39 



occasionally alighted on ships, in their way, had, 

 owing to stormy weather, contrary winds, or some 

 other casualty, been too much fatigued to proceed 

 without resting. And I think it further probable, 

 that great numbers of these birds, labouring under 

 the above disadvantageous circumstances, annually 

 fall into the sea and are drowned. For, as White 

 observes, in his " Natural History of Selborne," 

 unless these birds be very short lived indeed, 

 or unless they do not return to districts where 

 they have been bred, they must undergo some 

 great devastation somehow, or somewhere ; be- 

 cause the numbers that return in spring, bear 

 no manner of proportion to those which retire 

 in autumn. 



It seems, however, unnecessary to suppose that 

 swallows and other migratory birds must necessarily 

 always cross the wide ocean in their flights ; they 

 may cross over the Channel to the Continent' of 

 Europe, from Britain ; and again from Europe into 

 Africa, from Spain. I believe, however, that swal- 

 lows have power of wing enough to take a very long 

 aerial voyage: but the length of any journey to Africa 

 could be no objection to the idea of their migra- 



