Northern spotted owl populations are approaching or have already crossed functional extinction across large areas of the Pacific Northwest, a new study found. Researchers used artificial intelligence and advanced monitoring methods to assess long-term trends at an unprecedented scale.
While northern spotted owl populations have declined for decades, this study identifies where populations are at or near functional extinction, meaning numbers are so low that they no longer play a meaningful ecological role or cannot reproduce enough to persist. It also provides detailed population data on barred owls, which outcompete northern spotted owls for prey and habitat.
"These findings demonstrate that passive acoustic monitoring and machine learning can be used for large-scale ecological monitoring," said Damon Lesmeister, a wildlife biologist at the U.S. Forest Service's Pacific Northwest Research Station and a courtesy faculty member at Oregon State University. "Our hope is that they can help shape conservation strategies and improve conservation outcomes for the northern spotted owl."
Study findings include:
- Barred owl calls were heard eight times more often compared to spotted owls across the entire study area in Oregon, Washington and northwestern California.
- Northern spotted owls are approaching functional extinction thresholds in Washington and on the Oregon Coast.
- Northern spotted owls were not detected in the Washington Cascades at latitudes north of Seattle.
The conservation and management of northern spotted owls became one of the largest and most visible wildlife conservation issues in United States history after the species was listed as threatened under the Endangered Species Act in 1990 because of rapid declines in the owl's old-forest habitats. Four years later, the Northwest Forest Plan was adopted and reduced the rate of logging of old-growth forests on federal lands.
Despite more than 30 years of protection, northern spotted owl populations have continued to decline due to continued habitat loss from logging and wildfire and competition from barred owls, whose range in recent decades has increasingly intersected with spotted owl territory.
For the new study, scientists, led by teams at the U.S. Forest Service and Oregon State's Department of Fisheries, Wildlife, and Conservation Sciences, divided more than 38,000 square miles of federally managed northern spotted owl habitat in Oregon, Washington and northwestern California into 5-kilometer hexagon sampling units meant to replicate the typical territory of a northern spotted owl.
They randomly selected 1,027, or 3%, of those hexagons and deployed four passive acoustic recording devices in each hexagon for a six-to-eight-week period between February and September 2023. The devices collected more than 2.1 million hours of recordings.
Using machine learning models the researchers developed, those recordings were analyzed by research computers at Oregon State's Center for Quantitative Life Sciences. Among the findings from that analysis:
- Northern spotted owl calls were confirmed in 261 of the 1,027 hexagon sampling areas and barred owl calls were confirmed in 891 of the sampling areas.
- A total of 34,341 northern spotted owl and 279,439 barred owl clips were recorded, meaning barred owls were heard more than eight times more than northern spotted owls.
- More northern spotted owls were observed in sampling in the southern portions of the range. Levels ranged from 13% to 17% in Washington and the Oregon coast to 44% in the Oregon and California Klamath Mountains to 91% on the California coast.
- Barred owls were heard more frequently in northern sampling areas. They were heard in 100% of samples areas in the Oregon Coast, 94% on the Washington Coast and Western Cascades, 72% in Oregon and California Klamath Mountains and 45% at the California Coast.
This monitoring has continued since the 2023 period analyzed in this paper and preliminary findings from the additional monitoring mirror those outlined in this paper, Lesmeister said.
Lesmeister believes the findings can help focus northern spotted owl conservation strategies to specific geographic areas. The authors cite several conservation strategies, including ongoing barred owl removal efforts, conserving landscape well-suited for northern spotted owl nesting and bringing northern spotted owls into captivity for breeding, a strategy that has been adopted in Canada.
"Northern spotted owls are already functionally extinct in large swaths of their range. It's not a thing that's happening in the future, it has happened," Lesmeister said. "That doesn't mean we can't do anything. There is still an opportunity for carefully considered management actions."
