The woodpeckers are part of the Picidae family, a group of near-passerine birds that also consist of piculets, wrynecks, and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme polar regions. Most species live in forests or woodland habitats, although a few species are known to live in treeless areas, such as rocky hillsides and deserts.
The Picidae are just one of eight living families in the order Piciformes. Other members of Piciformes, such as the jacamars, puffbirds, barbets, toucans, and honeyguides, have traditionally been thought to be closely related to the woodpeckers, piculets, wrynecks, and sapsuckers. More recently, DNA sequence analyses have confirmed this view.
There are about 200 species and about 30 genera in this family. Many species are threatened or endangered due to loss of habitat or habitat fragmentation. Two species of woodpeckers, the ivory-billed woodpecker and the imperial woodpecker, have been considered extinct for about 30 years (although there has been speculation recently[when?] that these species may still exist).
Source: wikipedia
