Why have you been feeding toxic cane toads to rare reptiles?

Introduced cane toads have decimated populations of goannas – Australian monitor lizards – which are poisoned when they eat the adults. However, juvenile toads, which are smaller, make the lizards sick but don’t kill them. So we wanted to find out if feeding wild goannas juvenile toads would give them an aversion to the older ones.

Did it work?

Yes – 9 of 16 trained goannas survived the initial wave of toad invasion, compared with only 1 of the 31 untrained animals that we radio-tracked. The rest of the lizards died after eating large toads.

What happens now?

We’d like to protect goanna populations by releasing small toads ahead of an invasion front. This would need to be a decision we make with ranger groups, the public and government agencies, but we could potentially roll it out later this year.

Isn’t releasing more toads going to assist their spread?

It does seem counterintuitive to release an invasive species. But the numbers involved would be a drop in the ocean – a single female toad can lay up to 60,000 eggs a year. We’re hopeful that other native predators, including snakes and mammals, would also learn to avoid the toads after tasting small ones in the wild.