The consequences of environmental change on animal communities can be difficult to predict and measure because individual ecological stressors can interact in complex ways. Here, we assessed the relative and interactive effects of severe wildfire and invasive barred owls (Strix varia) on native forest owls in the northern Sierra Nevada, California, USA, using occupancy data collected via regional-scale passive acoustic surveys under a quasi-experimental design from 2018 to 2023. Our findings suggest severe wildfire reduced occupancy rates for flammulated owls (Psiloscops flammeolus) but not for great horned owls (Bubo virginianus) or northern pygmy owls (Glaucidium californicum). By contrast, barred owl removals did not increase occupancy rates for any of the three owl species. Our research demonstrates the pronounced impact of severe wildfires on some native owls, while the initial invasion of barred owls at low densities seems to have no adverse effects on them, underscoring the effectiveness of barred owl removals in protecting native owl populations. Using a rare Before-After Control-Impact design, our study highlights the importance of experimental methods in diagnosing causes of species endangerment and understanding ecosystem responses, while also elucidating the complexities of multifactorial studies at regional spatial scales.

Josh Barry is a PhD candidate in the Peery research laboratory at the University of Wisconsin–Madison, working to unravel the complex responses of forest owl communities to environmental change. Before the University of Wisconsin, Josh was a master’s student at Pace University where he studied the ecosystem engineering role of mountain lions in provisioning carrion resources for invertebrate scavenger communities in the Greater Yellowstone Ecosystem. Outside of his research endeavors, Josh finds fulfillment in his jiu-jitsu practice and embracing the beauty of rural western Pennsylvania with his family.