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.
Members of the nuthatch family live in most of North America and Europe and throughout Asia down to the Wallace Line. Nuthatches are sparsely represented in Africa; one species lives in a small area of northeastern Algeria and a population of the Eurasian nuthatch subspecies, S. e. hispaniensis, lives in the mountains of Morocco. Most species are resident year-round. The only significant migrant is the red-breasted nuthatch, which winters widely across North America, deserting the northernmost parts of its breeding range in Canada; it has been recorded as a vagrant in Bermuda, Iceland and England.
Most nuthatches are woodland birds and the majority are found in coniferous or other evergreen forests, although each species has a preference for a particular tree type. The strength of the association varies from the Corsican nuthatch, which is closely linked with Corsican pine, to the catholic habitat of the Eurasian nuthatch, which prefers deciduous or mixed woods but breeds in coniferous forests in the north of its extensive range. However, the two species of rock nuthatches are not strongly tied to woodlands: they breed on rocky slopes or cliffs, although both move into wooded areas when not breeding. In parts of Asia where several species occur in the same geographic region, there is often an altitudinal separation in their preferred habitats.
Nuthatches prefer a fairly temperate climate; northern species live near sea level whereas those further south are found in cooler highland habitats. Eurasian and red-breasted nuthatches are lowland birds in the north of their extensive ranges, but breed in the mountains further south; for example, the Eurasian nuthatch, which breeds where the July temperature range is 16–27 °C (61–81 °F), is found near sea level in Northern Europe, but between 1,750 and 1,850 m (5,740 and 6,070 ft) altitude in Morocco. The velvet-fronted nuthatch is the sole member of the family which prefers tropical lowland forests.