Researchers in Australia are tackling a unique challenge: the plight of freshwater crocodiles falling victim to invasive cane toads. These toads are not just an eyesore; they’re also toxic, and many native predators, including crocs, suffer deadly consequences after ingestion.
The innovative strategy involves filling deceased cane toads with a harmless chemical that induces sickness in crocodiles. The goal? Train them to steer clear of the live, toxic toads. A recent experiment, which utilized over 2,000 dead toads, proved effective in changing the crocs’ behavior, encouraging them to avoid both the deceased and living versions, as detailed in a paper published in the journal Proceedings of the Royal Society B: Biological Sciences.
Georgia Ward-Fear / ISTOCK / GETTY IMAGES PLUS
The team, hailing from Macquarie University in Sydney, collaborated with Bunuba Indigenous rangers and the Department of Biodiversity, Conservation and Attractions (DBCA) in Western Australia. Their approach leverages behavioral ecology, employing a technique known as conditioned taste aversion. Essentially, the crocs learn to link the bad experience of being sick with eating cane toads.
Cane toads (or Rhinella marina) are an invasive species in Australia, originally from Central and South America, and have swarmed the continent since their introduction in the 1930s. With numbers exceeding 200 million, they threaten various native species, leading to severe ecological imbalances.
The toxic bufotoxin secreted by the toads poses a significant risk to local wildlife, including goannas, snakes, and of course, freshwater crocodiles. Researchers noted a staggering decline of over 70% in some croc populations due to these toxic encounters. “Apex predators like freshwater crocs are vital to ecological health; hence, protecting them is crucial,” they stated in their findings.
In 2016, a report indicated that 75 species of Australian reptiles and freshwater turtles are at risk, with 16 classified as “threatened.” As croc habitats shrink during the dry season, they’re more likely to encounter cane toads, resulting in tragic outcomes.
The researchers crafted a unique bait, removing the toxin glands from 2,395 cane toads and replacing the toxic content with a non-harmful chemical. They also utilized chicken pieces as control bait to assess croc behavior. Notably, within days, the crocodiles began avoiding toads, showing a marked preference for chicken instead.
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The results were promising: in regions where the dead toads were strategically placed, croc fatalities from cane toad consumption dropped significantly. “We saw a 95 percent reduction in deaths in areas with established toad populations, and this effect lasted for years,” said Ward-Fear.
Post-study, crocodile numbers have started to recover, which is encouraging news for the ecosystem’s health. The absence of these apex predators could disrupt food chains, affecting various species like judembah and barramundi.
Moreover, freshwater crocodiles hold significant cultural importance for Indigenous communities. “These findings offer valuable tools for managing invasives,” noted DBCA representative Sara McAllister. “This collaboration is a fantastic example of how combined efforts in conservation can lead to success.”
References
Ward-Fear, G., Bruny, M., Rangers, the B., Forward, C., Cooksey, I., & Shine, R. (2024). Taste aversion training can educate free-ranging crocodiles against toxic invaders. Proceedings of the Royal Society B: Biological Sciences, 291(2028), 20232507.
Markula, A., Csurhes, S., & Hannan-Jones, M. (2016). Invasive animal risk assessment: Cane toad Bufo marinus.