By Lisa Horn

 

Cane toads were introduced as natural predators for crop management. Photo: Getty Images.

The year was 1935. Sugarcane crops in northern Australia were being decimated by native Australian cane beetles. A desperate Australian government needed reinforcements, so they brought in support from abroad. Thousands of large, warty amphibians, native to Central and South America, were released into sugarcane plantations and tasked with controlling beetle populations.

Unfortunately, the introduced cane toads barely made a dent in the beetle problem. Instead, they slowly hopped across northern Australia, voraciously consuming insects, small animals, and even unattended pet food, and reproduced easily and rapidly.  Today, their populations number in the millions, which has spelled disaster for native wildlife.

Toads take away food and shelter from native species, but the real danger is that cane toads are highly poisonous. They secrete toxins which target the heart and central nervous system, killing those foolish enough to try to eat them. And many native Australian animals do find the cane toad to be an irresistible, easy-to-catch meal, with dire consequences.  

Northern quolls are nocturnal predators native to Australia. Photo: Jonathan Webb

 

The endangered northern quoll, which looks like a giant, spotted mouse, is such a frequent victim of fatal cane toad poisoning that populations had to be moved to toad-free islands. It’s a sad reality that the toads are likely here to stay, at least for the foreseeable future. Eradicating them from large areas is practically impossible. If there are any hopes of restoring the northern quoll’s once-thriving mainland populations, conservation biologists need to find ways to allow the quoll and the toad to peacefully coexist.  

Successfully reintroducing endangered species is much more complex than simply opening a cage door and hoping for the best. Oftentimes, conservation biologists only have a few animals available to release, so they need to do everything in their power to help them survive in the wild. One tactic to better prepare animals for release is targeted training programs. 

Researchers in Australia have tried an innovative solution to prepare northern quolls for the challenge of living in cane-toad territory. In an article published in Austral Ecology, they show that quolls can be taught that cane toad is not an appetizing meal, helping them to survive longer in toad-infested areas.

 In similar studies some quolls are given “toad sausages” as part of aversion training. Photo: Australian Wildlife Conservancy

The experimental training program, called taste-aversion training, works by giving the quolls an unpleasant but non-lethal taste of cane toad. A portion of the captive quolls slated for reintroduction were offered up a tempting dinner of dead baby cane toad, seasoned with thiabendazole, a nausea-inducing chemical. Quolls which eagerly dug into their dinner became sick and later refused to eat more toads. 

Not only do quolls have to avoid eating toads, they also have to avoid animals that might find them to be a tasty snack. To help them learn how to recognize and avoid predators, every quoll in the program also received basic predator-aversion training. 

Equipped with microchips and radio-collars, ‘toad-smart’ trained quolls and ‘toad-naïve’ untrained quolls were released in Kakadu National Park, a place where quolls were once common before the arrival of the cane toads. Researchers followed the animals daily, having the morbid task of documenting who died, when, and how. 

Radio collars were placed on the quolls to determine survival rates. Photo: ABC News

Most of the untrained quolls were found dead within a few days of release, and not too surprisingly, cane toads were the culprit. ‘Toad-smart’ quolls, on the other hand, used their experience from the training to safely navigate the Park’s culinary offerings. Trained quolls were significantly less likely to be found dead from toad poisoning than their untrained counterparts.

Although we don’t yet know if training just one generation of quolls will be enough to help their populations survive long-term, the success of the taste-aversion training shows promise for helping native predators cope with living in toad-infested areas.

Even if the quolls learn to avoid toads, they are still easy meals for Australian dingoes. Photo: Australian Reptile Park

However, the predator-aversion training was not as successful, and most of the ‘toad-smart’ quolls died anyway from becoming someone else’s meal. Dingoes, wild dogs introduced to Australia thousands of years ago, picked off the released quolls, practically eradicating the population within weeks. Learning from failures (and successes) is essential to constantly improving and fine-tuning methods. In fact, the success of the taste-aversion training may actually help solve the dingo predation problem. The researchers wonder,  if quolls can be trained to avoid toads, maybe dingoes can be trained to avoid quolls. 

 

 

Jolly CJ, Kelly E, Gillespie GR, Phillips B, Webb JK. 2017. Out of the frying pan: Reintroduction of toad-smart northern quolls to southern Kakadu National Park. Austral Ecology Volume 43, Issue 2, 24 October 2017, Pages 139-149.

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Lisa Horn

Lisa Horn

Guest Blogger – MSc Candidate at York University in the Stutchbury Lab

Lisa is an ecologist with a passion for wildlife and conservation. Lisa has wide-ranging experience in conducting ecological inventories, assessing environmental impact of proposed developments, and navigating the framework of environmental legislation. She has a special interest in ornithology and species at risk and is currently investigating the effects of climate change in wintering habitats of migratory songbirds on their arrival condition in Ontario.