CHAP. I.
Of the Motion of Birds, and the Parts ministring thereto.
As this Tribe hath a different Motion from that of other Animals, and an amphibious Way of Life; partly in the Air, and partly on the Land and Waters; so is their Body accordingly shap’d, and all their Parts incomparably fitted for that Way of Life and Motion; as will be found by a cursory View of some of the Particulars. And the
I. And most visible Thing, is the Shape and Make of their Body, not thick and clumsy, but incomparably adapted to their Flight: Sharp before, to pierce and make Way through the Air, and then by gentle Degrees rising to its full Bulk. To which we may add,
II. The neat Position of the Feathers throughout the Body; not ruffled, or discompos’d, or plac’d some this, some a contrary Way, according to the Method of Chance; but all artificially plac’d[a], for facilitating the Motion of the Body, and its Security at the same Time, by way of Cloathing: And for that End, most of the Feathers tend backward, and are laid over one another in exact and regular Method, armed with warm and soft Down next the Body, and more strongly made, and curiously clos’d next the Air and Weather, to fence off the Injuries thereof. To which Purpose, as also for the more easy and nimble gliding of the Body through the Air, the Provision Nature hath made, and the Instinct of these Animals to preen and dress their Feathers, is admirable; both in respect of their Art and Curiosity in doing it, and the Oyl-bag[b], Glands, and whole Apparatus for that Service.
III. And now having said thus much relating to the Body’s Motion, let us survey the grand Instrument thereof, the Wings. Which as they are principal Parts, so are made with great Skill, and plac’d in the most commodious Point of the Body[c], to give it an exact Equipoise in that subtile Medium, the Air.
And here it is observable, with what incomparable Curiosity every Feather is made; the Shaft exceeding strong, but hollow below, for Strength and Lightness sake; and above, not much less strong, and fill’d with a Parenchyma or Pith, both strong and light too. The Vanes as nicely gaug’d on each Side as made; broad on one Side, and narrower on the other; both which incomparably minister to the progressive Motion of the Bird, as also to the Union and Closeness of the Wing[d].
And no less exquisite is the textrine Art of the Plumage[e] also; which is so curiously wrought, and so artificially interwoven, that it cannot be viewed without Admiration, especially when the Eye is assisted with Glasses.
And as curiously made, so no less curiously are the Feathers placed in the Wing, exactly according to their several Lengths and Strength: The Principals set for Stay and Strength, and these again well lined, faced, and guarded with the Covert and Secondary Feathers, to keep the Air from passing through, whereby the stronger Impulses are made thereupon.
And lastly, To say no more of this Part, that deserves more to be said of it, what an admirable Apparatus is there of Bones, very strong, but withal light and incomparably wrought? of Joynts, which open, shut, and every way move, according to the Occasions either of extending it in Flight, or withdrawing the Wing again to the Body? And of various Muscles; among which the peculiar Strength of the Pectoral Muscles deserves especial Remark, by Reason they are much stronger[f] in Birds than in Man, or any other Animal, not made for Flying.
IV. Next the Wings, the Tail is in Flight considerable; greatly assisting in all Ascents and Descents in the Air, as also serving to steady[g] Flight, by keeping the Body upright in that subtile and yielding Medium, by its readily turning and answering every Vacillation of the Body.
And now to the Parts serving to Flight, let us add the nice and compleat Manner of its Performance; all done according to the strictest Rules of Mechanism[h]. What Rower on the Waters, what Artist on the Land, what acutest Mathematician could give a more agreeable and exact Motion to the Wings, than these untaught flying Artists do theirs! Serving not only to bear their Bodies up in the Air, but also to waft them along therein, with a speedy progressive Motion, as also to steer and turn them this Way and that Way, up and down, faster or slower, as their Occasions require, or their Pleasure leads them.
V. Next to the Parts for Flight, let us view the Feet and Legs ministering to their other Motion: Both made light, for easier Transportation through the Air; and the former spread, some with Membranes for Swimming[i], some without, for steady Going, for Perching, for Catching and Holding of Prey[k], or for Hanging by the Heels to gather their Food[l], or to fix themselves in their Places of Retreat and Safety. And the latter, namely the Legs, all curved for their easy Perching, Roosting, and Rest, as also to help them upon their Wings in taking their Flight, and to be therein commodiously tucked up to the Body, so as not to obstruct their Flight. In some long, for Wading and Searching the Waters; in some of a moderate Length, answerable to their vulgar Occasions; and in others as remarkably short, to answer their especial Occasions and Manner of Life[m]. To all which let us add the placing these last mentioned Parts in the Body. In all somewhat out of the Center of the Body’s Gravity[n], but in such as swim, more than in others, for the better rowing their Bodies through the Waters, or to help them in that Diving[o] too.
FOOTNOTES:
[a] See before Book IV. Chap. 12. Note (l).
[b] Mr. Willughby saith, there are two Glands for the Secretion of the unctuous Matter in the Oyl-bag. And so they appear to be in Geese. But upon Examination, I find, that in most other Birds, (such at least as I have enquir’d into,) there is only one Gland: In which are divers little Cells, ending in two or three larger Cells, lying under the Nipple of the Oyl-bag. This Nipple is perforated, and being pressed, or drawn by the Bird’s Bill, or Head, emits the liquid Oyl, as it is in some Birds, or thicker unctuous Grease, as it is in others. The whole Oyl-bag is in its structure somewhat conformable to the Breasts of such Animals as afford Milk.
[c] In all Birds that fly much, or that have the most occasion for their Wings, it is manifest that their Wings are plac’d in the very best Part, to balance their Body in the Air, and to give as swift a Progression, as their Wings and Body are capable of: For otherwise we should perceive them to reel, and fly unsteadily; as we see them to do, if we alter their Æquipoise, by cutting the End of one of the Wings, or hanging a Weight at any of the extreme Parts of the Body. But as for such Birds as have as much occasion for Swimming as Flying, and whole Wings are therefore set a little out of the Center of the Bodies Gravity. See Book IV. Chap. 8. Note (q). And for such as have more occasion for Diving than Flying, and whose Legs are for that Reason set more backward, and their Wings more forward. Chap. 4. Note (k) of this Book.
[d] The wise Author of Nature hath afforded an Example of the great Nicety in the Formation of Birds, by the Nicely observ’d in a Part no more considerable than the Vanes of the Flag-feathers of the Wing. Among others, these two Things are observable: 1. The Edges of the exterior or narrow Vanes bend downwards, but of the interior or wider Vanes upwards; by which Means they catch, hold, and lie close to one another, when the Wing is spread; so that not one Feather may miss its full Force and Impulse upon the Air. 2. A yet lesser Nicety is observ’d, and that is, in the very sloping the Tips of the Flag-feathers: The interiour Vanes being neatly slop’d away to a Point, towards the outward Part of the Wing; and the exteriour Vanes slop’d towards the Body, at least in many Birds; and in the Middle of the Wing, the Vanes being equal, are but little slop’d. So that the Wing, whether extended or shut, is as neatly slop’d and form’d, as if constantly trimm’d with a Pair of Scissors.
[e] Since no exact Account that I know of, hath been given of the Mechanism of the Vanes, or Webs of the Feathers, my Observations may not be unacceptable. The Vane consists not of one continu’d Membrane; because if one broken, it would hardly be reparable: But of many Laminæ, which are thin, stiff, and somewhat of the Nature of a thin Quill. Towards the Shaft of the Feather, (especially in the Flag-feathers of the Wing,) those Laminæ are broad, &c. of a semicircular Form; which serve for Strength, and for the closer shutting of the Laminæ to one another, when Impulses are made upon the Air. Towards the outer Part of the Vane, those Laminæ grow slender and taper: On their under Side they are thin and smooth, but their upper outer Edge is parted into two hairy Edges, each Side having a different Sort of Hairs, laminated or broad at Bottom, and slender and bearded above the other half. I have, as well as I could, represented the uppermost Edge of one of these Laminæ in Fig. 18. with some of the Hairs on each Side, magnify’d with a Microscope. These bearded Bristles, or Hairs, on one Side the Laminæ, have strait Beards, as in Fig. 19. those on the other Side, have hook’d Beards on one Side the slender Part of the Bristle, and strait ones on the other, as in Fig. 20. Both these Sorts of Bristles magnify’d, (only scattering, and not close,) are represented as they grow upon the upper Edge of the Lamina s. t. in Fig. 18. And in the Vane, the hook’d Beards of one Lamina, always lie next the strait Beards of the next Lamina; and by that Means lock and hold each other; and by a pretty Mechanism, brace the Laminæ close to one another. And if at any Time the Vane happens to be ruffled and discompos’d, it can by this pretty easy Mechanism, be reduc’d and repair’d. Vid. Book IV. Chap. 12. Note (m).
[f] Pectorales Musculi Hominis flectentes humeros, parvi & parum carnosi sunt; non æquant 50am aut 70am partem omnium Musculorum Hominis. E contra in Avibus, Pectorales Musculi vastissimi sunt, & aquant, imò excedunt, & magìs pendent, quàm reliqui omnes Musculi ejusdem Avis simul sumpti. Borell. de Mot. Animal. Vol. I. Prop. 184.
Mr. Willughby having made the like Observation, hath this Reflection on it, whence, if it be possible for Man to fly, it is thought by them who have curiously weighed and considered the matter, that he would attempt such a Thing with Hopes of Success, must so contrive and adapt his Wings, that he may make use of his Legs, and not his Arms in managing them: (because the Muscles of the Legs are stronger, as he observes.) Willugh. Ornith. L. 1. c. 1. §. 19.
[g] Mr. Willughby, Ray, and many others, imagine the principal use of the Tail to be to steer, and turn the Body in the Air, as a Rudder. But Borelli hath put it beyond all doubt, that this is the least use of it, and that it is chiefly to assist the Bird in its Ascents and Descents in the Air, and to obviate the Vacillations of the Body and Wings. For as for turning to this or that Side, it is performed by the Wings and Inclination of the Body, and but very little by the help of the Tail.
[h] See Borelli ubi supr. Prop. 182, &c.
[i] It is considerable in all Water-Fowl, how exactly their Legs and Feet correspond to that way of Life. For either their Legs are long, to enable them to wade in the Waters: In which case, their Legs are bare of Feathers a good way above the Knees, the more conveniently for this Purpose. Their Toes also are all abroad; and in such as bear the Name of Mudsuckers, two of the Toes are somewhat joined, that they may not easily sink in walking upon boggy Places. And as for such as are whole-footed, or whose Toes are webbed together (excepting some few) their Legs are generally short, which is the most convenient Size for Swimming. And ’tis pretty enough to see how artificially they gather up their Toes and Feet when they withdraw their Legs, or go to take their Stroke; and as artificially again extend or open their whole Foot, when they press upon, or drive themselves forward in the Waters.
[k] Some of the Characteristicks of Rapacious Birds, are, to have hooked, strong, and sharp-pointed Beaks and Talons, fitted for Rapine, and tearing of Flesh; and strong and brawny Thighs, for striking down their Prey. Willughby Ornith. L. 2. c. 1. Raii Synops. Av. Method. p. 1.
[l] Such Birds as climb, particularly those of the Wood-pecker Kind, have for this Purpose (as Mr. Willughby observes, L. 2. c. 4.) 1. Strong and musculous Thighs. 2. Short Legs and very strong. 3. Toes standing two forwards and two backwards. Their Toes also are close joined together, that they may more strongly and firmly lay hold on the Tree they climb upon. 4. All of them——have a hard stiff Tail bending also downwards, on which they lean, and so bear up themselves in climbing.
[m] Swifts and Swallows have remarkably short Legs, especially the former, and their Toes grasp any Thing very strongly. All which is useful to them in building their Nests, and other such Occasions as necessitate them to hang frequently by their Heels. But there is far greater use of this Structure of their Legs and Feet, if the Reports be true of their hanging by the Heels in great Clusters (after the manner of Bees) in Mines and Grotto’s, and on the Rocks by the Sea, all the Winter. Of which latter, I remember the late learned Dr. Fry told this Story at the University, and confirmed it to me since, viz. That an ancient Fisherman, accounted an honest Man, being near some Rocks on the Coast of Cornwal, saw at a very low Ebb, a black List of something adhering to the Rock, which when he came to examine, he found it was a great Number of Swallows, and, if I misremember not, of Swifts also, hanging by the Feet to one Another, as Bees do; which were covered commonly by the Sea-Waters, but revived in his warm Hand, and by the Fire. All this the Fisherman himself assured the Doctor of. Of this, see more, Chap. 3. Note (d) of this Book.
[n] In Birds that frequent not the Waters, the Wings are in the Center of Gravity, when the Bird lies along, as in Flying; but when it stands or walks, the Erection of the Body throws the Center of Gravity upon the Thighs and Feet.