Nuthatch

The nuthatches (/ˈnʌthætʃ/) 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 upper parts 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.

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, was placed in the same family as the nuthatches, but in a separate subfamily "Tichodromadinae", in which case the nuthatches were classified in the subfamily "Sittinae". However, the wallcreeper is now 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 nuthatches.

The next closest relatives to nuthatches after the wallcreeper, are the treecreepers (Certhiidae) and spotted creepers (Salpornithidae), with these families placed in a larger grouping with the wrens (Troglodytidae) and gnatcatchers (Polioptilidae). This superfamily, the Certhioidea, is proposed on phylogenetic studies using mitochondrial and nuclear DNA, and was created to cover a clade of families removed from a larger grouping of passerine birds, the Sylvioidea.

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.