Encouraging trap test results...

Our high interaction rate traps are out in the field catching predators at multiple sites. Today we share some early results and a short update on some of the improvements we're making as we learn more.  One of our traps at a test site in Akaroa caught 8 possums in 12 nights - read on for details.

We currently have 10 traps out in various test sites exposing them to wild predator populations.  The following results are from 12 nights of testing two different configurations of Cacophony high catch rate traps.  The trap setup at our test site can be seen below (along with our updated designs).

The 3x1 and new 2x2 designs

For both traps the lure used was a possum paste. The triple sided trap also had an Active fence set up to guide predators into the trap (https://cacophony.org.nz/making-predator-fences-active).  Each trap had one of our high sensitivity thermal cameras pointing at the trap so we could understand how predators interacted with the trap. The goal was to measure the interaction rate of the new trap.  We already know that the interaction rate of most existing traps is only around 1-8% (https://cacophony.org.nz/why-improved-interaction-rate-holy-grail-trapping).

Results so far

Results from the first 12 nights of trapping are shown in the table below.

Trap ConfigurationSpeciesVisitsCatchesCatch rate
Triple sided (3x1)Possum4250%
 Rodent100%
 Hedgehog22100%
     
Double sided (2x2)Possum17847%
 Cat100%
 Rodent1000%

 

It's worth nothing that the possum density for the two sites is quite different. We measure this by the number of possum visits on camera per day on average. ​

SitePossum Density
Triple sided (3x1)Low: 0.15 visits per night
Double sided (2x2)Med-high: 1.1 visits per night

 

We recognise of course that this data set is too small to draw any firm conclusions from but we wanted to share this early data with you.  Our insight from this data is that the trap seems to be working very well for larger predators. We have some modifications to make it work for rodents but in the short term we will focus on making the device work well for larger predators.

Previous analysis of alternate NZ traps shows an average catch rate of less than 2 catches per year.  Compared to that, our 8 catches within 12 nights is very promising; a simple (but dangerous) extrapolation would give more than 150 catches in a year if the trap were set every night (and if there were enough possums left!).

These results are still a little surprising.  Previously, when seeing an average of 1 possum per night we assumed there could be a population of one or two in the area and that the same individual was repeatedly going past the camera. But catching 8 in 12 nights suggests that the animals we're seeing are mostly different individuals. We'd love to hear from you if you have any thoughts on this subject.

 

What we've learnt so far

Whenever we're testing an early version of a device in the field, one of our key goals is to learn what works and, more importantly, to learn what doesn't (so we can fix it).  We've been focusing on making sure the trap is reliable.  What we've learned so far has led to three key changes to our initial design:

  1. Triggering: We found the motion sensor was fairly unreliable and it would often trigger early in the night, leaving the trap closed for the rest of the night.  We have identified a more sophisticated motion sensor and will be integrating this in the mid term.  In the short term we have installed a prototype auto-resetting mechanism.  This allows the trap to reset itself after any false trigger, keeping it open for the next predator.  A big advantage of this is that the trap now has the potential to catch multiple predators in one night. 
  2. Cage Door mechanism: We're testing installations of the trap that guide predators into a standard live capture cage (triggered by a manual treadle plate) rather than one with an electronically operated door.  This simplifies the trap set up and lowers the cost for a multi-capture device (manual live capture cages are available from multiple suppliers).  The down-side is that live capture cages such as these do not always work as well for small predators like rats.
  3. Configuration: We have changed the configuration from a 3 blinds, 1 cage mechanism to a 2 blinds, 2 cages mechanism. This seems to work just as well, allows the 2x2 trap to catch 2 predators a night, and will also help with reducing the overall cost of the device

 

What next?

We have testing underway in other areas and will report on those results in due course.  As for the trap design, next on our list of improvements is to trial a digital trigger device that can visually detect the difference between birds and predators.  This would allow out trap to operate during the daytime (we currently restrict it to night-time operation to avoid the risk of by-catch).

We plan to rejuvenate our work on sound lures.  Our previous testing of sound lures provided promising results in attracting predators from a distance and provided a higher interaction rate of animals (https://cacophony.org.nz/powerful-new-way-test-sound-lures).  There was a reason we paused that testing to work on our trap - although the sound lures could attract predators to the area, the predators would not interact with whatever traditional traps we placed at the location.  We found that predators soon learnt to ignore the sound lures as they had previously found little of interest there (no reward).  Now that we have a trap with a substantially higher interaction rate, we can restart the sound lure testing with an increased confidence that the attracted predators will interact with the trap (they'll simply walk in to the open trap and find their reward).

We are also continuing the stress testing of the trap - this will ensure a robust and highly effective tool in predator control.  Watch this space for further updates.

 

More examples of the 3x1 and 2x2 trap configurations


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: 
Monday, 29 March 2021