Available at: https://digitalcommons.calpoly.edu/theses/3003
Date of Award
4-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Tim Bean
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
The California Channel Islands are unique in that two islands (Santa Rosa and Santa Cruz) support two endemic mesocarnivores, the island fox (Urocyon littoralis) and the island spotted skunk (Spilogale gracilis amphiala). Following the near-extinction of island foxes in the early 2000s, island spotted skunk populations increased significantly. Now that foxes have recovered, skunk captures have precipitously declined - possibly due to interspecific competition with foxes who have a similar diet but a larger body size and wider temporal niche. It has been proposed that skunks selectively use canyon bottoms and drainages with high vegetation cover and that these areas may represent particularly important habitat for island spotted skunk monitoring. I investigated occupancy probability and habitat associations via trail camera surveys on both islands, with 92 cameras placed in drainages to maximize detectability of these rare, cryptic mesocarnivores. Cameras were deployed from summer 2023 to summer 2024 to capture seasonal trends in detection probability. I detected skunks at 81% of cameras on both Santa Cruz and Santa Rosa over the study period. Out of 1,427 total 2-week sampling occasions, skunks were detected during 22% on Santa Cruz and 38% on Santa Rosa. My results suggest that detection probability was influenced by vegetation cover at the camera location and season, while locations with higher topographic roughness were more likely to be occupied on Santa Cruz. This survey design showed much higher detection rates than previous studies and suggests that skunks are likely more widely distributed spatially than expected. Due to the high proportion of camera sites occupied and lack of model support for predictors, precise assessment of island spotted skunk habitat distribution and variation in occupancy across the islands may require more fine-scale or multiscale monitoring in the future.