166 NATURAL HISTORY OF SELBORNE. 



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 a 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, etc. 



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

 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 appearance.] 



" The hirundines are a most inoffensive, harmless, entertaining, 

 social, and useful tribe of birds ; they touch no fruit in our gar- 

 dens 5 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 annoyances of gnats and 

 other troublesome insects. Some districts in the south seas, near 

 Guiaquil,* are desolated, it seems, by the infinite swarms of veno- 

 mous mosquitoes, which fill the air, and render those coasts in- 

 supportable. It would be worth inquiring whether any species of 

 hirundines is found in those regions. Whoever contemplates the 

 myriads of insects that sport in the sunbeams of a summer evening 

 in this country, will soon be convinced to .what a degree our 

 atmosphere would be choked with them was it not for the friendly 

 interposition of the swallow tribe. 



* See " Ulloa's Travels." 



