We’ve all been there. Who amongst us hasn’t felt sick after eating something dodgy, and then pledged to avoid it for life?
Now the same strategy is being used to help freshwater crocodiles avoid eating toxic cane toads, according to a new study published in Proceedings of the Royal Society B.
Cane toads produce a potent toxin that can be fatal to the species that consume them. Since their introduction to Australia in the 1930s, they have been decimating the native wildlife. This includes populations of freshwater crocodiles, which have been reduced by more than 70% in some areas.
So, conservationists have been using a method called ‘conditioned taste aversion’ to teach crocs to avoid eating the toxic amphibians.
Working with Bunuba Indigenous rangers, researchers from Macquarie University in Sydney and colleagues collected more than 2000 dead cane toads and removed their poisonous parts. They then injected the cadavers with a drug that produces powerful nausea and hung the bait from sticks overhanging rivers in the Kimberley region of north-western Australia.
Bits of untainted chicken meat were also dangled from sticks nearby, and motion capture cameras were set up, to catch the action that ensued.
“The first three days we noticed the crocodiles were taking the cane toads then they would go away... Then we noticed they would smell the cane toad before eating, and on the last day we noticed that it was mostly the chicken necks getting eaten,” says local ranger Paul Bin Busu.
Crunching the numbers, the researchers concurred. The crocodiles quickly learned to avoid eating the baited cane toads, but critically, the effect still held when the crocs were faced with live toads.
Areas where crocs completed the training went on to have greatly reduced mortality rates compared to unbaited control sites.
Baiting completely prevented deaths in areas where cane toads were arriving for the first time, and decreased deaths by 95% in areas where the amphibians were already established.
Conditioned taste aversion has been used to train other native Australian species, including quolls and monitor lizards, to avoid cane toads, but these have either been lab studies or small-scale field trials. This study demonstrates the feasibility of scaling things up.
“These are really exciting results because it provides land managers with tools to use ahead of the invasion, but also behind the invasion front” says Sara McAllister from the Australian Wildlife Conservancy.
“Together we’ve shown that collaborations between academics, indigenous rangers and land management agencies can be really effective for conservation science.”
Main image: Freshwater crocodile taking doctored cane toad bait. Credit: Georgia Ward-Fear
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