Comparing the cost-effectiveness of drones, camera trapping and passive acoustic recorders in detecting changes in koala occupancy
Description
Here we provide the code and the data that underpins the analysis presented in this manuscript. This investigation relies on occupancy modelling followed by power analysis and cost-benefit calculation for different monitoring scenarios. Abstract Quantifying the cost-effectiveness of alternative sampling methods is crucial for efficient biodiversity monitoring and detection of population trends. In this study, we compared the cost-effectiveness of three novel sampling methods at detecting changes in koala (Phascolarctos cinereus) occupancy: thermal drones, passive acoustic recorders, and camera trapping. Specifically, we fitted single-season occupancy-detection models to data recorded from 48 sites in eight bioregions of New South Wales, Australia, between 2018 and 2022. We explored the effect of weather variables on daily detection probability for each method, and using these estimates, calculated the statistical power to detect 30%, 50% and 80% declines in koala occupancy. We calculated power for different combinations of sites (1-200) and repeat surveys (2-40) and developed a cost model that found the cheapest survey design that achieved 80% power to detect change. On average, detectability of koalas was highest with one 24-hr period of acoustic surveys (0.32, 95% CI’s: 0.26, 0.39) compared to a 25-ha flight of drone surveys (0.28, 95% 0.15, 0.48) or a 24-hr period of camera trapping consisting of six cameras (0.019, 95% CI’s: 0.014, 0.025). We found a negative quadratic relationship between detection probability and air temperature for all three methods. Our power and cost analysis suggested that 148 sites surveyed with acoustic recorders deployed for 14 days would be the cheapest method to sufficiently detect a 30% decline in occupancy with 80% power. We recommend passive acoustic recorders as the most efficient sampling method for monitoring koala occupancy compared to cameras or drones. Further comparative studies are needed to compare the relative effectiveness of these methods and others when the monitoring objective is to detect change in koala abundance over time.
Files
Steps to reproduce
The data was gathered at sites where almost simultaenously methods were used to sample koala populations around New South Wales. This included 1x passive acoustic recorder (PAR), placed at the center of a 25-ha quadrat, 6x camera traps placed in two rows close to the PAR location, and two repeated drone surveys conducted per night, covering the entire 25-ha quadrat.