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Invasive Cane Toads In Australia Are Prey To Australian Water Rats

October 25, 2019



The cane toad is an invasive species in Australia that was introduced in 1935 to control beetles in sugar cane fields

The invasive cane toad (Rhinella marina), introduced in Australia in the 1930s and able to kill a crocodile with a single gulp may have met its match Down Under: Water rats. According to a study, the native water rat, known locally as rakali, have learned to eat cane toads without disturbing the poison that other animals, such as crocodiles, quolls and monitor lizards have died as a result of ingesting.

Reproductive biologist Dr. Marissa Parrott was out in the filed when she stumbled across a large number of dead cane toads, on their backs, with what appeared to be incisions on their chests. For days, she returned to the same area near a creek and found more dead toads.

“We found that in all the cane toads, the heart and liver had expertly been removed, and the gallbladder, which contains toxic bile salts, had been removed and placed outside the body,” Parrott told Vice. Intrigued how these toads ended up dead, and with precision like cuts in their bodies, she set up an infrared camera to do some sleuthing. The cameras captured the water rats performing surgery, most likely with their teeth on an amphibian that has caused population declines of several other species.

Australian water rat Hydromys chrysogaster

zoopro/wikipedia

Australian water rats have learned how to kill and eat invasive cane toads without getting poisoned.
 

“Within just two years of cane toads moving into the area, they had learned how to disable, kill, and eat something that had killed so many other predators in the region,” Parrott told Vice. She believes the water rats removed the organs via the underside as it is less toxic than the backside, and  interestingly, the dead toads were almost exclusively the larger ones, as they have larger organs and it was easier for the rats to avoid the gallbladder, which is toxic.


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“They didn’t eat as many medium-sized toads, but when they did, it was fascinating to note that as well as the heart and liver they had also eaten one or both of the thigh muscles after stripping away the toxic skin,” Parrott told Vice. “We’re not sure if they just wanted a bigger payoff for their efforts in overpowering the toad, or if it was easier to subdue the toads by holding down the legs first. Interestingly, they never attacked the leg muscles on the larger toads.”

Parrott noted that while the water rats have learned to prey on the cane toad successfully, and without getting killed, the sheer number of cane toads in Australia, and the small number of water rats, relative to the amphibian's populations, won't have any significant impact on the invasive species, but Parrott was proud that the rat, which she has studied in the past, was able to figure out a way to kill and eat the toads. 

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