Page:Bird-lore Vol 08.djvu/77

 Legs and Feet of Birds 53 birds have such elongated claws on their rear toes? Perhaps the fact that these birds live almost entirely on the ground may have something to do with this peculiarity. Any one who has kept a cage of small birds will have learned the fact that the claws of birds are continually growing. In a remarkably short time their claws become long and curved ; and in a neglected aviary I have seen birds prisoners on their own perch, unable to untwist their claws from it. When wild, birds wear down these claws by constant rubbing, and if given plenty of rough bark and wood in their cages, their claws will remain of normal length. Some species of swifts have all four toes pointing forward, forming a four-tined grapple by which they hang themselves up in their hollow nest- ing trees. Whippoorwills have a curious comb, or pecten, along the edge of the middle claw, which is perhaps of use in cleaning the long bristles about their mouths, or in arranging their very delicate, soft plu- mage. Kingfishers make so little use of their feet, that not only are the toes small and weak, but two of the front ones have grown together for over half their length. Perhaps the most interesting condition of toe structure is found among Wood- peckers, Parrots, Cuckoos and Owls. In these groups we find a similar plan of gen- eral arrangement, — two toes in front and two behind. With few exceptions it is the great, or first toe and the fourth, or outer toe which are reversed. This arrangement is known as yoke -toed, or zygodactyl. We have seen that in perching birds the arrangement is three toes in front and one behind; and now, turning to the Woodpeckers, we are impressed with the wise provision made by Nature for these climbing birds, — their toes spread out so that they point almost to the four points of the compass, thus forming an incomparable grapple or vise, which makes a vertical position as safe for a Woodpecker as a hori- zontal one for a percher. Woodpeckers, the world over, have feet and toes which are remarkably alike; but in Canada and the more northern parts of our own country there are two Woodpeckers which are almost unique among the birds of this order in possessing but three toes. For some reason, as yet unknown, their first or great toe, which in all other Woodpeckers points backward, has vanished, leaving no external trace, and the outer toe is reversed to take its place. In such a fashion does Nature occasionally upset our hard -worked -out theories, leaving us confused and baffled before her inexplicable surprises. FOOT OF CHUCK-WILL'S-VVIDOW, SHOWING COMB ON TOE-NAIL