Naturalists in Australia have spent decades battling to contain the explosive spread of cane toads, an invasive species of hardy – and poisonous – amphibian that eats just about anything.
Native to the Americas, cane toads were purposefully introduced into the state of Queensland in 1935 to control the beetles that were eating valuable sugar cane crops. The plan quickly backfired, however, when the toads began multiplying exponentially in their new environment. From the original 3,000 immigrants, an estimated 1.5 billion toad descendants now live across northeastern Australia and are inexorably marching southward.
The large terrestrial toads have no natural predators in Australia thanks to a potent toxin, known as bufotoxin, secreted from glands across their backs. Though many species in South and Central America have evolved to eat cane toads anyway, bufotoxin is deadly to nearly all Australia wildlife – even 8-foot-long (2.4-meter-long) freshwater crocodiles. The warty invaders have proved especially dangerous for curious cats and dogs (and ill-advised people) that make contact with them.
In an attempt to prevent future casualties, researchers are training wildlife to avoid the cane toads using a “taste aversion" strategy, wherein sausages containing a small proportion of toad meat are distributed to carnivore populations in regions where the toads have not yet established. After experiencing what is, essentially, unpleasant food poisoning, the predators learn that it’s a bad idea to eat the toads.
But Australian crows don’t need human help.
Australian Geographic photographer Steve Wilson has captured photographic proof that clever corvids north of Brisbane have figured out how to make a meal of the toads without ingesting any toxin.
"Crows avoid contact with the ooze by grasping them by the limbs or even the bony brow above the eye, avoiding the body itself," wrote Wilson in Australian Geographic.
"These clever birds have learnt to roll the toads onto their backs, sometimes doing so repeatedly if the luckless toad tries to hop away. Crows know which bits to eat – fleshy thighs, tongues, intestines – and how to get at these from below without contacting the lethal parts."
Anecdotal reports suggesting crows in other regions have mastered this crafty technique have circulated since at least 2007, but confirmed sightings have been limited.
Wilson writes that the crow he spotted spent about 40 minutes carefully picking out the safe parts of the toad while other crows stood and watched.
The presence of attentive witnesses may explain how crows living over 3,000 miles away from Brisbane have exhibited similar behaviors. Crows are well known for their ability to learn from one another. It's equally possible, however, that multiple populations have figured it out independently, given their propensity for problem-solving.
A Nambour resident reported seeing a crow thoroughly washing a captured cane toad in his bird bath before flipping it over and chowing down.
Regardless of how they get the job done, Australians are in full support of the crows' new talent.