Wildlife rangers at the World Heritage-listed Kakadu National Park in northern Australia have been told to abandon programs aimed at curbing numbers of one of the country's most destructive invasive pests. Cane toads have come to inhabit much of tropical Australia since they were introduced from Hawaii in the 1930s.
They are a voracious pest that has invaded vast swathes of northern Australia, and toxins in their bodies can kill goannas, crocodiles and snakes within minutes.
They have devastated many native species, but researchers now say wildlife is recovering, following the initial hit that occurred when the toads first arrived.
In the Kakadu National Park in the Northern Territory, the toad invasion began in 2002. Rangers have now abandoned active efforts to remove the toads or stop their spread, because they believe native animals are learning to not eat the toads or are avoiding them altogether.
This approach is supported by Professor Rick Shine, an evolutionary ecologist at the University of Sydney.
"The Australian wildlife has proved to be far more resilient than I ever gave them credit for. They take a hell of a hit when the toads first arrive, but, through time, they begin to recover," he said.
Cane toads are prolific breeders, and some estimates suggest there are as many as 1.5 billion in Australia, but it is impossible to know for sure.
In the 1930s, the toads were thought to protect sugar plantations by eating the grubs that were devouring the crop. They were then sent around the world as a pest control means.
In 1935, 101 toads arrived in Queensland, where they were bred in captivity and their progeny released to hunt and kill cane-destroying beetles along Australia's northeast coast. The experiment was a disaster. Not only could the toads not climb the sugar cane plants to catch the beetles, their numbers spread rapidly.
The toads prey on insects and other small animals, but they are at their most dangerous when they are eaten by larger predators, such as snakes, goannas and freshwater crocodiles. A large gland on the toad's shoulder is loaded with fast-acting cardiac toxins.