448 



BIRD 



rning foot all over, though one adapted to peculiar 

 places. The articulations of the tarsi have a rolling 

 motion, and those of the tibia also work outwards 

 when the feet act in swimming'. The looseness of 

 these two joints renders the bird incapable of moving 

 along the ground with the legs steady ; and this, more 

 than the mere form of the lobed toes, is the reason of 

 its being so bad a walker. 



But the feet are admirably fitted for aquatic motion. 

 They turn their thin edges nearly in the direction of 

 the resistance when they are drawn forward, but they 

 strike back with the full breadth of their webs, and 

 they can turn on the joints so as to give the stroke in 

 a variety of directions, and thus impel the body upon 

 any course which may be necessary to the bird in 

 following its prey in the water. The wings also come 

 into action in swimming, though more as points of 

 support, against which the legs act, than as propelling 

 organs. But the birds are altogether excellent swim- 

 mers, or rather coursers through the water with great 

 speed. They do not dabble like ducks, but plunge 

 freely into the water, and dash along, not by alternate 

 strokes of the feet, as in a common walking motion, 

 but by striking with both at once, as a frog does. It 

 is to enable them to perform this motion that the 

 wings are brought into action as well as the feet ; and 

 the same kind of motion could not be performed, and 

 the intended course kept, without the wings. This 

 is, in part at least, the reason why those aquatic birds, 

 which are incapable of flight, have the wings, though 

 destitute of flying feathers, much more produced and 

 capable of motion than those of the running birds 

 upon land. The different styles of motion through 

 the water, whether on the surface or below it, can, 

 however, be more briefly, as well as clearly explained, 

 when we come to consider the habits of those birds 

 which have entire webs on the feet, and range the 

 water in places where they are not liable to interrup- 

 tion from the stems of plants. 



Grebe. 



What may be considered as the normal swimming 

 foot consists of three toes directed to the front, and 

 one small one to the rear. There are always webs 

 of membrane between the front toes ; but in the spe- 

 cies which swim only and do not dive, there is no 

 web to the hind one. Divers have it marginated 

 with a small web ; those birds which Cuvier styles 

 totipalms, or entire feet, have the hind toe much 

 longer and stronger, and included in the same web 

 with the anterior ones, and they have the whole foot 

 turned in a particular direction, the purpose of which 

 will be explained afterwards ; and there are some 

 genera which are in the habit of tipping the surface 

 of the water with their feet, while their bodies are 



nearly or altogether supported by the wings in t/ie . 

 air, and these have the hind toe merely rudimental, and 

 the foot narrower in proportion than any of the others. 



In order clearly to understand the uses of the dif- 

 ferent forms of web feet, it is necessary to consider 

 the other actions of the bird to which the foot must 

 be subservient, or at least with which it must be in 

 accordance. These actions are of course either walk- 

 ing or flight; though they also admit of modification. 

 Thus, if the sea-bird alights only on solid surfaces, it 

 requires the feet to be somewhat different than if it 

 alighted on soft ones ; and if it dash at once down 

 on the water from high flight, it requires the feet to 

 be different from what would be more convenient if 

 it launched itself in a direction nearly parallel to the 

 surface. Also if the bird is in the habit of walking 

 much, it is necessary that the feet should retain a 

 considerable degree of that action of all the joints in 

 one plane, which we have already shown to be neces- 

 sary to the stability of a walking motion. If the bird 

 combines the three motions of walking, flying, and 

 swimming, in nearly equal perfection (and there are 

 many birds which do so combine them), it is necessary 

 that the feet should have a different structure ; and 

 if the motion is in the water only, the structure of the 

 feet requires still to be modified according as it is 

 more of a straight forward motion, or of an ascending 

 and descending one. 



There is, however, no bird with webbed feet which 

 can have that perfect adaptation of the feet for walk- 

 ing, which is possessed by ground birds upon land ; 

 because every bird with webbed feet is a swimmer ; 

 and though the swimming motion should be merely 

 a modification of the walking one, that is, by alternate 

 strokes of the two feet and never by both at once, 

 yet the articulation necessary for swimming is some- 

 what different from that which answers best for walk- 

 ing ; because the swimming feet must throw out a 

 little in order to clear the body, and this very throwing 

 out, which does not cause the body of the bird to 

 vibrate when it is supported by the water, does make 

 it vibrate when it is in the air. Sea birds as well as 

 sailors, may thus be known by the style of their 

 walking ; and though the causes be different, and the 

 one habit and the other structure, there is such a 

 resemblance between the rolling motion of the sea- 

 faring bird and the seafaring man, as alone would, to 

 careful observation, point them out as dwellers on the 

 same element. 



The web-footed birds which may be considered as 

 the least aquatic, at least among the flat-billed divi- 

 sion, are the geese, especially such of them as, like 

 the domesticated goose, graze the meadows, or 

 otherwise find the greatest part of their (boil upon 

 hind. These have most of the walking character in 

 their feet ; and when they swim they never use any 

 other than the walking motion, or that of paddling 

 alternately with the feet. 



But the body of the goose has a sort of boat, or 

 rather punt shape ; the sternum extends far back- 

 wards, and the tibiae are so articulated that the tarsal 

 joints project much farther from the sides than they 

 do in land birds. Thus, though the axis of the body 

 is borne in a position nearly horizontal, the advance 

 of the foot, wide apart as the feet are from each 

 other, does not carry the centre of gravity directly 

 forward, but swings it round ; so that, unless when 

 the motion is very slow and the bill in contact with 

 the ground, as is the case in feeding, the goose swinors 



