Invasive barred owls select old-forest structure: Functional habitat loss for spotted owls and a threat to old-forest fauna
| Authors: | Vitek Jirinec, Mourad W. Gabriel, J. Mark Higley, Raymond J. Davis, Jonathan E. Tenberge, Christina P. Varian, Daniel F. Hofstadter, M. Zachariah Peery, Julianna M. Jenkins, Alan B. Franklin, Greta M. Wengert |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Pacific Northwest Research Station |
| DOI: | https://doi.org/10.1016/j.biocon.2026.112035 |
| Source: | Biological Conservation |
Abstract
Invasive predators are leading drivers of native species decline, and their impact is heaviest where they concentrate in the habitats native species most depend on. The barred owl (Strix varia) is a generalist predator invading old forests across western North America. Using GPS telemetry of 56 barred owls across the range of the northern spotted owl (Strix occidentalis caurina) in northwestern California, we found consistent selection for an old-forest axis integrating high canopy cover, tall stands, large trees, diverse tree sizes, and old age. Because these attributes define old forest, selection concentrated owls in stands sustaining a distinctive old-forest fauna, and disproportionately in habitat of the spotted owl, an umbrella species for this forest, peaking in its highest-quality nesting and roosting forest. Each owl also appropriated a large area, roughly 28 times the home range recorded in its native range, magnifying the invasion's per-individual footprint. Because habitat is defined by the conditions permitting occupancy, pervasive barred owl presence converts structurally intact forest into functional non-habitat for the spotted owl, a biotic habitat loss invisible to structure-based monitoring, while concentrating novel predation on naive old-forest prey. Because the forest persists, removing barred owls can restore this habitat: we estimate each territorial pair removed frees several square kilometers, though gains require sustained control and are not spatially additive. More broadly, where an invader co-opts the structure defining a specialist's habitat, protecting that structure is necessary but not sufficient: the specialist becomes conservation-reliant, dependent on managing the invader itself.