92 
THE NATURAL HISTORY 
[LETT. 
curiously laid up in an hybernaculum artificially formed of grass 
and leaves. At one end of the burrow lay above a gallon of 
potatoes regularly stowed, on whicli it was to have supported 
itself for the winter. But the difficulty with me is how this 
ampliihiiis mus came to fix its winter station at such a distance 
from the water. Was it determined in its choice of that place 
by the mere accident of finding the potatoes which were planted 
there ? or is it the practice of the 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 1 have 
mentioned before, with respect to the invariable early retreat of 
the Hirundo apiis, 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 ^ (which by the bye is at present a nonde- 
script 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. IS'ow 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 tlie 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 jphalmnm that are short of 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 31st ; since which I have not seen or heard any. 
Swallows were observed on to ISTovember the third. 
Selborne, Dec. 8, 1769. 
1 The little Bat appears almost every month in the year ; but I have 
never seen the large one till the end of April, nor after July. They are 
most common in June, but never very plentiful. 
