Picinae

Woodpeckers
Hispaniolan woodpecker
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Piciformes
Family: Picidae
Subfamily: Picinae
Bonaparte 1838
Genera

Several, see text.

Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species.

Woodpeckers gained their English name because of the habit of some species of tapping and pecking noisily on tree trunks with their beaks and heads. 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.

Physiology and behaviour

Some woodpeckers and wrynecks in the order Piciformes have 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 tunnel by tapping on the trunk with its head. Once a tunnel is found, the woodpecker chisels out wood until it makes an opening into the tunnel. Then it worms its tongue into the tunnel to try to locate the 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 15–45 cm (6–18 inches) below the opening. These nests are lined only with wood chips and hold 2–8 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 grackles, starlings, some ducks and owls, and mammals, such as tree squirrels.

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 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'.[1]

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.

Systematics

The systematics of woodpeckers is quite convoluted. Based on an assumption of unrealistically low convergence in details of plumage and behavior, 5 subfamilies were distinguished. 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.

For example, the genera Dryocopus (Eurasia and Americas) and Campephilus (Americas) of large woodpeckers were believed to form a distinct group. However, they are quite unrelated and instead close to a Southeast Asian genus, Mulleripicus and Chrysocolaptes, respectively. In addition, the genus allocation of many species, e.g. the rufous woodpecker, has turned out to be in error, and some taxa with unclear relationships could be placed into the phylogeny.[2][3]

Unassigned fossil forms

Species in taxonomic order

This is a list of woodpecker species, presented in taxonomic order.

Tribe Dendropicini

Golden-fronted woodpecker, Melanerpes aurifrons
Hoffmann's woodpecker, Melanerpes hoffmannii
Male (left) and female American three-toed woodpecker, Picoides dorsalis. Plate by Louis Agassiz Fuertes.

Tribe Malarpicini

Tribe Picini

Tribe Megapicini

Female Western Ghats greater flameback, Chrysocolaptes lucidus socialis

References

  1. ↑ Cure for a headache, Ivan R. Schwab, British Journal of Ophthalmology. 86(8):843, August 2002.
  2. ↑ Evolutionary history of woodpeckers and allies (Aves: Picidae): Placing key taxa on the phylogenetic tree, Molecular Phylogenetics and Evolution, Brett W. Benz, Mark B. Robbins and A. Townsend Peterson Volume 40, Issue 2, August 2006, Pages 389-399
  3. ↑ Mitochondrial DNA phylogeny of the woodpecker genus Veniliornis (Picidae, Picinae) and related genera implies convergent evolution of plumage patterns, Biological Journal of the Linnean Society, William S. Moore, Amy C. Weibel and Andrea Aguis Volume 87 Issue 4 Page 611-624, April 2006
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