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Taking the bait



One of the Co-op’s land management conservation projects is addressing the threat posed by fox predation. We know from our own experience that foxes predate some our most vulnerable species, including lyrebirds, white-throated nightjars and phascogales.






One of our control measures is trialling a relatively new technology called CPE (Canid Pest Ejector) as a means of more precisely targeting foxes while minimising harm to non-target species such as our precious native wildlife.



Above: the White-throated Nightjar egg, chick and adult - all vulnerable to fox predation.



In Phase 1 of the CPE trial (November-December 2023), 12 CPE devices were deployed around the Western half of the Co-op in locations where we had evidence of fox presence.


In the first 3 weeks we received some very encouraging results; 3 ‘triggering’ events at one location,  (CPE 10) , each one purportedly indicating the demise of a fox. This was good news, but seemed too good the be true; the same CPE bait-station triggered over 3 successive weeks, while none of the other 11 had been triggered. Is there something else going on?


To get more definitive information, a motion-sensing camera was set at CPE 10 and 7 other bait-stations.


Over the following week the camera at CPE 10 recorded a brushtail possum having a very good feed on the bait surrounding the 1080 capsule that was embedded in the bait. And several days later, another brushtail possum (looking suspiciously like the first) returned to CPE 10; but this time, finding no bait, it wandered off into the night.



We do not know if the possum feeding on the bait caused the 1080 cannister to release, and it appears that our brushtail possum behaviour is ‘unusual’, and contrary to other studies. This gives us a rich vein of inquiry for the next phase of our CPE trial. An added tool will be cameras deployed at each bait-station to get more definitive information on fox (and other native animal) behaviour around CPEs; and to achieve habeas corpus.


It also means that we can no longer take for granted that a ‘triggering’ event means a fox demise.

Worried about the pre-Christmas over-indulgence of our brushtail possum at CPE 10, we took a deeper dive into the toxicity of 1080 on brushtail possums. Our pre-trial risk management review satisfied us of the safety of the CPE technology for our native wildlife, but we needed more detailed toxicity data.


The physical characteristic required to trigger the 1080 cannister into the mouth of an animal are limited to foxes and dogs. Further, irrespective of who gets the bait, native wildlife have greater tolerance to 1080 than foxes.


Our deeper dive told us that, not only were brushtail possums relatively tolerant to 1080 (because of the prevalence of the active ingredient (sodium fluoroacetate) in native vegetation, but that there is a considerable difference in tolerance between the West coast brushtails and East coast brushtails. WA brushtails are 100 times more tolerant to 1080 than their East coast cousins. So, if our Brush tail possums have a high tolerance to 1080, then their WA cousins are bullet-proof.


Phase 2 of our CPE trial will commence in Autumn 2024. In the meantime, we will continue our fox control work using old-school soft jaw traps.


Stay tuned for the next chapter in our fox campaign.


John Roberts


Footnotes

1. During Phase 1 of the CPE trial at least 5 ‘triggering’ events took place, none of which could be attributed conclusively.

2. In the instance of the brushtail possum feeding on the bait, it did so only by managing to pull the stake, on which the bait was housed, from the ground using it front legs. Having thus created a ‘bait on a stick’ like a shish kebab, it proceeded to gnaw at it from the side of the bait. It is not clear if that bait station 1080 had already been triggered prior to the arrival of the possum. Nevertheless, even if the canister was intact, the possum was unlikely to have ‘triggered’ the 1080 cannister, as this requires a considerable upward force. This CPE design feature is intended to limit triggering events to those animals capable of getting their mouth over the bait and pulling upward with force, eg a fox or dog. Even if the possum’s sideways attack at the bait did trigger the 1080 capsule, it is unlikely that any of the ejected stream of 1080 would have been into the mouth of the possum. An East coast possum would have to consume at least half of the 1080 to be at risk of toxicity. A fox only needs 20% of the cannister’s 1080 to have a toxic effect.


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