Contractors were then brought in to work along the sanctuary’s team of volunteers, Merz said.
“Knowing where the rat roughly is means you can set trapping devices really well.
“If you poison a rat, you will not catch it, and that means you are not 100% sure it’s dead.
“It [poisoning] also means that, if we do get a rat dog in there, it may detect the dead animal’s scent. That gives us a false reading.”
Rosi Merz says replacing the predator-free fence is a challenge the sanctuary faces over the next five to ten years. Catching an animal alive meant its gender could be checked.
The latest incursions, totalling three rats, were all male, which was “really good news”, Merz said.
“If it was a female, you can even check if it had been pregnant, meaning it potentially gave birth to a litter.
“Then there is genetic analysis. We can see if they were related.”
One rat was caught within 24 hours of detecting the ink prints, with another caught in a week and a half.
Another was caught after “complete silence” for five weeks.
“It was looking like we could wrap the incursion response up, then there was another print.
“After that, we found a tiny little hole in the fence that I think a rat can squeeze through.”
The 4.8km fence around the sanctuary was finished in 2005.
It cost $807,000, funded through donations.
Merz said that, apart from the trees and birds, the fence was the most important and valuable resource the sanctuary had.
Rat prints from a tracking tunnel at Whanganui’s Tarapuruhi Bushy Park. Photo / Jacqui McGowan “Every week, it is checked on foot, and we have to do a lot of maintenance work.
“For example, our fence posts have started to develop rot on the inside.
“There is definitely a case for a new one, and it’s a huge challenge the park faces in the next five to ten years: major upgrades or a replacement.”
Tarapuruhi Bushy Park is run and governed by Forest & Bird alongside the Bushy Park Trust.
Intruder problem Rats reach sexual maturity after nine weeks, and a female can give birth to six litters in a year.
Each litter can have up to 12 pups.
Last year, rat footprints were found in the sanctuary after a fallen tree from a neighbouring property provided a bridge over the fence.
Merz said it was likely that three or four rats got into the park via the tree, but they appeared to take lethal doses of bait from tracking tunnels.
There were food sources and “incredible habitat” for rats if they breached the fence, but, because they were social animals, they would eventually look for a mate.
“Rats are capable of circumnavigating the entire park in a day, searching their environment for social clues.
“They’ll realise they can’t find [a mate].”
In 2007, rats with tracking devices were released at the Maungatautari sanctuary in Waikato, and the majority climbed the fence and left, she said.
“The fence is only designed to keep them out one way.”
Mike Tweed is a multimedia journalist at the Whanganui Chronicle . Since starting in March 2020, he has dabbled in everything from sport to music. At present, his focus is local government, primarily Whanganui District Council.
