FORM AND HABIT: THE TAIL. 25 have formidable spurs on their wings, which they are supposed to use in combat. The Tail. — Except when sexually developed, the shape of the tail is largely governed by the character of its owner's flight. Male Lyre-birds, Pheasants, Fowls, Hummingbirds, and many others furnish well-marked instances of the tail as a sexual character. Indeed, as the least important to the bird of the four external organs we are speaking of, the tail is more often sexually modified than any of the other three. The main office of the tail, however, is mechanical, to act as a rudder in flight and a " balancer " when perch- ing. Short-tailed birds generally fly in a straight course, and can not make sharp turns, while long-tailed birds can pursue a most erratic course, with marvelous ease and grace. The Grebes are practically tailless, and their flight is comparatively direct, but the Swallow-tailed Kite, with a tail a foot or more in length, can dash to right or left at the most abrupt angle. Among tree-creeping birds, which always climb up- ward, the tail is used as a brace or prop. This character, as has been said, is possessed by all Woodpeckers, by the quite different Woodhewers of South America, the Brown Creep- ers of temperate regions, and other birds (see Figs. 3 and 4). The two middle feathers in the tail of the Motmot, of the American tropics, end in a racket-shaped disk, the result of a unique habit. Similarly shaped feathers are found in the tails of some Hummingbirds and Old World Kingfishers, but in the Motmot this peculiar shape is due to a self-inflicted mutilation. The newly grown feathers, as shown in the accompanying figure, lack the terminal disk, but as soon as they are grown, the birds begin to pick at the barbs, and in a short time the shaft is de- nuded, in some species for the space of an inch, in others for as much as two inches.
