To Edward Blyth [after July 1868]1
Please return this paper
I have said in my M.S. on your authority, (but I suppose it is a blunder on my part?) that the F. of Euplocomus has spurs.2 I see in Jerdon (III. p. 541) that the Fs. of Galloperdix have spurs, but fewer than in the Male3
[There are different types of Euplocamus (as admitted by Sclater).4 In one of them, consisting of the “small fire-back pheasants” (Acomus), the females bear spurs, but not in the other types of that group, as the “great fire-backs,” the Kallij-pheasants, the silver, the Swinhoe’s, and the Sha’n pheasants.5 Acomus comprises the Phasianus erythropthalmus, Raffles, of Malacca and Sumatra; and a “Duplicate race in Borneo.6 The ♀ of Galloperdix is spurless.]
In the Indian Field (1858. p. 52) you say that both sexes of Passer castanopterus 7 “may be said to approximate in plumage to the female of the common sparrow, with a spot of bright yellow on the breast & some maronne at the shoulder of the wing.”8 I also enclose an extract from one of your letters on 2 other species of Passer: In birds I know of no other case like that of Passer montanus, in which the young, as well as the adults of both Sexes, are clad in a plumage analogous to that characteristic of the adult male only of P. domesticus, while in other sparrows, as P. petronius, P. flavicollis, &c, both sexes retain the colouring analogous to that of the female and young of P. domesticus.9
Now will you consider whether I may say that the F. of the common Sparrow is closely analogous in plumage to both sexes of any of the above species.
[Yes. I think that you may fairly do so. But refer to the Ibis for April 1868, p. 205–6, with coloured figure published at the end of July No, & you will find another remarkable instance in Petronia brachydactyla, Tristram, of Palestine in which also the sexes are alike—clad in plumage analogous to the ♀ of common sparrow.10]
I see in Ibis vol. 6. p. 65 that the young Male of Petrocincla Cyanea acquires some blue as a nestling.11 How are the adult & young Females coloured? Is not this case analogous to that of Orocetes erythrop:?12 And are not these birds allied?
[In habit, Orocetes is a forest thrush, Petrocincla (QQQQ’s Petrocossyphus) a rock thrush; but as thrushes they are akin, & in both groups the males are chiefly blue, the females brown; now, in the first or nestling dress of the males, those feathers which are not shed and renewed at the first moult, viz. the primaries and rectrices, are blue-edged as in the adults in ♂, brown-edged as in the adult in ♀—13]
What does Swinhoe (Ibis. 1866 p. 296) mean by saying of the full grown young of Urocissa Cerulea that they have “a few of the occipital feathers tipped with violet: Darwin again!”?14
[Swinhoe evidently refers to the resemblance in this instance of the occipital feathers of the young (or distinguished from the adult) of Urocissa cærulea to what is seen in adults of U. sinensis, U. occipitalis, and U. magnirostris—three very nearly allied races.15 In the young of U. occipitalis (and probably of the others also) the occipital pale colouring referred to is more developed in the young than in the adult.]
Questions from CD related to bird plumage and sexual differences, with answers by EB.
Please cite as
Darwin Correspondence Project, “Letter no. 6532,” accessed on 1 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-6532