BLUE LAKE, Calif., Aug. 13, 2026 - Newly published research offers some of the clearest evidence yet of why the invasive barred owl has become one of the greatest threats to the northern spotted owl, and delivers encouraging evidence that managing barred owl populations can restore old-growth habitat for spotted owl recovery.
The study, led by scientists at the Integral Ecology Research Center (IERC) and published in the journal Biological Conservation , used GPS trackers on 56 barred owls across 4,070 square kilometers of forest in northwestern California. It is the first study to use GPS telemetry to determine, bird by bird, exactly which forest features invasive barred owls select, and how much old-growth habitat each one occupies.
The results are striking. Barred owls, native to eastern North America but now widespread across the West, consistently chose the tallest, oldest, and most structurally complex stands of forest: the same towering, dense-canopy, big-tree habitat that spotted owls need to nest and roost. On average, 64% of a barred owl's home range overlapped with mapped spotted owl habitat, and 38% was the very highest-quality nesting and roosting forest on the landscape.
Barred owls also claimed far more space in California than they do at home. Each bird's territory averaged 6.7 square kilometers, roughly 28 times larger than the home ranges IERC researchers previously measured for barred owls in their native range in Louisiana . That means every invading owl exerts outsized pressure on the old-growth forest, and the wildlife within it, well beyond what its native ecology would predict.
The most encouraging finding, however, is what happens once barred owls are managed out of an area. Because the forest structure itself remains intact, researchers found that managing a single resident pair out of a territory reopens several square kilometers of habitat that spotted owls can reclaim. Drawing on 1,171 barred owls removed under an ongoing, permitted regional research and management program, the study conservatively estimates that more than 1,800 square kilometers of spotted owl habitat, including nearly 1,150 square kilometers of the best nesting and roosting forest, have been freed up for spotted owl recolonization.
"Every stand of that forest still shows up as spotted owl habitat on our maps," said Dr. Vitek Jirinec, research scientist at IERC and lead author of the study. "But habitat isn't just trees, it's trees a spotted owl can actually live in, and barred owls have taken that off the table across much of the landscape. Managing the invader is proving just as critical as protecting the trees themselves."
Because barred owls are generalist hunters, they compete with spotted owls for staple prey like flying squirrels and tree voles while also preying on dozens of species spotted owls rarely touch: salamanders, reptiles, and even small carnivores like the western spotted skunk. Researchers say this concentrated pressure likely extends beyond spotted owls to the broader old-growth community, an implication the team says warrants further study.
"Spotted owls are the reason this study exists, but they're part of a much larger old-growth food web, one where every species plays a role in keeping the system intact," said Dr. Greta Wengert, Co-Founder and Co-Director of IERC and principal investigator on the study. "This means protection of the old-growth biological community requires staying committed to managing this invader for the long haul. This is exactly the kind of science IERC specializes in: rigorous enough for a peer-reviewed journal, specific enough for a manager to rely on for years to come."
The findings add scientific weight to ongoing regional efforts to manage barred owl populations, carried out in partnership with the University of Wisconsin-Madison, U.S. Department of Agriculture, Hoopa Valley Tribe, U.S. Forest Service, California Department of Fish and Wildlife, and other regional partners. The research was funded primarily by the California Department of Fish and Wildlife's Cannabis Restoration Grant Program.
About the Integral Ecology Research Center
Founded in Blue Lake, California, in 2004, IERC is a nonprofit conservation science organization dedicated to studying and conserving wildlife and the ecosystems they rely on across California and beyond. IERC partners with tribal, state, and federal agencies, as well as academic institutions, to conduct scientific research, from field ecology to molecular ecology, that translates directly into on-the-ground conservation action for species such as the northern spotted owl, Humboldt marten, and Pacific fisher. Learn more at IERCecology.org.
Publication: Jirinec, V., Gabriel, M.W., Higley, J.M., et al. 2026. Invasive barred owls select old-forest structure: Functional habitat loss for spotted owls and a threat to old-forest fauna. Biological Conservation 322, 112035.
Open Access at: https://doi.org/10.1016/j.biocon.2026.112035
Biological Conservation
Observational study
Animals
Invasive barred owls select old-forest structure: Functional habitat loss for spotted owls and a threat to old-forest fauna
7-Aug-2026