The northern spotted owl, a threatened species that’s experienced continued declines due to habitat destruction and competition with invasive species, has found temporary refuge in the lush forests of Marin County.

Results from passive acoustic monitoring and local in-person surveys conducted by teams from Golden Gate National Recreation Area and Point Reyes National Seashore show a normal, high number of spotted owls in the territories that were observed. 

“What’s exciting is that spotted owl populations here remain healthy and robust, and we’re not seeing population declines in Marin like we’re seeing in other parts of the range,” said Dave Press, a wildlife ecologist for the seashore. “They’re not necessarily doing better; they’re just holding strong here.”

A medium-sized bird with charcoal-colored eyes and brown plumage flecked with white, northern spotted owls are native to the Pacific coast, with Marin serving as the southern limit of their range. They are mainly nocturnal, and they form long-term pairs, each requiring an ample amount of land for hunting and nesting. 

Unlike other birds, northern spotted owls forgo migration unless forced to because of habitat disturbances or extreme seasonal change. 

In recent decades, the northern spotted owl population has been imperiled by competitively dominant barred owls, a larger, more aggressive bird native to eastern North America that has made its way west. Barred owls can quickly outnumber northern spotted owls because they need less territory, have a more diverse diet and enjoy greater reproductive success. Together with the loss of habitable forests, barred owls have reduced the number of northern spotted owl pairs left in California. Some estimate the total number to be as low as 500.  

Yet monitoring results from the multi-agency Northwest Forest Plan, an approach to federal land management designed to protect threatened species, indicate that Marin may be unique in the safe haven it provides for northern spotted owls. 

This spring, teams set out thousands of autonomous recording units across the owl’s range from Washington State to Northern California. So-called passive acoustic monitoring is a relatively new methodology used to supplement in-person monitoring, which no longer makes sense in areas where there simply are not enough owls left to count. 

Each ARU is deployed for several weeks and is set to record at specific intervals. Scientists then use an artificial intelligence program to help identity and count owl calls before estimating species volume and distribution.  

Relative to the entire survey area, the nearly 17,000 calls recorded in the forests of G.G.N.R.A., Muir Woods and Point Reyes represent about 30 percent of the range-wide total. Meanwhile, recording units picked up only about 200 barred owl calls in Marin’s national park units, just 0.03 percent of the more than half-million barred owl calls recorded over the entire monitoring area. 

Mr. Press credits the health of Marin’s northern spotted owl population to the region’s geography. Owls here are genetically distinct from those in Napa and Sonoma Counties, suggesting that the expanse of agricultural grasslands separating their forested habitats deters travel back and forth. These grasslands act as a barrier for barred owls. 

“So essentially, we also have very few barred owls here in Marin County,” Mr. Press said. “And for that reason, we continue to have very healthy populations of northern spotted owls.” 

Monitoring results showed more barred owl calls in the north, where the species initially began to expand its range. In those regions, there were markedly fewer northern spotted owl calls. 

In response to the continued decline of northern spotted owl populations, the United States Fish and Wildlife Service proposed lethally removing barred owls earlier this year. The strategy would be voluntary, but the service would encourage all agencies managing federal lands, including the National Park Service, to follow it.

Mr. Press told the Light earlier this year that the seashore had documented seven barred owls over the last five years, and it had lethally removed six of them. The only one found in 2023 left the area. A recent Point Blue Conservation Science survey of northern spotted owl nesting areas on lands adjacent to or owned by Marin County Parks and Marin Water confirmed the presence of only two barred owls in 2023. 

“Marin County is the last area within the entire range of the northern spotted owl that has not been completely saturated by barred owls,” Mr. Press said. “If we allow one or two to show up every year and we don’t do anything about it, then eventually Marin is going to get saturated, too.” 

He endorsed Fish and Wildlife’s barred owl strategy and said he would recommend implementing it in the seashore if the service adopts it.