Birds, then, are feathered, and this is a character common to them all and peculiar2 to them. Their feathers, too, are split and distinct in kind from the undivided feathers of insects; for the bird’s feather is barbed, these are not; the bird’s feather has a shaft3, these have none. A second strange peculiarity4 which distinguishes birds from all other animals is their beak5. For as in elephants the nostril6 serves in place of hands, and as in some insects the tongue serves in place of mouth, so in birds there is a beak, which, being bony, serves in place of teeth and lips. Their organs of sense have already been considered.
All birds have a neck extending from the body; and the purpose of this neck is the same as in such other animals as have one. This neck in some birds is long, in others short; its length, as a general rule, being pretty nearly determined7 by that of the legs. For long-legged birds have a long neck, short-legged birds a short one, to which rule, however, the web-footed birds form an exception. For to a bird perched up on long legs a short neck would be of no use whatsoever8 in collecting food from the ground; and equally useless would be a long neck, if the legs were short. Such birds, again, as are carnivorous would find length in this part interfere9 greatly with their habits of life. For a long neck is weak, and it is on their superior strength that carnivorous birds depend for their subsistence. No bird, therefore, that has talons10 ever has an elongated11 neck. In web-footed birds, however, and in those other birds belonging to the same class, whose toes though actually separate have flat marginal lobes13, the neck is elongated, so as to be suitable for collecting food from the water; while the legs are short, so as to serve in swimming. The beaks14 of birds, as their feet, vary with their modes of life. For in some the beak is straight, in others crooked15; straight, in those who use it merely for eating; crooked, in those that live on raw flesh. For a crooked beak is an advantage in fighting; and these birds must, of course, get their food from the bodies of other animals, and in most cases by violence. In such birds, again, as live in marshes16 and are herbivorous the beak is broad and flat, this form being best suited for digging and cropping, and for pulling up plants. In some of these marsh17 birds, however, the beak is elongated, as too is the neck, the reason for this being that the bird get its food from some depth below the surface. For most birds of this kind, and most of those whose feet are webbed, either in their entirety or each part separately, live by preying18 on some of the smaller animals that are to be found in water, and use these parts for their capture, the neck acting19 as a fishing-rod, and the beak representing the line and hook.
The upper and under sides of the body, that is of what in quadrupeds is called the trunk, present in birds one unbroken surface, and they have no arms or forelegs attached to it, but in their stead wings, which are a distinctive20 peculiarity of these animals; and, as these wings are substitutes for arms, their terminal segments lie on the back in the place of a shoulder-blade.
The legs are two in number, as in man; not however, as in man, bent21 outwards22, but bent inwards like the legs of a quadruped. The wings are bent like the forelegs of a quadruped, having their convexity turned outwards. That the feet should be two in number is a matter of necessity. For a bird is essentially23 a sanguineous animal, and at the same time essentially a winged animal; and no sanguineous animal has more than four points for motion In birds, then, as in those other sanguineous animals that live and move upon the ground, the limbs attached to the trunk are four in number. But, while in all the rest these four limbs consist of a pair of arms and a pair of legs, or of four legs as in quadrupeds, in birds the arms or forelegs are replaced by a pair of wings, and this is their distinctive character. For it is of the essence of a bird that it shall be able to fly; and it is by the extension of wings that this is made possible. Of all arrangements, then, the only possible, and so the necessary, one is that birds shall have two feet; for this with the wings will give them four points for motion. The breast in all birds is sharp-edged, and fleshy. The sharp edge is to minister to flight, for broad surfaces move with considerable difficulty, owing to the large quantity of air which they have to displace; while the fleshy character acts as a protection, for the breast, owing to its form, would be weak, were it not amply covered.
Below the breast lies the belly24, extending, as in quadrupeds and in man, to the vent25 and to the place where the legs are jointed26 to the trunk.
Such, then, are the parts which lie between the wings and the legs. Birds like all other animals, whether produced viviparously or from eggs, have an umbilicus during their development, but, when the bird has attained27 to fuller growth, no signs of this remain visible. The cause of this is plainly to be seen during the process of development; for in birds the umbilical cord unites with the intestine28, and is not a portion of the vascular29 system, as is the case in viviparous animals.
Some birds, again, are well adapted for flight, their wings being large and strong. Such, for instance, are those that have talons and live on flesh. For their mode of life renders the power of flight a necessity, and it is on this account that their feathers are so abundant and their wings so large. Besides these, however, there are also other genera of birds that can fly well; all those, namely, that depend on speed for security, or that are of migratory30 habits. On the other hand, some kinds of birds have heavy bodies and are not constructed for flight. These are birds that are frugivorous and live on the ground, or that are able to swim and get their living in watery31 places. In those that have talons the body, without the wings, is small; for the nutriment is consumed in the production of these wings, and of the weapons and defensive32 appliances; whereas in birds that are not made for flight the contrary obtains, and the body is bulky and so of heavy weight. In some of these heavy-bodied birds the legs are furnished with what are called spurs, which replace the wings as a means of defence. Spurs and talons never co-exist in the same bird. For nature never makes anything superfluous33; and if a bird can fly, and has talons, it has no use for spurs; for these are weapons for fighting on the ground, and on this account are an appanage of certain heavy-bodied birds. These latter, again, would find the possession of talons not only useless but actually injurious; for the claws would stick into the ground and interfere with progression. This is the reason why all birds with talons walk so badly, and why they never settle upon rocks. For the character of their claws is ill-suited for either action.
All this is the necessary consequence of the process of development. For the earthy matter in the body issuing from it is converted into parts that are useful as weapons. That which flows upwards34 gives hardness or size to the beak; and, should any flow downwards35, it either forms spurs upon the legs or gives size and strength to the claws upon the feet. But it does not at one and the same time produce both these results, one in the legs, the other in the claws; for such a dispersion of this residual36 matter would destroy all its efficiency. In other birds this earthy residue37 furnishes the legs with the material for their elongation; or sometimes, in place of this, fills up the interspaces between the toes. Thus it is simply a matter of necessity, that such birds as swim shall either be actually web-footed, or shall have a kind of broad blade-like margin12 running along the whole length of each distinct toe. The forms, then, of these feet are simply the necessary results of the causes that have been mentioned. Yet at the same time they are intended for the animal’s advantage. For they are in harmony with the mode of life of these birds, who, living on the water, where their wings are useless, require that their feet shall be such as to serve in swimming. For these feet are so developed as to resemble the oars38 of a boat, or the fins39 of a fish; and the destruction of the foot-web has the same effect as the destruction of the fins; that is to say, it puts an end to all power of swimming.
In some birds the legs are very long, the cause of this being that they inhabit marshes. I say the cause, because nature makes the organs for the function, and not the function for the organs. It is, then, because these birds are not meant for swimming that their feet are without webs, and it is because they live on ground that gives way under the foot that their legs and toes are elongated, and that these latter in most of them have an extra number of joints40. Again, though all birds have the same material composition, they are not all made for flight; and in these, therefore, the nutriment that should go to their tail-feathers is spent on the legs and used to increase their size. This is the reason why these birds when they fly make use of their legs as a tail, stretching them out behind, and so rendering41 them serviceable, whereas in any other position they would be simply an impediment.
In other birds, where the legs are short, these are held close against the belly during flight. In some cases this is merely to keep the feet out of the way, but in birds that have talons the position has a further purpose, being the one best suited for rapine. Birds that have a long and a thick neck keep it stretched out during flight; but those whose neck though long is slender fly with it coiled up. For in this position it is protected, and less likely to get broken, should the bird fly against any obstacle.
In all birds there is an ischium, but so placed and of such length that it would scarcely be taken for an ischium, but rather for a second thigh-bone; for it extends as far as to the middle of the belly. The reason for this is that the bird is a biped, and yet is unable to stand erect42. For if its ischium extended but a short way from the fundament, and then immediately came the leg, as is the case in man and in quadrupeds, the bird would be unable to stand up at all. For while man stands erect, and while quadrupeds have their heavy bodies propped43 up in front by the forelegs, birds can neither stand erect owing to their dwarf-like shape, nor have anterior45 legs to prop44 them up, these legs being replaced by wings. As a remedy for this Nature has given them a long ischium, and brought it to the centre of the body, fixing it firmly; and she has placed the legs under this central point, that the weight on either side may be equally balanced, and standing46 or progression rendered possible. Such then is the reason why a bird, though it is a biped, does not stand erect. Why its legs are destitute47 of flesh has also already been stated; for the reasons are the same as in the case of quadrupeds.
In all birds alike, whether web-footed or not, the number of toes in each foot is four. For the Libyan ostrich48 may be disregarded for the present, and its cloven hoof49 and other discrepancies50 of structure as compared with the tribe of birds will be considered further on. Of these four toes three are in front, while the fourth points backward, serving, as a heel, to give steadiness. In the long-legged birds this fourth toe is much shorter than the others, as is the case with the Crex, but the number of their toes is not increased. The arrangement of the toes is such as has been described in all birds with the exception of the wryneck. Here only two of the toes are in front, the other two behind; and the reason for this is that the body of the wryneck is not inclined forward so much as that of other birds. All birds have testicles; but they are inside the body. The reason for this will be given in the treatise51 On the Generation of Animals.
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1
scaly
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| adj.鱼鳞状的；干燥粗糙的 | |
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2
peculiar
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| adj.古怪的，异常的；特殊的，特有的 | |
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shaft
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| n.(工具的)柄，杆状物 | |
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peculiarity
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| n.独特性，特色；特殊的东西；怪癖 | |
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beak
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| n.鸟嘴，茶壶嘴，钩形鼻 | |
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nostril
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| n.鼻孔 | |
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7
determined
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| adj.坚定的；有决心的 | |
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8
whatsoever
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| adv.（用于否定句中以加强语气）任何；pron.无论什么 | |
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9
interfere
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| v.(in)干涉，干预；(with)妨碍，打扰 | |
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10
talons
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| n.（尤指猛禽的）爪( talon的名词复数 )；（如爪般的）手指；爪状物；锁簧尖状突出部 | |
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11
elongated
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| v.延长，加长( elongate的过去式和过去分词 ) | |
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12
margin
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| n.页边空白；差额；余地，余裕；边，边缘 | |
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13
lobes
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| n.耳垂( lobe的名词复数 )；（器官的）叶；肺叶；脑叶 | |
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14
beaks
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| n.鸟嘴( beak的名词复数 )；鹰钩嘴；尖鼻子；掌权者 | |
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15
crooked
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| adj.弯曲的；不诚实的，狡猾的，不正当的 | |
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marshes
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| n.沼泽，湿地( marsh的名词复数 ) | |
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marsh
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| n.沼泽，湿地 | |
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18
preying
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| v.掠食( prey的现在分词 )；掠食；折磨；（人）靠欺诈为生 | |
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19
acting
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| n.演戏，行为，假装；adj.代理的，临时的，演出用的 | |
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20
distinctive
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| adj.特别的，有特色的，与众不同的 | |
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21
bent
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| n.爱好，癖好；adj.弯的；决心的，一心的 | |
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22
outwards
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| adj.外面的，公开的，向外的；adv.向外；n.外形 | |
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essentially
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| adv.本质上，实质上，基本上 | |
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belly
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| n.肚子，腹部；(像肚子一样)鼓起的部分，膛 | |
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25
vent
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| n.通风口，排放口；开衩；vt.表达，发泄 | |
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26
jointed
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| 有接缝的 | |
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27
attained
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| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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28
intestine
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| adj.内部的；国内的；n.肠 | |
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vascular
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| adj.血管的，脉管的 | |
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30
migratory
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| n.候鸟，迁移 | |
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31
watery
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| adj.有水的，水汪汪的；湿的，湿润的 | |
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32
defensive
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| adj.防御的；防卫的；防守的 | |
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33
superfluous
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| adj.过多的，过剩的，多余的 | |
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34
upwards
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| adv.向上，在更高处...以上 | |
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35
downwards
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| adj./adv.向下的（地），下行的（地） | |
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36
residual
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| adj.复播复映追加时间；存留下来的，剩余的 | |
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37
residue
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| n.残余，剩余，残渣 | |
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38
oars
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| n.桨，橹( oar的名词复数 )；划手v.划（行）( oar的第三人称单数 ) | |
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39
fins
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| [医]散热片；鱼鳍；飞边；鸭掌 | |
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40
joints
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| 接头( joint的名词复数 )； 关节； 公共场所（尤指价格低廉的饮食和娱乐场所） （非正式）； 一块烤肉 （英式英语） | |
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41
rendering
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| n.表现，描写 | |
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42
erect
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| n./v.树立，建立，使竖立；adj.直立的，垂直的 | |
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43
propped
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| 支撑，支持，维持( prop的过去式和过去分词 ) | |
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44
prop
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| vt.支撑；n.支柱，支撑物；支持者，靠山 | |
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45
anterior
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| adj.较早的；在前的 | |
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46
standing
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| n.持续，地位；adj.永久的，不动的，直立的，不流动的 | |
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47
destitute
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| adj.缺乏的；穷困的 | |
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48
ostrich
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| n.鸵鸟 | |
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49
hoof
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| n.(马，牛等的)蹄 | |
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50
discrepancies
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| n.差异，不符合（之处），不一致（之处）( discrepancy的名词复数 ) | |
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51
treatise
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| n.专著；(专题)论文 | |
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