Threatened Australian Monitor Lizards Trained To Avoid Eating Toxic Toads

Australian researchers have taken an innovative approach to animal conservation that might help save endangered monitor lizards: Train them not to eat poisonous toads by feeding them small, less-poisonous cane toads.

Cane toads, an invasive species from Central and South America, were introduced to Australia in 1935 as a means of pest control. However, these poisonous amphibians are rapidly spreading across the continent and are so toxic they kill any predator that tries to eat them, causing catastrophic population declines.

In the latest study, researchers from the University of Sydney were able to teach wild goannas – common Australian monitor lizards – living in the Kimberley wilderness in northwestern Australia to avoid eating the toxic toads, according to a news release. This will help protect the lizards as the toads have recently invaded this floodplain. (Scroll to read more...)

"After training, giant monitor lizards survived when the toads arrived, whereas untrained lizards were immediately killed," Ph.D. candidate Georgia Ward-Fear, who led the research under the supervision of Professor Rick Shine and Dr. Gregory Brown, explained in the release.

Larger predators are increasingly susceptible to ingesting toxic toads because they prey on larger individuals, while smaller predators often survive because the toads they attack are smaller and less toxic, so they only make the predators sick. To teach these lizards not to eat poisonous toads, researchers fed small, non-lethal cane toads to wild yellow-spotted monitors – which have recently experienced a 90 percent population decline following toad invasions.

After the lizards were fed semi-toxic toads once or twice, and got sick, they quickly learned not to eat another, researchers say. When large toads charged the floodplain, the trained lizards simply ignored them. This suggests researchers could improve conservation methods by targeting vulnerable natives, rather than fighting to remove feral pests. For example, small cane toads could be released just before an expected invasion occurs. 

"This study shows that exposure to small cane toads can immunize free-ranging predators against the toad invasion," Professor Shine added in the release. "It sets the framework for a bold new method of conservation."

Their study was recently published in the journal Biology Letters. 

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