The plumage is moulted fully once a year apart from the wrynecks, which have an additional partial moult before breeding. Woodpeckers tend to be sexually dimorphic, but differences between the sexes are generally small exceptions to this are Williamson's sapsucker and the orange-backed woodpecker, which differ markedly. The colours of many species are based on olive and brown and some are pied, suggesting a need for camouflage others are boldly patterned in black, white and red, and many have a crest or tufted feathers on the crown. The plumage of woodpeckers varies from drab to conspicuous. The largest surviving species is the great slaty woodpecker, which weighs 430 g (15 oz) on average and up to 563 g (19.9 oz), and measures 45 to 55 cm (18 to 22 in), but the extinct imperial woodpecker, at 55 to 61 cm (22 to 24 in) and ivory-billed woodpecker, at about 48 to 53 cm (19 to 21 in) and around 516 g (18.2 oz), were probably both larger. Some of the largest woodpeckers can be more than 50 cm (20 in) in length. Woodpeckers range from tiny piculets, the smallest of which appears to be the bar-breasted piculet at 7.5 cm (3.0 in) in length and a weight of 8.9 g (0.31 oz). Almost 20 species are threatened with extinction due to loss of habitat or habitat fragmentation, with one, the Bermuda flicker, being extinct and a further two possibly being so.Ī black-rumped flameback using its tail for support The family Picidae includes about 240 species arranged in 35 genera. DNA sequencing has confirmed the sister relationships of these two groups. The Picidae are one of nine living families in the order Piciformes, the others being barbets (comprising three families), toucans, toucan-barbets, and honeyguides which (along with woodpeckers) comprise the clade Pici, and the jacamars and puffbirds in the clade Galbuli. They sometimes come into conflict with humans when they make holes in buildings or feed on fruit crops, but perform a useful service by their removal of insect pests on trees.
They mostly nest and roost in holes that they excavate in tree trunks, and their abandoned holes are of importance to other cavity-nesting birds. Some species vary their diet with fruits, birds' eggs, small animals, tree sap, human scraps, and carrion. They mostly forage for insect prey on the trunks and branches of trees, and often communicate by drumming with their beak, producing a reverberatory sound that can be heard at some distance. Members of this family are chiefly known for their characteristic behaviour. Most species live in forests or woodland habitats, although a few species are known that live in treeless areas, such as rocky hillsides and deserts, and the Gila woodpecker specialises in exploiting cacti. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme polar regions. Woodpeckers are part of the family Picidae, which also includes the piculets, wrynecks, and sapsuckers.