WATER RAT SWIFTS. 89 



aquatic rat to forsake the neighbourhood of the 

 water in the colder months ? 



Though I delight very little in analogous 

 reasoning, knowing how fallacious it is with 

 respect to natural history ; yet, in the following 

 instance, I cannot help being inclined to think 

 it may conduce towards the explanation of a 

 difficulty that I have mentioned before, with 

 respect to the invariable early retreat of the 

 hirundo apus, or swift, so many weeks before its 

 congeners ; 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 1 (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 2 . 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 high-flying gnats, scarabs, or phal&nce, that 

 are of short continuance ; and that the short stay 

 of these strangers is regulated by the defect of 

 their food. 



1 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. 



2 Mr. White has the merit of first noticing this species 

 in England : it is the vespertilio noctula of Dr. Fleming, and 

 said by that naturalist to winter in Italy. W. J. 



