Variations in the Black-backed Magpie [Gymnorhina tibicen)
By C. F. COLE, R.A.O.U.,Wangaratta, Victoria.
Probably there is no other species belonging to the avifauna of Austraha that varies so much in the adult plumage as does Gymnorhina tibicen, and in so conspicuous a type of marking, as that upon the back, from which it derives its vernacular name "Black-backed Magpie," thus separating, at a cursory glance, this bird from its allied species, the White-backed Magpie ( G. leuconota). Both species are to be met with in the north-east of Victoria, tibicen being common, whilst leuconota is rather rare. It is no uncommon sight to see from 50 to 100 of the tibicen species, in the late autumn, feeding upon freshly-fallowed land.
It was owing to seeing odd "white-backed" birds associated with the "black-backed" birds, and others having this black marking splashed with white, that my suspicions were aroused. The variations in the markings upon the back of many birds dissimilar from that of the birds with the typical marking were many and interesting. These variations were features peculiar to this species. G. tibicen, and that this variation in colour upon the back of individual birds, from a uniform black to white, was strong evidence that many of the "white-backed" birds associated with the other types already referred to. were really variations of G. tibicen.
If the tibicen and leuconota species had, and were still mating, this would account for this variation in the colour of the back. Probably, at times, this mating does occur where the two species inhabit the same locality, but the writer has failed to prove that this is so. If this mating should take place, it would be a natural sequence that many of the progeny would have this conspicuous marking upon the back, varying from black to white, as depicted in Figures A, B, C, D, E, and the progeny would perpetuate this variation. My object in compiling this article upon this species is to prove, after years of close observation, that this variation is perpetuated, and that a "white-backed" Magpie seen in the north-east of Victoria is not necessarily a G. leuconota, but it may be a variation of G. tibicen. There is a probability of this variation increasing to such an extent in numbers as to exceed the parent-typed species—the "Black-backed" Magpie. Roughly speaking, in Wangaratta and adjacent districts the percentage of birds classed under "variation" is very noticeable, at times five out of six birds seen being variations, and it may be safely stated that approximately 30 per cent, to 35 per cent, are variations.
