[ '75 ] 



I as little mean to deny that there may be a periodical flitting 

 of certain birds from one part of a continent to another : the Roy- 

 fton Crow, and Rock Ouzel, furnifli instances of iuch a regular 

 migration. 



What I mean chiefly to contend therefore is, that it feems to 

 be highly improbable, birds mould, at certain feaions, traverfe 

 large tracts of fea, or rather ocean, without leaving any of the 

 lame fpecies behind, but the fick or wounded. 



As this litigated point can only receive a fatisfaftory deciiion 

 from very accurate obfervations, all preceding naturalifts, from 

 Ariftotle to Ray, have fpoken with much doubt concerning it. 



Soon after the appearance of Monf. Adanfon's Voyage to Sene- 

 gal, however, Mr Collinfon firir, in the Philofophical Tranf- 

 aclions b , and after him the moft eminent ornithologies of Europe, 

 feem to have considered this traveller's having caught four Euro- 

 pean Swallows on the 6th of October, not far from the African 

 eoaft, as a decihve proof, that the common fwallows, when they 

 difappear in Europe, make for Africa during the winter, and re- 

 turn again to us in the fpring. 



It is therefore highly incumbent upon me, who profefs that 1 

 am by no means fatisfied with the account given by Monf. Adan- 

 fon of theie European fwallows, to enter into a very minute dif- 

 cuffiori of what may, or may not, be inferred from his obferva'don 

 according to his own narrative. 



I mall firft however consider the general arguments, from 

 which it is fuppofed that birds of paffage periodically traverfe 

 oceans, which indeed may be almoft. reduced to tins iingie one, 

 viz. we fee certain birds in particular fealbns, and aftewards we 

 fee them not ; from which circumifances it is at once inferred, 

 that the caule of their difappearance is, that they have crofled large 

 tracts of fea. 



1 Part II. 1760, p. 459, &ied«- 



' The 



