Safeguarding the northern quoll. Can we mitigate cane toad impacts through conditioned taste aversion?
- Publication Type:
- Thesis
- Issue Date:
- 2020
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Australia has the worldโs worst record of mammal extinctions. Changes to fire regimes, habitat loss and the impacts of invasive species are causal agents; but controlling invaders across landscapes is difficult. In northern Australia, the spread of toxic cane toads (๐๐ฉ๐ช๐ฏ๐ฆ๐ญ๐ญ๐ข ๐ฎ๐ข๐ณ๐ช๐ฏ๐ข) has caused population declines of the northern quoll (๐๐ข๐ด๐บ๐ถ๐ณ๐ถ๐ด ๐ฉ๐ข๐ญ๐ญ๐ถ๐ค๐ข๐ต๐ถ๐ด), a marsupial predator that dies from toad poisoning. Traditional methods have failed to halt the toad invasion, so we need new methods to reduce their impact.
In this thesis, I critically examined whether conditioned taste aversion (CTA) could reduce the impacts of cane toads on northern quolls. Trials on captive quolls confirmed that quolls fed toad meat infused with an emetic (of a substance causing vomiting) subsequently refused to attack live toads. This raised the question of whether we could use CTA ๐ช๐ฏ ๐ด๐ช๐ต๐ถ to train wild quolls to avoid cane toads. This thesis addresses that gap. Firstly, I analysed mark-recapture data to estimate quoll demographic parameters and used a population viability model to determine whether CTA could prevent quoll population extinction. The success of CTA in reducing the probability of extinction was strongly influenced by the baiting design and requires that a high proportion of the population can be trained prior to toad invasion. In addition, cultural transmission of food preferences from mothers to offspring is necessary for CTA to be a successful long-term mitigation strategy.
I developed a bait suitable for field deployment and demonstrated that captive quolls that ingested toad baits generalised their aversion to toads, and that wild quolls readily consumed baits. Importantly, bait uptake by non-target species was negligible. Next, using a BACI design, I carried out a replicated field experiment to determine whether baiting could mitigate the impact of toads. Surprisingly, at control and experimental sites, quoll populations went extinct following toad invasion. To understand this failure, I then determined the optimum level of bait deployment needed to reach my target species. I aimed to improve baiting design outcomes by employing a model that optimised the delivery of CTA, while accounting for the fact that some animals in the population could not be CTA trained.
Overall, my thesis highlights the challenges of implementing a novel technology in complex ecological systems and demonstrates the need for evidence-based data to guide decision makers. In a world experiencing rapid rates of mammalian extinction, novel conservation strategies such as CTA may help us mitigate threatened populations against the serious impacts of invasive species.
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