244 HIRUNDINUm 



not appear to me that much stress may be laid on the diffi- 

 culty and hazard that birds must run in their migrations, 

 by reason of vast oceans, cross-winds, &c. ; because, if we 

 reflect, a bird may travel from England to the equator 

 without launching out and exposing itself to boundless 

 seas, and that by crossing the water at Dover, and again 

 at Gibraltar. And I with the more confidence advance 

 this obvious remark, because my brother has always found 

 that some of his birds, and particularly the Swallow kind, 

 are very sparing of their pains in crossing the Mediterra- 

 nean : for when arrived at Gibraltar, they do not 



" ' Rang'd in figure wedge their way, and set forth 

 Their airy caravan high over seas 

 Flying, and over lands with mutual wing 

 Easing their flight : ' 



but scout and hurry along in little detached parties of six 

 or seven in a company ; and sweeping low, just over the 

 surface of the land and water, direct their course to the 

 opposite continent at the narrowest passage they can find. 

 They usually slope across the bay to the south-west, and 

 so pass over opposite to Tangier, which, it seems, is the 

 narrowest space." 



Again, in his thirty-third letter to Thomas Pennant, he 

 says, " I was much pleased to see, among the collection of 

 Birds from Gibraltar, some of those short-winged English 

 summer birds of passage, concerning whose departure we 

 have made so much inquiry. Now if these birds are found 

 in Andalusia to migrate to and from Barbary, it may easily 

 be supposed that those that come to us may migrate back 

 to the Continent, and spend their winters in some of the 

 warmer parts of Europe. This is certain, that many soft- 

 billed birds that come to Gibraltar, appear there only in 

 spring and autumn, seeming to advance in pairs towards 

 the northward, for the sake of breeding during the summer 



