Study charts northern spotted owl decline toward functional extinction across Pacific Northwest
A new study, published in the journal Ecological Applications, finds that northern spotted owl populations are approaching or have already crossed functional extinction across large areas of the Pacific Northwest. Researchers used artificial intelligence and advanced monitoring methods to assess long-term trends at an unprecedented scale, according to the report.
"Northern spotted owls are already functionally extinct in large swaths of their range," 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, in a news release. "It's not a thing that's happening in the future, it has happened."
What the study found
The study divided more than 38,000 square miles of federally managed northern spotted owl habitat into 5-kilometer hexagon sampling units. Researchers randomly selected 1,027 of these hexagons and deployed four passive acoustic recording devices in each for a six- to eight-week period between February and September 2023. The devices collected more than 2.1 million hours of recordings, which were analyzed by machine learning models at Oregon State's Center for Quantitative Life Sciences.
Northern spotted owl calls were confirmed in 261 of the 1,027 hexagon sampling areas, while barred owl calls were confirmed in 891. A total of 34,341 northern spotted owl and 279,439 barred owl clips were recorded.
Barred owl calls were heard eight times more often than spotted owl calls across the entire study area in Oregon, Washington and northwestern California. The researchers found that northern spotted owls are approaching functional extinction thresholds in Washington and on the Oregon Coast, and they were not detected in the Washington Cascades at latitudes north of Seattle.
Detection levels for northern spotted owls ranged from 13%–17% in Washington and the Oregon Coast to 44% in the Oregon and California Klamath Mountains and 91% on the California Coast. Barred owls, by contrast, were heard in 100% of sample areas on the Oregon Coast, 94% on the Washington Coast and Western Cascades, 72% in the Klamath Mountains, and 45% on the California Coast.
A long decline
The northern spotted owl became a symbol for Oregon's logging decline during the 1990s. The species was listed as threatened under the Endangered Species Act in 1990, and protection led to federal old-growth forest being put off limits to logging, marking a major decline in an industry that had dominated the state for a century. 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, 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, according to the news release. Barred owls outcompete northern spotted owls for prey and habitat, a major reason for their decline.
Lesmeister said the study could help shape conservation strategies and improve conservation outcomes for the northern spotted owl. "These findings demonstrate that passive acoustic monitoring and machine learning can be used for large-scale ecological monitoring," he said.
Monitoring has continued since the 2023 period, and preliminary findings from the additional monitoring mirror those outlined in the paper.
Conservation options
The authors cite several conservation strategies, including barred owl removal, conserving landscapes well-suited for nesting, and bringing northern spotted owls into captivity for breeding, a strategy adopted in Canada.
Lesmeister said there is still an opportunity for carefully considered management actions. "Northern spotted owls are already functionally extinct in large swaths of their range," he said. "It's not a thing that's happening in the future, it has happened."