'. NATURAL HISTORY. 69 
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times of indifpenfible’ neceflity. Their food, being, 
- generallv dry, hard, and crude, they havea gizzard, 
which with the help of fand, and other ftony particles 
they fwallow, aids them in digeftion. 
Mouvutrtine.....Although birds, from the fimpli- 
city of their ftructure, habitation of the air, and per- 
petual exercife, are lefs fubject to difeafe than other 
€reatures, yet they are liable to one to which no others 
are €xpofed; this is the ficknefs attending the annual 
renovation of their plumage, whichis called their 
moulting time. ) 
GENERATION.... Inthe fpring, when nature affords 
abundance of food, birds are {timulated to pair, toin- 
ereafe their fpecies. Having chofen their mate for 
the enfuing year, they proceed to thofe official cares 
_ which diftinguith the approach of being made parents, 
With all the fondnefs of fuch expectations, they pro- 
ceed to collect materials for their nefts, which they 
build with the fkill of the moft expertarchitect. The 
ifcover fo much conftancy to each other, with fuch 
inabating care and affection in breeding and rearing 
their young, that they might be taken as examples by- 
the human {pecies. 
HABITATION.....Birds are particularly attached to 
the place of their nativity. A rook, if undifturbed, 
will never quitits native grove; the blackbird and 
redbreaft are tenacious of their birthrights; and many 
ethers, that are known to emigrate annually from this 
eountry, have been found, by frequent experiments, 
to return to their ufual breeding places. : 
_. MieraArion.....Is that paflage of birds from one 
. climate to another, according as they are impelled by 
fear, hunger, or change offeafons. Many havebeen 
- the conjectures of naturalifts and travellers ref{pecting 
this extraordinary conduct in particular birds.—Some 
have fuppofed that thofe which were not {trong enqugh 
to fuftaina flight over expanding oceans, collected 
 ¢hemfelves in bodies, and repaired tq cha{ms in rocks, 
er fought a temporary tomb beneath the waters, 
- where they remained, in a flate of torpidity, until the 
