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.
Recommendations for Resource Managers
- Even with culling Barred Owls and all other factors remaining the same, Barred Owls and Spotted Owls cannot coexist in the long run, thus complete elimination of the Barred Owl population is required for conservation of the Spotted Owl population.
- Furthermore, the effort required to cull the Barred Owl population is high, requiring approximately half of the historical Spotted Owl sites containing Barred Owls to be culled completely each year. Even more ambitiously, the culling rate must clear around 90% of sites containing Barred Owls per year to ensure that the Barred Owl population is eliminated within 10 years.
- Given the high culling rate necessary, we recommend any proposed culling program be accompanied by a robust cost-benefit analysis, of which our study is a first step.