Why improved interaction rate is the holy grail for trapping

In recent blog posts we have gone into detail on different trapping strategies.  We chose to do this because we are convinced that many approaches that may seem intuitively to be great strategies won’t actually make much of a difference to the elimination of predators. Our camera experiments have shown consistently and across a number of different environments that, for an area that has been trapped for a while, there is a persistent population that avoids existing traps.  Today we introduce a collection of approaches and ideas that we believe can actually improve the predator interaction rate and give us a real chance of achieving our predator-free goals.

Trap Avoidance

If it feels like you haven't seen the same trap-avoidance behaviour, it may be due to the fact that existing monitoring tools fail to record the vast majority of predators wandering around.  Most predators don’t go into tracking tunnels and trail cameras often fail to trigger (most are designed for large animals and miss many rats, stoats, and some possums).  Initially, we also questioned this finding so we looked for ways to confirm that this low interaction rate was not just a quirk of all our camera experiments.  We turned to a rich data set from the 60 best monitored projects around NZ (as recorded on the trap.nz platform) and developed a model to interpret this data.  The only interpretation we've found that makes the predator numbers and trap densities match up is that predators must be living in the same space as traps and avoiding them i.e. existing traps have a very low predator interaction rate.

Once you accept the very low trap interaction rate you can test the following strategies and see what difference they make:

  • Automated traps - doesn’t make much difference as most predators continue to walk past traps
  • Automatic lures and long life lures - again not much difference as predators mostly avoid even freshly baited traps
  • Improved trap kill rates - when traps are triggered improving the kill rate doesn’t improve the outcome much - which is pretty obvious once we accept that most predators won't trigger the trap

If you are interested in predator suppression, all of the above strategies can be useful in terms of labour saving and cost reduction but they don’t get us very far in terms of achieving total elimination. Total elimination is our goal - it would mean we wouldn’t have to continually kill predators in the same area year after year. Not to mention the substantial risk that the existing partial suppression mechanisms could be breeding harder to catch predators.

Improving the Interaction Rate

The good news is that there are lots of strategies (beyond the ones mentioned above) that can actually improve the predator interaction rate.

Before we launch into how we might improve interaction rates, some definitions.  The diagram below describes three zones of interest that will help us discuss different strategies for higher interaction rate.

What follows is an extensive list of trapping strategies along with our educated guess as to the potential impact they could make in each of the three zones above.  We've also provided our assessment of how useful we think that strategy is likely to be:








Some of the strategies above may sound expensive but imagine a device that can identify, lure, and kill everything in an area in a week or two. No need to leave it there forever as it can be moved from location to location in a methodical manner to achieve total predator elimination. One of the undiscussed rules of trapping is that traps have to be cheap and designed to stay out forever ideally with low or zero maintenance.  That only makes sense because existing traps will never eliminate all predators, so they do indeed need to be out there permanently to stand a chance of catching at least the odd predator from time to time.



What next?

Future blog posts will explain the most promising of these strategies in more detail along with some initial tests of novel devices. Let us know if you think there are other strategies we have missed or if you disagree with our assessment of the potential of different methods. Very happy to post a detailed explanation by anyone who thinks what we are talking about is nuts - we would much rather you did that to help us focus our attention on things more likely to work. 

We worked on and chose to share this detailed series of posts and models because we are convinced that many projects that are currently being funded around automated trapping, lure improvements, and higher kill rates will make very little difference for total predator elimination. There are lots more promising options and we are keen to see more teams working on these things so we can get to the goal of predator free faster.

We hear again and again about hard-fought-for funding going to projects that focus on the things we are convinced won't help the dedicated trappers of New Zealand achieve the goals we all strive for.  Again and again cynics challenge our community to show that a truly predator-free status can be achieved.  If, as a country and as an industry, we continue to invest only in efforts that will have marginally beneficial effects on the level of suppression of predators, those cynics will be proved right.  If, however, we listen to what the data is telling us, choose to invest our time and money only on those things that will provide the next generation of massively more capable tools, then we firmly believe we can take a giant leap forward towards the eradication of predators in our native bush once and for all.  It is the least our native species would ask of us.

The time for all of us to rethink our approach is now.  Yesterday would've been good but that's already gone.  So today will have to do.

We're excited by what lies ahead - we think we have found some ways to make a really big difference in everyone's predator-free efforts and finally deliver some serious results in New Zealand's fight against introduced and invasive predators.  We sincerely hope you'll come with us on this journey - by collaborating and sharing results we can all find better ways of achieving eradication, not just suppression.

As always, we welcome your feedback so don't hesitate to get in touch - leave a comment below or email us at blog@cacophony.org.nz.


Publication Date: 
Tuesday, 1 September 2020