The nuthatches () constitute a genus, Sitta, of small passerine birds belonging to the family Sittidae. Characterised by large heads, short tails, and powerful bills and feet, nuthatches advertise their territory using loud, simple songs. Most species exhibit grey or bluish upperparts and a black eye stripe.
Most nuthatches breed in the temperate or montane woodlands of the Northern Hemisphere, although two species have adapted to rocky habitats in the warmer and drier regions of Eurasia. However, the greatest diversity is in Southern Asia, and similarities between the species have made it difficult to identify distinct species. All members of this genus nest in holes or crevices. Most species are non-migratory and live in their habitat year-round, although the North American red-breasted nuthatch migrates to warmer regions during the winter. A few nuthatch species have restricted ranges and face threats from deforestation.
Nuthatches are omnivorous, eating mostly insects, nuts, and seeds. They forage for insects hidden in or under bark by climbing along tree trunks and branches, sometimes upside-down. They forage within their territories when breeding, but they may join mixed feeding flocks at other times.
Their habit of wedging a large food item in a crevice and then hacking at it with their strong bills gives this group its English name.
Taxonomy
The nuthatch family, Sittidae, was described by René-Primevère Lesson in 1828.
Sometimes the wallcreeper (Tichodroma muraria), which is restricted to the mountains of southern Eurasia, is placed in the same family as the nuthatches, but in a separate subfamily "Tichodromadinae", in which case the nuthatches are classified in the subfamily "Sittinae". However, the wallcreeper is more often placed in a separate family, the Tichodromadidae.
The wallcreeper is intermediate in its morphology between the nuthatches and the treecreepers, but its appearance, the texture of its plumage, and the shape and pattern of its tail suggest that it is closer to the former taxon.
The nuthatch vanga of Madagascar (formerly known as the coral-billed nuthatch) and the sittellas from Australia and New Guinea were once placed in the nuthatch family because of similarities in appearance and lifestyle, but they are not closely related. The resemblances arose via convergent evolution to fill an ecological niche.
The nuthatches' closest relatives, other than the wallcreeper, are the treecreepers, and the two (or three) families are sometimes placed in a larger grouping with the wrens and gnatcatchers. This superfamily, the Certhioidea, is proposed on phylogenetic studies using mitochondrial and nuclear DNA, and was created to cover a clade of (four or) five families removed from a larger grouping of passerine birds, the Sylvioidea.
Genus name
The nuthatches are all in the genus Sitta Linnaeus, 1758, a name derived from : , Ancient Greek for this bird.
The English term nuthatch refers to the propensity of some species to wedge a large insect or seed in a crack and hack at it with their strong bills.
Species boundaries
Species boundaries in the nuthatches are difficult to define. The red-breasted nuthatch, Corsican nuthatch and Chinese nuthatch have breeding ranges separated by thousands of kilometres, but are similar in habitat preference, appearance and song. They were formerly considered to be one species, but are now normally split into three and comprise a superspecies along with the Krüper's and Algerian nuthatch. Unusually for nuthatches, all five species excavate their own nests.
The Eurasian, chestnut-vented, Kashmir and chestnut-bellied nuthatches form another superspecies and replace each other geographically across Asia. They are currently considered to be four separate species, but the south Asian forms were once believed to be a subspecies of the Eurasian nuthatch. A recent change in this taxonomy is a split of the chestnut-bellied nuthatch into three species, namely the Indian nuthatch, Sitta castanea, found south of the Ganges, the Burmese nuthatch, Sitta neglecta, found in southeast Asia, and the chestnut-bellied nuthatch sensu stricto, S. cinnamoventris, which occurs in the Himalayas. Mitochondrial DNA studies have demonstrated that the white-breasted northern subspecies of Eurasian nuthatch, S. (europea) arctica, is distinctive, and also a possible candidate for full species status. This split has been accepted by the British Ornithologists' Union.