BIRD. 



trees, and its bill is incapable of performing labours so 

 severe as those of the nuthatch, or even of the creeper; 

 for though the last is an insectivorous bird, and not 

 able to hew the shells of nuts to pieces like the 

 nuthatch, it has to dig its food out of the crevices of 

 trees. 



The different substances upon which birds with feet 

 of this structure feed, is strong evidence against the 

 classification of them by the form of the bill ; because, 

 if such a classification is to mean any thing, it should 

 mean similarity both of food and of manner of feed- 

 ing. But though most, if not all, of the birds which 

 have feet of the structure under consideration have 

 slender bills, their food is very varied, and the only 

 habit in which they all agree is that of being able not 

 only to adhere by the feet, but to move about upon 

 almost any form of surface, or in almost any position. 



Considered as mechanical structures, acting in con- 

 cert with the whole organisation of the birds, these 

 are, perhaps, the most extraordinary of all the varied 

 forms which birds possess. They act in concert with 

 the whole structure of the birds ; and thus, though 

 the mechanical contrivance that appears in them, 

 taken singly, is not very striking, yet it becomes 

 remarkably so when we consider bird and foot jointly, 

 and notice how the varying pressures which the weight 

 of the body gives in all the numerous positions which 

 it can assume, contribute almost equally to render 

 more firm and sure the hold taken by the feet. One 

 of the greatest beauties in those displays of the 

 mechanics of nature, and one of the greatest superior- 

 ities which they evince over all that human ingenuity 

 can contrive, is the wonderful simplicity with which 

 what, to us, seems the most difficult of all purposes, is 

 accomplished. When we have a mechanical difficulty 

 to overcome, we complicate part upon part, and often 

 defeat our object, because the artificial clogs and hin- 

 derances which we thus produce, are greater than the 

 difficulty which we sought to overcome ; and thus we 

 produce a negative effect, instead of a positive one, 

 and are further from our object at the end of our 

 labour than at the beginning ; but when we examine 

 nature, we find that the very difficulty itself becomes 

 one of the most effective means by which it is over- 

 come, as in the case of these singularly footed birds, 

 the weight which the feet have to sustain is actually 

 converted into a means of sit ! lining it. 



Scffii.wrin/ or climbing feet. The principal object to 

 be accomplished by these feet, is not simple adherence 

 to an upright overhanging surface, as in the case of the 

 swallows and swifts, or progressive motion along the 

 boles and branches of trees, as in that of the unixodctc- 

 ti/li. It is, in the more perfect specimens, motion 

 from branch to branch, and in the others stability on 

 the boles of trees, with the body in an upright position. 

 Feet which accomplish these purposes are all zygo- 

 dactyllc, or yoke-toed, that is, they have the outer toe 

 very readily reversible, so that the foot prvsenis two 

 toes to the front and two to the rear, both nearly of 

 equal power; and where there is a diifcreiit function 

 to be performed, that is done chiefly by modified arti- 

 culations of the other parts of the foot and leg. 



The extremes of this kind of foot are perhaps those 

 which are found in the woodpeckers and the parrots. 

 The woodpeckers an; trunk birds, and when upon 

 tree-% they are insectivorous ; the parrots, on the 

 other h:md, find no food upon boles or large branches, 

 but subsist chiefly upon fruits, and ramble about 

 among the smaller twigs and sprays iu quest of them. 



Thus, though both are climbers, they climb so very 

 differently, that when they are described as birds of 

 the same habit, a person who knew only one of them 

 would be apt to form a very inaccurate notion of the 

 other. The woodpecker cannot climb as the parrot 

 climbs, neither can the parrot climb as the woodpecker. 

 The woodpecker is a bark bird ; and though it can 

 adhere to the bark of a tree, so as to leave its bill, 

 neck, and head free for other action, it cannot adhere 

 in an inverted position; and unless the crevices of the 

 bark are particularly favourable for its claws, it must 

 use the stiff feathers of the tail as a prop. Whether 

 it requires to do this or not, it must always bend the 

 joints of the leg so as to make the claws hold with the 

 requisite firmness. Its foot is in fact a sort of double 

 crab foot, the two parts of which hold on in opposite 

 directions. It is by the claws which are turned to the 

 front that the weight is suspended ; and those which 

 arc turned to the rear, have their principal action in 

 tightening the hold of these. Then the line of the 

 body and tail acts in the same manner as a diagonal 

 strut under a beam ; and every one knows how small 

 a hold in the wall will support a beam if such a strut 

 is applied to it. The painter's scaffold, used in clean- 

 ing or repairing windows high above the ground, 

 which one sees every day in the streets, acts upon a 

 principle nearly similar to that of the woodpecker. 

 The following is the position of the foot when in the 

 act of holding on. 



Woodpecker. 



The foot of this bird has other functions to perform 

 besides keeping its hold on the bark of trees. It is an 

 insect-feeder, and at certain seasons these are much 

 more abundant on the ground between the trees, than 

 in the trees themselves. The seasons when the lame 

 are in the bark or the decaying wood, and when the 

 mature insects resort thitherto deposit their eggs, are 

 those at which the woodpecker is most active upon 

 the bark ; but there is an intermediate time during 

 which the bird is on the ground picking up beetles, 

 and especially ants, which last are gregarious or social 

 insects, and great frequenters of forests. In temperate 

 countries, woodpeckers answer, at those times, nearly 

 the same purpose which ant-eaters answer in more 

 tropical climates. 



This habit in the woodpecker requires a command 

 of itself upon the ground for which the parrot has no 

 necessity; and which, indeed, would be incompatible 

 with perfection in that peculiar structure of foot which 

 the parrot requires. Accordingly, although the wood- 

 pecker docs not require to be a runner, inasmuch as 

 food for it is very abundant at those times when it is 

 on the ground, yet it stands well on its legs, and is a 

 tolerable walker ; while on a level surface the parrot 

 makes sadly shambling work of it much like that of 

 a climbing ape, and it very soon gets fatigued, which 

 the woodpecker does not. 



Though three toes before and one behind, all free 

 at their bases, be the normal foot for a continued 

 slow pace on the ground, yet the form of the toes is 

 not that which constitutes a walking foot. The rela- 

 tive lengths of the bones, and more especially the 



