Audio and Scent Lure Rat Experiment (August - September 2019)

Author: David Blake

David Blake is a semi-retired property investor who now likes to spend his time trapping pests and planting native trees. From time to time he helps out by volunteering at The Cacophony Project doing some filming and occasionally contributing to parts of the software.

Throughout August and September 2019, The Cacophony Project ran an experiment exploring the efficacy of various audio and scent lures in attracting, and capturing, rats. This experiment was undertaken in Titirangi, Auckland on a 1660 sqm property of grass, concreted surfaces and bush, with further bush surrounding the section on 2 sides.

As shown in the photograph of the research site below, the thermal camera (the light grey rectangular box in the foreground) was set-up to record the activity around two live capture traps positioned on either side of a bait station, on top of which was placed a speaker (the smaller white box) attached via the visible white wires to the thermal camera. A GoodNature A24 trap was also set up in the background (of which a red plastic part is visible) and a Bushnell trail camera was mounted on the far side of the white post to the left of the thermal camera.

Experimental setup

Before undertaking testing of the effectiveness of audio and scent lures, baseline predator visit rates to the research site were determined over a 15 day period. During this time there were 78 predator visits (all rodents), five trap interactions, but zero captures, this equates to a visit rate of 5.2 visits per day.

Over the following 39 days, audio and scent lures were implemented in various combinations, with audio lures played through the speaker on 14 of the 39 days, and scent lures laid down on all 39 days. The audio lures used included rat vocalisations, weta noises and various bird calls (bellbirds, kiwi, and whiteheads). The scent lures, provided by Nicolas Sawyer of Sensient, consisted of synthetic scents of chocolate, peanut butter and ‘rat scent’ mixed with canola oil. ‘Rat scent,’ officially known as MouseTrap FLV N13802 DG, and is a scent developed following the work of Jackson, Keyzers, and Linklater (2018) which suggested that certain chemical compounds are more effective at luring rodents than the standard ‘best practice’ scent, peanut butter. These three scents were sprayed on different days in artificial ‘scent trails’ to the right or left of the live capture traps, so that the cameras could observe whether or not predators followed the trail.

Results

The following table summarises the results of the experiment:

There were 92 visits to the traps and bait station over the course of the experiment. A visit is defined as a rat viewed near the traps and bait station. A 15 minute window is used to distinguish between a rat coming and going vs the rat leaving and then another rat (or possibly the same rat) coming along to investigate.

3 rats were caught over the course of the experiment, 2 in the live capture traps and 1 by the GoodNature A24 trap. So the overall catch rate was 3.3% which is very low. As far as we could tell no rats ever entered the bait station.

The following results are derived from the above:

Conclusions and further work

Over the 25 days when scent lures were used without sound lures there were 53 predator visits captured by the thermal camera. This equates to a visit rate of 2.12 visits per day. While over the 14 days when both sound lures and scent lures were used there were 39 visits, thus the predator visit rate increased to 2.79 visits per day.

The capture rate of 3.3% is disappointingly low but aligns with previous observations using thermal cameras: most predators simply ignore traps. Such a low catch rate is not going to remove all rats from New Zealand as per the Predator Free 2050 goal.

Nevertheless, there are some encouraging results. For example, over the length of the experiment, there were 39 predator visits where rats showed interest in, and/or followed, the scent trails which equates to 42% of all rat visits. This suggests that scent lures have potential as an effective tool when attempting to trap wild rats in the New Zealand bush. However, further experimentation is required to determine the optimum scents, concentrations, and scent trail lengths. Furthermore given the boost to predator visit rates gained when audio lures were used alongside scent lures, there is definite scope for further research into which audio lures work best, at what volumes, and at what intervals.

As far as audio lures go, this experiment doesn't provide any evidence that they have a significant effect. More work needs to be done in this area.

Over the coming months The Cacophony Project will be continuing our investigations with scent and audio lures. This trial has highlighted the need for more in depth and systematic experiments in this area.

Finally, it’s interesting that two rats were caught in small live capture traps baited with Ditrac bait blocks. The bait station right next to these traps also contained Ditrac bait blocks but not a single rat was observed going into the bait station and indeed, the bait blocks were intact (bar some minor insect interaction) at the end of the experiment. This may be evidence for the fact that rats prefer to enter a more open trap than an enclosed space. More experiments around this idea could also be helpful.

Many thanks to Manaaki Whenua Landcare Research for their contribution and collaboration throughout the development of this tool.