. Bulletin of the British Ornithologists' Club. E. N. Panov 246 112A. 1 Figure 4. Proportion of males with different head colour (%%). Point 1 =Badkhyz (n= 16); Point 2 = central Kopet-Dag (n = 38); Point 3 — western Kopet-Dag (n — 33); and Point 4 = near Krasnovodsk (n = 57). Head colour scored on point-scale: 0 = pure picata; 7 = pure capistrata, 1-6 = intermediate ('hybrid') phenotypes. a = records of picata on its northern range limit in Afghanistan (from Paludan 1959); b = westernmost records of capistrata phenotype males in the USSR; c = records of capistrata in northern Afgh
. Bulletin of the British Ornithologists' Club. E. N. Panov 246 112A. 1 Figure 4. Proportion of males with different head colour (%%). Point 1 =Badkhyz (n= 16); Point 2 = central Kopet-Dag (n = 38); Point 3 — western Kopet-Dag (n — 33); and Point 4 = near Krasnovodsk (n = 57). Head colour scored on point-scale: 0 = pure picata; 7 = pure capistrata, 1-6 = intermediate ('hybrid') phenotypes. a = records of picata on its northern range limit in Afghanistan (from Paludan 1959); b = westernmost records of capistrata phenotype males in the USSR; c = records of capistrata in northern Afghanistan (Paludan 1959); d = records of breeding capistrata in the range of picata. In the histograms, the extreme left column (black) shows the proportion in the given sample of typical black- headed picata males (score 0). The white columns right of the black column are shown in order of increasing point score (1, 2, 3, and so on). back-crossing of hybrids, originating in the secondary contact zone of the 2 forms, with representatives of picata populations from its autochthonous range), and (b) may result from dispersal by individuals of the form capistrata into the range of picata. None of these possibilities can be refuted, but we are inclined to sup- port the hypothesis of gene introgression and, as evidence in favour of supposition 2b, we can at least cite the case of a capistrata male paired and breeding successfully with a picata female in the central Kopet-Dag (point 3 in Fig. 4; see also Bel'skaya 1961). Furthermore, supposition 2a appears to be contradicted at first sight by an increase in the proportion of 'white-headed' males with increasing distance from the range of capistrata. The latter circumstance may nevertheless be reconciled with the hypothesis of gene migration if one rejects the idea that the flow of alien genes across the range of picata is uniform in space and in time. In par- ticular, the dynamics of phenotypic composition may, in principle, be inf
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