Effects of the Australian 2019-2020 megafires on a population of endangered broad-headed snakes Hoplocephalus bungaroides

The 2019-2020 Australian megafires were unprecedented in their intensity and extent. These wildfires may have caused high mortality of adult broad-headed snakes Hoplocephalus bungaroides which shelter inside tree hollows during summer. We evaluated the impacts of two high-intensity wildfires (2002 Touga Fire and 2020 Morton Fire) on a broad-headed snake population in Morton National Park, south-eastern Australia. We analysed a 29-year mark-recapture data set to estimate survival rates of adults in years with and without wildfires, and with and without human disturbance to rock outcrops. To examine the short-term effects of fire on occupancy, we analysed presence-absence data collected from 25 sites during 2019 and 2020. Estimates of occupancy were higher for 2020 (0.93 +/- 0.09) than for 2019 (0.66 +/- 0.14), while detection rates were constant (0.40 +/- 0.06). Over the period 1992-2020, the best supported Cormack-Jolly-Seber model was one in which adult survival rates were high and stable (0.81 +/- 0.04), but were 23% lower in years when humans disturbed rocks (0.63 +/- 0.08). A model in which adult mortality was 20% higher in years with human disturbance and 14% higher in years with wildfires was also supported. Estimates of abundance revealed that the population declined by 34% after the Touga Fire, and 26% after the Morton Fire. Over the 29-year study, the population has declined by 60%. Our results highlight how mortality events from wildfires need to be evaluated in the context of other threatening processes. For this population, the removal of snakes and associated habitat disturbance poses a more serious threat to population viability than infrequent wildfires.