Sitta castanea Lesson, 1830
Of the three groups mentioned by Harrap (1996): a ‘plains group’ (nominate castanea), a ‘foothills group’ (almorae, cinnamoventris Blyth, 1842, koelzi and tonkinensis Kinnear, 1936), and the ‘neglecta Walden, 1870, group’, judging by plumage pattern, the last is the poorest fit with the others (as Quinn’s plate in Harrap, 1996, demonstrates). In addition to genetic sampling, further studies of voice and behaviour are required, especially in areas where two or more nuthatch populations are geographically in close proximity and perhaps separated altitudinally to an extent that might limit but not eliminate contact. Harrap wrote “Could tonkinensis be reproductively isolated from neglecta, thus meriting specific status [for neglecta]?” Another way to look at this is to ask whether separation of a monotypic species neglecta would require the then isolated tonkinensis to be treated as a species too? There are many cases among south-east Asian birds where large range gaps exist between forms that have been judged to be conspecific. Nuthatches are relatively easy to find and to see and must be among the easier birds to study intensively, yet little is known about the Asian ones.
Fisher & Warr (2003: 159) have suggested that Latham (1790) described Sitta longirostris  from one or two paintings from the collection of Lady Impey, and they reproduced two, one of which was labelled ‘Syam Chakar’ suggesting to them that the origin of the specimen depicted (either a syntype or holotype of Latham’s name) was probably Siam (Thailand). The artist, apparently called Shaikh Zayn-al-Din, may have been Persian or have learned his painting technique under Persian tuition and it may be no coincidence that the picture much more closely resembles south-west Iranian birds, which belong to Sitta europaea persica Witherby, 1903, than it does any from Thailand. There is a mausoleum to a 15th century sheikh of the artist’s name at Taybad in Iran (www.archnet.org/library/images/sites/one-site/tcl). If he was the artist the paintings are probably of considerable historical importance, but they may be copies produced much later.