Geographical variation and distribution of the Bearded Tit Panurus biarmicus (Linnaeus, 1758) (Aves)

The breeding distribution of the Bearded Tit Panurus biarmicus is not disjunct but continuous from western Europe to Manchuria (fig. 4). Colour variation allows for the partition in a group of light populations, a group of dark populations, and an extra dark population (fig. 5). The range of the dark group is disjunct. With respect to the amount of streaking on head and back of females, three groups could be distinguished (fig. 6). The so-called “variable group” coincides with the dark colour group, except for Greece and the Caucasus, and the “not variable group” coincides with the light colour group. The marking of individual mantle feathers in females shows no essential differences between populations. The marking of the outermost tail-feather shows great variability in each population. As a consequence, there are no differences between populations (appendix 3). Apart from sexual dimorphism in plumage, there are also sex-related differences in several biometrical characters (table II). The so-called dark populations are, as a group, often statistically different from other populations. The light populations, generally, group in the same nonsignificant subsets. Clinal variation in biometrical characters is not pronounced; with respect to males a slight increase in size from west to east may be observed in the characters “tipblack” (fig. 3, A), wing- and tail-length (figs. 7-9). Three subspecies may be distinguished, viz. Panurus biarmicus biarmicus (Linnaeus, 1758), P. b. russicus (Brehm, 1831), and P. b. kosswigi Kumerloeve, 1958 (see fig. 12).