Monitoring northern spotted owls on federal lands in Marin County, California: 2016 report

Ellis, Taylor

This report provides a summary of results from the 2016 field season of the National Park Service’s (NPS) northern spotted owl (Strix occidentalis caurina) monitoring program in Marin County, California. The northern spotted owl has been listed as a federally threatened species since 1990. 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 (S. varia) range expansion. The goals of our northern spotted owl monitoring program are to estimate trends in spotted owl occupancy and fecundity within the NPS legislative boundaries in Marin County. A total of 39 known spotted owl sites were randomly selected and monitored using standardized methods during the 2016 breeding season. Pairs of spotted owls occupied 28 of these 39 (72%) long-term monitoring sites. Of the 28 territorial females in 2016, 12 females (43%) attempted nesting. Eleven of the nests were successful and yielded a confirmed total of 17 young. A total of 12 non-nesting females were confirmed at the 39 sites. In 2016, the fecundity estimate of 0.35 (SE 0.09) was near the average fecundity of 0.36 (SE 0.08) measured at monitoring sites from 1999 to 2016. We recommend continued annual monitoring of the spotted owl population, and continuing to share information and work with land managers and county officials to reduce potential adverse impacts of projects on spotted owls. Research focused specifically on barred owls and their impacts on spotted owls in Marin County should be continued. In addition, studies investigating the effects of Sudden Oak Death on spotted owls also are needed. NPS should continue to provide outreach materials related to spotted owl awareness and recovery.

Monitoring northern spotted owls on federal lands in Marin County, California: 2016 report

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