According to Georgia Ward-Fear, a conservation ecologist at Macquarie University in Australia, eradication efforts have failed and cane toads “are here to stay”.
So Ward-Fear and her colleagues have taken a different approach to the toadpocalypse: training native wildlife to live alongside these invaders. To prevent predators from eating the toads, the team utilises a strategy called conditioned taste aversion. Ward-Fear compares the tactic to a beneficial bout of food poisoning, reasoning that conservationists could “train animals not to eat cane toads if we gave them nonlethal experiences with cane toad baits”.
To test this strategy with crocodiles, the team focused on Australia’s remote Kimberley region. There, rivers carve the rugged terrain into gorges that are suited for freshwater crocodiles. This area is also the front line of the toad invasion. The researchers conducted necropsies of deceased crocodiles and found cane toads in several of their stomachs.
To alter the local crocodiles’ eating habits, the team worked with Indigenous rangers to set bait along the riverbanks of four gorges (another river was left unbaited and used as a control). Each of the bait stations contained a cane toad carcass and a chicken neck dangling over the water. The team removed the toads’ poisonous glands and injected a nauseating lithium chlorine solution into the toads’ back legs. They monitored the crocodiles’ feeding activity with remotely triggered wildlife cameras.
Initially, the toad carcasses were a big hit with local crocs, who scarfed down equal amounts of toad carcasses and chicken necks on the first day. But, as the baiting period continued, the crocodiles consumed fewer toads. It wasn’t that they had lost their appetite – they still snapped up the chicken necks – but their tastes had shifted away from the tainted toads.
After the baiting experiment, the researchers observed a lower mortality rate among crocodiles at the four test gorges compared with the crocodile population at the unbaited control site.
Ward-Fear and her team believe that a taste aversion strategy can help make cane toads unpalatable to other predators. But she stresses that each predator needs an aversion strategy that is fine-tuned to its hunting style.
For example, the team has also worked with yellow-spotted monitors. These large lizards actively pursue live prey (the team originally tried cane toad sausages, but the aversion didn’t stick). So the team utilised young, nonlethal “trainer toads”. In another paper, the team concluded that yellow-spotted monitors who scarfed down juvenile cane toads largely avoided eating adult toads.
According to Steve Johnson, a wildlife biologist at the University of Florida who was not involved in the new paper, getting ahead of the toad invasion with these taste aversion tests will likely help prevent an initial mass mortality event among freshwater crocodile populations. But it remains to be seen how long these reptiles will retain this knowledge.
“It’s not a one-and-done thing,” Johnson said. “Even if it’s wildly successful, you have to maintain it.”
At least freshwater crocodiles seem to be willing to change their snacking habits.
“Thankfully, it looks like crocodiles might be a bit better than us at learning from their mistakes with invasive species,” Johnson said.
This article originally appeared in The New York Times.
Written by: Jack Tamisiea
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