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 the 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 to sit at all 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the fury of incubation is on her, will sit on a single shapeless stone instead of a nest full of eggs that have been withdrawn: and, moreover, a hen-turkey, in the same circumstances, would sit on in the empty nest till she perished with hunger.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 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.
I will endeavour to get a hen, and to examine.
Your supposition that there may be some natural obstruction in singing birds while they are mute, and that when this is removed the song recommences is new and bold; I wish you could discover some good grounds for this suspicion.
I was glad you were pleased with my specimen of the caprimulgus, or fern-owl; you were, I find, acquainted with the bird before.
When we meet, I shall be glad to have some conversation with you concerning the proposal you make of my drawing up an account of the animals in this neighbourhood. Your partiality towards my small abilities persuades you, I fear, that I am able to do more than is in my power: for it is no small undertaking for a man unsupported and alone to begin a natural history from his own autopsia! Though there is endless room for observation in the field of nature, which is boundless, yet investigation (where a man endeavours to be sure of his facts) can make but slow progress; and all that one could collect in many years would go into a very narrow compass.
Some extracts from your ingenious 'Investigations of the difference between the present temperature of the air in Italy,' etc., have fallen in my way, and gave me great satisfaction: they have removed the objections that always rose in my mind whenever I came to the passages which you quote. Surely the judicious Virgil, when writing a didactic poem for the region of Italy, could never think of describing freezing rivers, unless such severity of weather pretty frequently occurred!
P.S. Swallows appear amidst snows and frost.
Letter VI
To The Honourable Daines BarringtonSelborne, May 21, 1770.
Dear Sir,The severity and turbulence of last month so interrupted the regular progress of summer migration, that some of the birds do but just begin to show themselves, and others are apparently thinner than usual; as the white-throat, the black-cap, the red-start, the fly-catcher. I well remember that after the very severe spring in the year 1739-40 summer birds of passage were very scarce. They come probably hither with a south-east wind, or when it blows between those points; but in that unfavourable year the winds blowed the whole spring and summer through from the opposite quarters. And yet amidst all these disadvantages two swallows, as Imentioned in my last, appeared this year as early as the eleventh of April amidst frost and snow; but they withdrew again for a time.
I am not pleased to find that some people seem so little satisfied with Scopoli's new publication; * there is room to expect great things from the hands of that man, who is a good naturalist: and one would think that an history of the birds of so distant and southern a region as Carniola would be new and interesting. I could wish to see that work, and hope to get it sent down. Dr. Scopoli is physician to the wretches that work in the quicksilver mines of that district.
(* This work he calls his Annus Primus Historico-Naturalis.)When you talked of keeping a reed-sparrow, and giving it seeds, Icould not help wondering; because the reed-sparrow which Imentioned to you (passer arundinaceus minor Raii) is a soft-billed bird; and most probably migrates hence before winter; whereas the bird you kept (passer torquatus Raii) abides all the year, and is a thick-billed bird. I question whether the latter be much of a songster; but in this matter I want to be better informed. The former has a variety of hurrying notes, and sings all night. Some part of the song of the former, I suspect, is attributed to the latter.
We have plenty of the soft-billed sort; which Mr. Pennant had entirely left out of his British Zoology, till I reminded him of his omission. See British Zoology last published, p. 16.**(** See Letter XXV to Mr. Pennant.)
I have somewhat to advance on the different manners in which different birds fly and walk; but as this is a subject that I have not enough considered, and is of such a nature as not to be contained in a small space, I shall say nothing farther about it at present.*(* See Letter XLIII to Mr. Barrington.)
