Monitoring northern spotted owls on federal lands in Marin County, California: 2012 report
Ellis T, Schultz E, Press D. 2013. Monitoring northern spotted owls on federal lands in Marin County, California: 2012 report. Natural Resource Technical Report. NPS/SFAN/NRTR—2013/829. National Park Service. Fort Collins, Colorado
This report provides a summary of results from the 2012 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 only recently has this population been affected by the expansion of barred owls (Strix varia). 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 30 known spotted owl sites were randomly selected and monitored using standardized methods during the 2012 breeding season. Pairs of spotted owls occupied 26 of these 30 (87%) long-term monitoring sites. Of the 26 territorial females in 2012, 12 females (40%) attempted nesting. Nine of the nests were successful and yielded a confirmed total of 15 young. A total of 13 non-nesting females were confirmed at the 30 sites. Three nest failures were documented in 2012. In 2012, the fecundity estimate of 0.30 (SE ±0.09) was well below the average fecundity of 0.37 (SE ±0.06) measured at monitoring sites from 1999 to 2012. Barred owls were detected at four spotted owl territories in 2012, including a nesting barred owl pair with two fledged young near Muir Woods National Monument. NPS staff successfully captured two out of four known adult barred owls within the study area and fitted them with radio transmitters to better understand barred owl home range size and habitat use. 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.
- Type
- Published Report
- Authors
- Ellis, Taylor; Schultz, Emily; Press, David
- Date of Issue
- 2013-12
- Publisher
- National Park Service
- Units
- GOGA , MUWO , NRSS , PORE , SFAN
- Keywords
- Annual Report, Monitoring, Northern Spotted Owl, Spotted Owl, Spotted Owls, Strix occidentalis, Strix occidentalis caurina
- Subjects
- Ecological Framework: Biological Integrity | Focal Species or Communities | Birds , Ecological Framework: Biological Integrity | At-risk Biota | T&E Species and Communities