168 
NATURAL HISTORY OF* SELBORNE. 
It is curious to observe with what different degrees of archi- 
tectonic skill Providence has endowed birds of the same genus, 
and so nearly correspondent in their general mode of life ! for 
while the swallow and the house-martin discover the greatest 
address in raising and securely fixing crusts or shells of loam as 
cunabula for their young, the bank-martin terebrates a round 
and regular hole in the sand or earth, which is serpentine, hori- 
zontal, and about two feet deep. At the inner end of this bur- 
row does this bird deposit, in a good degree of safety, her rude 
nest, consisting of fine grasses and feathers, usually goose-fea- 
thers, very inartificially laid together. 
Perseverance wiH accomplish any thing : though at first one 
would be disinclined to beheve that this weak bird, with her soft 
and tender bill and claws, should ever be able to bore the stub- 
born sand-bank without entirely disabling herself; yet with these 
feeble instruments have I seen a pair of them make great dis- 
patch : and could remark how much they had scooped that day 
by the fresh sand which ran down the bank, and was of a dif- 
ferent colour from that which lay loose and bleached in the sun. 
In what space of time these little artists are able to mine and 
finish these cavities I have never been able to discover, for 
reasons given above ; but it would be a matter worthy of obser- 
vation, where it falls in the way of any naturalist to make his 
remarks. This I have often taken notice of, that several holes 
of different depths are left unfinished at the end of summer. To 
imagine that these beginnings were intentionally made in order 
to be in the greater forwardness for next spring, is allowing per- 
haps too much foresight and rerum prudentia to a simple bird. 
May not the cause of these latebrce being left unfinished arise 
from their meeting in those places with strata too harsh, hard, 
and solid, for their purpose, which they relinquish, and go to a 
fresh spot that works more freely ? Or may they not in other 
places fall in with a soil as much too loose and mouldering, liable 
to flounder, and threatening to overwhelm them and their labours ? 
One thing is remarkable — that, after some years, the old holes 
are forsaken and new ones bored ; perhaps because the old habi- 
tations grow foul and fetid from long use, or because they may 
so abound with fleas as to become untenantable. This species 
of swallow moreover is strangely annoyed with fleas : and we 
have seen fleas, bed-fleas (pulex irritansj, swarming at the mouths 
of these holes, like bees on the stools of their hives. 
