444 



BIRD. 



birds can stick to it very firmly. The annexed figure 

 of the swift's foot will show the structure. 



Swift. 



Anisodactylic feet. As "crab" feet, more espe- 

 cially in that form which they have in the swallows 

 and swifts, are the best fitted for holding-on while the 

 body generally of the bird is steady, upon an upright 



the front, and one behind, the same as in an ordinary 

 walking foot, only the middle and external toe have 

 a union at their bases which appears to be something 

 more than a merely membranous connexion, like that 

 of many of the insectivorous birds. It i?, however, 

 in these two toes, their union and the peculiar mode 

 of their articulation, that the whole peculiarity of the 

 foot, that to which it owes its wonderful climbing 

 power, consists. These two toes form a sort of second 

 foot, which can act upon its own articulation in 

 opposition to the two remaining ones, that is, to the 

 interior front one and the back ; and the joint by 

 which the two are articulated on the tarsvis admits of 

 so much and such varied motion, that the one part of 

 the foot can act in any direction against the other. 

 Owing to this, the action of the foot is universal as to . 

 direction, parallel to the axis of the body, or almost 

 at any angle to it. Thus the birds can run upon the 

 bark of trees in any direction, holding on upon the 



or an overhanging surface, so feet of the form now to 

 be described are the best adapted for motion upon such 

 surfaces. Birds which have them are all, generally 

 speaking, tree birds, or at all events woodland birds. 

 But, like the birds with feet of the immediately pre- 

 ceding form, they admit of subdivision into those 

 which feed more exclusively upon the bark of trees, 

 and those which feed more exclusively on the wing. 

 They are the same or nearly the same as the tenui- 

 rostres of Cuvier. 



But, although that illustrious naturalist has taken 

 the form of the bill as their distinguishing character 

 as a tribe, and though their wings, which are in 

 general very powerful, might also be made both a 

 general character of the whole and a means of divid- 

 ing them into different sections, yet the foot is 

 unquestionably their most prominent and remarkable 

 character. Their feet are entitled to the preeminence, 

 not because they are, as in those birds which cannot 

 fly, the only active organs except the bill, and not 

 because they are efficient organs of locomotion upon 

 the ground ; for, generally speaking, these birds are 

 not only very bad walkers, but they are seldom, if 

 ever, found upon horizontal surfaces. Indeed they 

 are not at all adapted for such surfaces, and those of 

 them which have their own peculiar feet in the 

 greatest perfection, are as helpless upon the ground 

 as the swifts. 



But their feet can adhere to, and, with the assist- 

 ance of the wings, move along any surface, be its 

 form or position what it may. Those which are bark 

 birds can run along the boles of trees, upwards, down- 

 wards, or round by a circular motion ; and others, 

 again, can hang by the feet to the petals of flowers, 

 while the bill reaches the bottom of the nectary, and 

 sips the sweet juice which accumulates there, as is 

 well exemplified in the humming-birds and the nectar- 

 suckers. 



The structure of foot, by means of which this 

 singular command of all manner of surfaces is ob- 

 tained, is apparently a very simple one ; and if we 

 had not so many instances in nature of the cleverest 

 action performed by organs apparently the most 

 simple, we should never imagine that the apparently 

 small difference of structure that there is between the 

 feet of these birds, and the feet of birds which cannot 

 climb at all, could be sufficient to effect so great a 

 difference of action. The ordinary appearance of 

 the foot, when in a state of repose, is three toes to 



irregularities of the bark with each foot, and at the 

 same time embracing the convexity with both. This 

 can be easily understood, when it is considered that 

 both the recurved toes of each foot press inward 

 towards the centre of the body ; and this action of 

 the two feet in opposition to each other converts 

 them into a sort of one clutching foot, which acts 

 without any direct exertion of muscles, and therefore 

 holds on for a long time without being in the least 

 fatigued. 



Anisodactylic feet are thus formed for concentrating 

 their action upon the centre of the body, without any 

 reference to the direction in which the weight presses, 

 just in the same way as the crab feet of swifts con- 

 centrate their action so as to support the centre of 

 gravity in the most effective manner. 



The best native example which we have of a bird 

 with this clever species of foot is the creeper, or the 

 common tree creeper (Certhia familiaris). It is a very 

 small bird, the smallest that we have in these islands, 

 with the exception of the crested wrens, which, like 

 it, are tree birds, and very clever on their feet, al- 

 though they are perchers and not climbers. It is a 

 resident bird in Britain, and by no means a rare one, 

 and its motions upon the trees are well worthy of 

 observation. The direction in which it runs (for its 

 motions, though aided by the wings, have more the 

 appearance of running than of any thing else) appears 

 to be of little consequence. Upwards or downwards 

 upon the bole of the tree, outwards or inwards upon 

 the branches, with the back or the belly uppermost, 

 appear to be all the same to it ; but, from the celerity 

 of its motion, and its diminitive size, it is not easily 

 seen. The nuthatch, of whose foot a figure is an- 

 nexed, is the only other species resident in Britain, 

 though the hoopoe, which is a very handsome bird, 

 with feet nearly of the same character, appears not 

 unfrequently as a summer visitant. 



Nuthatch 



The hoopoe differs, however, in many of its habits, 

 for it is more of a water bird than a frequenter of 



