Each year, Australian Wildlife Volunteers dedicate time, effort and their own money to rescue, rehabilitate and release tens of thousands of native animals. Their efforts get a lot of media attention, especially after huge disasters like the 2019 Black Summer megafires.
Readers will recall vivid images of rescued koalas as well as efforts to provide food to survivors in burned habitats.
But little is known about what happens to these creatures once they are released into the wild. Our new research on hand-reared brushtail possums has revealed that release into the wild can be fraught with difficulty.
In our study, nearly half were killed. The main culprit: foxes. But there are things we can do.
Rescue, rehabilitation and release
Brushtail possums are the fifth most rescued native species in New South Wales. When a mother opossum is attacked by a predator, hit by a car, or burned in a bushfire, human volunteers often artificially raise any orphaned offspring.
Raising babies as well as rescue and rehabilitation are important. But nature harbors threats such as hungry predators. Not only that, but the reason why an animal needed to be saved in the first place could still be there.
To learn the fate of rescued animals, we used radio tracking collars to track 20 hand-reared possums for up to 40 days after release. Of these, only eight (40%) survived to the end of the study, while nine (45%) were killed by foxes or had to be sent back to rehabilitation, and three opossums had a fate unknown, as they lost radio signal.
Foxes were responsible for all opossum deaths, and most occurred within three days of release. Unfortunately, hand-reared animals often haven’t learned the behaviors necessary to detect and avoid predators.
You might think survival would be a game of chance. In fact, we found opossums with more exploratory personalities, and those that were less tame were more likely to survive. These qualities may have helped opossums find food and shelter more efficiently on their own in the wild.
This means the odds are stacked against orphaned, hand-raised opossums. Because they were raised by humans, their personalities can be very different from those of wild opossums. In short, captivity can alter the development of behaviors that might be important for survival in the wild. The more time animals spend with humans and the more tame they become, the less efficiently they seek shelter, recognize predators, and find food.
By contrast, it didn’t matter whether the opossums were released without further support or whether caregivers left supplies to get them started. It also did not matter whether they were released in urban or rural areas.
The opossums that had the highest survival rates were those that had retained their wildness and had not become tame.
What can we learn?
So what should Australian wildlife carers do? It’s not as simple as advising wildlife rehabilitation organizations to minimize the time animals spend in captivity. Animals should remain in rehabilitation until their illness or injury is treated, they are physically ready for release, and a suitable release site has been found.
We believe we need to test and develop new ways to reduce tameness and encourage exploratory behavior during rehabilitation.
Wildlife rehabilitators could use databases like Feral Scan to assess how often introduced predators have been seen at particular release sites. Rehabilitators could also talk to local land managers to leverage fox control efforts and aim to release possums when fox numbers have been suppressed. We also need to continue to develop effective methods for training opossums to avoid predators, for example by borrowing from successful antipredator training used for other marsupials.
Where to go from here?
In our recent review, we analyzed 112 studies of wildlife survival rates during rehabilitation or after release. We found that factors affecting survival were often species- or context-specific, such as region of the world or why the animal needed rehabilitation.
Globally, we have found that human-related factors, such as collisions with cars and introduced predators, were the leading causes of injury and death in rescued and released wildlife. Addressing threats in the environment must remain a priority to reduce the need for wildlife rescue in the first place.
We hope that studies like ours can improve guidelines for wildlife rescue, rehabilitation and release. To improve survival rates, scientists, government agencies, and wildlife volunteers must develop evidence-based, species-specific protocols to give each rehabilitated animal the best chance at a life in the wild.
As urbanization fragments habitat and natural disasters are expected to be more frequent and severe due to climate change, we will need these protocols to enable fast and effective wildlife rescue programs.
/ Courtesy of The Conversation. This material from the original organization/authors may be ad hoc in nature, edited for clarity, style and length. The views and opinions expressed are those of the authors.