It is not a little remarkable that such nearly allied birds as the great green woodpecker, or yaffle, and the two kinds of pied or spotted woodpeckers should present such remarkable diversity in the matter of colouring; the former being mainly olive-yellow with a red skull-cap in both sexes, while the other two are pied above and chiefly white below, with a red band at the back of the head of the cock alone. A third group is represented by the great black woodpecker, which is wholly sable, with an ivory-white beak. The difference in the matter of colouring between the green and the pied species is probably due to their different habits, the former being to a great extent a ground-bird, fond of frequenting lawns and meadows near woods for the purpose of digging up ants’ nests, while the other two are almost completely arboreal. In the dappled shade cast by the leaves--especially those of pines--on the trunks of trees, these pied birds are comparatively inconspicuous; while among grass of moderate length the green woodpecker is absolutely invisible. It is further noteworthy that the pied species have most of the under surface of the body white, whereas in the green woodpecker the same aspect is grey. To a bird walking on grass a white under surface would certainly be no protection; but in bright sunshine on the trunk of a tree such a surface would undoubtedly tend to render the bird inconspicuous, as it would counteract the effect of the dark shade thrown by the body, in precisely the same manner as in the case of white-bellied quadrupeds. Very curious is the fact that while, as already mentioned, the red band on the back of the pied species occurs in the adult only in the males, such a band is found in both sexes of the immature birds. This fact, coupled with the occurrence of a red head in both sexes of the green species, may be taken as an indication that red on the head was at one time a feature in all woodpeckers, but that for some reason it has been discarded in the females of the pied group. [Illustration] Woodpeckers present some of the finest examples of the adaptation of bodily structure to be met with in the whole animal kingdom. The strong, conical beak is, for example, admirably suited for chiselling out, by repeated blows of the head, rotten wood in insect-infected trees, or prising off loose pieces of bark in order that the bird may be able to get at the insects and other creatures lurking beneath. Then, again, the short legs and the curious structure of the feet, with two toes turned forwards and the other backwards, enable these birds to obtain the most effective foothold on smooth, slippery bark. Lest, however, the feet should prove ineffectual, the bird is aided in climbing by its tail, the feathers of which have unusually strong quills, the tips of these being bare and shiny. When this tail is pressed firmly against the bark, the stiff tips of the feathers afford very considerable support to the ascending bird.