A clever piece of Kiwi ingenuity has again proven itself a lethal weapon in New Zealand's fight to rid itself of pest predators by 2050.
In a new study, led by Bay of Plenty Polytechnic researcher Chantal Lillas, 25 self-resetting A24 traps placed around Taneatua Forest attracted and killed 120 rats over 10 days last month.
By comparison, 25 of the Department of Conservation (DoC)'s standard single-action snap traps killed six rats, and one third of them were inoperative after the first night, either having caught rats or having been set off but not achieving a kill.
"The results for both traps were about the same after the first night, but then the A24 traps dominated every night following for the remainder of the trial," Lillis said.
"What was even more surprising was that when we reviewed the footage from the trail cameras we'd set up, we could actually hear Kiwi calling out to each other.
"This was a shock to locals we spoke with who didn't even know there were kiwi in the area."
The CO2-powered A24 trap, developed by Wellington company Goodnature in collaboration with DoC, is currently the only predator trap to self-reset up to 24 times before it needs to be reloaded.
Rats are attracted to it by a potent lure delivered constantly for six months, and when the rat brushes past its sensitive leaf-trigger, the trap is set into action.
A CO2-pressurised piston strikes the rat's head, killing it instantly, and then retracts on a light spring, as the dead rat falls to the ground and the trap automatically resets itself, ready for the next pest to arrive.
DoC has already used the traps to remove entire rat populations on many critical eco-systems including the 65ha Native Island, and a 600ha area of Harts Hill in Fiordland National Park.
"Six dead rats versus 120 dead rats is pretty compelling and is yet further validation of DoC's decision to invest in the development of self-resetting traps," Goodnature director Stu Barr said.
DoC predator expert Darren Peters said the study was useful as the country put in place a strategy to fight predators and achieve its ambitious predator-free 2050 target.
"This project is a great example of how we can use this device to save on labour and save more species."
Constant predator control was what allowed threatened bird species to return to healthy numbers, Peters said.
"The A24 is one very useful device for enabling constant control."
DoC is now deploying hundreds of the traps in major operations at the Hawdon Valley in Arthur's Pass National Park, home to orange-fronted parakeet, in South Westland, the habitat of Haast toeka kiwi, and in the Murchison mountains, where 1080 poison can't be dropped because of risk to its takahe population.