Anyone witnessing toads raining down from the sky would be forgiven for assuming that freak weather or biblical wrath were responsible. In northern Australia, however, aerial deployment of toads is a radical way of trying to save a bushy-tailed marsupial from extinction.
By showering the landscape with toad sausages that make the endangered quoll nauseous, scientists believe that they can deter them from eating poisonous cane toads.
The cat-sized quoll was once widespread in northern Australia and Papua New Guinea, but its population has plummeted since the toxic toad was introduced to Australia in 1935.
Eating a single toad is normally enough to kill a quoll, meaning that in the wild the animals never have the chance to learn not to eat them. The toads have driven quolls to extinction in many parts of northern Australia and will soon invade the Kimberley region, one of the quolls’ last strongholds.
The animals have a dappled coat and bushy tail and females have a pouch that opens when they are rearing young.
In a laboratory setting, scientists from Sydney University fed quolls small toads laced with the poison thiabendazole. The dose was not enough to be harmful, but the sickness the quolls experienced was enough to put them off eating the toads again.
The team is preparing to implement the technique on a large scale, with plans to drop toad sausages from an aircraft.
“If you can teach a predator that cane toads make you sick, then that predator will leave them alone afterwards. As a result, animals like quolls can survive in the wild even in a toadinfested landscape,” said Jonathan Webb, an ecologist at the University of Sydney, who led the study. However, the scientists first need to ensure that other endangered species, such as goanna or blue-tongue lizards, would not be put at risk.
In the study, published in the British Ecological Society’s Journal of Applied Ecology, the Sydney team collected 62 adult quolls from the Territory Wildlife Park and taught half of them, the so-called “toad-smart” group, to associate eating a cane toad with feeling sick. A few days before the quolls were reintroduced to the wild, the toad-smart group were fed a small dead cane toad laced with thiabendazole.
The toad was not large enough to kill the quoll but the chemical made them feel ill. To test whether the taste aversion process worked, both groups of quolls were given a small, live cane toad in a plastic container to see whether or not they attacked it. Their behaviour was videoed using a hidden camera, and the quolls were then fitted with radio collars and released.
The conditioned quolls were less likely to attack the toad in the plastic container, and once released into the wild survived up to five times longer than “toad-naive” quolls.