Conserving threatened mammals in the face of fire and predation.

Australia is in the midst of an extinction crisis, having lost more biodiversity than any other developed nation in the past 200 years. Invasive species are a major driver of this biodiversity loss. There is evidence that the impacts of introduced red foxes and feral cats on native fauna can be amplified following fire due to the loss of shelter. Managing the potentially synergistic threat posed by invasive predators and fire is a formidable challenge. Invasive predator management has traditionally focused on lethal control, however, additional methods for conserving threatened fauna in post-fire environments are needed, particularly in the face of climate change and intensifying fire regimes. The use of artificial refuges in burnt areas is a relatively new tool that may reduce predation rates and increase prey population persistence post-fire, but the approach requires rigorous testing to determine its effectiveness.

The overall objective of the project was to assess how ground-dwelling animals respond to the provision of artificial refuges in post-fire environments. Our project was conducted in the heathy woodlands of Wathaurong Country in the Otway Ranges, Victoria. The four specific objectives of the project were:

1. Determine if the provision of supplementary refuges results in their use by small animals (birds, mammals, and reptiles) and increases individual survival and population size of mammals  post-fire (relative to areas without shelters).
2. Determine whether surviving animals move out of burnt areas into unburnt patches post-fire, and how they interact with supplementary refuges.
3. Quantify relative predator activity pre- and post-fire at control and impact sites.

Objective 1 summary

To address this objective, we conducted a control-impact experiment by placing camera traps inside the artificial refuge tunnels (Figure 1) and burnt open areas adjacent to the tunnels. The tunnels were 50 m long and were constructed of chicken wire pegged to the ground and partially covered with shade cloth. Each treatment site had five tunnels. We found that a range of bird, mammal, and reptile species interacted with the tunnels. Notably, the detection rates of some species groups, including skinks and wrens, were considerably higher inside tunnels relative to outside. This may be due to a perceived decrease in predation risk by invasive predators, such as cats and foxes, as well as native predators such as currawongs and owls. However, the detection rates of small mammals were similar
inside compared to outside tunnels. We also conducted a before-after (prescribed-fire) control-impact (BACI) experiment by live-trapping small mammals at unburnt sites, burnt sites with artificial refuges, and burnt sites without artificial refuges. Surveying began several months before the fires, and sites were resampled regularly until 12 months post-fire. We found that prescribed fire reduced the abundance of the two most frequently detected small mammal species, the bush rat (Rattus fuscipes) and the agile antechinus (Antechinus agilis; Figure 2). Preliminary data analysis suggests that the provision of artificial refuge tunnels did not boost small mammal abundance relative to control sites.

Objective 2 summary

To address this objective, we used spool and line tracking and touch pole vegetation surveys to quantify microhabitat selection for bush rats and agile antechinus before and after a prescribed fire in the Otway Ranges. We found that the animals rarely ventured into recently burned areas (<3 months post-fire) and none of the tracked animals interacted with the tunnels. Bush rats showed strong selection for habitat variables such as complex vegetation, logs, and sedges, and the strength of this selection increased in response to fire. Agile antechinus showed little preference or avoidance for the measured variables. A strong selection of unburnt patches by bush rats suggests that prescribed burns that retain many unburnt patches may help bush rats persist at burnt sites.

Objective 3 summary

To address this objective, we conducted five repeated camera trap surveys across our study area (BACI experimental design). We conducted two 8-week surveys pre-fire and three surveys post-fire, until 12 months post-fire. Our camera trapping surveys provided 4,500 animal detections, of which around 10% were of cats and foxes. Cats and foxes did not show a strong response to fire. Detections of these predators increased at both burnt and unburnt sites post-fire, which either suggests a seasonal effect or a broader effect of fire that spanned both burnt and unburnt areas. Detections of medium-sized mammals (e.g., bandicoots, echidnas) were higher in unburnt areas, farther away from the burn edge, and at sites with a lower percentage burnt. Swamp wallaby detections increased over time in the burnt sites and decreased over time in the unburnt sites.

Conclusion

Our project has provided evidence that certain species of small, ground-dwelling vertebrates will use artificial refuge tunnels more than adjacent open areas after fire in woodland ecosystems. We have demonstrated that bush rats and agile antechinus avoid using recently burnt areas and that bush rats prefer to use structurally complex vegetation, logs, and sedges after fire. We did, however, detect small mammals inside the refuge tunnels—which were placed inside the burn scar—although we detected them outside the tunnels equally as often. Further, the preliminary data suggests that the artificial refuges did not improve small mammal population persistence in the 12 months following prescribed fire. This suggests that the artificial refuge tunnels used here may not be appropriate tools for conserving small mammals from the potentially elevated risk of predation following fire, although we emphasise that the data is preliminary, and our recommendation may change following further analyses. Nevertheless, we recommend further research on different artificial refuge designs, ecosystem types, and fauna communities.