BIRD. 



443 



centre of gravity of the whole body, acting in two 

 lines, which, produced, pass a little outwards of the 

 average hold of the feet, makes the whole bird hold 

 on with the feet, as if it were grasping or embracing a 

 substance between them. 



The goat-suckers, being more woodland birds, have 

 the feet better adapted for perching on twigs or other 

 horizontal supports, than the swallows. They have a 

 short membrane, connecting all the anterior toes at 

 their bases, and the middle front toe is longer than 

 the others, and the claw pectinated. 



There have been various speculations about the 

 use of this pectinated claw, some of them more and 

 some less ingenious, but none of them very much to the 

 purpose. That it does not in any way assist the bird 

 in perching, is proved, not only by the fact that the 

 toe which has it does not close so completely on the 

 terminal phalanx as the other toes, but by the general 

 principle in nature that animals never hold on firmly 

 by means of teeth or pectinations in one continuous 

 inflexible member, in maintaining the stability of their 

 own position. A single adhering point to each move- 

 able part of the organisation, is that which makes the 

 hold the most secure, because it is the one which 

 allows the greatest play in all directions. Accord- 

 ingly, in the articulation of animals, whenever we find 

 a joint upon which there are to be cross motions, we 

 always find the socket, and the head which plays in 

 that socket, simple, while, in those which have motion 

 in one plane only, the head and socket are often both 

 double, and not unfrequently ridged in addition. 



The speculations which have been made with 

 regard to the use of this pectinated claw, are hardly 

 worthy of repeating. That of White is the most 

 sagacious, because most agreeable with the general 

 analogy of nature. He says merely, that it appears 

 to be to aid the bird "in taking its prey;" as the 

 heron holds its slippery prey with a pectinated toe, 

 and mergansers and several other birds hold theirs 

 by serrated mandibles. But it has been also said 

 that this toothed claw is used in trimming the vibrissse 

 or hairs at the sides of the gape, and also in clearing 

 the bird of troublesome insects. 



The hint thrown out by White is that of a naturalist 

 of one who seeks a new use for a new form of organ ; 

 the other conjectures hardly deserve that character, as 

 they point at no additional use for the additional 

 structure, inasmuch as there are birds with plain claws 

 which live on similar food, and are more infested by 

 nirinides than the goat-suckers. White's hint points 

 to inquiry, the other conjectures do the reverse they 

 lead from nature to art. 



The goat-suckers themselves, though otherwise 

 noisy enough, are silent upon this subject; and as the 

 mode of their preying, from the time at which it 

 usually takes place, is not very open to observation, 

 it is difficult to come at the truth by observation. But, 

 from the time, and, as far as it can be observed, the 

 manner of their feeding, the goat-suckers must feed 

 upon beetles and moths, insects on which there is a 

 considerable quantity of substance not available as 

 food ; and as, though there are some points of resem- 

 blance between goat-suckers and owls, no mention is 

 made of the former returning the elytra of beetles 

 and the wings of moths in castings, as the owls do 

 the indigestible parts of their prey, it is not impro- 

 bable, though certainly not proved, that they may use 

 the pectinated claw in removing the indigestible parts 

 before they swallow the rest. It avails little, how- 



ever, to speculate upon the use of a structure which 

 we have so limited means of observing ; but we may 

 observe in passing, that though Wilson saw these 

 birds scratching their heads with the pectinated claw, 

 that proves nothing as to the specific use of the pecti- 

 nation, because birds which have not their claws pec- 

 tinated, scratch themselves in a similar manner, and 

 this one cannot alter the form of its claws while per- 

 forming this operation. It must, to use a homely 

 phrase, scratch itself with such claws as it has ; and 

 as no bird appears to have claws specially formed for 

 this secondary purpose, the analogy is against such 

 being the principal intention of this toothing of the 

 claw of these birds. 



Upon looking back at the figure of the goat-sucker's 

 bill, it will be perceived to be very Jissirostral ; and 

 that, though it might be capable of transfixing a tough 

 coated insect with the sharp points of the mandibles, 

 it cannot bruise any thing between the tomia. The 

 sharp points are obviously for capture ; for though 

 there are vibrissae along the edge of the upper man- 

 dible, there are similar hairs at the junction of the 

 upper mandible with the front, where they cannot by 

 any possibility assist in the capture of the prey, and 

 there are also similar bristles at the base of the bill in 

 many birds which do not catch insects or any thing 

 else with the bill while they fly open-mouthed ; so 

 that it is at least probable that w hile the coleopterous 

 insect is seized and held between the hard and sharp 

 points of the mandibles, the parts that are unfit for 

 food are stripped oft' by the pectinated claw of the 

 foot, which is certainly borne less bended, or in 

 advance of the other claws. The following figure 

 is an accurate representation of the foot of this bird. 



Goat-sucker. 



The swallow-tribe all have the foot less firm as a 

 perching foot, that is, less connected by membrane 

 between the bases of the toes, than the goat suckers ; 

 and the articulations of the toes with the tarsi have 

 more of the ball and socket form, and consequently 

 admit of more motion. This motion increases, and 

 the tarsus and toes become shorter, and the claws 

 more crooked, from the lowest building swallows to 

 the swifts, which have the most perfect crab foot, that 

 is, the one best adapted for individually holding-on 

 upon slight inequalities of a perpendicular surface, and 

 at the same time the least fitted for perching on a twig, 

 or walking upon the ground, for which last office they 

 are not at all fitted, and the birds are consequently 

 quite helpless there. 



The feet, admirably formed as they are, are not the 

 only organs by means of which these birds maintain 

 their perch upon perpendicular surfaces. The flying 

 feathers of their wings and tails are remarkably stiff 

 in the shafts and firm in the webs ; and though they 

 cannot, of course, take hold with their feathers, unless 

 when they, as it were, embrace a projection, yet the 

 pressure both of the wings and tail assists in tighten- 

 ing the hold taken with the claws ; so that, even 

 though the surface to which they cling overhangs, these 



