NATURAL HISTORY. 
95 
natnralifts and travellers refpefting this ex- 
traordinary condnft in particular birds. — 
Some have fuppofed that thofe which were 
not ftrong enough to fuftain a flight over ex- 
panding oceans, colle<fted themfelves in bo- 
dies, and repaired to chafms in rocks, or 
fought a temporary tomb beneath the waters, 
where they remained, in a ftate of torpidity, 
until the revolving feafons fltould recall them 
to the exercile of their former fundlions. 
Others have imagined, that- they aftually 
fought climes more congenial to their nature 
and fubftance, at a time when cold and fcar- 
city rendered the country of their fojonrn- 
nient both dangerous and inconvenient. The 
times of their departure and return are lb 
regular, that, in the courfe of five years, 
the average has not exceeded more than a 
Angle day. Thofe tribes which have not 
fufficient Itrength to crofs the immenfe de- 
fects and vaft oceans, fuch as fwallows, mar- 
tins, &c. are fuppofed to find a winter fub- 
fiftcnce in the fouthern countries of Europe, 
where the clemency of the feafon feems, moll 
hofpitably, to invite them to partake of their 
bounties. ^ 
It has been obferved, that fome birds, 
which migrate in particular climates, are con 
ftantly relident in others. According to He- 
rodotus, there is a fpecies of fwallow, that 
abides perpetually in Egypt ; which muft un- 
doubtedly arife from the equality of the fea- 
Cons in that part of Africa. This property, 
therefore, 
