Using a novel conservation strategy, Australian researchers have shown how an endangered wallaby species could be saved without costly nature reserves by giving their young a safe but pragmatic head start.
The headstart strategy, described in the journal Current Biology, involves putting juvenile bridled nailtail wallabies (Onychogalea fraenata) into an exclosure to protect them from predators and then releasing them back into the wild.
“About half of all young bridled nailtail wallabies, less than three kilograms, are eaten by cats,” says lead author Alexandra Ross, from the University of New South Wales.
“But when you look at the numbers of adults, the survival rate goes up to 80% – which shows that size is a good predictor of survival. So, to save the population from cat predation we don’t need to protect every single animal, we only need to protect the vulnerable small wallabies.”
To create the exclosure, or “nailtail nursery”, her team took young wallabies or mothers with dependent young from the wild and put them into a nine-hectare fenced paddock at Avocet Nature Refuge, south of Emerald in central Queensland, to keep them safe from alien predators like feral cats (Felis catus) while still learning to fend for themselves.
“The wallabies can still be snatched by native predators such as eagles and pythons,” says Ross, “which ensures they retain some of their predator awareness – they don’t become ‘naïve’ to predation, which would make them very easy prey after re-release into the wild.”
Between 2015 and 2018, 56 juveniles were raised within the exclosure, and 89% of those survived to grow large enough to be released. During that period, the nailtail population nearly tripled from 16 to 47 individuals – their largest increase since monitoring began in 2008.
Future projections comparing no headstart to five, 10, 20 and 50 years of the nurseries estimated that once they’ve ceased, extinction would result within two to 52 years, suggesting the strategy could be the wallabies’ only chance of survival.
As far as viability, the authors report the upfront cost of the small enclosure as less than $100,000 AUD, compared to nearly $1 million AUD for the cost of building a 1110-hectare predator-proof boundary fence (not including ongoing maintenance and management).
The idea was originally inspired several years ago.
“It was a fireside chat one day where a few of the nailtail people were spitballing about how to save a species that was barely clinging on, without needing a million dollars,” says Ross.
“The group started talking about how it was such a shame that conserving terrestrial animal populations requires large, fenced enclosures and sanctuaries, which are expensive and time consuming and separate the whole population from the wild.
“Wouldn’t it be great if there was some way of only protecting the vulnerable juveniles just for long enough to stop them getting eaten? And thus, the nailtail nursery was born!”
After putting the plan into action at the refuge, they kept catching healthy adult nailtails that had been released from the nursery.
“So we knew we had to get the word out that there was an alternative strategy to save terrestrial species,” says Ross. That spurred her team to collate all their catch-and-release data to prove scientifically what they were seeing on the ground and share their success.
“Australia has the worst record of extinction, and we hope this strategy adds an extra option for wildlife managers. Headstarting can save species that are particularly threatened in their early-life stage, especially species that maybe don’t have as much funding.”
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Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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