ORNITHOLOGY. 
confined in their habitation. It is a rule which Nature 
feems to have prefcribed to lierfelf, that the fmaller her 
progeny is, the more numerous and diverfified does Ihe 
produce it. The larger animals, which procreate feldom 
and in fmall numbers, have but few fpecies nearly allied 
to them ; while the fmaller are related to many kindred 
tabes, and each fpecies is fubjeft to much variety. 
Agreeable to this rule, birds, from the multiplicity of 
their number and the fmallnefs of their fize, are infi¬ 
nitely more varied in the fame fpecies than even the 
fmaller quadrupeds. In the latter clafs, too, the differ¬ 
ence between the male and the female is generally fo 
flight as to occafion but few miftakes; whereas, among 
birds, the female is often fo diftinguifhed from her mate 
both by fize and colour, that fome eminent naturalifts 
have miftaken them for different fpecies, and have ar¬ 
ranged them accordingly. 
In order, therefore, to obtain an accurate knowledge 
of this divifion of the animal kingdom, an individual of 
each fpecies will not fufHce ; two, and fometimes four, of 
the fame kind, mult come under the infpeftion of the 
naturaliff, becaufe the young are frequently different 
from the adult of the fame kind. If then there are only 
two thoufand different fpecies of birds, the naturaliff who 
would defcribethem accurately muff have examined eight 
thoufand individuals. Befides this circumftance, there 
are many other diverfities produced by climate and food, 
by domeftication and captivity, by natural and forced 
migrations. All thefe obftacles combine together againft 
the ornithologift, and increafe the difficulty of his labours, 
when conlidered merely in the light of a nomenclator 
whofe foie province it is to diftinguifh the animals from 
each other, and to affign them their names. How hard, 
then, muff his talk prove, when he attempts to delineate 
their manners and detail their economy)! 
The quadruped is in fome degree fixed in his refidence, 
and therefore forced to fubmit to the laws of the climate 
in which he is produced : hence, by knowing the conti¬ 
nent, or part of the continent, where he refides, you ob¬ 
tain fome general outlines to direft you in giving his par¬ 
ticular hiftory. With regard to the bird, even this is 
wanting : his faculty of traverfing a vaft fpace in a fliort 
time, renders him almoff independent of climate. A re¬ 
gular fupply of food is the principal circumftance that 
determines his habitation ; and, as that is procured, at 
different feafons of the year, in very diftant quarters of 
the world, you are obliged to follow his route, and exa¬ 
mine his manners, in all the remote regions through which 
he paffes. To furnifli a hiftory of birds, as complete as 
that of quadrupeds, muff, on thefe accounts, neceflarily 
prove the work of ages ; and, from thefe caufes, M. Buf- 
fon juftly afferts, that the number and charafters of birds 
are ftill in an ocean of obfcurity. 
The ftrufture of the feathered tribes, and their habits 
of life, are wonderfully adapted to the various funftions 
which they are deftined to perform. The pointed beak, 
the long and pliant neck, the gently-fwelling ftioulder, 
the expanfive wings, the tapering tail, the light and bony 
feet, are all wifely calculated to affift and accelerate their 
motion through the yielding air. Every part of ihcir 
frame is formed for lightnefs and buoyancy ; their bo¬ 
dies are covered with a foft and delicate plumage, fo dif- 
pofed as to proteft them from the intenfe cold of the at- 
mofphere through which they pafs; their wings are made 
of the lighteft materials, and yet the force with which 
they ftrike the air is fo great as to impel their bodies 
forward with aftonifhing rapidity, while the tail ferves the 
purpofe of a rudder to direft them to the different objefts 
of their purfuit. 
The internal ftrufture of birds is no lefs w’ifely adapted 
to the fame purpofes ; all the bones are light and thin, 
and all the mufcles, except thofe which are appropriated 
to the movements of the wings, are extremely light and 
delicate. The lungs are placed clofe to the back-hone 
Vol. XVII. No. 1215. 
769 
and ribs. The air, entering into them by a communica¬ 
tion from the windpipe, paffes through, and is conveyed 
into a number of membranous cells which lie on the lides 
of the pericardium, and communicate with thofe of the 
fternum. In fome birds, thefe cells are continued down 
the wings', and extended even to the pinions, thigh¬ 
bones, and other parts of the body, which can be filled 
and diftended with air at the pleafure of the animal. 
The feathers too, and particularly thofe of the wings, 
contain a great quantity of air. The almoff univerfal 
dift'ufion of this fluid in the bodies of birds is of infinite 
ufe to them, not only in their long and laborious flights, 
but likewife in preventing their refpiration from being 
flopped or interrupted by the rapidity of their motion 
through a refilling medium. Were it pofiible for man 
to move with the fwiftnefs of a fwallow, the aftual re¬ 
finance of the air, as he is not provided with internal 
refervoirs fimilar to thofe of birds, would foon fnffocate 
him. 
The wings of birds are fo conftrufted, that, in linking 
downwards, they expand very confiderably, and, except 
that they are fomewhat hollow on the under fide, they 
form, in this aft, almoff two planes. The mufcles that 
move the wings downwards are very large, and have been 
ellimated, in fome inftances, at not lels than the fixth 
part of the weight of the whole body. When a bird is 
on the ground, and intends to fly, it takes a leap, ftretches 
its wings from the body, and ftrikes them downwards 
with great force. By this ffroke, they are put into an 
oblique direftion, partly upwards and partly horizontally 
forwards. That part of the force which tends upwards 
is deftroyed by the weight of the bird, while the horizon¬ 
tal impulfe ferves to carry it forwards. The ffroke being 
completed, it moves its wings; and they, being contrafted, 
and having their edges turned upwards, meet with very 
little refiftance from the air. When they are fufficiently 
elevated, it makes a fecond ffroke downwards, and the 
impulfe of the air again moves it forward. Thefe fuc- 
ceflive ftrokes aft as fo many leaps taken in the air. 
When the bird wants to turn to the right or left, it ftrikes 
ftrongly with the oppofite wing, fo as to impel the body 
to the proper fide. If it wants to rife, it raifes its tail; 
and, if to fall, deprefles it. When in a horizontal pofi- 
tion, the tail keeps the body Heady. A bird, by fpread- 
ing its wings, can continue to move horizontally in the 
air for. fome time without ftriking, becaufe it has ac¬ 
quired a fufficient velocity ; and the wings, being pa¬ 
rallel to the horizon, meet with but fmall refiftance. On 
alighting, it expands its wings and tail full againft the 
air, that they may meet with all poflible refiftance. The 
centre of gravity in birds is fomewhat behind the wings; 
and, to counterbalance it, moll of them may be obferved 
to thruft out their head and neck in flying. This is very 
apparent in the flight of ducks, geefe, and feveral fpecies 
of water-fowl, whofe centre of gravity is farther back¬ 
ward than in the land-birds. In the heron, on the con¬ 
trary, whofe long head and neck, although folded up in 
flight, overbalance the reft of the body, the long legs 
are extended, in order to give the proper counterpoife, 
and to fupply what is wanting in the fhortnefs of the 
tail. 
The ftrongeft feathers, or quills, are placed in thofe 
parts of the body where they have moft duty to perform. 
They have large Ihafts, hollow at the lower end, but 
filled at the upper with a pith, convex above, and con¬ 
cave beneath, which ferves to give nourilhment to the 
vanes on each fide. Thefg vanes are broad on the one fide, 
and narrow on the other, each confifting of a number of 
thin laminae ; fluff, and of the nature of a fplit quill. 
The different laminae are braced together by the elegant 
contrivance of a multitude of fmall briftles ; thofe on the 
one fide being hooked, and the other ftraight: they lock 
into each other, and keep the vanes fmooth, compaft, 
and ftrong. The vanes being thus adjufted, aqdthefea- 
9 K thers 
