70 NATURAL HISTORY. 
revolving feafons fhould recall them to the exercife of 
their former fun¢tions. Others have iniagined,. that 
they actually fe zht climes more congemal to their 
nature and fubitance, at a time when cold and fear- 
city rendered the country of their fojouroment both 
dangerousandiaconvenient. The times their of depart- 
ure and return are fo regular, that, in the courfe of 
five years, the average has not exceeded more than a 
fingle day. Thofe tribes which have not fufficient 
ftrength to crofs the immenfe defarts and vaft oceans, 
fuch as {wallows, martins, &c. are fuppofed to finda 
winter fubtiftence in the fouthern countries of Europe, 
where the clemency of the ‘eafon feems, moft hofpit- 
‘ably, to invite them to partake of their bounties. 
It has been obferved, that fome birds ‘ which mi- 
grate in particular climates, are conftanly refident in 
others... According to Herodotus. there is a fpecies of 
{wallow, that abides perpetually in Egypt; which muft 
undoubtedly arife from the equality of the feafons in 
that part of Africa. This property, therefore, is nét 
peculiar to any particular {pecies of bird, but rather 
caufed by the difference of the country and climate in 
which they are bred. In Cayan, Java, and oth 
warm climates, thofe birds, which uniformly migrate 
in the cold regions of Norway, North America, and 
Kamtichatka, are conftant refidents through every 
change of feafon. The manner of their departure is 
too curious to pafs unnoticed. ‘They range themfelves 
in a column, like an I, or intwo lines, refembling the 
fides of a wedge. When they have taken flight, one 
particular bird takes the lead; after going a certain 
diftance he is relieved by another. in their progrefs, 
feveral particulars occur, to excite our wonder, as 
- well as our veneration, at thatimmenfity of wifdoma, 
which has formed them with fo extraordinary an in- 
ftinct. Who acquainted thefr young with the time, © 
place, and neceflity of their departure ; and what can 
induce them to change the place of their nativity for 
-aftrange country ? Who caufes the imprifoned bird 
to teel its captivity at the time of emigration; or who 
is the herald, to aifemble thefe feathered voyagers” 
‘and travellers? Who is it that forbids one to depart 
before the appointed time? Who forms their charts; 
er who fupplies them witha compats, to direét thera 
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