BIRD. 



437 



by any naturalist who has treated of the feathered 

 tribes, ami also because we cannot with propriety intro- 

 duce their, into the particular account of any one 

 group or genus. They are briefly as follows : 



In the first place, the flat-billed birds, which find 

 their food at the bottom of the waters, have a very 

 striking analogy to the ground-birds that feed upon 

 land. Their flesh resembles the flesh of the grazing 

 mammalia, the more exclusively that they are vege- 

 table in their feeding, as in the case of the goose. 

 The ducks, which are omnivorous, have more the 

 flavour of poultry; and those which feed chiefly upon 

 mollusca, ground worms, and the spawn of fishes, 

 partake of the racy flavour of the land "gut-birds." 

 As they become more and more feeders upon fish, 

 they acquire more and more of the rank flavour ; and 

 the auks and other species which scarcely fly at all, 

 abound very much in oil. 



It is not a little singular that it is in the two corre- 

 sponding divisions of the sea and land birds, where we 

 meet with the species which are confined to one 

 element, and lose the grand characteristic of birds, 

 the wings, though they retain the general structure 

 and habits. The feathery covering is never wanting; 

 but in the extreme of ground birds upon land it has 

 much of the loose character of fur, while in the 

 extreme of the divers at sea, it is so close and com- 

 pact, that it has the appearance of one unbroken 

 covering, in which the individual feathers cannot be 

 distinguished. 



In the second place, those sea-birds, from the 

 marsh-breeding-gulls, or rather from the skuas, to the 

 terns, which boar a resemblance to the omnivora 

 among land-birds, are all, like these, good walkers, 

 quite as much at home upon the shores as they are 

 in the water or on the wing. This coincidence is the 

 more worthy of being borne in mind, that the 

 omnivorous birds are the only land ones which have 

 the two motions of walking and flying nearly equal 

 throughout the group ; and the corresponding group 

 of sea birds are the only ones which possess all the 

 three in equal perfection. 



Those birds which are the most general in their 

 feeding, are thus, also, the best fitted for reaching 

 their food in all sorts of places ; and not only this, 

 but they are the most generally distributed over the 

 globe, and resemble each other the most in all lati- 

 tudes. They are not the most numerous at particular 

 spots, though many of them assemble in great num- 

 bers at their breeding places. 



Between the air-feeding birds of the sea and the 

 'Vand, there is not the same perfect correspondence, 

 because there are among sea-birds no literal preyers 

 on the wing. There cannot be, for there is no food for 

 them, as the sea sends up into the air nothing upon 

 which a bird can subsist. The level of the waters is 

 the upper level of sea-food, unless in that portion ol 

 the food of those birds which is cast up by the waves. 

 But still there is a correspondence : they keep more 

 to their own element, and have their motion more fitted 

 for that, and less for the other two. Those sea-birds 

 which seem never to tire on the wing, are all imper- 

 fect walkers ; and though they float very buoyantly, 

 much more so indeed than those which are habitually 

 on the water, they are by no means so expert at 

 swimming. 



The most perfect flight and the most expert action 

 in the water are indeed incompatible with each other. 

 Birds which float about the livelong day require to 



je light for their bulk and extent of feathers, though 

 t IK avier bird succeeds better on a momentary rush ; 

 and the air birds which fly over the sea in search of 

 heir food do not require the same rapid motion as 

 jirds which fly in the air in pursuit of their food. But 

 a bird which is to have the most perfect command of 

 itself in the water, and be able to dive, and come up, 

 and drive along, sometimes wholly immersed, and 

 sometimes not, must, in order to perform its various 

 evolutions with as little muscular exertion as possible, 

 be of nearly the same specific gravity as sea water. 



It is absurd to say, as has sometimes been said, 

 that if birds have not a certain specific gravity they 

 cannot dive. The lightest substance, the lightest 

 as, can be forced under water by mechanical means, 

 and it is rather too much for us to suppose that we 

 can beat nature with our small second-hand mechanics. 

 But still it accords with general principles that that 

 which is the most nearly of the same specific gravity 

 as water, should admit of motion in all directions in 

 water with the least effort. This principle is trace- 

 able in aquatic birds ; for we find that the diving 

 ducks ride deeper in the water than the swimming 

 ducks, and the divers still deeper than they. 



Then there is the difference of form. The motions 

 which a diving bird performs in the water are so 

 varied that to determine the solid of least resistance 

 with regard to them all would be no easy matter. 

 But the boat which rows fastest, keeps course or 

 turns most easily, and lives in the roughest water, is 

 an approximation. That boat is one with the two 

 ends nearly equal, and of an average length. If too 

 short it " yaws like a tub," and will not keep course, 

 and if too long it turns wide. This is the form which 

 we find in those birds \\ hich have the most complete 

 command of the water. If they go on long courses 

 after fish, as is the case with the divers, they have the 

 body elongated ; and if they search about among the 

 rocks after mollusca and Crustacea, as is the case with 

 the puffin, they have it shorter. These last, by the 

 way, have the most powerful bruising bills of any of 

 the sea birds, just as the parrots have among the land 

 ones ; and it is curious to notice that there is a con- 

 siderable resemblance both in the appearance and in 

 the harsh screaming voice, so much so that the puffin 

 is sometimes called the sea-parrot. 



The boat shape of those birds, and the backward 

 position of the feet, with the weight of muscles neces- 

 sary for moving them, are incompatible with that 

 structure which answers best for powerful flight. That, 

 in order to be performed with the least effort, requires 

 the weight to be concentrated near the centre ol 

 motion in the wings. 



From these few observations, short and imperfect 

 as they are, it will perhaps be seen that there might 

 be a much more natural arrangement of birds founded 

 upon their principal habit than any which can be 

 founded on a particular part of their organisation. 

 Air birds, ground birds, and those intermediate races 

 which have the double motion in the case of land 

 birds, and the triple one in the case of sea birds, 

 might form the leading divisions. 



An air bird is one which uses the wing in immedi- 

 ately obtaining its food ; thus an eagle which stoops 

 to ground prey, a falcon which captures in the air 

 but eats on the ground, a gannet which plunges in the 

 water, and a swift or other insect fe-xler which feeds 

 on the wing without stopping, are all equally air birds, 

 arming at their food by the action of the wings in 



