Rat bait proving lethal to endangered Australian species

Rat and mouse baits commonly used around the home and in the workplace could potentially wipe out as many as nine species of endangered Australian marsupial carnivores, including the iconic Tasmanian Devil and all of Australia’s quoll species, new research from Edith Cowan University (ECU) has found.

ECU researcher and Adjunct Lecturer Dr Michael Lohr tested five of Australia’s largest native marsupial carnivores for anticoagulant rodenticides (ARs), or poisons and the results were staggering. Half of the animals tested positive for ARs, with 21% having more than one AR compound in their blood stream.

“Ultimately, the research found that 15% of Tasmanian Devils, 20% of Eastern Quolls, 22.2% of Chuditch and 20% of Spotted-tailed Quolls tested were very likely to succumb to AR poisoning or a secondary proximate cause of death resulting from the sublethal effects of AR toxicity,” Dr Lohr said.

The Pilbara Northern Quoll, which is geographically restricted and confined to remote areas of the Pilbara region of Western Australia, had low levels of ARs, which Dr Lohr said could be a result of its remote location and the lack of interaction with human landscapes likely to contain ARs. Notably, however even these remote populations still showed evidence of ARs in their bodies.

ECU Associate Professor Dr Rob Davis said that in addition to directly poisoning the animals, ARs could also result in a weakened immune system, making the already endangered species more prone to infectious diseases, and predation.

Exposed to extinction

Using population viability modelling, the research found that if the juvenile mortality rate for the Tasmanian Devil increased by between 15% to 30%, the probability of extinction would increase from 20% to 100% in under 100 years.

“In our study, 5% of tested devils were exposed to lethal doses of rodenticides and 10% were exposed to likely toxic, and potentially lethal levels of rodenticides,” Dr Lohr said.

“Hence the exposure to rodenticides may be directly raising the mortality rate of Tasmanian Devils by 15%.

“A further 30% of Tasmanian Devils were exposed to sub-lethal doses that may make them more vulnerable to other causes of mortality.”

For the Spotted-tailed Quoll, a 10% to 20% increase in juvenile or adult mortality would result in a high probability of population extinction. In this study, 40% of Spotted-tailed Quolls were exposed to sub-lethal doses of rodenticides.

“Similarly, populations of the Northern Quoll are highly sensitive to juvenile and adult female survival, and a 2.5% reduction in the rate of mortality nearly doubles the probability of population persistence over 20 years.

Associate Professor Davis said this research now bring the total to nine threatened animal species in Australia that are being placed at risk due to the unregulated use of second generation ARs, which have a much longer environmental persistence time than ARs.

“We understand how difficult it is to contain mice and rat populations, and without bait some people might be unable to achieve control of this issue. But there are bait alternatives that do not use ARs.”

Associate Professor Davis and fellow researchers are calling on politicians to do more to regulate the use of these poisons.

“Our hope is that the Australian Government restricts the widespread sale of pesticides or SAGRsin line with other countries, including Europe and North America,” Dr Davis said.

“In the meantime though, consumers can make a difference and do their bit to stop the unnecessary deaths of native wildlife by educating themselves on the correct choice of bait.

“There is no need to use SGAR baits containing brodifacoum, bromadiolone, difethialone, difenacoum and flocoumafen. Instead choose FGAR containing warfarin, coumatetralyl and other alternative non-AR formulas.,” Dr Davis said.

More information on safer bate choices can be found on https://owlfriendly.org.au/rodent-control/

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Media contact: Esmarie Iannucci, Media Advisor, 0405 774 465 

e.iannucci@ecu.edu.au