Ackerson Meadow Great Gray Owl Prey Inventory

The genetically unique subspecies (Strix nebulosa yosemitensis) of great gray owls in the Sierra Nevada are a primary focus of Yosemite National Park management activities, and understanding predator-prey relationships and the effects of habitat management on prey populations is essential to the continued persistence of the great gray owl. The recent Ackerson Meadow Restoration Project presents an opportunity to enhance habitat for prey species, ultimately benefiting the state-endangered great gray owl and many other species. However, information about great gray owl prey, and how management activities will impact prey, is unknown. This inventory focused on providing baseline data on great gray owl prey populations at the Ackerson Meadow Complex and Hodgdon Meadow, including variation in prey across sites and years, whether variation was related to vegetation or soil properties, and the suitability of a non-traditional method for assessing abundance change in great gray owl prey through time. We surveyed voles and gophers across two habitat types (forest and meadow) at three sites (Ackerson Main Meadow, Ackerson South Meadow, and Hodgdon Meadow) in 2023 and 2024. We used multiple methods to assess vole populations, including live-trapping, chew block removal, and camera trapping, and indirect estimates of gopher abundance via surveys for gopher activity. At each site, we also characterized a set of vegetation and soil properties. Overall, while there was some variation in prey population abundance estimates, we did not find strong consistent spatial or temporal variation in great gray owl prey populations across sites and through time, in part due to limited sample sizes across the survey period and many zeros in the final dataset. We found that soil wetness was the strongest predictor of great gray owl prey presence—positively associated with vole presence and negatively associated with gopher presence. Finally, we found that there were strong correlations between different measures of vole abundance, providing a potentially valuable indirect survey method for voles (chew blocks, with or without cameras). Overall, our results echo findings from previous surveys of vole and gopher populations, and point to new, less invasive management tools for surveying vole populations in wildland settings.