Apr 25, 2010
The cane toad in Australia is a text book example of a feral
species. As an introduced species, it has no natural predators and
out-competes native animals for food and habitat. Things are made
worse by the fact that cane toads are highly poisonous - so
poisonous that they can kill animals as large as crocodiles.
One species imperilled by the cane toad is the Northern Quoll. The northern quoll
has been almost driven to extinction in many parts of northern
Australia because they attack the toad and are subsequently
poisoned. The poison kills the quolls too quickly for them to learn
not to do it again. In a recent study Conditioned
taste aversion enhances the survival of an endangered predator
imperilled by a toxic invader in the Journal
of Applied Ecology, Stephanie O'Donnell, Jonathan
Webb and
Richard Shine from the University of Sydney tested whether
quolls could be taught to avoid eating cane toads through
"conditioned taste aversion" (CTA).
I spoke to Dr Webb about their study and how quolls can possibly be
saved from extinction by CTA. Working with the Territory Wildlife
Park, the researchers took a group of quolls and taught half
(the "toad-smart" group) to associate eating a cane toad with
feeling sick by feeding them a small dead cane toad laced with
thiabendazole. The
cane toad was too small to kill the quolls with its poison, however
the tiabendazole made them feel sick. The second half of the quoll
group ("toad-naive") were not fed the cane toad. The next part of
the experiment was to feed the quolls a small, live cane toad in
plastic container to see whether or not they attacked it. It was
found that the toad-smart group was less likely to attack the toad
in the plastic container. It was also found that the toad-smart
group survived up to five times longer in the wild than
"toad-naive" quolls. The researchers also found that male quolls
were far more likely than female quolls to attack cane toads. Dr
Webb thinks that aerially deployed 'toad baits' ahead of the cane
toad invasion front could educate quolls to avoid attacking cane
toads before the toads invade.
Cane toads were introduced to Australia from Hawaii in June 1935 to
control the native Cane
Beetle. They bred immediately in captivity, and by August 1935
more than 102 young toads were released in northern Queensland.
Toads now number over 200 million and have steadily expanded
through Queensland, reaching the border with New South Wales in
1978 and the Northern Territory in 1984. It is estimated that cane
toads migrate at an average of 40 kilometres per year.