No bird has ever been found with more than four toes; and four seem to be ample for all purposes. A fifth toe for a bird would be as useless as a fifth wheel on a wagon. Quite a number of species have only three toes, most of them among the walkers and waders, and none, I believe, among the true perchers. Take the plovers and sanderlings, for example, which spend most of their time, when not on the wing, in running about on the ground, especially along the seashore or the banks of streams and lakes, and seldom, if ever, sit on a perch--in their case a fourth toe would be worse than a superfluous appendage; it would be an encumbrance, dragging along in the mud and mire. In these species it is the hind toe that is lacking, their three digits all being in front, where they are of the greatest service. There is another class of birds that have hind toes, though very much reduced because their owners do not perch, but scuttle about on the beach. This class includes the little spotted sandpipers which you often see running or flying along the shores of a river or lake. Curious to tell, several species of woodpeckers are tridactyl--that is, three-toed--and still more curious is the fact that in their case the true hind toe is lacking, while the outer front toe is bent backward, or "reversed," as it is called, and is thus made to do service for a hind toe. The other species of woodpeckers have four toes, two in front and two behind, the outer one of the latter pair being a reversed digit. Why some of the woodpeckers should have four toes and others only three is an unsolved enigma, and is especially puzzling in view of the fact that the four-toed kinds do not seem to possess any advantage over their cousins. The tridactyl species are as expert climbers as any members of the family, and are extremely hardy birds, too, some of them dwelling the year round in cold northern climates, where the food question must often be a serious one. [Illustration: Spotted Sandpiper, or "Peet-weet"] Here is still another conundrum for the bird student: Why do the four-toed woodpeckers have two hind digits, despite the fact that they always clamber upward when they take their promenades on the boles and branches of the trees, whereas the agile little nuthatch, which glides upward or downward, as the impulse moves him, has only one rear toe and three in front, like the true perchers? Nor is it less puzzling that the cuckoos, which are perching birds, should have two toes in front and two behind. Then, there is the little brown creeper which never perches and is forever creeping, creeping, upward, upward--save, of course, when it takes to wing--and yet its toes are arranged in the normal percher style, the hind digit having an especially long, curved claw. It is a mistake to suppose that all the problems of the bird world have been solved.