Koala greater glider detection histories: Richmond Range NP

Multi-year investigations of population dynamics are fundamental to
threatened species conservation. We used multi-season occupancy based on
spotlight surveys to investigate dynamic occupancy of the koala and the
greater glider over an 8-year period that encompassed a severe drought in
year 6. We combined our occupancy estimates with literature estimates of
density to estimate the population sizes of these species within the focal
conservation reserve. Both species showed substantial yearly variation in
the probability of detection (koala: 0.13–0.24; greater glider:
0.12–0.36). Detection of the koala did not follow any obvious pattern. Low
detection of the greater glider coincided with the drought and two
subsequent years. We suggest the low detection reflected a decline in
abundance. The probability of occupancy of the koala was estimated to be
0.88 (95%CI: 0.75–1.0) in year 8. Autonomous recording units were also
used in year 8, enabling an independent occupancy estimate of 0.80
(0.64–0.90). We found no evidence of a drought-induced decline in the
koala. Habitat variables had a weak influence on koala occupancy
probabilities. The probability of occupancy of the greater glider changed
little over time, from 0.52 (95%CI: 0.24–0.81) to 0.63 (0.42–0.85) in year
8. Modelling suggested that the probability of colonisation was positively
influenced by the percentage cover of rainforest. Increased cover of these
non-browse trees may reflect thermal buffering, site productivity, or soil
moisture. We estimate that our study reserve is likely to contain
>900 adult koalas and >2400 adult greater gliders. These are
among some of the first reserve-wide estimates for these species. Our
study reserve can play an important role in the conservation of both
species.