Motorways, drought and wildfire: do they shape trajectories of arboreal mammal populations in eastern Australia?

Abstract Motorways have the potential to create barriers to the movement of wildlife, increase mortality and cause edge effects, producing declines in abundance in nearby habitat. We investigated the response of six nocturnal arboreal mammal species to the construction of a new motorway in eastern Australia: five gliding species (three small, < 300 g; two large, > 500 g) and one generalist non-gliding species (4 kg). The two large gliding species are listed nationally as threatened. We employed dynamic occupancy modelling using repeat surveys at 75 sites over an 8-year period, beginning one year before motorway construction commenced. We predicted that if species were adversely affected by the motorway, then the probability of occupancy and/or detection should decline at sites near (< 300 m) the motorway compared to reference sites (≥ 1 km from the motorway). A severe drought occurred in year 4, leading to wildfires across a third of our sites, followed by three years of above average rainfall. The five gliding species showed declines in the probability of detection following the drought, suggesting abundance had declined. The drought declines appear to have masked detecting a response to wildfire. Detection subsequently increased to pre-drought levels in the small gliding species. The probability of occupancy in these species and the non-gliding species was high (> 0.5) across all years suggesting there was no influence due to the motorway. The probability of occupancy and detection in the large gliding species declined across the eight years. These findings support the hypothesis that differences in life history (slow vs. fast) among the gliding mammals influence their response to disturbances (landscape change, drought, wildfire). This suggests a much longer period to assess recovery is needed for species with a slow life history.