The cane toad, native to Central and South America, is a large warty toad, poisonous with big paratoid glands (the round spots located behind the eyes near the neck) which exude bufotoxin as a means of defense. They are prolific breeders, with a female often laying between 8000 to 25000 eggs embedded in long strings of jelly. Most of the tadpoles, which themselves are poisonous, usually die during the time they metamorphose to adults as this is the time when they lose their juvenile toxins and are defenseless until the adult paratoid glands develop. Their main enemies at this critical period are … well ….other young cane toads, who cheerfully devour their brethern.
Their voracious appetites and rapid reproduction caught the eyes of agriculturalists, hoping to find a ‘natural means’ of controlling crop pests. One place they were brought in, was Australia. In 1935, about a hundred toads were introduced, with the hopes they would have an impact on cane beetles, who were attacking sugar cane fields. Needless to say, things did not work out as was hoped.
One would think Australians would have learned their lesson with the debacle of the introduction of rabbits back in the nineteenth century.
But evidently not. As with the European rabbit, with no natural enemies and an ideal environment, the toads did what their predecessors, the rabbits, did, which was reproduce like mad and spread like a bio-tsunami across the landscape. It’s hard to say what the Australians hate more now, rabbits or cane toads.
Efforts to control the exploding numbers of toads, now estimated to be 250,000,000, have been fruitless. The march of the toads seems relentless as they overrun not only ecosystems but human towns and cities, devouring anything smaller than themselves and poisoning inquisitive pets who lick or bite at them. Efforts to control them, ranging from introducing sterile males to compete with fertile males, using cane toad toxin to trigger cannibalism in tadpoles, or just bludgeoning the things to death with a hammer (illegal by the way) have born little fruit.
But a curious thing has been happening while humans have been pulling out their hair over their latest screw-up. It seems the local wildlife has begun a counter-offensive.
Recently white ibises have been observed ‘playing’ with cane toads. The birds are often called ‘bin chickens’ by locals for their habit of foraging in trash cans. But this insulting nickname may get dropped in light of what’s happening. It turns out the birds weren’t playing, they were stressing the toads, forcing them to release their poison, then either wiping them on grass or rinsing them in a nearby water source. Then the ibises would eat the toads without ill effect.
And they are not the only ones who have stumbled on a way to devour the formerly inedible cane toad. A local species of crow has developed the simple expedient of flipping the toad on its back and tearing open the abdomen and eating the non-toxic internal organs. Rakali water rats have also mastered the trick of eating the toad without running afoul of its poison by using the same technique.
If this doesn’t heighten your respect for the intelligence of animals in figuring out how to do all this, then I don’t know what will. There must have been a hefty amount of experimentation, fueled by hunger, by the ibises, ravens and water rats, before hitting on the best method of getting a meal out of these unpleasant invaders. Bird brains indeed!
Food for thought, if you’ll pardon the expression.
Have a happy and peaceful New Year.
