Rats trapped in Karori Sanctuary

KENT BLECHYNDEN/The Dominion Post

FATAL FORAY: Raewyn Empson with one of the two rats that got into Wellington's Karori Sanctuary.

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It appears to be the year of the rat at Wellington's Karori Sanctuary, with two of the rodents found inside its supposedly impregnable fence in the past 12 months.

The discovery of two ship rats marked the first known rat invasion since the pest was eradicated from the sanctuary in 1999. Four weasels were also caught, the sanctuary's 2007-08 annual report reveals.

In February, a weasel was spotted inside the 225-hectare sanctuary. It was soon trapped and later put down by a vet.

In May three more weasels and the two rats were found and caught.

Sanctuary conservation scientist Raewyn Empson said dna testing revealed that the weasels were all related to each other.

"But we don't know if they came from one pregnant female, or if they all came over together."

Ship rats, named because they arrived as stowaways with European settlers, are believed to be responsible for the decline or extinction of many New Zealand land birds, and to have also decimated the populations of insects such as giant weta.

Weasels also pose a serious threat to native wildlife.

Ship rats are highly fertile - one pair can produce a population of 3000 in a year.

Ms Empson said there was no evidence of a pest population inside the sanctuary. The rats and weasels could have gained entry by making use of a fallen tree that briefly provided a bridge across the predator-proof fence. The entire 8.6-kilometre-long fenceline was checked at least once a week.

Stoats and weasels were often seen sniffing around outside it, Ms Empson said.

"To be honest, with a land-based `island' like this, you are always going to have issues."

The Karori Sanctuary recorded 68,553 admissions in the 2007-08 financial year, up 6.5 per cent from the previous year.

It also recorded a surplus of $2.6 million, in part because of $1.3 million of government funding toward its new visitor centre, which is being built at present.

- © Fairfax NZ News