Blue nuthatch

The blue nuthatch was first described in 1830 under its current binomial name, Sitta azurea, by the French naturalist René Primevère Lesson (1794–1849).[3][4] Sitta is derived from the Ancient Greek name for nuthatches, σίττη, sittē.[5][6] "Nuthatch", first recorded in 1350, is derived from "nut" and a word probably related to "hack", since these birds hack at nuts they have wedged into crevices.[7] The genus may be further divided into seven subgenera,^{[fn. 1]} of which the blue nuthatch is placed alone in Poecilositta (Buturlin 1916).[8]

The nuthatches constitute a genus, Sitta, of small passerine birds in the family Sittidae,[9] typified by short, compressed wings and short, square 12-feathered tails, a compact body, longish pointed bills, strong toes with long claws, and behaviorally, by their unique head-first manner of descending tree trunks. Most nuthatches have gray or bluish upperparts and a black eyestripe.[10] In 2006, ornithologist Edward C. Dickinson Proposed splitting Sitta in multiple genera on the basis of distinct morphological traits. He suggested as candidates the velvet-fronted nuthatch (Sitta frontalis) and the blue nuthatch, the morphology of which he describes as "rather aberrant ... in spite of a character trait (white edges to wing feathers) shared with Sitta formosa", and that doing so might, in turn, require the beautiful nuthatch (S. formosa) to be split off as well. He stated, however, that a molecular study would be warranted prior to any re-classification.[11][12]

In 2014, Eric Pasquet and colleagues published a phylogeny based on examination of nuclear and mitochondrial DNA of 21 nuthatch species.^{[fn. 2]} The position of the blue nuthatch within the genus was not established with certainty, having a far lower correlation than many others in the model. Nevertheless, under the findings the species appears best represented by a clade comprising the velvet-fronted nuthatch and the sulphur-billed nuthatch (S. oenochlamys). These tropical Asian nuthatches are themselves a sister clade to one comprising the subgenus Sitta (Micrositta) (sometimes called the canadensis group), along with the brown-headed nuthatch (S. pusilla) and the pygmy nuthatch (S. pygmaea).[10][13]

The blue nuthatch is a medium-sized nuthatch that has an average length of 13.5 cm (5.3 in). The weight is not known,[18] but may be comparable to the Algerian nuthatch (Sitta ledanti), which also measures 13.5 cm (5.3 in) long, and weighs between 16.6 g (0.59 oz) and 18 g (0.63 oz).[19] Its appearance differs significantly from all other nuthatches. All of its subspecies are broadly black and white[20] (especially when viewed in low-light conditions in which their dark blue coloring is not apparent) and have upper plumage shot through with dramatic notes of cobalt, azure and other lighter shades of blue, as well as grays and purples. The head is black, or blackish-blue with a broad, pale blue eye ring.[21][22]

The three subspecies vary predominantly in the coloring of their mantles, chests and bellies. The upperparts are dark blue at the mantle or purplish in some subspecies. The rectrices, which are the tail's flight feathers, are pale blue in the middle with a black border and contrast sharply with the dark areas of the coat. The throat and breast are white, or washed buff, especially in S. a. nigriventer. The belly and abdomen are blackish, contrasting with blue-gray or purplish coverts. The bill is lavender, slightly tinged with green, and black at the tip; the legs are a pale blue-gray and the claws are slate or black.[21][22]

The species displays no significant sexual dimorphism, but Japanese ornithologist Nagamichi Kuroda describes the female as having slightly duller upperparts. Juveniles resemble adults, but have a duller crown and ear coverts, as well as a brown cast that does not cover their entire body. The belly is a dull black and the undertail coverts are variably edged creamy white. The juvenile's bill is blackish, with a pink base. Adults experience a partial moult before the breeding season (February–March for S. a. expectata; March–April for S. a. azurea) involving the throat, chest and mantle; a complete moult takes place after the breeding season (March–April and August in Java in Malaysia).[22]

• The three subspecies of the blue nuthatch and their distinct morphological characteristics
• 
  Sitta azurea expectata - note the dark blue upper parts and azure coverts.
• 
  Sitta azurea azurea - note the purple upper parts and violet coverts.
• 
  Sitta azurea nigriventer - note the purplish-blue upper parts, blue coverts and buff-colored belly.

The blue nuthatch is very active, often seen running in pairs,[23] in larger groups, or mingling in mixed-species foraging flocks.[24]

A blue nuthatch on a tree trunk at Fraser's Hill, Malaysia.

This species lives in the Malay Peninsula (in extreme southern Thailand and northern Malaysia) and in Indonesia on the islands of Sumatra and Java.[1][14] In Malaysia, the species has been observed in Bukit Larut, in the state of Perak, in the Titiwangsa Mountains, in southern Hulu Langat, in the state of Selangor, as well as some isolated populations on the slopes of the massive Mount Benom in the state of Pahang, on Mount Tahan located at the Pahang-Kelantan border, on Mount Rabong in Kelantan and at Mount Padang in the Sultanate of Terengganu.[24]

In Sumatra, the bird is found throughout the Barisan Mountains, and has been observed in the Gayo Highlands of Aceh province, the Batak Highlands of northern Sumatra, and at Dempo in the south of the island.[24] In a 1918 expedition by Robinson and Kloss, they commented: "from the commencement of heavy jungle on the valley slopes up to about 8,000 feet on Korinchi Peak this strikingly coloured little Nuthatch was very common, feeding on tall tree trunks in parties of six or seven."[27]

The blue nuthatch is typically found on mountains, inhabiting subtropical or tropical moist lowland forest and subtropical or tropical moist montane forest. In Malaysia, it is found from 1,070 m (3,510 ft) to the highest point in the country at 2,186 m (7,172 ft). In Sumatra, the species has been reported at an altitudinal range of between 900 m (3,000 ft)[24] and 2,400 m (7,900 ft),[24] and on Java, between 915 m (3,002 ft) and 2,745 m (9,006 ft). Ornithologist John MacKinnon has reported some rare sightings at lower altitudes on the plains of Java.[28]

The blue nuthatch is a common bird in Sumatra, including in the area of Kerinci Seblat National Park[27] and relatively common in Malaysia and Java.[24] It has a very wide distribution area, approaching 361,000 km² (139,000 sq mi).[29] The population has not been rigorously estimated but is considered significant and at low risk, despite BirdLife International's observation that some decline is likely (but not as yet confirmed) due to known destruction and fragmentation of areas the species is known to inhabit.[29] The blue nuthatch is placed in the category of least concern by the International Union for Conservation of Nature.[1]