Cyanistes

Eck, Siegfried, 2006, The Palaearctic Titmouse Species (Aves: Paridae: Parus sensu lato) — A current survey *, Zootaxa 1325, pp. 7-54 : 21

Subgenus Cyanistes , type species Parus caeruleus L., 1758

(Blue Tits)

The subdivision of the Blue Tits into species has also changed recently ( Eck 1988: 1 species; Salzburger et al. 2002b: 3 species). Traditionally the difference between Blue Tits s.l. and Azure Tits has been thought to be older than that between the European Blue and the North African/Canarian Ultramarine Tits. Evidently the reverse applies, and the blue and ultramarine forms, which seem more similar to our eyes, are the result of an older differentiation. Even between the Blue Tits in central and in southern Europe, the subtle population comparisons made by Taberlet and Bouvet (1990), Blondel et al. (1991) and Kvist et al. (2004) have revealed biological, ecological and genetic differentiations that could not yet have been suspected to lie behind the description of Parus caeruleus ogliastrae HARTERT 1905.

Blue and Ultramarine Tits are strictly allopatric, and at least since Martin (1988: 136–137) a species distinction between them has been considered. Blue and Azure Tits are not strictly allopatric, and hybridisation occasionally occurs ( Johansen 1952; Vaurie 1957; Meise 1975; Portenko et al. 1982). According to voice and genetic distance (cyt b) they could be subspecies, but there is no population­mixing region! How does the sympatry of these tits prove to be, in concrete terms? If Parus cyanus only recently split off from caeruleus , it would not be surprising for there to be no clear molecular­genetic differentiation between flavipectus and tianschanicus. This is not to say that there are no biological isolating mechanisms between them, but interbreeding of flavipectus with cyanus populations is known to occur ( Harrap and Quinn 1996 etc.). On the map by Portenko et al. 1982 the areas of the three southern, yellow­breasted Azure Tits are unfortunately not specially marked.