170 NATURAL HISTORY OF SELBORNE. 
These birds have a pecuhar 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 theii- 
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 w^hat 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 XXL To. the Hon. DAINES BARRINGTON. 
(DEAR SIR, Selhorne, Sept. 28, 1774. 
As the swift or black martin is the largest of the British hirun- 
dines, 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, t 
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 plumag^ 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 tertiarics ; altogether imparting a pretty mottled appearance to 
the bird. This plumage is wholly changed in winter. — Ed. 
t And very generally after a tempest.— Ed. 
