Northern Spotted Owl Monitoring in the San Francisco Bay Area

Spotted owl leers at camera from perch in tree
A juvenile Northern Spotted Owl peers down through a coast redwood forest. In Marin, owls also nest in mixed hardwood, bishop pine and Douglas fir forests.

NPS / Jessica Weinberg McClosky

Map showing that spotted owl monitoring occurs in segments of the GGNRA, Muir Woods NM, and Point Reyes NS.

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
Northern spotted owl perches on branch
An adult female Northern Spotted Owl. Females are slightly larger than males, but the best way to distinguish them is by their calls.

NPS / Heather Jensen

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
Dave Press

Barred Owls in Marin County
San Francisco Bay Area Inventory & Monitoring Network
Pacific Coast Science and Learning Center

Summary by Jessica Weinberg McClosky, August 2013.
Download PDF from the NPS Data Store

Golden Gate National Recreation Area, Muir Woods National Monument, Point Reyes National Seashore

Last updated: March 30, 2020