ey.

When they happen to breed near hedges and enclosures, they are
dispossessed of their breeding holes by the house-sparrow, which is on
the same account a fell adversary to house-martins.

These hirundines are no songsters, but rather mute, making only a little
harsh noise when a person approaches their nest. They seem not to be of
a sociable turn, never with us congregating with their congeners in the
autumn. Undoubtedly they breed a second time, like the house-martin and
swallow; and withdraw about Michaelmas.

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 single cottage-chimney that has not its
swallow; while the bank-martins, scattered here and there, live a
sequestered life among some abrupt sand-hills, and in the 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 country
people, probably from their desultory jerking manner of flight, _Papilion
de Montagna_.

LETTER XXI.

SELBORNE, _Sept._ 28_th_, 1774.

Dear Sir,--As the swift or black-martin is the largest of the British
_hirundines_, so it is undoubtedly the latest comer. For I remember but
one instance of