Great Tit (Parus major) - HBW 12, p. 739

Taxonomy: Parus major Linnaeus, 1758, Europe.
Part of a species group which includes also P. bokharensis, P. monticolus and P. nuchalis. Forms a superspecies with P. bokharensis; has been treated as conspecific, but the two interbreed only rarely and locally, and genetic evidence indicates that they are better considered separate species. Hybridizes, very rarely, also with Periparus ater and Cyanistes caeruleus, and possibly with Poecile palustris. Geographical variation highly complex, and to some extent clinal, but three groups of races, or “sections”, traditionally recognized: “nominate section”, in Palearctic (except far E), containing the green-backed, yellow-bellied races (the first 12 of those listed below); “cinereus section”, from SW Asia and Indian Subcontinent E to Indochina and Indonesia, containing the grey-backed, whitish-bellied forms (the next 13 in list); and “minor section”, from E Asia and Japanese islands, incorporating the greenish-backed, white-bellied races (the final 9 in list). Recent analyses, using DNA evidence and hybridization studies, suggest that these sections should perhaps be treated as three separate species, largely isolated from one another by major landforms (e.g. Himalayas); also some differences in voice and habitat. On the other hand, a degree of intergradation and/or hybridization is evident in areas where groups meet, e.g. intergrades between blanfordi and intermedius and between kapustini and minor occur; further, race karelini thought by some to represent intermediate population between the first two of those, and is often included within nominate, and, moreover, intermedius and commixtus are themselves sometimes considered to represent merely intergrade populations. Some intergradation also within sections (e.g. between nominate and aphrodite in S Europe). Otherwise, within “minor group”, birds from S China (SW Sichuan S to SE Xizang, Yunnan and W Guizhou) currently included within race tibetanus, but sometimes separated as subtibetanus, and kagoshimae merged with minor by some authors. Thirty-four subspecies presently recognized.