NATURAL HISTORY 
LETTER XXXIX. 
TO THE SAME. 
DEAR SIR, SELBORNE, May 13, 177^. 
A MONG the many (ingularities attendhig thofe amufing birds the 
fwifts, I am now confirmed in the opinion that we have every year 
the fame number of pairs invariably; at lead the refult of my in- 
quiry has been exa<flly the fame for along time paft. The fwallows 
and martins are fo numerous, and fo widely diftributed over the 
village, that it is hardly poffible to recount them; while the fwifts, 
though they do not all build in the church, yet fo frequently 
haunt it, and play and rendezvous round it, that they are eafily 
enumerated. The number that I conftantly find are eight pairs ; 
about half of which refide in the church, and the reft build in 
fome of the loweft and meanell thatched cottages. Now as thefe 
eight pairs, allowance being made for accidents, breed yearly 
eight pairs more, what becomes annually of this increafe ; and 
what determines every fpring which pairs fliall vilit us, and re- 
occupy their ancient haunts ? 
Ever fince I have attended to the fubjecft of ornithology, I have 
always fuppofed that that fudden reverfe of affedion, that ftrange 
«mjTopj/n, which immediately fucceeds in the feathered kind to the 
moft paflionate fondnefs, is the occalion of an equal difperfion of 
birds over the face of the earth. Without this provifion one 
favourite diftrid would be crowded with inhabitants, while others 
would 
