Blue nuthatch
The blue nuthatch is a bird species in the family Sittidae, collectively known as nuthatches. It is a medium-sized nuthatch, measuring in length. The species, which lacks sexual dimorphism, has dramatic coloration unlike any other member of its genus. Its head is black or blackish-blue dark blue upper parts close to purple with azure feathers. The wings are edged with black. The throat and chest are white or a washed buff color, contrasting with the upper and the belly of a very dark blue; the feathers are generally clear, blue-gray or purplish.
The blue nuthatch is found in the Malay Peninsula and in Indonesia, on the islands of Sumatra and Java, inhabiting subtropical or tropical moist lowland forest and subtropical or tropical moist montane forest above in altitude. Its ecology is poorly known, but it feeds on small invertebrates found on trees; reproduction takes place from April to June or July.
Three subspecies are distinguished: S. a. expectata, S. a. nigriventer and S. a. azurea, which vary chiefly in the coloring of their mantles, chests and bellies. The species' apparent closest relatives are the velvet-fronted nuthatch, the yellow-billed nuthatch and the sulphur-billed nuthatch. The population of the species has not been rigorously estimated but the species appears to be at low risk of extinction because of the extent of its distribution. It has been classified as of Least Concern by the International Union for Conservation of Nature.
Taxonomy
The nuthatches constitute a genus – Sitta – of small passerine birds in the family Sittidae, 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. Sitta is derived from the Ancient Greek name for nuthatches, σίττη, sittē. "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. The genus may be further divided into seven subgenera, of which the blue nuthatch is placed alone in Poecilositta.The blue nuthatch was first described in 1830 under its current binomial name, Sitta azurea, by the French naturalist René Primevère Lesson. In 2006, ornithologist Edward C. Dickinson proposed a revision of the nuthatch genus, in which certain species would be split off into separate genera, based on distinct morphological traits. He suggested as candidates the velvet-fronted nuthatch and the blue nuthatch, the morphology of which he describes as "rather aberrant... in spite of a character trait shared with Sitta formosa", and that doing so might, in turn, require S. Formosa to be split off as well. He stated, however, that a molecular study would be warranted prior to any re-classification.
In 2014, Eric Pasquet, et al. published a phylogeny based on examination of nuclear and mitochondrial DNA of 21 nuthatch species. The position of the blue nuthatch within the genus was not established with certainty, having a far lower statistical association 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, and probably the yellow-billed nuthatch, despite not being in the study's sample group. These tropical Asian nuthatches are themselves a sister clade to one comprising the subgenus Sitta , plus the brown-headed nuthatch and the pygmy nuthatch.
The blue nuthatch has three recognized subspecies:
- S. a. expectata, described in 1914 by German ornithologist Ernst Hartert as Callisitta azurea expectata from a holotype taken in the Malay Peninsula's Semangko Pass in Pahang; it is also found in Sumatra;
- S. a. nigriventer, described in 1919 by British zoologists Herbert Christopher Robinson and Cecil Boden Kloss as Poliositta azurea nigriventer from a holotype taken at Mount Gede in West Java, Indonesia. British ornithologist William Swainson had described the subspecies under the name dendrophila flavipes in 1838, but the name was subsequently little used, and can be considered a nomen oblitum ;
- S. a. azurea, the nominate subspecies, was described in 1830 by René-Primevère Lesson from a specimen possibly taken on the Arjuno-Welirang stratovolcano; inhabits central and eastern Java.
Description
The upper parts are dark blue at the mantle or purplish in some subspecies. The rectrices 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 subspecies 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.
There is no significant sexual dimorphism, but Japanese ornithologist Nagamichi Kuroda describes the female as having slightly duller upper parts. Juveniles are similar to adults, but with the crown and ear coverts duller, and having a brown cast. The belly is a dull black and the undertail coverts are variably edged a creamy white. The juvenile's bill is blackish, with a pink base. Adults experience a partial moult before the breeding season involving the throat, chest and mantle; a complete moult takes place after the breeding season.
The species is of medium size compared with other nuthatches, measuring in length. The folded wing measures in males and in females. The tail is in males and from to in females. The beak measures from in length, and the tarsus. The weight is not known, but may be comparable to the Algerian nuthatch, which also measures long, and weighs between and.
The only nuthatch sharing its range is the velvet-fronted nuthatch, which completely covers the distribution of the blue nuthatch, but these two species are not easily confused.
Ecology and behavior
Voice
The vocal repertoire of the blue nuthatch is quite varied and is reminiscent of the velvet-fronted nuthatch and, to a lesser extent, the sulphur-billed nuthatch. According to the Handbook of the Birds of the World, blue nuthatch vocalizations include: "a mellow "tup" or "tip", an abrupt "whit", a thin sibilant "sit" and a fuller, harder and more emphatic "chit"; in excitement "sit" and "chit" notes often given in short rapid repetitions, "chi-chit, chit-chit-chit" or "chir-ri-rit", which can be extended into fast series, accelerating into staccato trilling "tititititititik", or even become a winding rattle, "tr-r-r-r-r-r-t". Also thin, squeaking "zhe" and "zhe-zhe", and nasal "snieu" or "kneu" ; flight call a buzzy "chirr-u"."Feeding
The blue nuthatch is very active, often seen running in pairs, in larger groups, or mingling in mixed-species foraging flocks. It feeds on invertebrates, of which some have been particularly identified as common in its diet, including species of Trachypholis Zopheridae beetles, typical click beetle, leaf beetles and spiders and moth caterpillars. It typically forages for prey in the upper half of large trees, and occasionally in smaller trees. While prospecting on tree trunks, the bird protects its corneas from falling bark and other debris by contracting the bare skin around its eyes – an adaptation apparently unique to the species.Breeding
in the species has not been extensively studied. The nest is made in a small tree hole in which it lays three to four dirty-white eggs, washed in lavender and densely speckled with reddish-brown and gray, that measure. In Peninsular Malaysia, juveniles just reaching maturity were observed in late June; on the island of Java, the breeding season takes place from April to July, and on Sumatra an adult feeding its young was observed on May 9.Predation
Little has been specifically reported on blue nuthatch predators, but one individual was seen to freeze during the passage of a prospecting black eagle.Distribution and habitat
This species lives in the Malay Peninsula and in Indonesia on the islands of Sumatra and Java. 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.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 Sumata, and at Dempo in the south of the island. 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."
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 to the highest point in the country at. In Sumatra, the species has been reported at an altitudinal range of between and, and on Java, between and. Ornithologist John MacKinnon has reported some rare sighting at lower altitudes on the plains of Java.