Northern Spotted Owl Monitoring for the San Francisco Bay Area Inventory and Monitoring Network: 1998-2023 – Data Package

The northern spotted owl (NSO) has been listed as a federally threatened species since 1990, and the National Park Service (NPS) and partners began regular long-term monitoring in 1999 after conducting inventories in 1997 and 1998. Northern spotted owls inhabit forested regions from southern British Columbia through Washington, Oregon, and northwestern California, where Marin County is the southern limit of their range. NSOs face a variety of threats in Marin County including loss of habitat due to development and catastrophic fire, displacement by barred owls (Strix varia), change in habitat due to Sudden Oak Death, human disturbances during the breeding season, and mortality due to West Nile Virus. Although NSOs are typically found in old growth forests, in Marin County they reside in second growth Douglas-fir (Pseudotsuga menziesii), coast redwood (Sequoia sempervirens), bishop pine (Pinus muricata), mixed conifer-hardwood, mixed evergreen hardwood forests, as well as remnant old-growth stands of coast redwood and Douglas-fir. The primary food source for the NSO is the dusky-footed woodrat (Neotoma fuscipes). The Marin County population of spotted owls is of interest because of its isolation from other populations, high density and fecundity, and because they have been minimally impacted by barred owl range expansion. The goals of the northern spotted owl NPS San Francisco Bay Area Network (SFAN) monitoring program are to estimate trends in spotted owl occupancy and fecundity within the NPS legislative boundaries in Marin County.