This is both a means of communication to signal possession of territory to their rivals, and a method of locating and accessing insect larvae found under the bark or in long winding tunnels in the tree or upright log.

Cavities created by woodpeckers are also reused as nests by other birds, such as grackles, starlings, some ducks and owls, and mammals, such as tree squirrels.

It has few shock-absorbing adaptations, and prefers to feed on the ground or to chip away at rotting wood and bark, habits observed in birds outside of the woodpecker family.

A "continuum" in skull structures, from little- to highly specialized for pounding is seen in different genera (groups of related species) of woodpeckers alive today.

In his classic "Birds of America," John James Audubon describes the slight gradations in hyoid horn length found in different species of living woodpeckers.

However, it has turned out that similar plumage patterns and modes of life are not reliable to determine higher phylogenetic relationships in woodpeckers, and thus only 3 subfamilies should be accepted.

[2][3] In 1975 John Morony and colleagues in their Reference List of the Birds of the World divided the true woodpeckers into six tribes: Melanerpini, Campetherini, Colaptini, Campephilini, Picini, Meiglyptini.

[7] Hemicircus Nesoctites Dinopium Gecinulus Meiglyptes Micropternus Dryocopus Mulleripicus Celeus Colaptes Piculus Picus Chrysophlegma Pardipicus Campethera Geocolaptes Campephilus Blythipicus Chrysocolaptes Reinwardtipicus Melanerpes Sphyrapicus Picoides Yungipicus Chloropicus Dendropicos Dendrocoptes Leiopicus Dendrocopos Dryobates Leuconotopicus Veniliornis The world bird list maintained by Frank Gill, Pamela Rasmussen and David Donsker on behalf of the International Ornithologists' Union recognises 208 species of true woodpecker which are split up into 33 genera.