Effects of experimental removal of barred owls on population demography of northern spotted owls in Washington and Oregon—2015 progress report

Wiens, J. David; Dugger, Katie M.; Lewicki, Krista E.; Simon, David C.

doi:10.3133/ofr20161041

Cited by 5 publications

(3 citation statements)

References 5 publications

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“…Removal experiments were first enacted on a small scale in California's Green Diamond study area in Humboldt and Del Norte counties in 2009 (Diller et al., ), in California's Hoopa Valley Reservation starting in 2013, and in the coastal ranges of Oregon and central Washington starting in 2015 (U.S. Fish & Wildlife Service, ; Wiens, Dugger, Lewicki, & Simon, ). Using occupancy modeling, Diller et al.…”

Section: Introductionmentioning

confidence: 99%

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Can culling Barred Owls save a declining Northern Spotted Owl population?

Bodine

Capaldi

2017

Natural Resource Modeling

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Data collected over the past 25 years reveal that Northern Spotted Owls (Strix occidentalis caurina) of the Oregon Coast region are being displaced by invasive Barred Owls (Strix varia). A component of the U.S. Fish and Wildlife Service recovery plan is studying the culling of Barred Owls from Spotted Owl habitat. Using information theory to perform a model selection, we fit the most parsimonious ordinary differential equation competition model to the data. We then augment the model to incorporate Barred Owl culling and determine the minimum culling rate required to completely eliminate the Barred Owl population and the amount of time required to achieve such an elimination for various culling rates. Our analysis shows that even with culling Barred Owls, there exists no coexistence equilibrium given the current growth and competition parameters.

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Section: Introductionmentioning

confidence: 99%

“…() report that lethal removal of Barred Owls improved Spotted Owl recovery in the Green Diamond study area. However, this effect is local and likely temporary, and when culling subsides the global survival of the Northern Spotted Owl again comes into question (Wiens et al., ).…”

Section: Introductionmentioning

confidence: 99%

Can culling Barred Owls save a declining Northern Spotted Owl population?

Bodine

Capaldi

2017

Natural Resource Modeling

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“…The primary factor influencing the northern spotted owl population at the time of listing was habitat loss [ 6 ], but competition with non-native, invading Barred Owls ( S . varia ) has more recently become a major contributing factor [ 7 – 8 ]. Since its listing, the taxon has been the subject of extensive research and monitoring to identify habitat requirements and demographic trends.…”

Section: Introductionmentioning

confidence: 99%

Isolation by distance versus landscape resistance: Understanding dominant patterns of genetic structure in Northern Spotted Owls (Strix occidentalis caurina)

et al. 2018

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Landscape genetics investigations examine how the availability and configuration of habitat influence genetic structure of plants and animals. We used landscape genetics to evaluate the role that forest connectivity plays in determining genetic structure of the federally-threatened Northern Spotted Owl (Strix occidentalis caurina) using genotypes of 339 Northern Spotted Owls obtained for 10 microsatellite loci. Spatial clustering analyses identified a distinct genetic cluster at the southern extent of the region examined. This cluster could not be linked to landscape connectivity patterns and suggested that post-Pleistocene processes were involved with its development rather than contemporary landscape configuration. We also compared matrices of pairwise inter-individual genetic distances with resistance distances derived from a circuit-theory based framework. Resistance distances were obtained for an idealized raster map that reflected continuous unimpeded dispersal habitat across the landscape along with five empirically-derived raster maps reflecting the 1870’s, 1940’s, 1986, 1994, and 2012. Resistance distances from the idealized map served as surrogates for linear geographic distances. Relative to idealized conditions, resistance distances were ~250% higher in the 1940’s and ~200% higher from 1986 onward. Resistance distances from the 1870’s were ~40% higher than idealized conditions. Inter-individual genetic distances were most highly correlated with resistance distances from the idealized map rather than any of the empirical maps. Two hypotheses explain our results. First, our results may reflect temporal lags between the onset of large-scale habitat alterations and their novel effects on genetic structure in long-lived species such as Northern Spotted Owls. Second, because Northern Spotted Owls disperse over long distances, our results may indicate that forest habitat has never been sufficiently fragmented to the point where connectivity was disrupted. The second hypothesis could indicate that forest management practices mandated by the Northwest Forest Plan succeeded with one of its primary goals. However, our results do not represent a complete portrayal of the status of Northern Spotted Owls given detection of significant population declines and bottlenecks in other studies. Future investigations based on computer simulations may help distinguish between hypotheses.

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Barred Owls reduce occupancy and breeding propensity of Northern Spotted Owl in a Washington old-growth forest

et al. 2019

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Protected lands like national parks are important refuges for threatened and endangered species as environmental pressures on wildlife and their habitats increase. The Northern Spotted Owl (Strix occidentalis caurina), a species designated as threatened under the Endangered Species Act, occurs on public lands throughout the western United States including Mount Rainier National Park (MRNP), Washington. With virtually no history of timber harvest or large forest disturbance within MRNP boundaries since the park’s creation in 1899, MRNP provides an ideal place to evaluate potential impacts of climate change and invasive Barred Owls (Strix varia) on the Northern Spotted Owl. We used a multi-state, multi-season occupancy model to investigate how Northern Spotted Owl occupancy dynamics and breeding propensity are related to the presence of Barred Owls, local and regional weather, and habitat characteristics at MRNP from 1997 to 2016. Historical occupancy of Northern Spotted Owl breeding territories in MRNP has declined by 50% in the last 20 yr, and territory occupancy by breeding Northern Spotted Owls also decreased, reaching a low of 25% in 2016. Occupancy rates were higher on territories with steeper terrain and breeding rates were lower when Barred Owls were detected within historical territories. Our results also indicated that breeding propensity was higher when early nesting season temperatures during March and April were higher. In addition, the ability to detect breeding Northern Spotted Owls decreased when Barred Owls were present in the territory. Habitat variables from LiDAR were not correlated with Northern Spotted Owl occupancy dynamics, likely reflecting the dominance of old-growth forest in this protected park. This study illustrates the strong relationship between Barred Owls and Northern Spotted Owl demographics and breeding site selection in a landscape where habitat loss by timber harvest and fire has not occurred.

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Effects of experimental removal of barred owls on population demography of northern spotted owls in Washington and Oregon—2015 progress report

Cited by 5 publications

References 5 publications

Can culling Barred Owls save a declining Northern Spotted Owl population?

Can culling Barred Owls save a declining Northern Spotted Owl population?

Isolation by distance versus landscape resistance: Understanding dominant patterns of genetic structure in Northern Spotted Owls (Strix occidentalis caurina)

Barred Owls reduce occupancy and breeding propensity of Northern Spotted Owl in a Washington old-growth forest

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