26 Jul 2016

Controlling predators without fences

From Afternoons with Jesse Mulligan, 2:16 pm on 26 July 2016

Under the Government's plan for a predator-free New Zealand by 2050 is that by 2025 we have the ability to clear a 20,000-hectare area of predators without needing protective fences.

Dr Elaine Murphy with some of the stoat bedding being used as a lure.

Dr Elaine Murphy with some of the stoat bedding being used as a lure. Photo: RNZ / Conan Young


Predator Free NZ: Is it feasible?

Dr Elaine Murphy is head of  Principle Scientist from Zero Invasive Predators, (or ZIP)  – the team behind a predator research enclosure which is conducting trials on new ways of eradicating pests, including using scent as a lure.

She talks to Jesse Mulligan.

Read an edited excerpt of their conversation

How realistic is the government’s predator-free plan?

I think it’s entirely realistic, so at the moment we have been very good at sustained control. But the problem is that these pests just start coming back in so we need to get better at keeping them out. One way of doing that is using a fence, but what we are looking at is the concept of a virtual fence. So you clear the area of all the rats, stoats and possums and then you have various techniques to catch those animals as they come in. So at the moment we are trying various traps, and different lures and we are also going to be looking at deterrents. There’s a whole raft of things we can use.

How close do these traps need to be to each other to create such a barrier?  

At the moment we are just experimenting with different things. So at the moment there is an area in the Marlborough sounds at Bottle Rock and the possum traps there are about 10 metres apart… But we are trialling different things to see if we can increase that spacing.

With the lures we have been trailing different social lures for rats and stoats, we tried food lures, but we found that stoat bedding was very attractive to other stoats – and it’s the same with rats.

How does it work with the bedding?

Stoats are very clean animals so they have these dens which they normally lie in with their prey – feathers from the birds they’ve been eating. And it gets that smell of a stoat itself and they are solitary, so if they start to smell another stoat they get quite curious as to who it is. So we have found that if you put another stoat bedding in a trap or a monitoring device another stoat will come to investigate it quite quickly.

Are stoats one of the hardest predators to catch?

They are really hard to catch, hey move over such a large area. A stoat home range might be 1-400 hectares. Which is quite low density but they cause so much damage and that’s the problem.

I was actually tracking stoats in Fiordland in the 1990s. We put a collar on a young stoat in December, and she was caught in January 65km away. So in one month she had travelled 65km in a straight line.

Whereas a rat can only travel about 50km maximum, right?

Well, a rat can weigh the same as a stoat, but its home range could only be quarter of a hectare. So in some ways, rats are a lot easier to work with and control because they move over such be small area. But there’s a lot more of them… and we’ve actually found that rats are talking to each other all the time in an ultrasonic way, and we have been looking at that try and develop ultrasonic lures.