Taxonomy above the species level
There has long been general acceptance that the wallcreeper, Tichodroma muraria (Linnaeus, 1766), deserves its own genus and, indeed, subfamily. This is not further discussed below; no changes in taxonomy have been proposed recently.
The species-group of nuthatches that has Sitta europaea at its core comprises birds of dry-land, non-equatorial forests. While mainly Palaearctic they also occur on the southern slopes of the Himalayas and extend east through Burma and continental Thailand to Vietnam. They are largely limited to pines and deciduous forests. In more humid forests at low and middle elevations their place is taken by two southern species that are morphologically very distinct from the europaeaassemblage. Sitta frontalis Swainson, 1820, and its relatives form three groups. Red bills characterise the birds occupying the bulk of collective range and these extend to the Greater Sunda islands and Palawan. Yellow-billed Sitta solangiae(Delacour & Jabouille, 1930) occupies southern China, southern Laos and most of Vietnam and, apart from Palawan where the red-billed population resembles Bornean relatives, yellow-billed populations inhabit the Philippines. For these Philippine birds, the oldest name available is Sitta oenochlamys(Sharpe, 1877). The interrelationship of these three groups requires analysis at molecular level. In the montane tropical rain forest the very distinct Sitta azurea Lesson, 1830, appears, limited to the highlands of western Malaysia, Sumatra and Java. No nuthatches occur in Sulawesi, the Moluccas or the Lesser Sundas.
I implied above that the genus Sitta may need to be split. On morphological grounds, especially the appearance of the head with its distinctive eye-ring and black frontal patch, the Sitta frontalis group is one candidate for elevation, and the rather aberrant Sitta azurea, in spite of a character trait (white edges to wing feathers) shared with Sitta formosa Blyth, 1843, must be a second candidate – although this might lead to a need to recognize a genus for Sitta formosa as well. Generic names have already been provided; indeed Greenway (1967: 125) listed 11 generic names that are available. Recognition should wait on sufficient molecular information and, ideally, that will be made available for each of the species now lumped in Sitta.
Not all Asian species require comment. For those that do, the sequence of accounts below
Fig. 1. Map of the distribution of Sitta europaea reproduced, with permission, from Voous & Van Marle (1953), Ardea 41, Extra nummer.
reflects that in the accompanying paper (Dickinson et al., 2006) in which the following adjustments to Greenway (1967), have been made, without further comment therein: Sitta cashmirensis is placed between S. nagaensis Godwin-Austin, 1874, and S. castanea; Sitta magna Wardlaw Ramsay, 1876, followed by S. formosa, is placed before the more aberrant tropical species, and in this context, in view of the shared character trait mentioned above, it was felt desirable to place Sitta azurea next to Sitta formosa.