Abundance estimates of koalas (Phascolarctos cinereus) and southern greater gliders (Petauroides volans) on the Illawarra Range, New South Wales, from spatiotemporally-replicated thermal drone surveys

Reliable estimates of abundance are critical for threatened species conservation. This study aimed to provide baseline abundance estimates of koalas (Phascolarctos cinereus) and southern greater gliders (Petauroides volans) on the Illawarra Range, New South Wales, from spatiotemporally-replicated thermal drone surveys. Koalas were detected at 19/47 sites (40.4%), whereas southern greater gliders were detected at 30/47 sites (63.8%). Using N-mixture models, 147 koalas [95% CI: 121, 173] and 195 southern greater gliders [95% CI: 174, 216] were estimated across the surveyed sites, with respective detection probabilities of 0.14 [95% CI: 0.05, 0.36] and 0.25 [95% CI: 0.18, 0.34]. After correcting for imperfect detection, the mean koala density was estimated at 0.13 individuals ha−1 [95% CI: 0.10, 0.15] and the mean southern greater glider density was estimated at 0.17 individuals ha−1 [95% CI: 0.15, 0.18]. These findings provide baseline data that will be valuable for monitoring population trends and potential declines of two endangered arboreal marsupials occurring on the Illawarra Range.