The sittellas are a family, Neosittidae, of small passerine birds found only in Australasia. They resemble nuthatches, but whilst they were considered to be in that family for many years they are now afforded their own family. They do not migrate other than for local movements.
The sittellas are small woodland birds with thin pointed down-curved bills, which they use to extricate insects from bark. Nests are open cups in forked branches.
They were formerly classified in two separate genera with the black sittella in Daphoenositta and the varied and Papuan sittellas in Neositta. The two genera are now usually merged, with Daphoenositta having priority.
The true evolutionary affinities of the sittellas have long been clouded by their close resemblance to the Northern Hemisphere nuthatches.[2] As late as 1967 the sittellas were retained in that family by some authorities, although doubts about that placement had been voiced in the previous decades. Both their climbing technique and overall morphology are extremely similar; however they differ both in their sociality and their nesting behaviour, as sittellas create nests on branches whereas nuthatches nest in cavities in trees. In addition the specifics of the morphology of the leg differed, with sittellas having leg muscles more similar to those of the honeyeaters. Their placement was then moved to various families, including the Old World babblers (an infamous wastebasket taxon), the true treecreepers (Certhiidae, which range across the Holarctic and Africa) and the Australian treecreepers (Climacteridae). Their relationship with the Australian radiation of passerines was suggested by S.A. Parker on the basis of egg colour, nest structure and nestling plumage, and their position in this radiation was vindicated by Sibley and Ahlquist's DNA–DNA hybridization studies.[3] These researchers placed the sittellas in a monotypic tribe within the superfamily Corvoidea. Today they are afforded their own family in a clade close to the berrypeckers and longbills (Melanocharitidae) and the whistlers (Pachycephalidae).[2] A molecular genetic study published in 2019 found that the family Neosittidae was sister to the family Mohouidae containing the yellowhead, whitehead and pipipi.[4]
The sittellas comprise a single genus, Daphoenositta, which contains two species. The two species were once considered to be two genera, but when the two were lumped the genus name of the less well known black sittella was adopted (due to priority), while the family retained the family name based on the junior synonym (Neositta). The most common species, the varied sittella, was once thought to represent several separate species, including five species in Australia, but in spite of considerable variation in plumage there are extensive zones of hybridization where the forms overlap (including an area of Queensland where all five Australian subspecies exist),[5] and are now thought to be a single species with eleven subspecies. The black sittella has three recognized subspecies.
Daphoenositta trevorworthyi is a fossil sittella species from the middle Miocene, representing the oldest known fossil record of the sittella family. The species was described from a distal tibiotarsus discovered in the Riversleigh World Heritage Area in northwestern Queensland, Australia.[6]