Life’s tough when you’re a fox. Bandicoots don’t just sit around waiting for you to catch them. And when you finally sniff one out, all that dense understorey gets in the way of a speedy chase.
But what happens if there’s no understorey in the way? Does the fox’s job become easier? And do things become a lot tougher for bandicoots?
In a land that is increasingly fire-prone, the interactions between predators, fire and native mammals in forest ecosystems is an important knowledge gap for land managers aiming to conserve native fauna. Both planned (or prescribed) fires and wildfires tend to remove a lot of understorey vegetation cover, at least temporarily.
During my PhD with the Fire Ecology and Biodiversity group at the University of Melbourne, I worked with an Honours student, Craig Mildwaters, and land management agencies, to determine how foxes, feral cats and their native prey responded to a prescribed burn. Our work was recently published in the Journal of Mammalogy.
The study took place in the stringybark – peppermint forests of the Otway Ranges, in
south-western Victoria. It was a before-after control-impact experiment based around a prescribed fire conducted by Parks Victoria and the Department of Environment, Land, Water and Planning (DELWP) in autumn, 2013.
Our field work involved using motion-sensing cameras to survey invasive predators and native mammals, and collecting fox scats to analyse what they were eating.
Our first session of camera surveys took place before the fire, and showed that
invasive predators and swamp wallabies were more commonly found at sites with an open understorey. In contrast, smaller native mammals such as bush rats and long-nosed bandicoots were positively associated with understorey cover in unburnt forest.
The prescribed fire was patchy. It burnt just over half of the 1200 ha block, and created a mosaic of burnt ridges and unburnt strips of vegetation along gullies.
After the fire, there was a five-fold increase in the occurrence of invasive predators at burnt sites (relative to changes at the unburnt control block). In contrast, there was no change in fox occurrence at unburnt sites within the burn block.
Foxes also began preying heavily on medium-sized native mammals such as echidnas and long-nosed bandicoots, instead of the swamp wallabies which had made up ~50% of their diet prior to the fire.
This suggests that fire made the forest more suitable habitat for invasive predators, and increased the vulnerability of medium-sized native mammals to fox predation. Such changes are highly concerning, as interactions between threatening processes can exacerbate the risk of extinction, particularly for already vulnerable species.
Whether or not the changes we observed were large enough to impact the native mammal populations was unclear ― this needs further investigation.
Our findings only relate to one fire at one block of forest, and require further replication. Nonetheless, if predation by invasive species limits the recovery of native fauna after fire, integrated management of fire and invasive predators may be essential for biodiversity conservation in flammable forest ecosystems.
Australia has an enormous challenge with managing foxes and feral cats. This challenge becomes even greater when you introduce fire into the mix. By continuing to collaborate with land managers to tackle important knowledge gaps regarding the management of invasive predators and fire, my research aims to improve conservation outcomes for threatened species in forest ecosystems.
With thanks to David Salt from the Threatened Species Recovery Hub for his help in developing this story for the Science for Saving Species Magazine.