Birds have also another use for their wings. They are a strong weapon to defend themselves, or to fight others. A large bird can give a severe blow with his wing, and when pigeons fight, it is said they hold up one wing to protect themselves while they strike at the enemy with the other. Sometimes wings serve as musical instruments. Woodcocks make whistling sounds with their wings as they fly, and mourning doves softly murmuring ones. Ruffed grouse produce with theirs a rolling drum-like effect, and others rattle theirs like castanets. [Illustration: FIG. 13. Tail of Ruffed Grouse.] If wings are not used, they slowly get to be smaller and weaker, each generation having them more and more useless, till after a while they are of no use whatever, and the birds cannot fly at all. This has happened, it is supposed, to the ostrich family and to some birds living in the sea. [Illustration: BROWN THRASHER] [Illustration: FIG. 14. Tail of Vireo.] The tail of a bird is formed of an equal number of feathers in pairs, most often twelve. When spread they are the shape of a fan (Fig. 13), and when closed they lie over each other with the middle pair on top. [Illustration: FIG. 15. Tail of Swallow-tailed Kite.] The tail feathers are not always of the same length, and that makes a difference in the shape of the end. Sometimes they are even (like Fig. 14), when the tail is said to be "square." Sometimes the middle feathers are a little longer than the outside ones, and then it is "rounded" or "pointed." If the outside feathers are longest, the tail is "forked" (Fig. 15). The feathers of the tail are called _rectrices_, or "rudders," because they are supposed to be used to steer, or direct the bird's course in flying. But the tail is used also as a brake to check the speed in alighting. The tail is used more than any other organ to express the emotions. Some birds, like the catbird and thrasher, keep it moving nearly all the time, jerking it this way and that, and tossing it upward. [Illustration: FIG. 16. Tail of Sapsucker.] In woodpeckers and swifts the tail feathers are not soft at the end like others, but the stems or shafts project beyond the feathery part, and are stiff like the tail of a sapsucker (Fig. 16) or sharp like this of the chimney swift (Fig. 17). These birds use the tail as a prop to hold them against the tree trunk or chimney wall, and to help them in climbing. [Illustration: FIG. 17. Swift Tail.] Tail feathers are not so strongly rooted as wing feathers, and are easily pulled out. Sometimes, when a man or boy tries to catch a bird by the tail, the bird will escape, leaving the tail in his hand. XXVI HIS DRESS A BIRD'S whole dress is made of feathers, but the feathers are not all alike. There are, indeed, several kinds of feathers, and four of them are found on every bird. There are flight feathers, clothing feathers, downy feathers, thread feathers, and powder-down feathers.