Eurasian Nuthatch (Sitta europaea) - HBW 13, p. 127

Taxonomy: Sitta europaea Linnaeus, 1758, Europe and America = Sweden.
Forms a superspecies with S. nagaensis, S. cashmirensis, S. castanea, S. cinnamoventris and S. neglecta; has often been treated as conspecific with some or all of these. Geographical variation complex. Races usually divided into three main groups, buff-breasted “caesia group” (in W Europe, N Africa and Middle East), white-breasted “nominate group” (N Palearctic from Scandinavia E to Japan, S to E Tien Shan and N China), and buff-breasted “sinensis group” (C & E China), with large race arctica (NE Siberia) as a separate “group”; recent detailed morphological studies of Asian populations, combined with examination of mitochondrial DNA (mtDNA) from many localities across range (but excluding Turkey, the Levant, Iran and China), have revealed a more complex situation, but details not yet resolved. Present treatment tentative, based on incomplete molecular-genetic material: European “nominate group” (now including “caesia group”), within which mtDNA reveals a European clade, as well as a separate clade based on individuals of race caucasica (but other Middle Eastern populations not sampled and limits of Caucasian grouping impossible to define, hence provisionally combined with European clade); Asian “asiatica group”, comprising white-bellied N forms and buff-bellied SE forms, which shown by mtDNA to form a natural grouping (although birds from Hokkaido, in N Japan, differed by c. 1% uncorrected mtDNA, and some or all of Japanese forms may represent a distinct subgroup); “sinensis group” of China (no DNA data); NE Asian arctica, which differs significantly in mtDNA from all other races and may well represent a separate species (several reports of its occurring sympatrically with “asiatica group”). Also, “nominate group” meets or overlaps with “asiatica group” in two small areas (S Urals, and lower basins of R Kama and R Vyatka), with hybridization reported as limited and not significantly affecting the phenotype of adjacent “pure” populations; these two groups possibly represent distinct species. In addition, nominate race and caesia intergrade over broad front from E Denmark E to Lithuania and W Belarus and S to W Ukraine, E Bulgaria and NW Turkey; birds in N Turkey are intermediate between caucasica and caesia/levantina; race amurensis intergrades with baicalensis in Amur valley (SE Russia) and with sinensis in relatively narrow zone in NE Hebei (E China). Birds of this species in Altay region of N Xinjiang (NW China) of uncertain racial identity, provisionally included in seorsa. Races baicalensis, sakhalinensis, clara and takatsukasai often merged with asiatica, and race formosana often synonymized with sinensis. Twenty-two subspecies currently recognized.