=Place of birds in the animal kingdom.= Zoölogists rank mammals higher than birds because man is a mammal and his general superiority to other creatures determines the rank of the class to which he belongs. Yet, while placing birds below mammals in a simple classification of animals, naturalists point out that birds are the most distinct class in the animal kingdom. If we compare birds and the lower mammals, and compare the relations of each class to man, we see at once that nothing else could take the place of birds either in nature or in civilization. Among birds are found the highest developments of animal locomotion and of the natural voice, capacity for language far beyond that of other creatures (except man), and family and community relations resembling those of the human race. Hitherto in the history of the world mammals have been more useful to man than birds, but birds have given him some of his best ideas, and with the advance of civilization the lower mammals become less necessary and birds more necessary to him. =Flight of birds.= It has been said that "on the earth and on the sea man has attained to powers of locomotion with which, in strength, endurance, and velocity, no animal movement can compare. But the air is an element on which he cannot travel, an ocean which he cannot navigate. The birds of heaven are still his envy, and on the paths they tread he cannot follow." Since that was written practical flying machines have been invented, but in these, as in boats and ships, man has merely devised a machine which under his control can do laboriously and at great risk what the bird does naturally and easily. To birds man is indebted for his first lessons in navigating the water as well as for his ideas about airships. =Voices of birds.= With few exceptions the different kinds of animals have natural languages through which individuals of the same species can to some extent hold communication with each other, and which are partly intelligible to other creatures. In all mammals except man, and in most birds, the range of expression is very limited and the sound of the voice is disagreeable; but a great many species of birds have very pleasing notes, many have very beautiful natural songs, and some readily learn the songs of other species. Man learned melody from the song birds. There are also many species of birds that can imitate a great variety of sounds, and even learn to speak words and short sentences. Birds that learn to talk often show intelligence in their use of words. This is the more remarkable because the intelligence of birds is not of a high order, but is distinctly inferior to that of the common domesticated mammals.