It is difficult to account for so small a creature as a bird making a tone as loud as some animal a thousand times its size ; but a recent discovery has shown that, in birds, the lungs have several openings communicating with corresponding air bags or cells, which fill the whole cavity of the body from the neck downward, and into which the air passes and re-passes in the progress of breathing. This is not all. The very bones are hollow, from which air pipes are conveyed to the most solid parts of the body, even into the quills and featEei's. The air being rarified by the heat of their body, adds to their levity. By forcing the air out of the body, they can dart down from the greatest hights with astonishinjj velocity. No doubt the same machinery forms the basis of their vocal powers, and at once resolves the mystery into a natural ordering of parts.—Gardner's Music of Nature.
This article was originally published with the title "Vocal Machinery of Birds"