You can usually hear the acorn woodpecker (Melanerpis formifurus) before you see them. Medium-sized woodpeckers with bright red hats can be seen flapping back and forth. Acorn woodpeckers live in extended family groups called colonies and can be heard calling each other in a loud waka-waka-waka sound.
Habitat and range of the California acorn woodpecker
Native to the southwestern and Pacific coastal regions of the United States, the acorn woodpecker’s range extends across much of California. Acorn woodpeckers are highly adaptable birds, which contributes to their widespread distribution in Northern California.
The acorn woodpecker can be found in a range of ecosystems, including oak forests, conifer forests, riparian areas, and even urban environments. The woodpecker will adapt to most places that provide an abundant supply of acorns and places to store them. This adaptability allows them to thrive in Northern California from coastal areas to the Sierra Nevada foothills.
Within this range, the actual presence of the acorn woodpecker depends on the suitability of the habitat. As their name suggests, woodpeckers depend on an abundant supply of acorn-producing oak trees. Acorns are collected and stored by woodpeckers as a winter food source.
Oak woodpeckers are adapted to living near human structures at the urban-wildland interface, often taking advantage of wooden structures and utility poles to store acorns brought from nearby oak trees.
Acorn woodpecker populations are more stable with acorn diversity
A published 1999 study by Koenig and Hayduk found that acorn woodpecker populations along the Pacific Coast are affected by oak tree diversity. Pacific Coast habitats have a greater diversity of oak tree species which in turn stabilizes the availability of acorns each year. This, in turn, leads to a higher number of acorn woodpeckers in this area and less population variation from year to year.
While acorn woodpeckers are typically non-migratory birds in the Northern California region, there can be some seasonal movements within their range. In response to changing resource availability, they may change foraging areas or move to lower elevations during the winter months when food becomes scarce at higher elevations.
Acorn woodpecker colonies are also known to break up and disperse if the acorn supply in the area fails or their granary is destroyed.
Acorn woodpecker colonies
Acorn woodpeckers are known for their cooperative social structure. They often live in groups, known as colonies, made up of several individuals of different generations, and these groups work together to maintain their grain stores.
The dominant members of the group usually play a major role in protecting and managing the granaries, while other members help raise the young. Acorn woodpeckers create nesting cavities by digging holes in dead or living trees.
Within these colonies, nesting responsibilities are shared. Dominant males and females usually take the lead in reproduction, but are assisted by other colony members in different ways. Non-breeding members help incubate the eggs, feed the chicks, and protect the nest from potential threats.
The acorn woodpecker feeds mainly on insects, fruits and tree sap with acorns stored in large storerooms known as granaries. Acorn woodpeckers will use dead trees, snags, utility poles, light poles, wooden fence posts, and the sides of wooden buildings as grain stores.
The process of creating a granary begins when woodpeckers dig small holes, or “acorn chambers,” in the dead tree or wooden structure. They then collect the nuts and carefully place them in these holes, creating a neatly organized storage space. These stores can contain thousands of acorns, forming an important winter food reserve for birds.
Granaries help woodpeckers reduce the risk of food theft. By storing acorns in a central location, birds can better defend their valuable resources against potential thieves such as squirrels or other birds. Large groups of acorn woodpeckers will contribute acorns and guard grain stores.
The acorn woodpecker helps regenerate oak trees
Oak woodpeckers are highly adaptable and can be found in various environments in Northern California, including oak woodlands, conifer forests, riparian areas, and even urban environments. This adaptability allows them to thrive in diverse geographic environments.
The acorn woodpecker plays a vital ecological role by scattering oak tree seeds. Their habit of storing acorns in granaries leads to the inadvertent planting of these seeds, which contributes to the regeneration of oak forests.
Acorn Woodpecker Group – CWHR B296 [ds1543] GIS dataset. (2021). California Department of Fish and Wildlife. https://map.dfg.ca.gov/metadata/ds1543.html
Koenig, W. D., & Haiduk, J. (1999). Acorns, acorns, and the geographic ecology of the acorn woodpecker. Journal of Biogeography, 26(1), 159-165. https://doi.org/10.1046/j.1365-2699.1999.00256.x
Koenig, Western Digital (1980). Acorn hoarding by acorn woodpeckers in an oak forest: an exergonic analysis. By: Timothy R. Plumb, technical coordinator. Proceedings of the Symposium on the Ecology, Management and Utilization of California Oaks; June 26-28, 1979; Claremont, California. Gen Tech. Delegate PSW-44. Berkeley, CA: USDA, Forest Service, Pacific Northwest Rangeland and Forest Experiment Station: 265-269.
Olive, E. (2007). Melanerpis formifurus. in: Fire Impact Information System, [Online]. USDA, Forest Service, Rocky Mountain Research Station, Fire Science Laboratory (Product). Available: www.fs.usda.gov/database/feis/animals/bird/mefo/all.html