Vulnerability assessment and conservation recommendations for the northern spotted owl in Marin County, California

Cormier, Renée; Brown, Margaret; Humple, Diana; Merkle, William; Press, David; Dybala, Kristen

doi:10.36967/2303475

Vulnerability assessments are a common approach to identifying conservation priorities for species and informing resource management decisions by evaluating species’ exposure (spatial extent and frequency/intensity) and sensitivity (whether and how a species will respond) to a threat. We assessed the vulnerability of the Northern Spotted Owl (NSO; Strix occidentalis caurina) in Marin County to eight distinct threats: 1) competition with Barred Owls (S. varia); 2) climate change; 3) wildfire; 4) sudden oak death (SOD); 5) other habitat loss/disturbance, specifically from urban development or fuels management; 6) noise disturbance; 7) rodenticide poisoning; and 8) disease. Specifically, we reviewed evidence from published literature for the relative vulnerability of NSOs to each potentially relevant threat in the region; surveyed local experts on the relative vulnerability of NSOs to each potential threat; ranked the vulnerability of NSOs to each threat in Marin County; and made conservation recommendations. We identified three threats to which NSOs are currently most vulnerable in Marin County: climate change, competition with Barred Owls, and wildfire (specifically high-severity fires); exposure to each of these threats is expected to increase over the next 30–50 years. We identified rodenticides and SOD as moderate threats, and habitat loss (from urban development and fuels management), noise disturbance, and disease were identified as the lowest relative threats. However, except for urban development, the local experts’ confidence in their assessment of the sensitivity of NSOs to the lower-ranked threats was low, suggesting a need for further research. Conservation recommendations include: continued habitat protections that consider NSOs and dusky-footed woodrat habitat on a landscape scale; management of Barred Owls to maintain the current low level of exposure; continued avoidance of noise disturbance to nesting NSOs; and community education and outreach efforts to help reduce the threat of rodenticides, noise, and other types of human disturbance. We identified research needs and uncertainties including evaluating the response of NSOs and their prey in Marin County to: weather and climate, including extreme events; habitat change including to fuels management and SOD; and noise and other human disturbance. Conservation actions to protect NSOs and the habitat and prey on which they depend, and outreach to local communities and land managers will be an essential part of the future health of this population.

Vulnerability assessment and conservation recommendations for the northern spotted owl in Marin County, California

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