English sparrows can be kept out of wren houses by making the opening too small for the bigger bird. An auger hole one inch in diameter will be large enough for wrens, but too small for sparrows. A sparrow has sometimes been seen trying to get into one of these wren boxes, and very droll he looks, when he sticks his head in, and struggles and kicks violently to push himself in. I found a pair of house wrens in Colorado one summer. The singer spent most of his time scrambling about a pile of brush, apparently trying to make me think that was where he lived. But I was sure he had a mate and a nest somewhere else, and I kept watch for them. One day I happened to see a little brown bird fly up under the eaves of a summer cottage not much bigger than a tent. On looking closely, I found that there were openings under the eaves. The birds had taken one of these for a door, and built a nest inside, in the box frame over a window. After that I looked at them through another window. Everything went well till the wrenlings left the nest and began to fly around. Then they seemed to lose their wits, or not to mind their parents. They flew wildly about in the cottage, bumping against the glass, and seeming not able to find the door to get out. I had not the key to open the big door, so I could not help them in their trouble. And the old birds were so frantic when I looked in at the window, while they were trying to get their family out, that I went away and left them. In an hour or two I went back, and found everything quiet, and the wren babies all out on the trees. FOOTNOTE: [6] See Appendix, 5. VII THE CAVE-DWELLING FAMILY SECOND BRANCH THE second branch of this family is very different from the first; it is composed of mockingbirds, catbirds, and thrashers. These birds were once placed with the thrushes, and by habits and manners they seem to belong there. But, as I told you, families in the bird world are made by structure,--by the way the bird is made. These birds have scales on the leg, and some other things like the wrens, so now they belong to the cave-dwelling family, though they never dwell in caves. They live in shrubbery and low trees. They are larger than any wren, but they are like those birds in being good singers and dressed in plain colors. Wherever they are placed in the books, they are interesting and delightful birds to know. The most famous of this branch is the MOCKINGBIRD, found in the Southern States and California. He is a beautiful and graceful fellow in gray, with large white patches in his wings. The nest of the mockingbird is a rather rough affair, built in a low tree or a bush. One that I saw was in a tree about as high as an apple-tree. The bird gets his food on the ground, and has a curious habit of lifting his wings as he is about to attack a beetle.