78 NATURAL HISTORY OF SELBORNE. 
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. 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 J 
would conclude that these Azvundines and the larger bats are sup- 
ported by some sorts of high-flying gnats, scarabs, or phalene, 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. Swal- 
lows were observed on to November the third. 
* See also Letters XXII., XXXVI., and note. 
