Effective biodiversity monitoring requires survey designs that balance volunteer feasibility with sufficient statistical power to detect meaningful population change. This report uses data from the citizen science-led Bailiwick Bat Survey (2021—2024) to evaluate alternative passive acoustic monitoring protocols for bats in the Channel Islands, with a focus on Guernsey, Alderney, and Sark. 

Using verified acoustic identification for bat species, we simulated 25-year monitoring datasets under scenarios of 5—25% population declines and compared the power of alternative designs to detect long-term trends. 

Our findings demonstrate how citizen science acoustic surveys can underpin statistically robust monitoring of bat populations, while highlighting the importance of representative sampling designs and geographic coverage. 

The analyses provide a template for developing a Channel Islands-wide bat monitoring scheme and offer transferable insights for other small-island contexts where resources and site numbers are constrained.