'The Natural History of Selborne 219 



had been the mansion of owls for centuries, he discovered at 

 the bottom a mass of matter that at first he could not account 

 for. After some examination he found that it was a congeries 

 of the bones of mice (and perhaps of birds and bats) that had 

 been heaping together for ages, being cast up in pellets out of 

 the crops of many generations of inhabitants. For owls cast 

 up the bones, fur, and feathers, of what they devour, after the 

 manner of hawks. He believes, he told me, that there were 

 bushels of this kind of substance. 



When brown owls hoot, their throats swell as big as an 

 hen's egg. I have known an owl of this species live a full year 

 without any water. Perhaps the case may be the same with 

 all birds of prey. When owls fly they stretch out their legs 

 behind them, as a balance to their large heavy heads, for as 

 most nocturnal birds have large eyes and ears they must have 

 large heads to contain them. Large eyes I presume are 

 necessary to collect every ray of light, and large concave ears 

 to command the smallest degree of sound or noise. 



I am, &c. 



[It will be proper to premise here that the sixteenth, eigh- 

 teenth, twentieth, and twenty-first letters have been published 

 already in the " Philosophical Transactions " ; but as nicer 

 observation has furnished several corrections and additions, it 

 is hoped that the republication of them will not give offence; 

 especially as these sheets would be very imperfect without 

 them, and as they will be new to many readers who had no 

 opportunity of seeing them when they made their first appear- 

 ance.] 



The hirundines are a most inoffensive, harmless, enter- 

 taining, social, and useful tribe of birds ; they touch no fruit 

 in our gardens ; delight, all except one species, in attaching 

 themselves to our houses ; amuse us with their migrations, 

 songs, and marvellous agility ; and clear our outlets from the 

 annSyances of gnats and other troublesome insects, Some 



