Why do the notes of different species of birds vary?
Because, probably, of the structure of the organs of each species enabling them more easily to produce the notes of their own species, than those of any other, and from the notes of their own species being more agreeable to their ears. These conditions, joined to the facility of hearing the song of their own species, in consequence of frequenting the same places, determine the character of the acquired language of the feathered tribes. – Fleming. Those who have paid attention to the singing of birds, know well that their voice, energy, and expression, differ as widely as in man ; and, agreeably to this remark, Mr. Wilson, the celebrated ornithologist, says he was so familiar with the notes of an individual wood-thrush, that he could recognise him among all his fellows the moment he entered the woods.
