418 



BIRD. 



and stiffer than if the same quantity of horny matter 

 were equally distributed over the entire surface, often 

 give a quadrangular form to the section of the bill. 

 Bills which dig- into the bark or wood of trees, into 

 hard ground, or into other substances which offer 

 considerable resistance, are also provided with ridges. 

 This is the case with even those very small bills which 

 pick minute insects and larvae from the crevices of 

 bark, and thus such bills are often much stronger than 

 others, which, having a larger diameter, look more 

 formidable. All bills, too, which are used in striking 

 or thrusting with the point, are fortified by ridges, 

 and such bills never have so much curvature in their 

 general shape, as that the line joining the tip and the 

 centre of the base falls anywhere without, or even 

 near the surface of the bill. If they act both by 

 thrusting and by cutting between the edges, the 

 ridge of both mandibles is usually a little arched, 

 the arch in that part being the form which, with an 

 equal quantity of matter, enables the mandibles to 

 compress any substance between them with the 

 greatest force. But if the thrust be the only powerful 

 action of the bill, the ridges of the mandibles are 

 generally concave, with the curvature increasing 

 towards the base of the bill, something in the same 

 manner as that of the bole of a tree increases near 

 the surface of the ground. This is the outline of 

 greatest stability, and as such it is adapted for 

 lighthouses and other structures which are much 

 exposed to strains from the action of the wind or the 

 waves. In those bills, this enlargement toward the 

 base, over which the tip is generally situated in a 

 perpendicular line, causes the bill to strike with more 

 precision, and also with much less jarring of the 

 cartilaginous substance by which it is united to the 

 bones of the head than if it had any other form. 

 Thus we see that in those organs of birds which have 

 not generally any sensibility or proper motions of 

 their own, the same mechanical perfection is dis- 

 played as in the more sentient or more active parts. 



We need hardly say that the bill or beak is 

 adapted to the general structure of the bird, because 

 all the parts of every organised body, be the organi- 

 sation what it may, are always the best adapted to 

 each other, and to the whole ; but there are certain 

 other parts of the structure with which the bill has a 

 more immediate agreement. If the bill has to tug 

 and wrench in tearing asunder the food of the bird, 

 the neck has always great strength and great power 

 of lateral motion united. If the bill has to strike 

 forwards, the neck admits of less lateral motion ; but 

 it moves the head in. the direction of the stroke with 

 great celerity. Thus the blows of the woodpecker 

 are given in such rapid succession that the motion of 

 the bill can hardly be seen, or the strokes counted ; 

 and though the neck and bill of the heron tribe appear 

 unwieldy, they strike out with amazing rapidity. 



The adaptation of the bill to the other acting 

 parts of birds depends, however, in no small degree 

 upon their habits ; for, after all, it is to the habit 

 that the whole parts of the bird are adapted. Thus, 

 though the taking of the same food, generally speak- 

 ing, requires a bill of the same structure in its 

 working parts, yet as that bill is brought within 

 reach of the food in different ways, and by means of 

 different organs, it must be so modified as to accord 

 with these. 



If the principal action of the bill consists in de- 

 taching the food or breaking it, it is always short, or 



only of moderate length, and stout in proportion to 

 its length ; if the bill is used in hewing or digging 

 for the food, it is longer, straight, and hard and 

 pointed at the tip ; if it bores into sludge, it is still 

 longer, straight, broader at the tip, and generally sen- 

 tient, so as to discover eatable substances by touch ; 

 and if the bird feeds in the free air, or on the clear 

 surface of the ground, the bill is, in general, of 

 moderate length. But all birds which capture living 

 food, either in the water, or concealed among her- 

 bage, by a sudden thrust of the bill, have it long. 



There are other purposes to be answered hv the 

 form of the bill besides the mere capture of the food, 

 and adaptation to the place where it is, and the 

 manner of getting at it. It is a general law in the 

 economy of animals, that they shall be safe while 

 they are feeding, at least from dangers connected 

 with the food itself, or the place where it is. 



Now, besides being primers and weeders to the 

 vegetable kingdom, and a sort of general scavengers 

 for removing the waste of all nature, birds appear 

 specially appointed for keeping within proper bounds 

 the numbers of fishes, mollusca, insects, and reptiles. 

 The power of production in all of these is very great ; 

 and, with the exception of the fishes, which settle 

 matters by eating each other (often their own species), 

 this productiveness is far above the average support, 

 or even the room which there is for them in nature. 

 The tadpoles which appear in one brook would, 

 were they all to live and breed, speedily cover a 

 county with frogs ; the caterpillars on one branch 

 would, if so breeding, soon clear a forest ; and the 

 snails would speedily multiply till not a green leaf 

 were to be found. The ophidian and saurian rep- 

 tiles are, in many of their species, co-operators with 

 the birds; but they frequent the places where the 

 food of birds is abundant, and they are not fitted for 

 long migrations. The motions of molluscous animals 

 are proverbially slow ; and though many of the insert 

 tribes are clever on the feet, the wing, or both, they 

 are not capable of long journeys. Locusts and some 

 other tribes do migrate ; but no insects can continue 

 long on the wing. They want the feathers, llie cha- 

 racteristic organs of long flight ; and though their 

 muscles act to very considerable advantage, they 

 must move their wings so incessantly that they are 

 soon worn out, and fall to the earth. 



There is here a very beautiful chain of adaptations, 

 which is worthy of study in itself, besides being 

 intimately connected with the general economy and 

 structure of birds. All these natural trimmers of the 

 exuberance and removers of the waste of growing 

 nature are wanted up to the full amount of their 

 powers. But they are so wanted only for a season ; 

 and though that season varies in length in different 

 latitudes and climates, there is not a spot on earth 

 where it could be perennial, or even of one whole 

 year's unbroken duration, unless the laws of the whole 

 system, that is, the qualities of the several parts of 

 which it is made up, were totally changed. The 

 vegetables could not bring all their " briards" and 

 buds to maturity, nor would the earth supply sowing 

 ground for all their seeds ; and the creatures, of what- 

 ever kind, which keep down the superabundance of 

 these, would, in like manner, speedily overstock the 

 room that there is for them. But still they must 

 all have that elasticity by means of which they can 

 instantly adapt themselves to the changes of the 

 system. The earth consists of a definite quantity 



