'Old school' plan to stop invasive predators causing extinctions on Aussie island
Three species of rodent have devastated parts of Norfolk Island. But two simple tools are being used to learn more about them.
On a remote Australian outpost, that’s actually closer to New Zealand than the mainland, a plan has been hatched to track three species of predatory rodents that are picking off the island's unique native birds. Oddly it involves a can of yellow paint and a UV light.
The method is a simple one. It was used well before scientists started attaching radio trackers to animals and standing on mountain tops with large aerials to monitor their movements.
It’s hoped by understanding how Polynesian rats, black rats and house mice move around Norfolk Island, the researchers can eradicate them and protect the bird species whose nests they are raiding.
If they can bait the rats and keep them from returning, it’s even hoped areas denuded of native species could be rewilded.
Why paint is better than modern technology
The leader of the project, conservation biologist Professor Matt Hayward, explained to Yahoo News that this “old school” method of using non-toxic dye actually has benefits over high-tech GPS and VHF systems.
“They take measurements every one or two hours so you miss out on the intervening movement period, but what we’re hoping is to fill in those gaps,” he said.
“The dye only lasts for a couple of hours. It leaves a trail, and you go through afterward with the UV torch. It starts off really thick and then as the animal moves away, it drops off and you see little patches as you go further along.”
What it's like searching for rats in Norfolk Island's forests
Hayward, a professor at Newcastle University, revealed that heading out into the darkness on the island can be eerie.
“You get into these forests with the massive Norfolk Island pines, it's really kind of a dark and pretty spooky place. There’s not a lot of shrubs down low because the canopy blocks out the light,” he said.
Most of the rats were discovered living in a small 50 x 50 metre area, but some of them were oddly travelling up to a kilometre, which the team found surprising.
How rats wiped out Norfolk Island's native species
Like in New Zealand, where birds also made up the majority of animal species, extinction has been a major problem for Norfolk Island.
It has no endemic mammals, and the only two species of bat known to have inhabited it have been wiped out.
The invasive rodents have flourished since they were introduced. Polynesian rats came 500 years ago, but black rats only appeared in the 1940s and they directly contributed to the extinction of both the Grey-headed Blackbird and Norfolk Island Long-tailed Triller.
Today, Norfolk Island is home to at least 50 threatened animal and plant species, many of while have failed to adapt to the predators.
“The problem we’re seeing is kind of the naivety of some of these species. If there's a hollow low in a Norfolk Island pine, the green parents will still nest there, even though it’s accessible to the rodents,” Hayward said.
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What the paint tracking has revealed about rats
The project has received funding from the National Environmental Science Program’s Resilient Landscapes Hub, Parks Australia and University of Newcastle. It is expected to run for two years. But already, the tracking of the rodents has revealed new insights about their movements.
“We’re finding black rats spend almost all their time in trees, and I wasn’t expecting that at all. That’s probably because that’s where all the food is,” Hayward said.
“Whereas down the ground, you've got Polynesian rats — which are a little bit smaller — so we're assuming that the black rats are the dominant competitor. And you’ve also got the house mice down there too.
“We think they’re probably petitioning that space on the ground. So where you get one, you don’t get the other.
“The island has already lost lots of species, but by understanding the rodents, we're just trying to keep those species that are still around hanging on."
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