Big decline in rats

New traps trigger big decline in rats at Pelorus

Gas triggered traps are being used to trap rats at the Bat Recovery Project at Pelorus Bridge scenic reserve.

Gas-powered traps have triggered a "dramatic decline" in rat numbers in the Pelorus Bridge Scenic Reserve, conservationists say.

The 60 automatic traps, which can automatically reset up to 24 times, were introduced to the Pelorus catchment five weeks ago. 

The Pelorus Bridge reserve is home to a critically endangered population of long-tailed bats. 

Te Hoeire Bat Recovery Project manager Debs Martin said there had been a big drop off in rat density in the area where the traps had been used compared to the control area  within the Pelorus catchment where no traps were placed.

The team had not collated exact numbers, but would have more data after the next check up in mid-October. 

Martin said the lure inside the trap only needed replacing once every six months, making it an economic way of pest trapping. Once the animal is killed, it falls from the trap, which is then reset.

One of the Goodnature A24 traps cost $130. That was more expensive than other traps, but they needed frequent checking. 

"Cost weighed up against effectiveness and need for frequent checking, especially during a rat plague," Martin said.

It took the team of three members two hours to attach the traps to trees spaced 100 meters apart in the 200 hectare trapping area. The traps were placed 900mm up trees so weka were not caught. 

"Weka are really inquisitive ... but the weka would have to fly up and extend their necks straight up to get into it. 

"They're just not that agile."

Martin said they did not know exactly how many bats were in the catchment, but estimated there were at least two or three colonies. 

The bat recovery project aimed to create a predator-free Pelorus catchment that would help other species as well.

"We know that the bats really like the Pelorus catchment, we don't really know why, although we suspect there's still some big old big grand trees that are in that catchment and there's so much that hasn't been cut down."

Martin said the group would eventually like to see the reintroduction of some species, such as the blue duck, kākāriki, robins, toutouwai and ultimately the great spotted kiwi.