234 HIRUNDINIDyE. 



to the west of their true course. Gilbert White, in his 

 ninth letter to the Hon. Daines Barrington, says, " it 

 does not appear to me that much stress may be laid on 

 the difficulty and hazard that birds must run in their 

 migrations, by reason of vast oceans, cross-winds, &c. ; be- 

 cause, 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 Mediterranean : 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 de- 

 parture 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 



