The nuthatches belong to the family Sittisdae. Characterised by large heads, short tails, and powerfull bills and feet, nuthatches advertise their territory using load, simple songs. Nutatches are very vocal, using an assortment of whistles, trills and calls. Their breeding songs tend to be simple and often identical to their contact calls but longer in duration. All nuthatches nest in cavities; except for the two species of rock nuthatches, all use tree holes, making a simple cup lined with soft materials on which to rest eggs. In some species the lining consists of small woody objects such as bark flakes and seed husks, while in others it includes the moss, grass, hair and feathers typical of passerine birds. Nuthatches are omnivorous, eating mostly insects, nut and seeds. They forage for insects hidden in or under bark by climbing along tree trunks and branches, sometimes upsidedown. They forage within their territories when breeding, but may join mixed feeding flocks at other times.