Mini-acoustic sensors reveal occupancy and threats to koalas Phascolarctos cinereus in private native forests.
Forests on private land have a wide range of uses that span activities such as recreation, primary production and nature conservation. Traditionally, it has been difficult for researchers to access private land to undertake systematic surveys. We used mini-acoustic sensors (Audiomoth) mailed via the postal service to overcome landholder concerns about researchers accessing private property, with a focus on properties used for private native forestry. We surveyed koalas, an iconic threatened marsupial, in north-east New South Wales, Australia using passive acoustics, with repeat surveys over consecutive nights to account for imperfect detection in an occupancy modelling framework. Over 3 years, we surveyed 128 sites and recorded 2,560 male bellows. Detection probability over seven nights was high (>0.79), but varied substantially between years, due to use of different sensors, housings and weather conditions. After accounting for detection probability, modelling revealed that koalas commonly occupied private native forests of the study region (probability of occupancy = 0.58 ± 0.08). Occupancy was modelled against several covariates and it varied with the landscape extent of sealed roads (-ve), NDVI (-ve) and a habitat suitability model (+ve, but minor). There was no support for occupancy in private forests to be related to a range of other factors including extent of surrounding cleared land, timber harvesting history, fire and other measured habitat features. Synthesis and applications. We conclude that mini-acoustic recorders mailed to landholders were a highly effective method for assessing koala occupancy, after accounting for variable detection, and the approach could be deployed more widely for a range of species. Private native forests in partly cleared landscapes are commonly occupied by koalas, highlighting that this tenure is crucial for koala conservation and that practices seeking to balance conservation and production should be encouraged. In addition to sensitive habitat management in private forests, sealed road density is a major threat needing to be addressed.