Trapping moderates the rise and rise of rat numbers

  • Published Date 16 May 2018

While the second census of rat numbers on the Miramar Peninsula shows rising numbers, local trapping groups are holding the line in the face of a significant rise in rat numbers throughout the country. 

"We've come through a long hot summer and a warm autumn which has provided plenty of food, perfect breeding conditions for fast-growing rat populations," says Greater Wellington Regional Council environmental scientist Dr Philippa Crisp.

This year's census of the rat population on the peninsula recovered 95 per cent of chew cards (which attract rats and if chewed records their presence) up from 91 per cent last year; 17 per cent had been chewed by rats, an increase of just five per cent from last year.

"Given the weather, we could have expected more," says Dr Crisp. "That we haven't is probably a sign of the success of Miramar's backyard trappers, who have grown in number and enthusiasm over the past year.  They are almost holding the line, but this year's results shows the challenges faced in keeping rat numbers down over time."

The second census of rats and stoats on the Miramar Peninsula was supported by volunteer groups which worked with Greater Wellington to place 281 chew cards throughout the peninsula on a grid at 200m x 200m intervals.

The cards, left in place for three nights, used peanut butter to attract rats, stoats and other native bird predators.

The highest proportion of rat chews was once again found on the coast, where 35 per cent of cards were chewed. Increases were also found in urban areas where rats have easy access to sources of food.

Only two cards showed evidence of stoats, down from six last year, but mice chews were common and found on nearly half of all cards.

"A really positive sign in the fight to protect our native birds is the explosive growth in the number of people getting involved in predator control," says Predator Free Wellington project director James Willcocks.

"In the year since the last predator census, backyard predator trapping in Miramar and around the region has grown rapidly to involve almost every community in Wellington.

"More and more people are getting on board and establishing trapping groups," he says. "At last count we had some 23 backyard groups across 36 suburbs throughout the city, which shows phenomenal interest in making us the first predator free capital. There may well be more we don't know of.

"There are also some 40 community groups actively trapping in the city's reserves and about 80 community groups are working in the broader ecological restoration space, in reserves throughout the city, which is fantastic.

"A very positive critical mass is no doubt developing as people take control of what's happening in their own backyards. Participation is remarkable, we estimate around 12,000 people are involved.

"But we need to maintain this momentum in light of the growth in rat numbers, we don't want to fall behind. We need to get more people involved in trapping, so we urge people to connect with their local groups via the Predator Free Wellington website," says Mr Willcocks.

Wellington City Council is partnering with NEXT Foundation and Greater Wellington Regional Council to make Wellington the first predator-free capital city. The initial focus is on eradicating rats and stoats from Miramar Peninsula, with a plan to extend the strategy to the eradicating introduced predators of native birds across the entire Wellington City area.


For more information: Stephen Heath at Greater Wellington Regional Council 027 873 0342 or read the Miramar Peninsular Rat Monitor Summary (PDF 457 KB)

Updated April 28, 2022 at 1:07 PM

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