Outsmarting the fox

I was doing an honours project in my fourth year, catching small mammals and testing ideas about what factors limit their numbers during winter, and if they were food-limited. But I had a fox disturbing all my traps. That got me interested in foxes.

Then I got the chance to do a PhD down in the Australian Alps looking at their impact, working with the CSIRO on plans to introduce an agent to sterilise them, but for all sorts of reasons the plan didn’t work out. My research turned into looking at the impacts of foxes on native small mammals, rabbits and kangaroos. I also looked at the behavioural responses of these native animals. Were they naïve to foxes? Did they recognise them? Ever since then I’ve kept an interest in trying to work out what impact they have, what’s the nature of the impact, how it works – and then, importantly, how we can potentially stop it.

The introduction of foxes and cats in Australia has been devastating for our native wildlife. A recent study found that cats and foxes wipe out 697 million reptiles, 510 million birds and 1.4 billion small animals annually in Australia. Just huge numbers. Foxes alone kill more than 300 million native mammals a year. There’s in the order of 20 mammals that have probably gone extinct or dramatically declined because of foxes and cats in Australia.

And all that killing is in addition to the mortality that goes on from natural predation, from creatures like goannas and the other native predators here, so all this predation is extra – we did a study showing that introduced predators have twice the impact of native predators, and the reason for that is probably because Australian mammals don’t show the right sorts of responses to these novel predators. They either don’t recognise them as dangerous, or they respond in a way that’s just not right for that type of predator, or they just get outrun.

Foxes are a global success story really – they’re the most widespread of the carnivores apart from domestic dogs. They’re beautiful animals in their own right. You have to admire their adaptability and flexibility. Right here in Sydney’s inner west there are foxes in the park, just across the road from me. And then there are foxes in the Simpson Desert. They’re incredibly adaptable and flexible, and they can succeed everywhere. It’s just that there’s such a mismatch between what they do to hunt and what our native animals can do to avoid predation.

It would be an uphill battle to try and 100% eradicate foxes in Australia. Some people would like to use genetic modification to try and control these pest animals but this is a long way off and has ethical hurdles. Unfortunately, the only sort of blunt tool we’ve got at the moment is poisoning or other lethal control, but it doesn’t get all the problem animals – individual animals can cause particular problems with their own sort of personality types. Some of them are just surplus killers.

Alternative tactics are needed. We’ve got to try to outsmart them.

One of the methods that we’re developing, with Dr Catherine Price at USYD, is taking the information that they use to hunt, their sense of smell, and making that information useless to them. Foxes find a lot of native species by smell; they hunt them down by finding where they’re hiding by their odours.

We’ve shown that foxes will investigate the odours of species they’ve never even encountered before as potential food. We exposed foxes in western Victoria to bandicoot nest odours where bandicoots have never occurred, and the foxes visited those odour spots and were sniffing around looking for a meal on the first day.

We’re trying to neutralise that effect by basically training them that chasing that particular odour is not going to lead to a reward. By spreading that odour widely, foxes can’t pinpoint exactly where their prey is, and they quickly learn to ignore useless information.

We’ve had success with this in a number of circumstances. It all began working on mice in enclosures and looking at how they use odours to find food. We then showed that we could use the technique to stop rats from finding birds’ nests and preying upon the eggs. We then took it to New Zealand on a big scale working with Landcare Research, trying to protect some endangered bird species that breed on the braided rivers coming off Mt Cook that are at risk from ferrets, hedgehogs and cats. And we showed that the technique led to the doubling of bird breeding success over a couple of years. If that success is sustained it would really turn their population decline around completely – and that was without killing anything.

We’ve sparked interest in this idea, and are now in discussions with quite a number of people in Australia and overseas to try and stop problem predators, not just introduced foxes. Sometimes those problem predators are native, sometimes they are introduced but culturally important, so killing isn’t an option.

Using this sort of non-lethal technique is what has been called “nudging”. We just nudge the predators in a different direction without harming them, but they can go on and keep eating things like rabbits and introduced rats, which is potentially a good thing. It’s just the critical things that we don’t want them to kill – we make them hard to find.

Every predator wants that easy meal. Because the predators are hungry and motivated to eat, they can’t go around chasing things that are hard work. So we use this misinformation technique to exploit their motivation.

We’ve got many proofs of concept. Now we’re trying to work out the exact mechanism of how we can apply it cost-effectively. We don’t yet know how often we need to expose them to it, or how difficult the hunt needs to be. But their hunger means that they can’t keep looking for meals that don’t exist, and this is something they can’t evolve adaptations to overcome.

Foxes like many mammals navigate their landscape with their nose. We’ve got to use this misinformation strategically. But it definitely looks like odour is a valuable new tool in our toolkit to try and stop the damage caused by these predators.

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