166 THE NATURAL HISTORY [LETT 



Though in some particular districts they may happen to 

 abound, yet in the whole, in the south of England at least, is 

 this much the rarest species. For there are few towns or large 

 villages but what abound with house-martins ; few churches, 

 towers, or steeples, but what are haunted by some swifts : scarce 

 a hamlet or a single cottage-chimney that has not its swallow ; 

 while the bank-martins, scattered here and there, live a seques- 

 tered life among some abrupt sand-hills, and in the precipitous 

 banks of some few rivers. 



These birds have a peculiar manner of flying : flitting about 

 with odd jerks, and vacillations, not unlike the motions of a 

 butterfly. Doubtless the flight of all hirundines is influenced 

 by, and adapted to, the peculiar sort of insects which furnish 

 their food. Hence it would be worth inquiry to examine what 

 particular genus of insects affords the principal food of each 

 respective species of swallow. 



Notwithstanding what has been advanced above, some few 

 sand-martins, I see, haunt the skirts of London, frequenting the 

 dirty pools in Saint George's Fields, and about Whitechapel. 

 The question is where these build, since there are no banks or 

 bold shores in that neighbourhood : perhaps they nestle in the 

 scaffold holes of some old or new deserted building. They dip 

 and wash as they fly sometimes, like the house-martin and 

 swallow. 



Sand-martins differ from their congeners in the diminutiveness 

 of their size, and in their colour, which is what is usually called 

 a mouse-colour. Near Valencia in Spain, they are taken, says 

 Willughby, and sold in the markets for the table ; and are called 

 by the countiy people, probably from their desultory jerking 

 manner of flight, Papilion de Montagna. 



SKLBORNE, Feb. 2C, 1774. 



