Using thermal drones to validate historical koala surveys

Accurate population estimates can show trends that are fundamental to detecting species’ declines and to designing and assessing conservation strategies. We compared spotlighting, diurnal line transects and thermal drone flights for detecting koalas in a rural landscape and evaluated a time series of data at our site to test sampling error and understand the influence of survey type and temporal variability on population estimates. Historically, diurnal koala detections were biased towards searches with a southerly view, suggesting that aspect with relation to the sun was a source of sampling error. No method detected all koalas, with drone flights, diurnal surveys and spotlighting transects detecting, on average, 79%, 48% and 43% of koalas respectively across repeated surveys, but detection differences were not significant. Estimates of koala population density based on diurnal surveys had large confidence intervals. Combining techniques enhanced detection; a combination of drone and daytime surveys detected an average of 88% of koalas present. We conclude that, where possible, drone detection is currently the most effective way to detect koalas, and by combining methods, accuracy is improved.