to the persuasions of the male, control their young, and otherwise express themselves, require a vocal apparatus similar to that of the male, which shall not be stunted by non-use. Instead of regarding, as Darwin did, the singing organs of female birds as an instance of the partial but useless transmission of secondary male characteristics to the female, I think we might now plausibly consider it a transmission in undiminished perfection of a faculty generally characteristic of both, but which is most freely exercised in the male on account of its relation to the most important act of his life, and hence to the maintenance of the species.
Singing out of rivalry finds an explanation in the disposition of the exultant songster to show himself off and to surpass others. If this exultant feeling is wanting, as, for instance, when it is depressed by some uncomfortable condition, the emulative singing stops. Hence, freshly-caught birds are songless in the cage, as are also males when several of them are confined together. In these cases the birds are pining for their lost freedom, or are suffering from the feeling of being crowded or hampered in their movements.
Domesticated birds sing also from a kind of gratitude to please their master, after they have discovered that he likes their songs, and the act produces in return a wholesome effect upon them. Under such influences, they sing all through the year, and more than they would do in freedom. I have had the opportunity of making a remarkable observation which shows that singing-birds desire the notice and applause of their attendant, and are affected by them. I had a yellow thrush (Turdus saxatilis), taken from the nest, which had become quite tame and confiding. Its cage hung behind the window-curtain of my study, and this adjoined my bedroom. I sometimes heard early in the morning a clear, melodious cock-crowing that seemed to come from a distant barn-yard. I thought of everything to which I might attribute it except my bird, which had never indulged in anything but the simplest song when I was present; but I soon found out his trick. Having risen early one morning and gone into the study while the bird's head was still hidden under his wing, I sat still in a farther corner of the room till matters began to get lively in the cage. Unobserved by my pet, I could see him through the folds of the curtain stretch out his wings and one foot, and plume himself. Then he found his voice and sounded out the cock-crow which I had heard so often from my bedroom without suspecting its real origin. Had I not seen the bird's mouth open and his throat vibrating, I should still have thought the sound came from a distance. Suddenly I stepped behind the curtain, when the bird, perceiving me, broke off at once in the midst of his crowing—a thing he had never done when I appeared as a witness to his ordinary singing—and fluttered timorously around as if he had done something wrong. I went out from the room and waited near, but the bird did not crow any more, nor again for two days afterward.
