The California spotted owl (Strix occidentalis occidentalis) – an older forest species of conservation concern – has declined in many forests due to loss of habitat via severe wildfire and vegetation change. While population trends and factors responsible for trends have been well studied in the Sierra Nevada, less is known about their population status at the range boundary in southern California - a region undergoing rapid environmental change. Therefore, we conducted extensive spotted owl nighttime surveys during the 2022 breeding season in the Los Padres, Angeles, and San Bernardino National Forests, and compared remotely-sensed data on vegetation conditions and disturbance between currently occupied and vacant territories, and at vacant territories during historical occupancy versus after the loss of territorial owls. We made 1,913 visits to call points, surveying an area of 1,100 km2, yet located only eight occupied territories. Only three of the 13 historically occupied territories we surveyed remained occupied (23%). Vacant territories had a lower basal area of deciduous trees compared to occupied territories, and vacant territories had greater drought-related tree mortality after the loss of territorial owls compared to during historical occupancy. Our results coincide with other recent work indicating declines in spotted owl populations in southern California.

Josh Barry is a Ph.D. student in the Peery Laboratory at the University of Wisconsin – Madison, where he leads two ongoing projects in the Sierra Nevada mountains that seek to understand patterns of owl species diversity in response to environmental variation and change. Josh earned his master's degree in environmental science from Pace University in New York, where he also published his master's thesis exploring the ecosystem engineering effects of mountain lions on insect communities in the Greater Yellowstone Ecosystem. The topic of Josh's presentation today is on the potential widespread decline of spotted owl populations in southern California.