KEY POINTS:
A single rat print has raised fears that predators are threatening the security of an ecological island in Waikato.
The Maungatautari ecological island, south of Cambridge, has been fenced off from predators for more than a year, and two major air-drops of poison baits have virtually wiped out all mammals in the reserve.
Only several small populations of mice are known to still exist inside the bush enclosure.
But Maungatautari Ecological Island Trust chief executive Jim Mylchreest said recent storms through had led to minor breaches of the pest-proof fence as branches had blown down.
A single rat print found inside the enclosure and an alarmingly high number of predator animals seen patrolling the outside of the 40km pest-proof fence, have combined to cause a rethink over the vulnerability of the special 3400ha conservation site, he said.
An alarm system notified staff of the breaches to the fence and they were quickly closed, but it's thought at least one rat was able to use a downed branch to climb over the fence and get into the reserve.
Rat bait was spread widely in the area and it was believed to have now been eliminated.
A fenceline survey carried out by Waikato University biological sciences Masters degree student Trevor Connolly showed a "startlingly high number of predators patrolling the outside of the fenceline every night," Mr Mylchreest said.
"His infra-red cameras caught cats catching mice along the fenceline, another cat with two kittens, and numerous possums, rats, ferrets and stoats.
"And the level of mice outside the fence is phenomenal - we thought rats would be bad, but the mice are much worse."
It showed that if pests were removed from an area it took only a short time for the vacuum to be filled by pests coming in from outside the area, he said.
"If the fence wasn't there, all those pests would be pouring straight into our pest-free island right after our poisoning operations."
He said staff at the trust would now rethink methods to ensure any breaches of the fence were even more rapidly mended.
- NZPA
