Feeding carcasses of cane frogs to freshwater crocodiles can protect the species from pests

As cane frogs continue their walk across the Kimberley River, an innovative study using their chemical-coated carcasses as bait could help protect freshwater crocodiles in their path.

It has been scholars, traditional owners and volunteers Working to mitigate the infestation of cane toads in Western Australia For more than 10 years, but despite their efforts and the rugged Kimberley terrain, pests continued to spread.

Recent monitoring efforts by the Department of Biodiversity, Conservation and Attractions (DBCA) have estimated that the front line will hit Derby this year and Broome by 2025.

If their expectations come true, Kimberly will soon be fully covered; This leaves groups of important predators in the area, such as freshwater crocodiles, at risk.

Researchers found last year 60 reptiles died in Danggu Gorge National Park (formerly Geikie)However, he expected the actual losses to be much higher.

Freshwater crocodiles can be seen in the hundreds at Bandilngnan (Windjana Gorge). (ABC Kimberly: Taylor Thompson Fuller)

Trial can save fresh food groups

A two-hour drive away in Bandilngnan (Windjana Gorge), scientists use the carcasses of the venomous pest as bait for fresh food, as freshwater crocodiles are known, in an effort to stop the reptile’s death.

The study, conducted by Macquarie University (MQ), Bonoba Rangers and the DBCA, contained cane frogs, washed and injected with nausea-causing chemicals.

Picture of Windjana George with stakes
Two rations of cane carcasses for freshwater crocodiles in Bandilngnan (Windjana Gorge) are ready. (ABC Kimberly: Taylor Thompson Fuller)

The crocodiles had a bout of nausea when the crocodiles took the bait, said Dr. Georgia Ward-Fear, senior researcher in ecology at MQ, and the cane frogs associated the feeling and never ate one again.

“We essentially generated a response to food poisoning in native predators for a taste and smell [cane] Frog said.

A dead cane frog is being washed
Dead frogs are culled, washed and injected with disgusting chemicals before being placed as bait. (ABC Kimberly: Taylor Thompson Fuller)

This so-called “conditioned aversion to taste” approach appears to work on freshwater crocodiles that soon developed an aversion to warty amphibians.

“There is quite a bit of uptake of the grafts when we started the bait trials, and that’s very fast within two days of the grafts coming out and regenerating,” she said.

Cane frog beheaded
Dead frogs are cut off before being washed and injected with a disgusting chemical.(ABC Kimberly: Taylor Thompson Fuller)

The hope was that the method, which had also been used to a similar effect with northern goannas and quolls, would protect the reptiles from the first wave of invading cane frogs.

“With the frogs entering the landscape for the first time, they are considered new prey and the animals have had no interaction with them,” she said.

“So there is no developed resistance to the venom, predators just have to put a cane toad in its mouth for 10 seconds and then die.”

Three people holding guana smiling
Dr. Georgia Ward-Fear used this technique to teach guanas not to eat sugarcane frogs, too. (Supplied: Melissa Broughton)

Dr Ward-Fair said the results of the study were still to be finalized, but initial indications showed that fewer freshwater crocodiles had died where the baits had been deployed.

“There were a lot of deaths before we moved into these areas and started training and we saw a drop in deaths in the areas we treated,” she said.

Croc is getting close to the cane toad bait
Carcasses of chemical injected cane frogs make freshwater crocodiles sick, so never eat one again. (Supplier: Department of Biodiversity, Conservation and Tourist Attractions)

The cane frogs are coming for the derby

DBCA Project Officer Tamichia van der Donk, is part of the five-person field team creating stakes, motion-sensing cameras and performing crocodile counts.

Mish Adjust Motion Sensing Camera
Tamisha van der Donk sets up a motion-sensing camera to detect when freshwater crocodiles are taking bait. (ABC Kimberly: Taylor Thompson Fuller)

Another important part of her job is observing the Reed Toad front line as it advances through the Kimberley, which she said could hit the derby by the end of this year.

“The cane frogs move at a rate of about 50 km per year and are 30 km from Derby so … they will probably be in and around Derby this year,” she said.

Map showing the spread of cane toads in the Kimberley (2022)
Map of 2022 showing the gradual spread of cane toads in Australia. (Supplier: Department of Biodiversity, Conservation and Tourist Attractions)

Residents of the city and its surroundings may hear the approach of the front line, with the appearance of larger frogs heading towards the invasion.

Myles Bruni, a DBCA field officer, said he’s heard it many times before.

It still troubles him to know what kind of devastation cane toads can bring.

DBCA Field Officer Miles Bruni holds a cane toad
DBCA field officer Miles Bruni has heard of a cane frog approaching the front line more than once. (ABC Kimberly: Taylor Thompson Fuller)

“It kind of looks like a thousand high-pitched helicopters arriving on the horizon and they’re very powerful,” he said.

“To see that there’s a wave of one kind running towards you and causing so many deaths on the way…it’s a bit hard to turn around.”

Freshwater crocodile swimming behind a reed toad
A crocodile swims in fresh water, bypassing a bait used to deter it from eating cane frogs. (Supplier: Department of Biodiversity, Conservation and Tourist Attractions)

Mr Bruni said the days of stopping their march are over and “never would have worked,” but new research has given him hope that more species could be protected in the future.

“It’s a lateral thinking game now, we need to come up with really creative solutions, like hate the taste, and be ready by the time they get there,” he said.

Frogs can go on their way

If they do eventually conquer the Kimberley River, Dr Ward-Fair said, the sugarcane toads would ‘challenge’ when crossing the arid Pilbara River landscapes, but they may take advantage of the water sources to continue walking south.

Freshwater crocodile found dead
A number of freshwater crocodiles were found dead in Danngu Geikie Gorge National Park last year. (ABC Kimberley: Hannah Barry)

“There are a lot of agricultural areas and water points that they might be able to tap to move through that area, so don’t say never, they could end up in Perth,” she said.