You will read in books about birds, that a certain warbler says "Witches here," or that the white-throated sparrow says "Old Sam Peabody," and other birds say still different things. The writer means that the words remind one of the bird's notes, and so it is useful to know them, because it helps you to know the bird when you hear him.
I have many times seen birds act as if they were talking to each other. You can often see the city sparrows do so.
There is nothing in a bird's ways that we like so well as his singing. And in all the many species of birds in the world, no two sing exactly alike, so far as I can find out. You may always know a bird by his song. A robin does not sing like a thrush or a catbird. And what is more, not one of the sounds he utters is like those made by any other bird. If you know him well, whatever noise he makes, you will know at once that it is a robin.
But there is something still more curious about it. No robin sings exactly like another robin. When you come to know one bird well, you can tell his song from any other bird's. Of course, all robins sing enough alike for one to know that it is a robin song, but if you listen closely, you will see that it is really different from all others.
Persons who have kept birds in cages have noticed the same thing.
There is still another point to know. One bird does not always sing the same song. I have heard a song sparrow sing five or six different songs, standing all the time in plain sight on a fence. In the same way I have known a meadowlark to make six changes in his few notes.
Besides their own natural songs, many birds like to copy the notes of others. Our mockingbird is very fond of learning new things, and he does not always choose songs either.
He will imitate the noise of filing a saw, or the pop of a cork, as readily as the sweetest song. I have heard one sing the canary's song better than the canary himself.
