Northern Spotted Owl Monitoring in the San Francisco Bay Area
Why Are Northern Spotted Owls Important?
Federally threatened Northern Spotted Owls are key predators in the woods they inhabit, keeping rodent and other small animal populations in balance. They are also vital indicators of forest health since their survival depends on the presence of diverse, robust evergreen forest ecosystems. The National Park Service Inventory and Monitoring Program and its partners began long-term monitoring of Northern Spotted Owls in Golden Gate National Recreation Area, Muir Woods National Monument, Point Reyes National Seashore and other public lands in Marin County in 1999.
Why Do We Monitor Northern Spotted Owls?
- To determine long-term trends in Northern Spotted Owl territory occupancy
- To track trends in Northern Spotted Owl reproductive success
- To identify long-term trends in Northern Spotted Owl nesting site characteristics (e.g. tree size) and nesting habitat preferences
How Do We Use the Monitoring Data?
- To inform land managers about where owls are during the breeding season so they can avoid disruptive activities like trail maintenance near nests
- To plan and evaluate Northern Spotted Owl conservation efforts
- To learn more about Northern Spotted Owl biology and potential threats such as encroaching barred owls, sudden oak death, west nile virus, and climate change—often in collaboration with other researchers
What Have We Learned?
National Park Service lands in Marin County support the southernmost population of Northern Spotted Owls, as well as what could be the densest population on record anywhere in their range. Though specific results vary year to year, the Marin Northern Spotted Owl population has remained relatively stable. Still, they face a variety of potential threats. Barred Owls, for instance, just began breeding in Marin in 2007. These larger, more aggressive owls have wrought havoc on Northern Spotted Owl populations, outcompeting them in Canada, Washington and Oregon as they have expanded their range over the last century.
For More Information
Point Reyes Wildlife Ecologist
Summary by Jessica Weinberg McClosky, August 2013.
Download PDF from the NPS Data Store
Last updated: September 21, 2018