240 The Natural History of Selborne 



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 ques- 

 tion 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 country people, probably from their desultory jerking manner 

 of flight, Pavilion de Montagna. 



