Researchers stop threatened lizards eating toxic cane toads

Australian researchers have taught free-ranging goannas to avoid eating poisonous cane toads about to invade their study area – a floodplain in the remote Kimberley wilderness.

“After training, giant monitor lizards, known as goannas, survived when the toads arrived, whereas untrained lizards were immediately killed,” said PhD candidate Georgia Ward-Fear, who led the research under supervision from University of Sydney Eureka Award-winner Professor Rick Shine with colleague Dr Gregory Brown.

Worldwide, invasive species cause devastating impacts on native predator populations. The 7kg, yellow-spotted monitor, or floodplain goanna, is central to Aboriginal culture and plays a pivotal ecological role.

In Australia, the spread of cane toads has caused catastrophic population declines in many native predators because of fatal poisoning when toads are ingested. Smaller predators often survive because the toads they attack are small enough to make them sick but not kill them. Small toads contain much less poison than large adult toads. So, the predators learn not to eat toads.

Immediately prior to the arrival of toads at a remote floodplain at Oombulgurri in the Kimberley region of northwestern Australia, researchers offered small (non-lethal) cane toads to wild lizards. Follow-up trials confirmed just one or two toad meals were enough to convince a goanna not to eat another toad.

The trained lizards then went on to ignore the large toads that arrived a few months later. Eighteen months after the study started, many of the trained lizards are still alive despite the presence of toads.

The research led by University of Sydney is published today in the journal Biology Letters. The work was carried out in collaboration with the Western Australian Department of Parks and Wildlife and Balanggarra Rangers.

University of Sydney Professor Rick Shine said the findings suggest a potential buffer against invasive species impacts by targeting vulnerable natives rather than feral pests.

“This study shows that exposure to small cane toads can immunise free-ranging predators against the toad invasion,” Professor Shine said. “It sets the framework for a bold new method of conservation.”

Dr Brown concluded: "Releasing small toads just before the invasion front arrives could prolong the lives of native predators."