The University of Sydney’s Professor Rick Shine hopes to reduce the deadly threat from cane toads invading Australia’s Kimberley region by teaching native predators to eat small toads instead of large ones.
The novel experiment, which has won an $860,000 Australian Research Council Linkage Grant, is the latest in a history of endeavors that have sought to lessen the ecological damage wrought by cane toads since their introduction into Australia in 1935 to control beetles in Queensland’s sugarcane crops.
Most predators that eat cane toads are killed by a poison contained in glands on the toad’s upper surface. This has devastated many species of quolls, snakes, goannas and lizards, cutting numbers by more than 90 per cent within a few months of invading toads.
The situation is dire, because the western Kimberley, is one of the last remaining biodiversity hotspots in tropical Australia.
“Methods for controlling cane toads, such as culling, are only suitable for small-scale efforts,” says Professor Shine, a Laureate Fellow of the Australian Research Council and winner of the Prime Minister’s Prize for Science.
“This means we have no effective landscape-scale control methods before these alien amphibians penetrate all the way through to the coast of northwestern Australia, probably, within five years.
“The situation is dire, because the western Kimberley, recently added to the national heritage register, is one of the last remaining biodiversity hotspots in tropical Australia.”
Large poisonous adult toads always make up the first wave of invading toads, making them highly deadly to the naïve native predators that eat them as they move through the landscape.
In recent experiments, scientists have cut deaths in several native species by training them to avoid eating large toads by first exposing them to younger, smaller toads and toad-flavoured baits. The smaller toads and baits contain less toxin and induce nausea in the predators without killing them.
Known as conditioned taste aversion (CTA), scientists showed the effectiveness of this method, for example, in free-ranging floodplain monitors (Varanasi panoptes) by exposing them to small toads just before the main toad invasion arrived. Eighteen months later, half the trained lizards were still alive whereas all the untrained lizards were dead.
This means the vulnerable predators learnt to avoid larger deadly toads by being made ill through earlier exposure to smaller toads and baits.
“If CTA-trained predators generalise their aversion to toads of all sizes, the ecological impact of cane toads would be massively reduced,” Professor Shine says.
Professor Shine says there is now widespread support to start the “teacher toad” strategy as soon and as widely as possible.
“When I first suggested this idea in 2008, it was opposed by most wildlife managers, government agencies and community “toad-busting” groups, but our empirical evidence has changed that situation.
The novel experiment funded by the Australian Research Council Linkage Grant will be led by the University of Sydney in partnership with the Western Australian Department of Parks and Wildlife, the Australian Wildlife Conservancy, Kimberley Land Council, Worldwide Fund for Nature Australia, Matsos, Rangelands NRM Western Australia, and the Dunkeld Pastoral Company.