Acorn Woodpeckers in Northern California

Caitlin Dempsey

Updated:

You can usually hear acorn woodpeckers (Melanerpes formicivorus) before you see them. These medium-sized woodpeckers with bright red caps can be seen flitting back and forth. Acorn woodpeckers live in extended family groups called colonies and they can be heard calling loudly to each other with a waka-waka-waka sound.

Habitat and range of the acorn woodpecker in California

Native to the Southwest and Pacific coastal areas of the United States, the range of the acorn woodpecker extends across much of California. Acorn woodpeckers are highly adaptable birds, which contributes to their wide distribution in Northern California.

Acorn woodpecker can exist in a range of ecosystems, including oak woodlands, coniferous forests, riparian areas, and even urban environments. These woodpeckers will adapt to most places that offer a plentiful 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.

A shaded relief map with grayscale, a blue ocean, and a light orange overlay showing the range of acorn woodpeckers in California.
Acorn woodpecker range (light orange shading) in California. Map: Caitlin Dempsey using data from California Department of Fish and Wildlife, 2021.

Within this range the actual presence of acorn woodpeckers depends on the suitability of the habitat. As their name implies, these woodpeckers are reliant upon a plentiful supply of acorn producing oak trees. The acorns are gathered and stored by the woodpeckers as a winter food source.

Acorn woodpeckers are adapted to living near human structures in the urban-wild land interface, often taking advantage of wooden structures and utility poles to store acorns fetched from nearby oak trees.

An acorn woodpecker holding a large acorn in her beak while perched on a tree stump.
A female acorn woodpecker with an acorn in her mouth in the Santa Cruz Mountains. Photo: Caitlin Dempsey.

More stable acorn woodpecker populations with oak diversity

A published study from 1999 by Koenig and Haydock found that acorn woodpecker populations along the Pacific Coast are influenced by the diversity of oak trees. Pacific Coast habitats have a greater diversity of oak tree species which in turn stabilizes the availability of acorns each year. This is turn results in a higher population of acorn woodpeckers in this area and less year-to-year population variation.

A male acorn woodpecker perches on a moss covered tree.
A male acorn woodpecker in the Santa Cruz Mountains. Photo: Caitlin Dempsey.

While acorn woodpeckers are generally non-migratory birds in the Northern California area, there can be some seasonal movements within their range. In response to changing resource availability, they may shift their foraging areas or move to lower elevations during the winter months when food becomes scarcer at higher altitudes.

Acorn woodpecker colonies are also known to disband and disperse if an area’s acorn supply 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, consisting of multiple individuals from different generations, and these groups work together to maintain their granaries.

A pair of acorn woodpeckers on a snag.
A pair of acorn woodpeckers bring food to nestlings in a cavity in a dead tree. Photo: Caitlin Dempsey.

The dominant members of the group usually play a key role in protecting and managing the granaries, while other members help in raising the young. Acorn woodpeckers create nesting cavities by excavating holes in dead or living trees.

An acorn woodpecker peers out of a nesting hold in a tree stump.
An acorn woodpecker peers out of a nesting hold in a tree stump. Photo: Caitlin Dempsey.

Within these colonies, nesting responsibilities are shared. Dominant males and females typically take the lead in breeding, but they are assisted by other colony members in various ways. Non-breeding members help incubate eggs, feed nestlings, and protect the nest from potential threats.

Granaries

Four woodpeckers on a wooden light pole with holes filled with acorns.
These acorn woodpeckers have create a granary on a wooden light pole. Photo: Caitlin Dempsey.

Acorn woodpeckers mainly feed on insects, fruit, and tree sap with acorns stored away in large storehouses known as granaries. Acorn woodpeckers will use dead trees, snags, utility poles, light poles, wooden fence posts, and the sides of wooden buildings as their granaries.

A woodpecker perched on the side of a barn with acorns in holes on the side of the barn.
Acorn woodpeckers will set up granaries on the sides of wooden buildings like this barn in the Santa Cruz Mountains. Photo: Caitlin Dempsey.

The process of creating a granary begins with the woodpeckers drilling small holes, or “acorn storage chambers,” into the dead tree or wooden structure. They then collect acorns and carefully fit them into these holes, creating a neatly organized storage space. These granaries can hold thousands of acorns, forming a critical winter food reserve for the birds.

Granaries help acorn woodpeckers reduce the risk of food theft. By storing acorns in a centralized location, the birds can better defend their valuable resource against potential thieves like squirrels or other birds. Large groups of acorn woodpeckers will contribute acorns and guard granaries.

A females acorn woodpecker perched outside of a nest which is a hole in a tree.
A female acorn woodpecker perched outside of a nest. Photo: Caitlin Dempsey.

Acorn woodpeckers help regenerate oak trees

Acorn woodpeckers are highly adaptable and can be found in various habitats in Northern California, including oak woodlands, coniferous forests, riparian areas, and even urban environments. This adaptability allows them to thrive in diverse geographic settings.

Acorn woodpeckers play a vital ecological role by dispersing oak tree seeds. Their habit of storing acorns in granaries inadvertently plants these seeds, contributing to the regeneration of oak woodlands.

References

Acorn woodpecker range – CWHR B296 [ds1543] GIS dataset. (2021). California Department of Fish and Wildlife. https://map.dfg.ca.gov/metadata/ds1543.html

Koenig, W. D., & Haydock, J. (1999). Oaks, acorns, and the geographical ecology of acorn woodpeckers. Journal of Biogeography26(1), 159-165. https://doi.org/10.1046/j.1365-2699.1999.00256.x

Koenig, W. D. (1980). Acorn Storage by Acorn Woodpeckers in an Oak Woodland: An Energetics Analysis’. In: Plumb, Timothy R., technical coordinator. Proceedings of the symposium on the ecology, management, and utilization of California oaks; 1979 June 26-28; Claremont, CA. Gen. Tech. Rep. PSW-44. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station: 265-269. 

Ulev, E. (2007). Melanerpes formicivorus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.usda.gov/database/feis/animals/bird/mefo/all.html 

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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.

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