e 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.)
No doubt the reason why the sex of birds in their first plumage is so difficult to be distinguished is, as you say, 'because they are not to pair and discharge their parental functions till the ensuing spring.' As colours seem to be the chief external sexual distinction in many birds, these colours do not take place till sexual attachments begin to obtain. And the case is the same in quadrupeds; among whom, in their younger days, the sexes differ but little: but, as they advance to maturity, horns and shaggy manes, beards and brawny necks, etc., etc., strongly discriminate the male from the female. We may instance still farther in our own species, where a beard and stronger features are usually characteristic of the male sex: but this sexual diversity does not take place in earlier life; for a beautiful youth shall be so like a beautiful girl that the difference shall not be discernible:
Quem si puellarum insereres choro, Mire sagaces falleret hospites Discrimen obscurum, solutis Crinibus, ambiguoque vultu.--HOR.
Letter VII To The Honourable Daines Barrington
