(2 Feb. 2018) I remember from my own observations the abundance of monitor lizards in Kakadu in the 1990s. Cane toads were first reported in Kakadu in January 2001 and since then the impact on native wildlife has been massive. The cane toad poison causes a heart attack in the animal that catches and consumes the pest, which was intentionally introduced to Australia in 1935. Goanna populations were almost entirely wiped out, as were many other animal species: king brown snakes, freshwater crocodiles, northern quolls, dingos, death adders and western brown snakes. Water monitors are far less impacted.
Remarkably, I’ve seen during my recent 10 days visit to Kakadu about five yellow spotted monitors at different times and locations. It looks like populations are picking up, a phenomena that also has been seen in Queensland. Surviving specimen of goanna’s don’t like cane toads as food, or have a method of eating them without being impacted by the poison.
In Kakadu goanna’s have also followed training programmes: captive goanna’s were taught only to eat tadpole cane toads, not the mature ones. They are then released into the wild again.
Despite the huge impact of cane toads on native wildlife, experts still consider the cane toad issue relatively small to the invasion of feral cats: they form a much bigger problem in Kakadu than the cane toads.