Editing Picinae (section)

== Physiology and behaviour ==
Some woodpeckers and [[wryneck]]s in the order Piciformes have [[Dactyly|zygodactyl]] feet, with two toes pointing forward, and two backward. These feet, though adapted for clinging to a vertical surface,  can be used for grasping or perching. Several species have only three toes.  The woodpecker's long [[tongue]], in many cases as long as the woodpecker itself, can be darted forward to capture insects. The tongue is not attached to the woodpecker's head in the same way as it is in most birds, but instead it curls back up around its skull, which allows it to be so long.

The woodpecker first locates a [[wikt:tunnel|tunnel]] by tapping on the trunk with its head. Once a tunnel is found, the woodpecker [[chisel]]s out wood until it makes an opening into the tunnel. Then it worms its [[tongue]] into the tunnel to try to locate the [[Larva|grub]]. The tongue of the woodpecker is long and ends in a barb. With its tongue the woodpecker skewers the grub and draws it out of the trunk.

Woodpeckers also use their beaks to create larger holes for their nests which are 15&ndash;45&nbsp;cm (6&ndash;18&nbsp;inches) below the opening. These nests are lined only with wood chips and hold 2&ndash;8 white eggs. Because the nests are out of sight, they are not visible to predators and eggs do not need to be camouflaged. Cavities created by woodpeckers are also reused as nests by other birds, such as [[grackle]]s, [[starling]]s, some [[duck]]s and [[owl]]s, and mammals, such as [[tree squirrel]]s.

Several adaptations combine to protect the woodpecker's brain from the substantial pounding that the pecking behaviour causes: it has a relatively thick skull with relatively spongy bone to cushion the brain; there is very little [[cerebrospinal fluid]] in its small [[subarachnoid space]]; the bird contracts [[Mandible|mandibular]] muscles just before impact, thus transmitting the impact past the brain and allowing its whole body to help absorb the shock; its relatively small brain is less prone to concussion than other animals'.<ref>Cure for a headache, Ivan R. Schwab, British Journal of Ophthalmology. 86(8):843, August 2002.</ref>

Some species have modified joints between bones in the skull and upper jaw, as well as muscles which contract to absorb the shock of the hammering. Strong neck and tail-feather muscles, and a chisel-like bill are other hammering adaptations which are seen in most species. Other species of woodpecker, such as the Flicker, uses its long tongue primarily to grab prey from the ground or from under loose bark. 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.  The slack of tongue is kept under the loose skin behind its neck. The tiny bones divide into essentially two tongues, coming back together before entering the beak.