442 



BIRD. 



ture their prey, though probably by the bill, which is 

 even wider in the gape than in the day-feeding spe- 

 cies ; but as the foot of some species at least is different, 

 they may use that in some instances in the capture of 

 their food. As they feed in the twilight, they must 

 feed in part on moths ; but that is also the time when 

 the larger coleopterous insects are on the wing ; and 

 these may require preparations for the stomach dif- 

 ferent from what are requisite in the case of the 

 naked winged insects, which form the principal food 

 of the swallow tribe. Still, in the form of their bo- 

 dies, in the texture, and even in the colouring of 

 their plumage, the nocturnal species differ from the 

 diurnal ones much in the same way that the owls 

 differ from the nocturnal birds of prey. 



There is even a similar distinction in respect of ha- 

 bitation. The diurnal species, like the diurnal birds of 

 prey, are all dwellers in open places, and they do not 

 nestle in trees : the nocturnal ones are copse or 

 woodland birds ; and though some of them are un- 

 derstood to nestle on the ground, the greater number 

 certainly nestle in trees and bushes. Yet further : 

 the diurnal ones have a harsh, sharp scream, which 

 though not exactly like the chirrup of hawks, has 

 some resemblance to it ; and they are in general 

 silent : the nocturnal ones, on the other hand, have 

 a more continued and stridulous cry; and in the 

 depths of the tropical forests, especially those of 

 America, they keep not only the common night, but 

 the sultry and otherwise silent night of the burning 

 noon, alive with their cries. 



Being all chiefly insect feeders, they are most 

 abundant in tropical climates ; and those which fre- 

 quent cold and temperate regions in the summer 

 always quit them before winter. The nocturnal 

 feeders, being birds of less firm feather and less 

 powerful wing, are by no means so migratory as the 

 diurnal ones. These last, as will be more particularly 

 shown when we come to give some account of wings, 

 are among the most exclusively wing-birds, and the 

 best winged in the whole class. Their food is in 

 smaller portions than that of any of the class, and 

 therefore they have more labour in the procuring of 

 it. Not only this, but many of them have much 

 labour in the construction of their nests, whether they 

 build them of mortar in the crevices of rocks or the 

 apertures or angles of buildings, or excavate them in 

 the banks ; and all of them have much to do in the 

 rearing of their broods, which, as is general with 

 birds that have very perfect feathers, continue a long 

 time in the nest. 



Their feet more resemble the syndactylic ones 

 than those of any other form, though these have the 

 toes united, and consequently a narrow foot, while the 

 birds under consideration have one remarkably broad 

 for its length ; but they both agree in this, that the 

 tarsi and toes are short, and they use the feet only for 

 resting or holding-on, and rarely if ever for progressive 

 motion. It is worthy of remark, as a striking instance 

 of agreement in two very important nabits, that though 

 the syndactylic birds build low, and the ones under 

 consideration build high (for even the sand-martins, or 

 bank-swallows, build in lofty banks and rarely in low 

 ones), they should both have covered nests, and both 

 feed their broods for a long period, as well as both 

 capture their prey on the wing. And the height at 

 which they build corresponds to that at which they 

 fly. The kingfishers and bee-eaters never have 

 their nesting-hole far above the surface of the water ; 



and their flight, when in search of food, is invariably 

 low. Of the swallow tribe, again, the sand-martin, 

 which builds in holes of the banks, is the bird of 

 lowest flight ; and the flight and position of the nest 

 rise together, till we come to the swift at the top of 

 the sky with the one, and the top of the rock or the 

 tower with the other. 



The feet correspond : the syndactylic foot, with 

 its soldered toes, forms a steady base for resting by 

 pressure upon a horizontal perch ; and the foot of the 

 swift, which is the opposite extreme in all the birds 

 which prey upon insects on the wing, is the best 

 adapted for holding-on upon the slightest inequalities 

 of an upright surface. Although, therefore, the feet 

 of all these birds are small, apparently feeble, and 

 not adapted for locomotion, there are no feet better 

 adapted to the habits of their owners. 



The general character in which the "crab" foot, or 

 foot of the Fissirostres, differs from that of all other birds, 

 is the equality of the three front toes, and the reversi- 

 bility of the back one. In most birds the middle toe 

 and the external front one, have each four phalanges 

 of bone, while the inner one has only three, and in 

 some of them, more particularly in the zygodactylic 

 birds, the feet of which remain yet to be noticed, the 

 outer toe is reversible backwards, so that it acts in 

 concert with the hind one and in opposition to the 

 other two. But in the crab foot, the back one is 

 reversible, so that all the four points can be turned 

 forward, or rather into the circumference of a circle, in 

 which the articulation of the toes with the tarsus forms 

 a fifth point. 



The feet with the reversible outer toe, have the 

 strongest action in opposite directions toward the 

 centre of the foot, and therefore they grasp firmly any 

 substance to which that is applied, although the tarsal 

 joint is straight, or even the bird suspended by the 

 leg at full length, or standing up with it in the same 

 position. But the greatest action of the crab foot is 

 concentrated upon the articulation of the tarsus in 

 one direction only, and that is the direction against 

 which the weight of the bird pulls. The tarsal, and 

 also the tibial joints are bent as far as they will bend, 

 when these birds hold on upon the upright surface of 

 a rock or wall, and the articulation of the toes is, at 

 the same time, in contact with that surface. There- 

 fore, if there is the least hold for the points of the 

 claws, the strain upon them is always such as to make 

 them retain that hold the more firmly the greater the 

 strain. 



Upon carefully examining these feet, of which the 

 most perfect is that of the swift, a figure of which will 

 be found in the sequel, it will be perceived that, 

 while the spread of the toes gives great stability to the 

 individual foot, the two are, when the bird hangs, or 

 adheres by means of them, so placed as that the 

 greatest resistance of each is in the direction of the 

 centre of gravity of the whole bird, so that the weight 

 actually draws them into close contact with the surface 

 of which they have hold. If in common mechanics, 

 it were required to find an instrument consisting of 

 hooks which should be the best for holding on against 

 a strain, parallel or nearly parallel, to the surface on 

 which it held on, the very best model would be the 

 foot of the swift. The pull upon the individual toes, 

 being toward the point of their general articulation, 

 draws them together so that they clutch the surface 

 upon which they have a hold ; and then the strain of 

 the bird's weight pulling upon each foot toward the 



