Denizens of the Dark:

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• Denizens of the Dark
• Tracking Northern Spotted Owls

Presenter Heather Jensen Inventory Monitoring
Wildlife Technician
All Photos in Presentation H. Jensen
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• Introduction
• Natural history of spotted owls
• Conservation status
• Northern Spotted Owls in Marin
• County
• Study Objectives Results
• Threats to population
• Conclusions
• Additional Information

Photo H. Jensen
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Spotted Owl (Strix caurina) 3 Subspecies
Northern Spotted Owl California Spotted
Owl Mexican Spotted Owl Northern Spotted
Owl Range Southern British Columbia south to
Marin County, CA (British Columbia, WA, OR, and
CA)
Spotted Owl Range Map

USGS
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Northern Spotted Owl (Strix occidentalis caurina)
Characteristics

• Medium sized owl (18 tall and 48 wingspan)
• Dark brown with white spotting on head, neck,
  
• back, and underparts
• Dark brown eyes
• Sexed by vocalizations
• Lifespan up to 20 years in wild
• Primarily nocturnal
• Non-migratory
• Generally mate for life
• Breeding Season February to August

Photo H. Jensen
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• Conservation Status
• Listed as a federally Threatened species- June
  1990
• -3.7 annual population decline from 1985-2003
• Declines greatly attributed to habitat loss
• Continued range expansion of barred owls into the
  spotted owls range

Photo H. Jensen
Photo H. Jensen
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• Study Background
• NPS surveys began in 1993
• 1997 1998 inventory of public lands completed
• Currently, NPS monitors owl locations within
  federally legislated boundaries and PRBO
  Conservation Science monitors owls on County
  lands
• NPS is primary contact for spotted owl and barred
  owl information in Marin County

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• Study Objectives
• Monitor changes in spotted owl occupancy and
  reproductive success
• Determine the long-term changes of nest site
  characteristics

Photo H. Jensen
Photo H. Jensen
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• Monitoring information is used to determine
• Long-term status
• and trends in spotted owl population
• Inform short-term management e.g., trail and
  culvert work

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• Study Results
• Broader habitat use than expected
• Highest crude density
• High fecundity
• Marin population currently stable
• 2007 1st non-breeding year

Photo H. Jensen
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• Study Results
• Marin County population is small (75 pairs)
• Southernmost northern spotted owl population
• Limited gene flow between northern populations
  and Marin population

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• Threats to Marin population
• Habitat loss (anthropogenic and natural causes)
• Barred Owl
• Possible genetic isolation
• Suppression of fire ? risk of high intensity
  wildfires
• Non-consumptive recreational activities
• West Nile Virus

Recreation
Barred Owl
Urban Development
Spotted owl roosting in tanoak dying from Sudden
Oak Death.
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• Conclusions
• Northern spotted owls in Marin have
• high breeding density
• high reproductive success
• different habitat requirements
• Faced with different conservation challenges
• Communication with landowners, managers, and the
  public who live/work in potential spotted owl
  habitat is important
• Through the spotted owl monitoring program, we
  can attempt to understand the factors influencing
  northern spotted owl population in Marin

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• Acknowledgments
• PRBO Conservation Science
• Marin Municipal Water District
• County of Marin - Marin County Open Space
  District
• California State Parks
• National Park Foundation
• The David and Vicki Cox Foundation
• Point Reyes National Seashore Association
• Dawn Adams, Bill Merkle, Dave Press, Sarah Allen,
  Daphne Hatch, Katie Fehring, Renee Cormier, Diana
  Stralberg, Tom Gardali, Mia Monroe, and all the
  field staff and volunteers over the years

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Additional Information San Francisco
Inventory and Monitoring Program http//science.na
ture.nps.gov/im/units/sfan/vital_signs/Spotted_Owl
/birds.cfm (Annual reports/executive
briefings) Muir Woods National
Monument http//www.nps.gov/muwo/naturescience/owl
s.htm (General information)