Woodpeckers

Woodpecker Facts

Classification:

• Kingdom: Animalia
• Phylum: Chordata
• Class: Aves
• Order: Piciformes
• Family: Picidae (woodpeckers and allies)
• Subfamily: Picinae (true woodpeckers, 25 genera, 181 species); Jynginae (wrynecks, one genus, two species); Picumninae (piculets, three genera, thirty-one species)
• Geographical location: Every continent except Australia and Antarctica
• Habitat: Wooded areas with temperate climates
• Gestational period: One to seven days
• Life span: Up to fifteen years
• Special anatomy: Feathers, including stiff retrices and bristles; two wings, low-aspect ratio; zygodactyl feet; stout bill; long tongue

Woodpeckers are found worldwide in areas with trees and a temperate climate. They range in size from 3.5 inches to 2 feet. The largest North America species is the pileated woodpecker, which is 16.5 inches long with a wingspan of 29 inches. Most species have a dominant plumage pattern of black or brown and white, with additional splashes of red or yellow. Woodpeckers are scansorial, much like the ancient bird Archaeopteryx. To facilitate tree climbing, they have sharply curved claws and strong zygodactyl feet. Most birds have four toes, with one toe (hallux) directed backward and the others forward (anisodactyl foot). This type of foot is ideal for perching, but in woodpeckers the fourth toe is directed backward along with the hallux to produce a foot with two toes forward and two toes rearward, more suited to tree climbing and clinging. A few woodpecker species have lost one of the rear toes and are referred to as three-toed woodpeckers. Rectrices act as props for the woodpecker when climbing, resulting in a hitching motion as the bird moves. These stiff tail feathers are critical for climbing activities, and during molting, the center two feathers are preserved until the rest of the tail feathers are replaced, whereas in other birds the center feathers are the first to be lost.

Stout, chisel-like bills are used to peel bark and excavate wood in search of insects or larvae to eat. Bills are also employed to carve out roosting and nesting cavities in trees and for drumming. Both the skull and bill are designed to absorb the shock of repeated pounding on wood. The sturdy feet and claws together with the rectrices form a triangular brace for the hard pounding by the bill. Woodpecker tongues are very long and wrap around the skull to anchor at the base of the bill. Extension of the tongue to retrieve food is accomplished by a complex system featuring long hyoid (tongue-base) bones. Some woodpecker tongues have barbs to help extract insects and larvae from chiseled holes, while sapsucker tongues are shorter, with fine, hairlike processes to aid in capturing sap and associated insects. Nostrils of woodpeckers are protected from the “sawdust” that excavating bills create by bristles or by being reduced to narrow slits.

Wings are tapered, with a low aspect ratio (ratio of length to width). This wing configuration is designed for rapid takeoff and swift evasive flight maneuvers to capture prey, such as flying insects, or to escape predators. The eyes are positioned on the side of the head, giving the bird a wide field of vision to help spot predators. This ocular arrangement produces a predominantly monocular vision in which the environment is seen by only one eye. Binocular vision, providing depth perception important for flying and landing, is present in a relatively narrow field of vision straight ahead.

Woodpecker Behavior

Some species of woodpeckers live up to fifteen years in the wild. Woodpeckers are monogamous (one male mates with one female). Some of the earliest sounds emanating from the woods in the spring are the drumming of woodpeckers. Woodpeckers vocalize with calls rather than songs. Drumming functions instead of song to proclaim territorial boundaries and attract mates. Both males and females drum. Dry branches, hollow tree trunks or logs, or any other object capable of producing a loud noise may be selected. Most woodpeckers drum in a burst with a rate characteristic of the species. For example, hairy woodpeckers drum at a rate of twenty-six drums per second, but the smaller downy woodpecker drums at a rate of fifteen drums per second. Sapsuckers drum more rhythmically, with a varying rate slowing at the end. Territoriality and courtship are also announced by displays. Bowing, bobbing, and side-to-side head motions, along with partial spreading of wings and tail, are performed during these displays. Some of the most lively and spectacular displays are given by flickers in the spring.

Nearly all woodpeckers nest in unlined tree cavities, which they excavate. Typically, both male and female birds excavate a new site each year, and old sites are abandoned, to be used by other species of cavity-nesting birds that lack the carving talents of woodpeckers. Cavity nesting protects the eggs and young birds from predators and bad weather. Holes often face the sun to help with warming. Eggs are laid on wood chips and “sawdust” that are deposited at the bottom of the nesting cavity as a consequence of excavation. These remnants are not supplemented by other nesting materials. An average of four (a range of three to nine) eggs are laid. The eggs are white since the protection afforded by the nest cavity obviates the need for camouflage coloration. Incubation takes about two weeks and is shared by both male and female birds during the day, but is done solely by the male at night. Incubation begins prior to the last egg being laid, resulting in asynchronous hatching. Hatchlings are born immobile, downless, and with eyes closed, and are fed by the parents (altricial development). Feeding is by regurgitation and is performed by both parents until the birds are completely developed, in about four weeks. First-born birds have an advantage and are more likely to survive.

Woodpeckers eat insects lodged in the trunks or limbs of trees, and some species also feed on the ground or catch insects in the air. Nuts, fruit, seeds, and tree sap are also consumed, depending upon the particular species. Ants are the insect preferred by many woodpeckers. It should be noted that the effects of woodpeckers on trees are rarely harmful and are usually beneficial as a result of pest control. Nest holes are drilled in diseased or dead trees.

Bird watchers can easily identify woodpeckers at a distant by their characteristic posture and flight. They are usually seen clinging to branches or tree trunks using their rigid tail feathers as props. Woodpeckers fly in a pattern of moderate rises and falls. This bounding flight pattern is produced when a short burst of wing beats (rising) alternates with a closed-wing glide (falling). Woodpeckers are not long-distance flyers, and most species are permanent residents or migrate modest distances, which may vary with the abundance of food. Most species are solitary or paired, but the acorn woodpecker lives in communal groups of up to sixteen birds. This clown-faced bird has a complex social structure and is known for its acorn hoarding. Birds harvest acorns in the fall and ram them into holes drilled in one or two “granary” trees, usually at the center of their territory. As many as fifty thousand acorns are each carefully matched to a hole which will result in a tight fit. As the acorns shrink in size with age they are relocated into slightly smaller holes to produce another snug fit. The secure fit makes it difficult for robbers to steal acorns from the tree without alerting the vigilant acorn woodpecker family.

Environmental Ecology

The largest (with a length of twenty-one inches) and most spectacular North American woodpecker was the ivory-billed woodpecker, now thought to be extinct. When European settlers first came to the United States, this species was found throughout the southeast, as far north as North Carolina and up the Mississippi Valley to southern Illinois and Ohio. These birds were killed for their bills, which were prized for head ornaments. Hunters could get two or three buckskins in trade for one bill. An even greater impact resulted from logging. These huge birds required large trees for nest cavities which are up to nine inches across and fourteen inches deep. In the twentieth century, ivory-bills had been exterminated from all but a few isolated areas in Louisiana, Florida, and South Carolina. Their last stronghold was in the Singer Tract of large cyprus trees in Louisiana. Unfortunately, the Singer Tract was heavily logged with the help of German prisoners of war in 1941, destroying much of the habitat for the few remaining birds. The last authenticated sighting of an ivory-billed woodpecker was in April 1944, in northwest Louisiana. Since that time there have continued to be unconfirmed sightings, and a glimmer of hope remains that some of these magnificent birds may yet live in the fifty thousand remaining acres of the Singer Tract, or in other forests in the southeastern United States or Cuba.

Principal Terms

altricial: type of development in which hatchlings are born naked, blind, nearly immobile, and helpless

bristles: specialized feathers that protect the nostrils

display: visual signal used by a bird to trigger behavior in courtship or attacks

drumming: type of nonvocal communication produced by banging bill on a hollow tree trunk or other noise-producing object

rectrices: tail feathers

remnants: nesting material not deliberately placed in nest by birds

zygodactyl: type of foot with two toes directed forward and two toes directed backward

Bibliography

Bent, Arthur Cleveland. Life Histories of North American Woodpeckers. 1939. Reprint. Bloomington: Indiana UP, 1992. Print.

Ehrlich, Paul R., David S. Dobkin, and Daryl Wheye. The Birder’s Handbook. New York: Simon, 1988. Print.

Gill, Frank B. Ornithology. 3rd ed. New York: W. H. Freeman, 2006. Print.

Gorman, Gerard. Woodpeckers of the World: A Photographic Guide. Richmond Hill: Firefly, 2014. Print.

Short, Lester L. Woodpeckers of the World. Riverton: Weidner, 1983. Print.

Shunk, Stephen A. Peterson Reference Guide to Woodpeckers of North America. New York: Houghton Mifflin Harcourt, 2016. Print.