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.

Methods
The main dataset is based on spotlight surveys of 34 forest transects over 8 years. It has been analysed with multiseason occupancy modeling. Additional datasets include audio surveys at night of 39 forest sites including 31 of the transect sites during year 8. A comparison of spotlighting and audio surveys was conducted in year 8 using a multi-method occupancy analysis.