Scientists Trained Monitor Lizards Not to Chow Down on Poisonous Toads

And they did it by feeding them smaller and less-poisonous toads

Monitor Lizard
This monitor lizard is definitely not thinking of eating poisonous toads. Axel Gomille/Nature Picture Library/Corbis

Cane toads spell big trouble in Australia—not just for humans, who consider them an invasive species, but for greedy, omnivorous monitor lizards, who die when they eat the poisonous toads. Now, reports Rebecca Morelle for the BBC, scientists have come up with an ingenious, if simple, solution for the mass poisonings of one of Australia’s most beloved reptiles: Train them not to eat poisonous toads by feeding them small, less-poisonous cane toads.

Monitor lizards, which the locals call goanna, have special significance in Australia, where they are a sacred symbol in aboriginal art and culture. Though Australia has a high diversity of goanna, Morelle reports that up to 90 percent of one species, yellow-spotted monitors, have died from eating the toads.

"A goanna only has to mouth a toad for less than 30 seconds and it can kill them," Lead researcher Georgia Ward-Fear tells Morelle. The potent amphibians number in the hundreds of millions, spread in various habitats across northern Australia. And that’s a real problem for monitor lizards, which feed on pretty much everything.

Cane toads were imported to Australia in the 1930s as a means of pest control for sugar cane farmers, but with few predators, they quickly began to multiply and spread. These days, they’re considered an invasive species, and Australian officials say their biological effects are a “key threatening process” for the continent’s environment.

To help monitors fight back against the toads, a team of conservation scientists decided to train the lizards not to eat them. By feeding wild, yellow-spotted monitor lizards smaller, less-potent cane toads, they were able to convince them not to eat toads at all. The small toads were potent enough to make the lizards slightly sick without doing permanent damage, Morelle reports.

“Just one or two toad meals were enough to convince a goanna not to eat another toad,” the team notes in a release. The team suggests that conservationists release the small, less-toxic toads into the wild to help lizards gain “an opportunity to learn rather than to die.” They recently published their results in the journal Biological Letters.

Perhaps Australia’s monitor lizards will be inspired to eat fewer toads in 2016—or at least fewer deadly ones.

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