The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker that is found in oak woodlands across western North America. Their range stretches from southwestern British Columbia down through the western United States to California and into Central America. Acorn woodpeckers are best known for their unique habit of storing acorns in storage holes they drill in trees. But where are acorn woodpeckers most abundant within their range? Let’s take a closer look at the habitat and range of this fascinating bird.
Acorn Woodpecker Habitat
Acorn woodpeckers are found in a variety of oak woodland habitats across their range, but are most abundant in certain types of oak forests and woodlands where acorns are plentiful. This includes woodlands dominated by oaks such as coast live oak, Engelmann oak, canyon live oak, interior live oak, Oregon white oak, and Emory oak. In particular, acorn woodpeckers thrive in:
- Oak savannas
- Oak woodlands
- Riparian oak forests
- Montane oak-conifer forests
These habitats provide the right mix of large, mature oak trees that produce abundant acorn crops, open areas with scattered trees for foraging, and suitable dead snags and branches for the woodpeckers to drill their acorn storage holes. The presence of oaks with exfoliating bark, which creates easy drilling and nesting sites, is also important.
Range Within Western North America
Within their overall range, acorn woodpeckers reach their highest densities in certain areas of California and the Southwest. These include:
- Coastal central California
- Sierra Nevada foothills
- Transverse and Peninsular Ranges of Southern California
- Oak woodlands of Arizona and New Mexico
For example, oak woodlands in the San Francisco Bay area, the Los Angeles Basin, the San Gabriel Mountains, and the Tehachapi Mountains support particularly high densities of acorn woodpeckers. Farther south, oak forests in the Sky Islands mountain ranges of southeastern Arizona, southwestern New Mexico and northwestern Mexico also harbor abundant populations.
California
California is really the epicenter of acorn woodpecker abundance, as the species reaches its highest densities here. The region’s mild climate, with a distinct wet season that drives acorn production, combines with extensive oak woodland and savanna habitats to create ideal conditions. Along the coast, acorn woodpeckers are a conspicuous resident of live oak woodlands from Mendocino County south to San Diego County.
Densities generally decrease north of Mendocino County and south of San Diego County, but healthy populations occur in oak habitats throughout coastal California. Inland, acorn woodpeckers thrive in foothill oak woodlands, blue oak savannas, and lower elevation riparian oak forests of the Sierra Nevada and Coast Ranges. Again, abundance peaks in Central California and declines toward the north and south range extremes in California.
Southwest
After California, the Southwest region probably hosts the next largest and most widespread populations of acorn woodpeckers. They are common in oak savannas, woodlands, and pine-oak forests from southern Nevada and Utah south through Arizona into New Mexico and western Texas. The Sky Islands mountain ranges of southeastern Arizona and southwest New Mexico are a particular stronghold, where productive stands of Emory oak and Arizona white oak support high densities.
The birds also thrive in lowland riparian corridors lined with Fremont’s cottonwood and willows, where the trees provide nesting cavities. Throughout the Southwest acorn woodpeckers depend on annual acorn crops from a variety of southwest oak species, including Gambel’s oak, silverleaf oak, grey oak and Netleaf oak. Localized populations even occur in the Four Corners region, where they use acorns of the Gambel oak.
Pacific Northwest
Acorn woodpeckers are uncommon and very localized in the Pacific Northwest, reaching the northern limits of their range here. The core population is centered in southern Oregon, where breeding birds are found sporadically west of the Cascades in open oak and pine-oak habitats. These woodlands are dominated by Oregon white oak, a consistent acorn producer. North of southern Oregon acorn woodpeckers are rare vagrants, occasionally wandering north to the Willamette Valley after the breeding season.
There are only a few confirmed nesting locations in Washington, predominantly in the Puget Sound lowlands. Again, Oregon white oak provides critical nesting and food resources. Recent breeding has been confirmed on Joint Base Lewis-McChord and in the vicinity of Olympia. sparsely scattered reports also come from the eastern slopes of the Cascades in both Washington and Oregon, but no sizeable populations persist.
Mexico
Acorns woodpeckers range south in Mexico through Baja California – where they are relatively common in oak woodlands – down into mainland Mexico to Guerrero and Oaxaca. Abundance decreases toward the southern extent of their range, but locally common populations occur in highland oak forests and pine-oak woodlands. For example, acorn woodpeckers have been recorded in pine-oak forests above 7,500 feet in the Sierra Madre del Sur range of Guerrero and Oaxaca.
Other Southwestern States
Outside of California and southern Arizona/New Mexico, acorn woodpeckers occur much more sporadically and in lower densities in other Southwestern states. Small breeding populations have been confirmed in western Nevada, where the birds inhabit scattered stands of canyon live oak and California black oak. There are also small numbers in riparian woodlands of western Colorado, predominantly along the Colorado and Gunnison Rivers.
Acorn woodpeckers likely breed in very low density across Utah where gambel oak woodlands provide pockets of habitat. The overall population here is small and localized, despite the widespread distribution of oak. There are also a few records from extreme southwestern Wyoming along the Utah border. Finally, in Texas acorn woodpeckers occur in very low density in the western Trans-Pecos region, mainly in the Guadalupe and Davis Mountains.
Summary of Highest Density Regions
In summary, acorn woodpeckers reach their highest population densities and are most abundant in the following general regions:
- Central coastal California from Mendocino County to Los Angeles County
- California’s interior foothills and mountain ranges, including the western Sierra Nevada and southern Cascades foothills, Coast Ranges, Transverse Ranges, and Peninsular Ranges
- Oak savannas, woodlands, and pine-oak forests of southern Arizona and central to southern New Mexico
- Oak forests in Mexico’s Sierra Madre Occidental and Sierra Madre del Sur mountain ranges
Within these overall regions, the highest concentrations occur in more localized oak woodlands and savannas where acorn productivity is consistently high. However, even in dense oak woodlands, acorn woodpecker numbers fluctuate annually depending on the size of the acorn crop. These fascinating social birds continue to thrive in healthy Southwest oak habitats that provide food and nesting resources.
Region | States/Provinces | Example Oak Habitats |
---|---|---|
Central California Coast | California | Coast live oak woodlands |
California Interior Foothills | California | Blue oak savanna, mixed oak woodlands |
California Mountains | California | Canyon live oak, California black oak |
Southern Arizona | Arizona | Emory oak, Arizona white oak |
Southwestern New Mexico | New Mexico | Emory oak, Gambel’s oak |
Sierra Madre Occidental | Mexico | Arizona white oak, silverleaf oak |
Conclusion
In conclusion, acorn woodpeckers reach their highest densities in the oak savannas, woodlands and forests of California and the American Southwest. Core populations centers occur along coastal central California, in the Sierra Nevada foothills, across southern Arizona and New Mexico, and in the highlands of Mexico. Within these regions, healthy oak habitats with mature trees and abundant acorn crops are key to supporting thriving acorn woodpecker populations. Their specialized habitat needs and dependence on consistent acorn crops make them a good indicator species for the health of southwest oak ecosystems.