SELBORNE, _April 12th_, 1770.
Dear Sir,--I heard many birds of several species sing last year after
Midsummer, enough to prove that the summer solstice is not the period
that puts a stop to the music of the woods. The yellow-hammer no doubt
persists with more steadiness than any other: but the woodlark, the wren,
the redbreast, the swallow, the whitethroat, the goldfinch, the common
linnet, are all undoubted instances of the truth of what I advanced.
If this severe season does not interrupt the regularity of the summer
migrations, the black-cap will be here in two or three days. I wish it
was in my power to procure you one of those songsters; but I am no
bird-catcher, and so little 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, etc.; 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 overbalances the repletion occasioned by a
checked perspiration. I have observed, moreover, that some human
constitutions are more inclined to plumpness 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, etc., can be
induced at all to sit on the egg of the cuckoo without being scandalised
at the vast disproportionate 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that have been withdrawn: and, moreover, a hen-turkey, in the same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 opening 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.