Slide 1:Title
Slide 2: P hotos of Northern Spotted and Barred owls
Slide 3: Map of Barred owl range, pre-1900
Slide 4: Map of Barred owl (current range)
Slide 5: Map of Barred owl/Spotted owl range overlap
Slide 6: BARRED OWL INVASION ECOLOGY
- Causes of range expansion debatable
- Southward expansion into NSO’s range
- Rapid colonization of PNW forest types
- Currently outnumber NSO in BC, WA, OR?
Slide 7: WHY ARE BARRED OWLS SUCH SUCCESSFUL INVADERS?
- Generalist habitat requirements
- Opportunistic predators
- Growing source population
- Long-distance dispersers
- High fecundity and survival?
Slide 8 : Chart: OREGON’S INCREASING BARRED OWL POPULATION
Barred owls detected in 63% of 204 NSO territories monitored in the Oregon Coast Range (Chart showing increasing proportion of territories each year.)
Slide 9: COMPETITIVE DOMINANCE?
Spotted Owl- Native
- Habitat: Specialist
- Food Habits Specialist
- Territorial behavior: Passive (vocal)
- Productivity: 1-3 Young (high variance)
Barred Owl- Invasive
- Relative body size: 10-20% larger
- Habitat: Generalist
- Food Habits: Opportunistic
- Territorial behavior: Aggressive (vocal + physical)
- Productivity: 1-5 Young (low variance?)
Slide 10: ESCALATING EVIDENCE OF NEGATIVE IMPACTS
- Spatial exclusion of NSO (Hamer 1988, Hamer et al. 2007)
- Declines in NSO territory occupancy rates (Kelly et al. 2003; Olson et al. 2005)
- Declines in NSO apparent survival probabilities (Anthony et al. 2006)
- Long-term NSO population declines sharpest where barred owls have been present the longest (Anthony et al. 2006)
Slide 11: CRITICAL UNCERTAINTIES
- Role of barred owls in observed population declines?
- Synergistic effects of barred owl presence, past habitat loss, and climatic variation?
- Mechanisms and magnitude of competition? (e.g, exploitation vs. interference pathways)
- Implications for research, management, and recovery efforts?
Slide 12: RESEARCH AND MANAGEMENT OPTIONS (from Buchanan et al. 2007)
- No action
- Ecological studies (focus on mechanisms)
- Removal experiments (focus on causation)
- Habitat management
- Diversionary or supplemental feeding
- Disrupt barred owl reproduction
- Lethal control of barred owl populations
Slide 132: Ecological Relationships Between Northern Spotted Owls and Barred Owls in Western Oregon
J. David Wiens1
Robert G. Anthony1 & Eric D. Forsman2
1USGS, Oregon Cooperative Fish and Wildlife Research Unit
Department of Fisheries and Wildlife
Oregon State University
2USDA Forest Service, Pacific Northwest Research Station
Slide 14: FUNDING AGENCIES (photos of 6 agency logos)
Slide 15: Research questions
- What is the potential for, and possible consequences of, competition for space, habitat, and food resources between spotted and barred owls?
- How do barred owls influence site occupancy, resource selection, and demographic performance of spatially associated spotted owls?\
- Under what range of forest conditions are spotted owls most likely to be susceptible to competitive pressure from barred owls?
Slide 16: COMPONENTS OF ONGOING RESEARCH
EXPLOITATION OF COMMON RESOURCES
(Chart of space, habitat, food)
INTERSPECIFIC INFLUENCES ON DEMOGRAPHY
(Chart of site occupancy, survival, reproduction)
Slide 17: PREDICTED HABITAT RELATIONSHIPS
Hypothesis : Prediction
Moisure dependence : Proportional use of riparian and wetland habitats by BDOW is greater than that of SPOW
Specialist vs. generalist : Proportional use of young and mid-aged forest types by BDOW is greater than that of SPOW
Interspecific avoidance : SPOW use areas more distant from areas of concentrated use by BDOW than expected by chance
Interspecific exclusion : SPOW use areas more distant from preferred habitats when BDOW is present
Slide 18: Map of study areas in western Oregon and photo of spotted owl
Slide 19: Map of land ownership in study area
Slide 20: Same map area with LSAT overlay
Slide 21: Photo of clearcut logged area
Slide 22: OWL SURVEYS (photo of barred owl)
Slide 23: SURVEY METHODS: STAGE 1
SPOW surveys of historic territories (n = 45) and intervening habitat (map of area and photo of spotted owl)
Slide 24: SURVEY METHODS: STAGE 2
BDOW survey within 1.5 km radius of all OCCUPIED SPOW territories (map of area and photo of spotted owl)
Slide 25: 2007 SURVEY RESULTS: STAGE 1
- 45 Territories surveyed (photo of Spotted owl)
- 14 (31%) Occupied by spotted owls
- 9 (42%) Occupied by barred owls
- 12 (27%) No owls detected
- 8 barred owl pairs identified in intervening habitat
Slide 26: 2007 SURVEY RESULTS: STAGE 2 (photo of Barred owl)
- 14 occupied spotted owl territories surveyed
- 9 additional barred owl pairs identified (a 25% increase!)
- 7 previously undetected barred owl pairs identified within 1.5 km survey radius
- Barred owls detected in 12 (86%) of 14 spotted owl territories
Slide 27: Map of survey results
Slide 28: Map of survey results plus radii
Slide 29: Four photos of owls and researchers with owls
Slide 30: TELEMETRY STATUS: YEAR 1
- 53 OWLS RADIO-MARKED
- 27 Spotted owls
- 12 females, 15 males
- 14 territories
- 26 Barred owls
- 14 females, 12 males
- 20 territories
- >3000 Nighttime activity locations
- 8 Mortalities (6 Spotted, 2 Barred)
- 0 Unexplained losses/radio failures
Slide 31: Map of telemetry sites
Slide 32: Map of telemetry sites
Slide 33: OWL DIETS
Photo of Northern flying squirrel
Slide 34: Photo of owl in tree
Slide 35: Photos of owls and researchers, tree, and owl pellets
Slide 36: Photos of mammals, birds, and invertebrates that owls eat
Slide 37: Photo of a crayfish in a stream
Slide 38: Photo of stream and riparian area
Slide 39: Photo of prey debris from a feeding station
Slide 40: CONTINUING FIELDWORK:
May, 2008 – August, 2009
- Continue to monitor the movements, habitat use, survival and productivity of radio-marked owls.
- Conduct multi-species owl surveys during 2008-09 breeding seasons to further assess co-ccupancy of breeding territories.
- Capture and radio-mark additional owls as needed.
- Conduct vegetation sampling and mapping to develop and compare species-specific models of multi-scale habitat selection.
Slide 41: ACKNOWLEGEMENTS
- Co-advisors: Bob Anthony & Eric Forsman
- Graduate committee: Bill Ripple, Barry Noon (CSU), David Hibbs
- Field Crew: Scott Graham
- Patrick Kolar
- Kristian Skybak
- Amanda Pantovich
- Jim Swingle
- Photography: Patrick Kolar
- Research cooperators: Raptor Research Center, Boise State University
- BLM; Eugene District
- Roseburg Forest Products
- Weyerhaeuser Company
- Westside Ecological
- Swanson Superior, NCASI, BIS
Slide 42: Photo of a Spotted owl on a branch
For more information about this presentation, contact:
davidweins@oregonstate.edu