Endangered Wallaby No Longer Extinct! Population Grew as Feral Predators Fenced Out

Since conservation scientists led by UNSW Sydney successfully trialed an intervention strategy never before used on land-based mammals, a population of bridled nailtail wallabies in Queensland has been taken back from the verge of extinction.

The researchers rounded up bridled nailtail wallabies under a certain size and put them in a protected environment where they could survive until maturity without fear of their biggest predators-feral cats-before being released back into the wild using a technique known as 'headstarting.'

Defending Juvenile Wallabies

The scientists explain their decision to defend only the juvenile wallabies from wild cats in Avocet Nature Refuge, south of Emerald in central Queensland, where there were only 16 in 2015.

According to Alexandra Ross, the lead author of the article, wild cats feed on juvenile wallabies weighing less than 3 kilograms, or less than the size of a rugby football.

"Previous experiments had found that wild cats killed more than half of these young bridled nailtail wallabies before they reached maturity," Ms. Ross says.

"However, when the number of adults is considered, the mortality rate rises to 80%, demonstrating that height is a strong indicator of survival."

Wallaby Enclosure

The findings backed up the scientists' suspicions. Around 2015 and 2018, 89 percent of the 56 bridled nailtail wallabies raised in the headstart enclosure lived to be big enough to be released back into the wild. One had to be euthanized due to illness, two were found dead from injuries or unexplained causes, and four were killed by birds of prey.

Professor Mike Letnic, one of the article's co-authors, claims that headstarting is a more cost-effective intervention than other more nuanced interventions such as establishing vast nature reserves after wild animal eradication, such as the one implemented in Sturt National Park in 2019.

Related Article: Mammal Extinction Capital of the World: 5 of Australia's Critically Endangered Mammal Species

Bridled Nailtail Wallabies

According to Ms. Ross, the population of bridled nailtail wallabies in the Avocet Nature Refuge more than doubled after three years of headstarting, which is the largest increase in this population since surveillance began in 2011.

Worryingly, as Ms. Ross and her colleagues crunched the numbers for how the population would do without, or with different periods of headstarting scenarios-none, five years, ten years, twenty years, and fifty years-the estimates showed that extinction occurred within two to 52 years once headstarting ceased.

Headstarting Initiative

However, the team's execution of the first headstarting initiative for a land-based animal gives hope to other endangered animals in Australia-and perhaps around the world-where the size of young is a factor in population survival.

Ms. Ross and Prof. Letnic contend that headstarting has worked well in the past for birds, fish, snakes, and seals, and there's no reason why it shouldn't work for terrestrial mammals as well.

Disadvantages

One of the disadvantages of dividing animals for extended periods of time in feral-free enclosures, according to Prof Letnic, is that they unlearn their distrust of predators on the outside. "Evolution sets in after just a few years in a protected zone, and species begin to learn new ways to compete with one another. To be the first to the meal, they seem to become more daring. If they were then released back into the wild by feral animals, the brave ones would be eaten because they had lost their predator sense."

Ms. Ross, on the other hand, argues that headstarting could alleviate this issue because animals are only isolated from predators for a few months or a year at most. There is also no human contact, and the species are constantly preyed upon by natural predators such as eagles and snakes, meaning that they are conscious of their surroundings.

Future Studies

Her next experiment will look at how the bridled nailtail wallabies behaved after being released from the headstarting enclosure and how long it took them to completely transition back into the wild.

Also Read: Australia's Treasured Outback Now Needs Urgent Protection

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