Forgotten Fauna Part 19: The Woylie — a case study that can help inform our plans, both inside and outside the predator-proof fence, at Mt Vandyke

In the article I wrote last year for the forgotten mainland fauna series, we explored the interesting case study of the introduction of the Eastern Barred Bandicoot to offshore islands in Victoria, where — in the absence of foxes — they are co-existing with feral and domestic cats, consistent with a pattern that has also been long observed in Tasmania. Needless to say, testing how threatened small mammals interact with introduced predators outside of fences is absolutely critical if we are to adopt strategies capable of leading to the effective recovery and persistence of these species in the wild into the future.

Learning from others who are testing small mammal recovery ideas both inside and outside of fences is of great interest to us at NGT, because – as many of you will know – we are gradually working towards implementing our own small mammal experiment, both inside the fence at Mt Vandyke, and outside the fence in the surrounding Cobboboonee National Park. At this strategically located NGT Reserve, our initial focus has been to progress the restoration of a functioning tussocky native grassland / sedgeland ecosystem, as our plans to introduce small mammals into the ecosystem continue to unfold in the background.

With this in mind, it has been interesting to see some of the things that have been reported over the past couple of years in relation to Woylie (brush-tailed bettong) research in Western Australia. Although not on our initial target species list, the Woylie is a marsupial species that (like other critical weight range small mammals we’ll also be working with) used to occur in this region (see historical distribution below) and is known to be especially susceptible to fox predation.

After a drastic contraction in its national range, after the spread of foxes more than 100 years ago, the Woylie continued to persist at a handful of locations in the wild in south-west WA. However, the species then experienced a further precipitous decline at these remaining wild locations about 20-25 years ago, and remains highly threatened.

As a result, the Woylie has now been translocated to a number of new locations across its former range and also released into predator proof-fenced “safe havens” (aka “free-ranging enclosures”), with positive results in the absence of introduced predators. But in some interesting research released in this paper a couple of years ago, it seems that this success is only one part of the story, and eventually (in a relatively short space of time) can come at a significant cost.

That ‘cost’ is the loss of the natural anti-predator fear response that all animals develop when they live in places where they are at risk of being the next meal for other animals in the ecosystem around them. To understand what the loss of a fear response can look like, one need look no further than the stories of animals first encountered on long-isolated islands with no predators, where all fear has been lost – this is sometimes referred to as “island tameness“.

This lack of fear resulted in the easy hunting and rapid decline to extinction of species you may have heard of, after humans first encountered them on predator-free islands,; species such as the dodo of Mauritius, or the dwarf emu once found on Kangaroo Island right here in Australia. When we put up a predator-proof fence, we artificially create conditions equivalent to those found on predator-free islands.

In the case of the research referred to above, which is also discussed here in an article in The Conversation, some interesting things happened when woylies were given safety from all predators. The researchers examined ten years of monitoring data collected from woylie populations both inside and outside a safe haven in Western Australia, and compared the two groups.

As stated in the article, “inside the free-ranging enclosure, where there were no predators, competition for food was the biggest pressure. Bold, carefree woylies ate before more cautious individuals which likely discouraged cautious behaviour”, and “in just four generations, woylies born inside havens became successively smaller than previous generations and their feet became shorter. The data showed protected woylies also became less reactive and fearful. It meant humans (and potential predators) could get relatively close to the animals before they fled.”

Given that the ultimate goal of projects that involve protecting species behind predator-proof fences is to see the progeny of those animals eventually released back into the wild, this loss of key predator avoidance behaviour is something that needs to be factored into our plans, or we’ll end up with animals that – despite best intentions – become less resilient and suitable for wild releases over time. The authors suggested that to proactively address this risk, “animals in safe havens may need to be exposed to low levels of predators to reinstate survival traits.” Indeed this concept has been previously tested with the Burrowing Bettong at the Arid Recovery project area in South Australia, as described in this paper, with positive results.

Fast forward to a couple of years later, and in January this year, the researchers in WA published new research that demonstrated how exposure to the Chuditch / Western Quoll inside a safe haven, could effectively maintain the fear-response of animals released into the wild, where they then encountered feral foxes and cats for the first time. If you would like to learn more about this interesting research in a less technical format, a nice short-form overview can be found in this Biodiversity Council story.

The final step in this story is the recent news of the experimental release of 147 woylies ‘outside the fence’ at AWC’s Mt Gibson Wildlife Sanctuary in WA, which was reported in the ABC media a couple of months ago, to complement a small number animals naturally “leaking” in small numbers into the surrounding environment (as yes, some animals have managed to escape by clearing the fence!). You can take a closer look at their leaping ability in the video of their release below (from the ABC article linked above)…

There are a number of ingredients in this fascinating story that are directly relevant to our plans at Mt Vandyke, where we intend to expose southern brown bandicoots and long-nosed potoroos to eastern quolls inside the fence, and to eventually see all three species either supplement or kick start new populations outside the fence.

The ability to compare notes, learn from others and not have to ‘reinvent the wheel’, is a tremendous help in our collective efforts to restore ecosystems, by recovering threatened species that we need to play key functional roles across Australia.

When our time comes at Mt Vandyke, we also look forward to freely sharing what we learn to aid the general conservation effort for our threatened small mammals on the mainland.

The ongoing habitat restoration work at Mount Vandyke is currently being made possible thanks to a number of NGT’s supporters, including Purryburry Trust, Leith Hope Memorial Foundation, Pixel Seed Fund, NGT monthly donors and other individuals who wish to remain anonymous. The project is also receiving significant public co-investment in the form of a grant from the Victorian State Government, via the Nature Fund program.