In connection with learning the different kinds of birds in a locality, together with their names, observations should be made, and notes of them recorded, on their habits and on the relation or adaptation of structure and habit to the life of the bird. Some of the special subjects for such observation are pointed out in the following paragraphs. A suggestive book, treating of the adaptive structure and the life of birds is Baskett's "The Story of the Birds." =Bills and feet.=--The interesting adaptation of structure to special use is admirably shown in the varying character of the bills and feet of birds. The various feeding habits and uses of the feet of different birds are readily observed, and the accompanying modification of bills and feet can be readily seen in birds either freshly killed or preserved as "bird-skins." Such skins may be made as directed on p. 467, or may be bought cheaply of taxidermists. A set of such skins, properly named, will be of great help in studying birds, and should be in the high-school collection. In some cases the general structure of feet and bills may be seen in the live birds by the use of an opera-glass. The characters of bills and feet are much used in the classification of birds, so that any knowledge of them gained primarily in the study of adaptations will have a secondary use in classification work. [Illustration: FIG. 143.--Russet-backed thrush, _Turdus ustulatus_. (Photograph from life by Eliz. and Jos. Grinnell.)] Note the foot of the robin, bluebird, catbird, wrens, warblers and other passerine or perching birds. It has three unwebbed toes in front, and a long hind toe perfectly opposable to the middle front one. This is the _perching_ foot. Note the so-called _zygodactyl_ foot of the woodpecker, with two toes projecting in front and partly yoked together, and two similarly yoked projecting behind. Note the webbed swimming foot of the aquatic birds; note the different degrees of webbing, from the _totipalmate_, where all four toes are completely webbed, _palmate_, where the three front toes only are bound together but the web runs out to the claws, to the _semi-palmate_, where the web runs out only about half way. Note the _lobate_ foot of the coots and phalaropes. Note the long slender wading legs of the sandpipers, snipe and other shore birds; the short heavy strong leg of the divers; the small weak leg of the swifts and humming-birds, almost always on the wing; the stout heavily nailed foot of the scratchers, as the hens, grouse, and turkeys; and the strong grasping talons, with their sharp long curving nails, of the hawks and owls and other birds of prey. In all these cases the fitness of the structure of the foot to the special habits of the bird is apparent.