We supported management of the California Least Tern (CLT) Preserve at Huntington State Beach by establishing a baseline of nocturnal small mammals relevant to nest depredation risk. In Year 1 (Oct 2024–Aug 2025), we deployed 30 Sherman live traps across three arrays (north, southeast inside fence, southeast outside fence) for three consecutive nights (90 trap-nights). We recorded five captures, all House Mouse (Mus musculus), yielding 5.6 captures/100 trap-nights and 0 recaptures. All detections occurred on the southeast perimeter (inside and just outside the fence). Weather was cool and calm with waxing gibbous illumination during all trap nights, a factor known to suppress nocturnal small-mammal activity and potentially bias detection low. Vegetation structure, tracks, and burrows identify the southeast perimeter as current high-probability use areas. These results provide a defensible baseline, refine trap placement for Year 2, and begin to separate habitat structure (riprap/vegetation/trash availability) from detection effects (lunar illumination). Management implications include prioritizing trash abatement at riprap edges, pre-season focused trapping on the southeast perimeter, and maintaining short, humane handling windows. Complementary daytime efforts targeting California ground squirrels (selective depletion; CPUE tracking) will proceed in spring to directly address a likely CLT predator. Ongoing integration with weekly CLT nest monitoring will link mammal activity to nest outcomes and guide adaptive effort in Years 2–3.

Barry Nerhus is a wildlife biologist and restoration ecologist with 20 years of field experience. He is Founder & CEO of Endemic Environmental Services (17 years) and founded Cambriate in 2025 to advance practitioner training. Barry has 15 years working with California Least Terns and has focused on the Huntington Beach colony for the past 4 years, integrating small-mammal monitoring, depredation risk assessment, and adaptive management. Through the Institute for Conservation Research & Education (ICRE), he leads applied R&D that translates boots-on-the-ground methods—trapping design, camera deployment, and decision rules—into scalable conservation frameworks agencies and contractors can adopt.