170 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 enquiry to examine what parti- 

 cular genus of insects affords the principal food of each respec- 

 tive 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 swal- 

 low. 



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, Papilion de Montagna* 



LETTER XXI. To. THE HON. DAINES HARRINGTON. 

 DEAR SIR, Selborne, Sept. 28, 1774. 



As the swift or black martin is the largest of the British hirun- 

 dinesy so is it undoubtedly the latest comer. For I remember 

 but one instance of its appearing before the last week in April : 

 and in some of our late frosty, harsh springs, it has not been 

 seen till the beginning of May. This species usually arrives in 

 pairs.f 



The swift, like the sand-martin, is very defective in architec- 

 ture, making no crust, or shell, for its nest ; but forming it of 

 dry grasses and feathers, very rudely and inartificially put toge- 



* The male and female of this species of swallow are exactly similar, and can be distinguished 

 only by dissection. The young have the wing-primaries somewhat shorter, and the tail less 

 forked. The upper plumage is more or less mottled with a pale tint, particularly about the rump 

 and upper tail-coverts; and the tail itself is also margined in the same manner, as are also the 

 wing-coverts, and especially the tertiaries ; altogether imparting a pretty mottled appearance to 

 the bird. This plumage is wholly changed iu winter. ED. 



t And very generally after a tempest. ED. 



