238 The Natural History of Selborne 



grasses and feathers, usually goose-feathers, very inartificially laid 

 together. 



Perseverance will accomplish anything, though at first one would 

 be disinclined to believe that this weak bird, with her soft and 

 tender .bill and claws, should ever be able to bore the stubborn 

 sand-bank without entirely disabling herself ; yet with these feeble 

 instruments have I seen a pair of them make great despatch, and 

 could remark how much they had scooped that day by the fresh 

 sand which ran down the bank, and was of a different 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 observation, 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 be- 

 ginnings were intentionally made in order to be in the greater 

 forwardness for next spring is allowing perhaps too much foresight 

 and rerum prudentia to a simple bird. May not the cause of these 

 latebr<e 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 habitations 

 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 irritant), 1 swarming at the mouths of these holes, like 

 bees on the stools of their hives. 



The following circumstance should by no means be omitted that 

 these birds do not make use of their caverns by way of hybernacula, 



1 White is here mistaken. The flea which infests the sand-martin is a 

 special species. ED. 



