Monitoring the impact of habitat restoration on multi-taxa wildlife diversity in the California Delta

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Michelle Mah, Kristen A. Zumdahl, Andrew Engilis Jr., Danielle T. Fradet and Jason Riggio, Wildlife, Fish, and Conservation Biology, University of California, Davis, CA, Molly Ferrell, California Department of Water Resources, Sacramento, CA

Background/Question/Methods
The California Department of Water Resources (DWR) is conducting habitat management and restoration at six locations across the Sacramento-San Joaquin Delta. These projects have focused on restoring freshwater marsh and riparian forest habitats to island systems that had been levied for agricultural use (primarily pasture and row crops). Wildlife surveys at 35 study sites across the DWR project locations are being conducted to assess species diversity at each site across habitat types and restoration status. The goal of this project is to establish baseline data collection of multiple taxa and be the foundation for a long-term biomonitoring program in the California Delta.
During the breeding season of 2020 we conducted 304 avian point counts at 152 stations across our study area. Small mammal, passive bat acoustic, and camera trap surveys were conducted during fall of 2020. We established 35 small mammal traplines (each with 50 Sherman traps) and 69 passive acoustic bat monitoring and camera trap stations across the 35 sites. These were run over three consecutive nights for the survey period. Additionally, we placed 279 herpetofauna (amphibian and reptile) coverboards across the sites and checked them during avian and mammal surveys. Finally, we conducted visual encounter surveys for sign of any species and recorded any direct observations of species not detected during our other survey methods.

Results/Conclusions
A total of 92 bird species were identified using the sites during the breeding season. Avian species richness was higher in riparian forest sites than in agriculture/pasture and freshwater marsh sites, and highest in restored sites. We captured five species of small mammals in traplines, while incidental encounters reported an additional three. Small mammal species richness was similar across habitat type and restoration status. We observed 17 species of larger mammals across the study area. Mammalian mesocarnivore and herbivore species richness was highest in restored sites but was similar across habitat types. Passive bat acoustic surveys detected a total of seven species across the Delta, with Free-tailed Bats being most widespread across all study sites. We observed a total of 11 herpetofauna species with higher richness in riparian forest and restored sites.
Species response to habitat management activities, climate change events, vegetation structure and habitat design can improve DWR’s adaptive management strategies. This can be used to help restore and conserve habitats that are providing resilient ecosystem services such as biological diversity, nutrient cycling and flood protection.