130 NATURAL HISTORY 



explanation of a difficulty that I have mentioned before, 

 with respect to the invariable early retreat of the Hi- 

 rundo Apus, or swift, so many weeks before its con- 

 geners ; and that not only with us, but also in Andalusia, 

 where they also begin to retire about the beginning of 

 August. 



The great large bat s (which by the by is at present 

 a nondescript in England, and what I have never been 

 able yet to procure) retires or migrates very early in 

 the summer: it also ranges very high for its food, 

 feeding in a different region of the air ; and that is the 

 reason I never could procure one 4 . Now this is exactly 

 the case with the swifts ; for they take their food in a 

 more exalted region than the other species, and are 

 very seldom seen hawking for flies near the ground, or 

 over the surface of the water. From hence I would 

 conclude that these Hirundines, and the larger bats, are 

 supported by some sorts of highflying gnats, scarabs, 

 or Phalcence, that are of short continuance ; and that the 

 short stay of these strangers is regulated by the defect 

 of their food. 



By my journal it appears that curlews clamoured on 

 to October the thirty-first : since which I have not seen 

 , or heard any. Swallows were observed on to Novem- 

 ber the third. 



3 The little bat appears almost every month in the year ; but I have 

 never seen the large ones till the end of April, nor after July. They 

 are most common in June, but never in any plenty: are a rare species 

 with us. 



4 Vespertilio Noctvla certainly winters in England. I once procured 

 some in a torpid state in February. It flies high in the early part of the 

 evening; but descends, as the night closes in, towards the surface of 

 waters to procure its food. G. D. 



