The Northern Spotted Owl has been hit hard by the twin threats of habitat loss and competition from the Barred Owl, according to a major new study by federal scientists. The research, published earlier this month in the journal The Condor, examined survey results from monitoring areas across the Pacific Northwest range of the imperiled Northern Spotted Owl.
Since monitoring began in 1985, Northern Spotted Owl populations have declined by as much as 77 percent in Washington, 68 percent in Oregon, and 55 percent in California, the study found. The scientists also found fewer owls in study areas in southern Oregon and northern California that previously had experienced little to no detectable population decline.
“This study confirms that we need immediate action to reduce the impact of Barred Owls and to protect all remaining Northern Spotted Owl habitat,” said Steve Holmer, senior policy advisor with American Bird Conservancy. “It also points to the need to restore additional habitat by maintaining and expanding the successful reserve network of the Northwest Forest Plan.”
The Northern Spotted Owl is a rare raptor that depends on the complex features and closed canopy of mature or old-growth forests. Because of that connection, it serves as an “indicator species”: Its presence signals that the forest is healthy and functioning properly.
The Spotted Owl was listed as a threatened species under the Endangered Species Act in 1990. Historically, the owl's decline has been linked to habitat loss caused primarily by logging of old-growth forests. Once logged, these forests can take many decades to become suitable owl habitat again.
Katie Dugger, a research biologist at the USGS Oregon Cooperative Fish and Wildlife Research Unit of Oregon State University and the lead author of the new study, emphasized the importance of suitable nesting and roosting habitat for the Northern Spotted Owl. Survival rates and the number of young produced “tend to be higher in areas with larger amounts of suitable habitat,” she said.
But the study also highlighted the growing threat posed by the Barred Owl, whose range has increased in recent years to coincide with the Northern Spotted Owl and which can outcompete it for food and territory. “We observed strong evidence that Barred Owls negatively affected Spotted Owl populations, primarily by decreasing apparent survival and increasing local territory extinction rates,” Dugger and her co-authors wrote.
Wildlife officials in some areas have turned to Barred Owl culls to try to contain the Barred Owl threat. Holmer stressed that adequate habitat is the long-term solution to the problem. “Science shows that Northern Spotted Owls and Barred Owls can coexist where there is enough high-quality habitat,” he said.
The Northwest Forest Plan, established in 1994 by the Clinton Administration, set up reserves and reduced logging on federal lands across much of the Northern Spotted Owl's range. After more than 20 years, Holmer said, USDA Forest Service monitoring reports indicate the plan is working as designed to restore wildlife habitat, improve water quality, and ensure that Northwest forests store carbon instead of contributing to emissions. But proposed changes to the plan could lead to more logging, putting more pressure on the Spotted Owl.
The new study shows that the Northern Spotted Owl needs more habitat protection, not less. “The system of reserves has slowed the Spotted Owl's decline,” Holmer said. “Expanding the reserves will give the Spotted Owl the best chance to coexist with the Barred Owl, and provide numerous other benefits to western communities such as bird-watching opportunities, clean water, and carbon storage.”