Woodpeckers are birds of the family picidae, order piciformes. They are adapted for climbing up the bark of trees, and picking out insects to eat from the crevices. The feet, though very short, are usually strong; the nails are broad and crooked and the toes placed in pairs, two forward and two backward. As an additional support their tail feathers terminate in points, and are uncommonly hard. Woodpeckers have a long extensile tongue, which has muscles enabling the bird to dart it forth and to retract it again quickly. There are about 200 species worldwide.
North American woodpeckers include four species of sapsuckers (genus Sphyrapicus), which drill and then tap holes in trees for sap and the attracted insects. The pileated woodpecker dryocopus pileatus is the largest, about 43 cm/17 in long, with a red crest.
In 2005 the existence of the ivory-billed woodpecker (Campephilus principalis), the USA's largest woodpecker and thought to be extinct for 50 years, was confirmed. It was originally sighted in February 2004, in the ‘Big Woods’ region of Arkansas, but its existence was only confirmed by a year-long expedition by a team of researchers from Cornell University, New York. The largest species of woodpecker, the imperial woodpecker campephilus imperialis of Mexico, is very rare and may already be extinct.