Otago Peninsula Biodiversity Group

The Otago Peninsula Biodiversity Group was incorporated in 2010 to enhance the peninsula and make the most of its unique environment. Possum control was tackled initially and to date 10,000 possums have been eliminated. One of the problems now is that although there are still pockets of possums, they are not obvious. The group has made effective use of “chew cards” – a low-tech, safe and cheap indicator of presence or absence of the pest, which allows targeted deployment of traps.

The Otago Peninsula is a long, hilly indented finger of land east of Dunedin City, joined to the mainland by an isthmus about 1.5km wide. It forms one side of the Otago Harbour and is 20km long and 9km at its widest point. One of its claims to fame is the abundance of bird life including colonies of royal albatross, the endangered yellow-eyed penguin and the little blue penguin. It is also home to about 10,000 people living in coastal pockets, lifestyle blocks and hilly farms.

In 2008 a number of residents started talking about forming some sort of landcare group to enhance the peninsula. Brendon Cross, a cattle and sheep farmer, was one of them.

“When we first got together we sent out a survey to all residents to see what they would like to achieve. Rats and rabbits were a concern for some people but possums were a problem for both urban and rural communities so we decided to start by controlling them,” says Brendon.

“Possums eat grass, damage trees and eat birds’ eggs and there is always the risk of their carrying TB. However, TB has never been a problem on the peninsula and the possums here had never been exposed to control methods so that was an advantage for us.”

The Otago Peninsula Biodiversity Group was incorporated in 2010 and began by commissioning a report indicating how it could go about possum control. Brendon says it was based on how pest eradication had been done on offshore islands and so the group modified the ideas to suit their situation.

“The peninsula is just under 10,000 ha so we broke it down into five sectors. Starting at the far end and working our way back towards town meant we could work on manageable chunks one at a time as funding became available,” he says. “It turned out to be a good approach because the few people who were apprehensive about getting work done on their land were able to see how it had been done further down the peninsula and we had some success stories to tell them. People became more aware of us and what was going on, and were more accepting.”

Initial funding for the group came from DOC to employ a part-time project manager to initiate a control programme and to get more funding so that there would be no cost to landowners. Typically the group would hold public meetings to explain what they proposed to do and how they would do it. Consents were obtained from each landowner and took into account their preferences as to the types of baits and traps to be used. That was a major task because of multiple landowners and many small blocks.

Outside contractors were employed to carry out the work on farmland. They worked in teams of four or six, stapling bags of bait onto trees or fence posts. It was fairly quick and often landowners would not realise that the team had been on their property, says Brendon.

“Initially we followed up the work of the contractors by setting residual trap lines to evaluate the effect of what they had done. After that we rolled out some trapping initiatives through the communities. We managed to purchase some Timms traps and the project manager operates a sort of trap ‘library’ so that people could borrow them,” he says.

As possum numbers decreased, people saw fewer and fewer on roads and heard almost none on their properties. Baiting and trapping became less cost effective because it was difficult to find residual pockets of infestation. However, the group made good use of a novel yet simple piece of technology – the “chew card”. Moira Parker, secretary of the group and a trustee, says that chew cards have been very effective.

“They are pieces of white corflute plastic 18cm x 9cm that we buy ready-made with a rather nice fruity flavoured attractant for possums inserted into the channels in the corflute. You bend the card over to double it and then nail it to a tree or a fencepost at a height of 30 cm,” says Moira.

“Then to encourage possums to come towards it, we add a blaze, which is a 4:1 flower/icing sugar mix with some flavour added, maybe curry or cinnamon. That shows up at night and again it has a smell that attracts possums. We leave that card out for seven nights and then check to see what might have bitten into the card to try to get out that lure.”

“The most likely possibilities are possums, rats and mice and in the summer the occasional hedgehog or rabbit. Each species leaves a quite distinct bite mark on the chew cards so you can tell what has been there. The possums don’t actually cut into the card, they press hard on it and pull out the lure. Rats will actually bite pieces off the card and in fact they can often eat most of the card; mice make a smaller little nibble perhaps in the top layer of plastic.”

The beauty of the chew cards is that they show clearly if possums are present and hence where to set the traps, and the success rate for subsequent trapping is quite high.

Other advantages are that the cards are non-toxic to humans, domestic animals and desirable species and so are safe to use in any location. They are also cheap – 47c each. Volunteers set out the cards, monitor them, and follow up with Timms traps where necessary. A number of volunteers also work in the community setting traps out where people have seen possums or dropping traps off to landowners who will set the traps themselves.

There are also a couple of trap lines that are set permanently for monitoring and other purposes on farmland and these are generally monitored by volunteers.

Prior to starting on the possum programme in 2010, the group carried out benchmark observations on possums, birds, rodents and types of vegetation. Moira says that they have been monitoring rats for the past five years.

“In some North Island forests where possums have been reduced, there has been an increase in the number of rats. The two seem to compete in some way for food, so we felt it was really important to monitor what was happening to rat numbers here. So we have 14 lines of rat tunnels, and four times a year volunteers put in a tracking card for one night along with a peanut butter the lure so any animal that walks on the tracking card will leave telltale footprints, but we have found only a slight increase in rats,” she says.

“At this stage we are thinking now about what to focus on next, and rats are likely to be the next target. Stoats are also a problem and there are ferrets as well. We are aiming for a predator free peninsula because it has tremendous potential with such a variety of habitats. As well as the common birds, we have a few riflemen and tomtits and on the coast there are albatross and penguins. There are also some great forest remnants with rimu, matai and totara.”

About 70 volunteers are involved in bird, rodent and vegetation monitoring as well as the chew card and trapping programme. Experts on bird and rodent monitoring have helped set up those initiatives and a herpetologist has recently started monitoring lizards.

While DOC supplies expertise in pest control, other experts advise on bird and rodent monitoring. To check on progress, the group has 10 vegetation plots that are assessed once a year, 20 bird walks that are monitored eight times of the year, 14 rodent monitoring lines and recently 11 lizard monitoring lines.

Brendon says about 70 volunteers are involved in the monitoring, chew card and trapping programmes, and the general population has now become part of possum monitoring.

“The thousands of people living on the peninsula are quite observant. In the past they might have seen four or five possums on the road as they drove home and would hardly notice them, but these days they might not have seen a possum for four or five months and if they do see one on the way home then they usually tell us,” he says.

“I think we have been incredibly successful as a group to start out and work within the community to take out more than 10,000 possums off the peninsula at no cost to the landowners. The project has involved a huge number of volunteer hours and continues to do so.”

“There is such good feedback from people on the peninsula in terms of seeing more birds and seeing them where they haven’t seen them before, having fruit and flowers where they haven’t had them in the past, and all the positive data coming in now from the bird walks and vegetation monitoring.”

“We have always envisaged being predator free by 2050, and now someone else has got the idea from us and taken it nationally!”