As we thus see that chequered birds occur mingled with the true rock-pigeon at three distinct sites, namely, Faroe, the Orkney Islands, and Islay, no importance can be attached to this natural variation in the plumage.
Prince C.L. Bonaparte (6/13. 'Coup-d'oeil sur l'Ordre des Pigeons' 'Comptes Rendus' 1854-55.), a great divider of species, enumerates, with a mark of interrogation, as distinct from C. livia, the C. turricola of Italy, the C. rupestris of Daouria, and the C. schimperi of Abyssinia; but these birds differ from C. livia in characters of the most trifling value. In the British Museum there is a chequered pigeon, probably the C. schimperi of Bonaparte, from Abyssinia. To these may be added the C. gymnocyclus of G.R. Gray from W. Africa, which is slightly more distinct, and has rather more naked skin round the eyes than the rock-pigeon; but from information given me by Dr. Daniell, it is doubtful whether this is a wild bird, for dovecote-pigeons (which I have examined) are kept on the coast of Guinea.
The wild rock-pigeon of India (C. intermedia of Strickland) has been more generally accepted as a distinct species. It differs chiefly in the croup being blue instead of snow-white; but as Mr. Blyth informs me, the tint varies, being sometimes albescent. When this form is domesticated chequered birds appear, just as occurs in Europe with the truly wild C. livia. Moreover we shall immediately have proof that the blue and white croup is a highly variable character; and Bechstein (6/14. 'Naturgeschichte Deutschlands' b. 4 1795 s. 14.) asserts that with dovecote-pigeons in Germany this is the most variable of all the characters of the plumage. Hence it may be concluded that C. intermedia cannot be ranked as specifically distinct from C. livia.
In Madeira there is a rock-pigeon which a few ornithologists have suspected to be distinct from C. livia. I have examined numerous specimens collected by Mr. E.V. Harcourt and Mr. Mason. They are rather smaller than the rock- pigeon from the Shetland Islands, and their beaks are plainly thinner, but the thickness of the beak varied in the several specimens. In plumage there is remarkable diversity; some specimens are identical in every feather (I speak after actual comparison) with the rock-pigeon of the Shetland Islands; others are chequered, like C. affinis from the cliffs of England, but generally to a greater degree, being almost black over the whole back; others are identical with the so-called C. intermedia of India in the degree of blueness of the croup; whilst others have this part very pale or very dark blue, and are likewise chequered. So much variability raises a strong suspicion that these birds are domestic pigeons which have become feral.
From these facts it can hardly be doubted that C. livia, affinis, intermedia, and the forms marked with an interrogation by Bonaparte ought all to be included under a single species. But it is quite immaterial whether or not they are thus ranked, and whether some one of these forms or all are the progenitors of the various domestic kinds, as far as any light can thus be thrown on the differences between the more strongly-marked races. That common dovecote-pigeons, which are kept in various parts of the world, are descended from one or from several of the above-mentioned wild varieties of C. livia, no one who compares them will doubt. But before making a few remarks on dovecote-pigeons, it should be stated that the wild rock-pigeon has been found easy to tame in several countries. We have seen that Colonel King at Hythe stocked his dovecote more than twenty years ago with young wild birds taken at the Orkney Islands, and since then they have greatly multiplied. The accurate Macgillivray (6/15. 'History of British Birds' volume 1 pages 275-284. Mr. Andrew Duncan tamed a rock-pigeon in the Shetland Islands. Mr. James Barclay, and Mr. Smith of Uyea Sound, both say that the wild rock-pigeon can be easily tamed; and the former gentleman asserts that the tamed birds breed four times a year.