Dead toads may keep natives away
Early evidence suggests native animals may be trained to avoid poisonous cane toads, using dead toads spiked with a chemical that induces nausea, say researchers.
Professor Ric Shine and Dr Jonathan Webb from the University of Sydney have been supervising a trial of the method in the Northern Territory.
"It only takes one toad to kill," says Shine. "Even vastly reducing the number of cane toads in the system may not actually reduce the impact on natives.
"The challenge is whether we can teach native predators to leave cane toads alone when they arrive."
Shine says one of the native animals affected by the toad is the Northern Quoll, a marsupial whose numbers have been declining.
"There are plenty of suggestions that the arrival of the cane toads is the last straw for the quolls," he says.
To try and protect quolls, Shine says Northern Territory authorities have been translocating the animals to toad-free islands.
Shine and colleagues have trialled their idea on captive quolls that are part of this translocation program.
They have tested what happens when quolls are fed small dead toads laced with a chemical that makes the quolls feel nauseous.
"The basic idea is to make this association in the quoll's mind that whenever they eat something that tastes like a toad they feel sick," says Shine.
Early results are encouraging, he says.
"It's possible to teach quolls to leave toads alone," says Shine. "You can throw toads into the cages of these quolls and they just walk over to them and sniff them and just walk away."
The researchers will radio track the 'taught' quolls to assess whether they survive longer than those that have not been taught.
If the system works, dead toads could be distributed at the front of the advancing cane toads, to "teach" the native predators not to eat the toxic toads once they arrive.
Shine says a related idea is to use live "teacher toads" - baby male toads that are less toxic than the larger adults.
He says trials involving teacher toads and quolls have not yet delivered definitive results.
This live toad idea is opposed by Graeme Sawyer, co-ordinator of Frog Watch in Darwin.
"We think it's an appalling idea," he says.
He says small snakes, frill-necked lizards and other reptiles are susceptible to small toads.
Sawyer also questions whether native animals would transfer the learning to the next generation.
He says the idea of using dead toads would be preferable to live toads if it was feasible.
Sawyer says one cane toad control method that has had a lot of success is fencing off water sources with knee-high fences so the toads die of thirst.
He says this has had little impact on natives which can by and large get around the fences.
Sawyer says another method he is keen to see developed is a transgenic native toad predator.
Shine agrees some kind of biological control is necessary for controlling toads because the animal has 30,000 eggs in a single clutch.
He agrees some native species are remarkably susceptible to small toads and research on live teacher toads would include looking at the impact on reptiles.
"I think the example of the toad itself - biological control gone wrong - says that you don't want to jump in there and start manipulating these systems until you know what's going on," Shine says.