Reducing the impact of a toxic invader by inducing taste aversion in an imperilled native reptile predator

Abstract

It is virtually impossible to eradicate invasive organisms once they have spread widely, and even low densities of invaders may have devastating impacts. We need to explore alternative management options that accept the inevitability of encounters between alien and native taxa, but reduce the negative consequences of those encounters. Conditioned taste aversion (CTA) is one approach that offers promise in this respect. The spread of the invasive cane toad Rhinella marina across northern Australia is devastating populations of predators such as the bluetongued skink Tiliqua scincoides intermedia. Predators unable to tolerate the toads' powerful bufadienolide chemical defences are likely to die if they ingest a toad. We trained field-caught skinks to avoid eating cane toad flesh, by offering them toad sausages laced with a nausea-inducing chemical (lithium chloride). These individuals (and controls) were then released and radio-tracked as toads arrived at our study site in north-western Australia. Skinks that regurgitated after consuming the toad sausage survived after release, whereas most untrained animals were fatally poisoned by toad ingestion. Even if we cannot eradicate invasive cane toads, we can ameliorate their ecological impact by CTA training of vulnerable predators. bs_bs_banner Animal Conservation. Print

Ecological immunization: in situ training of free-ranging predatory lizards reduces their vulnerability to invasive toxic prey

“…Previous work to induce predators to avoid cane toads has relied upon smaller sample sizes of animals trained while in captivity. These studies used nausea-inducing chemicals to intensify CTA learning and monitored subsequent survival over shorter periods (less than 75 days) [9,10]. By contrast, we trained a larger number of free-ranging predators, by exposing them to small toads in the wild without additional chemicals, and monitored subsequent survival over 18 months.…”

“…CTA therapy has been used to mitigate human-wildlife conflict (deterring bears from spoiling food stocks, and coyotes from eating sheep [7,8]). More recently, CTA has been used to buffer vulnerable Australian predators from the impact of toxic cane toads (Rhinella marina), by training captive-bred quolls (Dasyurus hallucatus) or wild-caught bluetongue lizards (Tiliqua scincoides intermedia) to associate the sight and scent of cane toads with nausea-inducing chemicals [9,10]. We have taken this work an important further step, inducing long-term toad-avoidance by exposing free-ranging predators (varanid lizards) to small live toads (without using additional chemicals to intensify CTA).…”

Eliciting conditioned taste aversion in lizards: Live toxic prey are more effective than scent and taste cues alone

“…Most obviously, a live toad moves around in ways that may trigger a predator's attack; and the scent cues emanating from a sausage or dead toad may differ in many ways from those that are emitted by an intact live toad. The success of toad flesh and sausage-based CTA training in quolls and bluetongue lizards (O'Donnell et al 2010;Price-Rees et al 2013) shows that some types of predators can, indeed, forge a strong aversion to live toads based upon encounters with a lifeless or synthetic bait. However, the contrasting result of our 2 CTA-training studies with floodplain monitors suggest that for these animals, training based on a live toad provides a more long-lasting deterrent to feeding on toads.…”

“…One fundamental question is the protocol used to induce CTA. Previous studies on the cane toad system have largely relied on captive-raised predators that are trained prior to release into the wild (O'Donnell et al 2010), or have captured predators and brought them into captivity for training prior to re-release (Price-Rees et al 2013). In both of those studies, predators were presented with lifeless or synthetic stimuli (toad flesh or sausages made of toad flesh) and the effectiveness of CTA was enhanced by adding a nausea-inducing chemical to the stimulus.…”

Trends in behavioural ecology: Putting South African research in a global perspective

“…Of particular interest would be linking these themes with conservation biology. 68 For example, basic associative learning experiments can be used to train naïve animals to avoid predators 69 or avoid novel, toxic prey species 70 . Knowledge of how prey animals detect predators using olfactory, visual or acoustic cues could potentially improve the management of direct human-wildlife conflict: acoustic deterrents have been used to reduce crop raiding by elephants 71 , and prey avoidance of predator faeces 72 suggests that such chemical cues can be used to deter some pests.…”