only delayed, and the interest of hope is maintained for the strains which will follow. One of the reasons why the song of the nightingale is so striking, and produces so much effect, is, as Mr. Barington has well said, because he sings in the night, which is the most favourable time, and he sings alone, whereby his voice is heard in all its splendour, and is undisturbed by any other voice. He eclipses all other birds, adds Mr. Barington, by his soft flute-like tones, and by the uninterrupted duration of his warble, which lasts sometimes for twenty seconds. The same observer reckoned in this warble sixteen different strains, well marked by their first and last notes, the intermediate notes being tastefully varied by the bird; and he ascertained that the space filled by the nightingale's voice is no less than an English mile in diameter, especially when the air is calm: this equals the compass of the human voice.
"It is surprising that so small a bird, which weighs only half an ounce, should have such force in the vocal organs. Mr. Hunter has observed that the muscles of the larynx, or gullet, are stronger in proportion, in this species, than in any other, and also stronger in the male which sings, than in the female which does not sing.
"Aristotle, and Pliny after him, say, that the song of the nightingale lasts in all its strength for fifteen days and fifteen nights uninterruptedly, at the time that the trees are putting forth their leaves; this can refer only to wild nightingales, and must not be taken literally; for these birds are not silent either before or after the period fixed by Aristotle. It is true they do not continue to sing with so much ardour and constancy. They generally begin in the month of April, and do not completely end till the month of June, about the time of the solstice; but the time when their song diminishes most, is when the young are hatched, because they are then occupied in feeding them, and in the order of instincts, that which tends to the preservation of the species is pre-eminent. Captive nightingales continue to sing for nine or ten months, and their song is sustained not only for a longer time, but it is more perfect and studied. Hence Mr. Barington infers, that in this species, and in many others, the male does not sing to amuse the female, and enliven her fatigue when sitting; which appears a very just and probable inference. Indeed, the female when she sits performs her office from an instinct, or rather a passion, stronger in her than even the passion of love; she finds in it an internal satisfaction of which we can form no idea, but which she appears to feel sensibly, and we cannot therefore suppose that at such moments she is in any want of consolation. Since then it is neither from duty nor virtue that the female sits, neither is it on that account that the male sings: indeed he does not sing during the second incubation. It is love, and especially the first season of love, which inspires the song of the bird; it is in spring that they experience the want both to love and to sing; it is the males which have most desire, and it is they who sing the most. They continue to sing during the greater part of the year if we preserve around them a perpetual spring, which incessantly renews their ardour, without affording an occasion for extinguishing it; this happens to caged nightingales, and even, as it has been already mentioned, to those which have been taken full grown. Some have been known to begin to sing with all their strength a few hours after being caught. They must, however, have been insensible of their loss of liberty at first. They would starve the first seven or eight days if they were not fed, and would injure their heads against the top of the cage if their wings were not tied; but at last the passion for singing prevails, because it is produced by a still deeper passion.