Bird Bio: Acorn Woodpecker
By Ellie Armstrong, KBO Research and Monitoring Intern
The Acorn Woodpecker (Melanerpes formicivorus) is common year-round in oak woodlands near the West Coast. Oregon was believed to hold the most northerly population of this species until a colony was discovered in Washington in 1989. Considered clown-faced in appearance, the Acorn Woodpecker’s distinctive “waka-waka” call can often be heard whenever oak trees are near. Male and females look similar, although males can be distinguished by the presence of more red on the top of their heads.
There are several morphological adaptations shared by woodpeckers. One of these is the zygodactyl foot. While many birds have three toespointing forward and one backwards on each foot, woodpeckers have two toes pointing forwards and two pointing backwards; this arrangement allows woodpeckers to cling securely to the sides of trees. They also have extremely long, sticky, and barbed tongues that help them probe crevices and collect insects. Their tongues wrap completely around their skulls and can extend out as far as 5 inches. To accommodate a lifestyle of drumming on wood, the bone at the base of their bill is porous and acts as a shock absorber.
Acorn Woodpeckers are communal breeders, a characteristic shared by only three percent of all bird species. Up to as many as 15 individuals from multiple generations will live together in an established territory. Only some of these individuals breed, while others help raise the young. The number of breeding individuals varies, but usually consists of one or two females and up to four males per female. An Acorn Woodpecker group will excavate several large cavities in dead or live trees; one cavity is typically used for the nest and the remaining cavities are used for roosting.
Acorns and insects comprise the bulk of the Acorn Woodpecker diet. The woodpeckers collect acorns during autumn and winter and store them in dead trees and telephone poles and other manmade structures, including the siding of houses. These acorn storage sites are called granaries, and one granary may contain as many as 50,000 acorns. All of the woodpeckers that live in a community are responsible for collecting and storing acorns. Old granaries are used year after year, but new ones are made as well.
Ehrlich, Paul, David Dobkin, and Darryl Wheye. The Birder’s Hnadbook. New York: Simon & Schuster Inc., 1988. 283-285. Koenig, Walter, Peter Stacey, Mark Stanback, and Ronald Mumme. “Acorn Woodpecker.” Birds of North America. 194. (1995)
Marshall, David B. et al, eds. Birds of Oregon: A General Reference. Corvallis: Oregon State University Press, 2003.;
Sibley, David. The Sibley Guide to Bird Life and Behavior. New York : Alfred A Knopf, Inc. , 2001.