150 
NATURAL HISTORY 
used to birds in a cage, that I fear if I had one it would 
soon die for want of skill in feeding. 
Was your reed sparrow, which you kept in a cage, the 
thick-billed reed sparrow of the Zoology, p. 320; or was it 
the less reed sparrow of Ray, the sedge-bird of Mr 
Pennant^s last publication, p. 16 ? 
As to the matter of long-billed birds growing fatter in 
moderate frosts, I have no doubt within myself what should 
be the reason. The thriving at those times appears to me 
to arise altogether from the gentle check which the cold 
throws upon insensible perspiration. The case is just the 
same with blackbirds, &c. ; and farmers and warreners 
observe, the first, that their hogs fat more kindly at such 
times, and the latter that their rabbits are never in such 
good case as in a gentle frost. But when frosts are severe, 
and of long continuance, the case is soon altered ; for then 
a want of food soon over-balances the repletion occasioned 
by a checked perspiration. I have observed, moreover, 
that some human constitutions are more inclined to plump- 
ness in winter than in summer. 
When birds come to suffer by severe frost, I find that the 
first that fail and die are the redwing fieldfares, and then 
the song-thrushes. 
You wonder, with good reason, that the hedge sparrows, 
&c., can be induced at all to sit on the egg of the cuckoo 
without being scandalized at the vast disproportioned size 
of the supposititious egg ; but the brute creation, I suppose, 
have very little idea of size, colour, or number. For the 
common hen, I know, when the fury of incubation is on her, 
will sit on a single shapeless stone instead of a nest full of 
eggs that have been withdrawn ; and, moreover, a hen- 
turkey, in the same circumstances, would sit on in the empty 
nest till she perished with hunger. 
I think the matter might easily be determined whether a 
cuckoo lays one or two eggs, or more, in a season, by open- 
ing a female during the laying-time. If more than one 
was come down out of the ovary, and advanced to a good 
size, doubtless then she would that spring lay more than 
one. 
