When we release a group of endangered animals into the wild, we always hope that they will survive. Usually they don’t. We find Bilby corpses under bushes, feral cats ripped apart by feral cats, and tufts of rugged, lumbering fur in the remains of foxes.
Over the past 25 years, I have seen the devastation caused by the introduction of foxes and cats firsthand during attempts to conserve our threatened mammals. On one of my research sites, Arid Recovery, we have repeatedly tried to protect bilbies, bettongs and wallabies outside fences.
Unfortunately, our native animals have not evolved with these dexterous predators and simply do not possess the anti-predator behaviors or physical traits needed to avoid them.
So what do you do? After years of frustrating results, we’re trying something new. We want to help our native marsupials evolve to be more alert and better at survival. Not in fenced sanctuaries – but in the wild, along with these unusually intelligent predators.
Why are our native mammals easy prey? If our native marsupials had more time to adapt, we wouldn’t have to. But rabbits, foxes, and cats act like an unholy trinity. European settlement brought high numbers of rabbits.
These animals competed with local marsupials for food and became food for cats and foxes – in turn inflating their numbers. The damage has been exacerbated by widespread land clearing and overgrazing.
Our mammal extinctions to date include burrows or smaller marsupials, including wallabies, bands, and rodents mostly within the critical weight range of 35g to 5.5kg. Those that are smaller or larger are safer. Those in the middle? Cat and fox food.
The problem we face in conservation is doubly difficult because to protect the species that are most at risk – bay sharks, burrowers, stick nest rats – we have to raise them on safe islands. They live behind high walls while predators roam outside.
When you keep animals in captivity, they become more naive about predators. So what is the solution? Do we simply keep stocks of these rare marsupials on life support devices? We spend millions of dollars a year controlling cats and foxes by trapping, shooting and baiting them. Much less effort was made to improve the responses of predators.
If our native mammals are to reclaim any part of their former range, they will eventually need to co-exist with cats and foxes in more places in the wild. And to do that, they need our help.
Can we speed up adaptation? To date, most efforts to improve the responses of naive predators to predators have coupled an unpleasant experience with a predator cue. Rubber bands, water pistols, loud noises, or physical pursuit of animals are paired with cues such as stuffed foxes, models, cat smells, or sounds. Unfortunately, results are generally poor or short-lived.
In response to these challenges, we tested a more invasive approach – in situ predator exposure. This is where we expose threatened mammals to low densities of true predators over long periods of time to accelerate natural selection and direct learning through true predator encounters.
Over the six years we have conducted this trial in South Australia, this approach has yielded some promising results.
We put blubbers and butamas hiding in a fenced field and added a few numbers of feral cats. Then we waited. Over the next six years, we compared their physical and behavioral traits over time with a control group not exposed to predators.
We found that cat-exposed bilby became more cautious and sought out areas of thicker cover in just two years. Not only that, but their survival rates were higher than those of Bilby birds when they were reintroduced to a cat-inhabited area.
Within 18 months, it became more difficult to approach predators at night. Remarkably, their hind feet became longer compared to the control population over several years and had faster reaction times while escaping from predators, although not fast enough to show a significant difference in survival between the control group and the cat-exposed population.
In summary, exposing naive prey to predators led to a change in behavior and in some cases survival after only a few generations. This is positive news.
You may be wondering why this doesn’t happen naturally in wild populations. In some cases it happens. Many local mammals now recognize and respond to dingoes, which were only present in Australia a few thousand years ago. The problem is that densities of cats and foxes are likely to be too high to allow prey to adapt before local extinction occurs.
Studies have shown that anti-predatory behavior can be lost in just a few generations. It’s encouraging to know that they can be restored quickly, too.
Will these changes continue? What we need to know is whether these changes are due to plasticity or selection. If it is plasticity, it means that the changes and learning that both bilbies and bettongs experience may not be passed on to the next generation.
If selection is working, this means that continued exposure to the predator can lead to changes in the species’ genetic makeup, with further improvements and adaptations over time.
So what is it? Our preliminary results suggest that selection may occur in some traits such as hind foot length. Similar efforts to teach northern quolls to avoid cane toads found that learned behavior can be inherited.
This kind of catalytic evolution is also being experienced in corals to give them the adaptations needed to survive in our warming oceans.
To realize the dream of a successful coexistence between the introduced predators and our native mammals, we will need a combination of methods. This includes better ways to control predators to reduce numbers, improve habitat quality for our mammals, and improve prey responses.
We urgently need a better understanding of predator thresholds – the level of predation at which native species can maintain stable or increase populations while applying sufficient selective pressure to develop new behaviors and traits. Under these conditions, we can expect some (but not all) native species to eventually adapt to the introduced predators.
After spending the past three decades watching our native animals continually decline, we are now at the point where we need to carefully explore new options with an open mind.
(This story has not been edited by the Devdiscourse staff and is automatically generated from a shared feed.)