Saturday, 09 January 2016

Juvenile toad snacks save local goannas

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Contracted researcher Miles Bruny captures a male floodplain monitor lizard to change his radio transmitter. Contracted researcher Miles Bruny captures a male floodplain monitor lizard to change his radio transmitter.
  • Goannas and monitors successfully swore off cane toad meals following taste aversion project
  • Juvenile toads placed ahead of adult colonisers can protect many native Kimberley predators
  • Ranger can impart key knowledge on other ranger groups to test method elsewhere

NATIVE reptiles in the remote East Kimberley have been taught by scientists and Indigenous Rangers to avoid dining on toxic cane toads (Rhinella marina), which would otherwise make for the natural predator’s last meal.

Invasive cane toads continue to spread throughout the Kimberley, poisoning and killing native animals that are large enough to eat them and separate studies have shown they disrupt the natural predator-prey relationship.

In this study large yellow-spotted monitors (Varanus panopte) and sand goannas (Varanus gouldii) were caught by Sydney University PhD candidate Georgia Ward-Fear and Balingarra rangers and then encouraged to eat less toxic, juvenile cane toads.

The young toads made the goannas sick but did not kill them, instilling in the goanna the idea that toads make for a bad snack and that they will avoid eating the more toxic adult toads when they invade the region.

The theory of conditioned taste aversion has been around for quite a long time but it hasn’t been tested in the wild like this, Ms Ward-Fear says.

Trained floodplain monitor lizard sizes up approaching researchers.

 

“We know that many native animals have the ability to learn,” she says.

“By the end of the 18-month study, only one of 31 untrained lizards had survived longer than 110 days, compared to more than half (nine of 16) of trained lizards.

“The maximum known survival of a trained lizard in the presence of toads was 482 days.”

Her work follows an earlier taste-and-scent aversion study in the upper Ord Valley in which quolls were fed cane toad sausages but goannas would not eat the sausages.

Ms Ward-Fear says her study shows juvenile toads released ahead of the first wave of colonisers, which are always large adults, can be used to protect many native predators from poisoning.

Georgia Ward-Fear with juvenile goanna number 57.

 

Juvenile toads are at their least toxic life stage, she says.

“They’ve used up all the toxin that their mothers put into the eggs to grow into tadpoles,” she says.

“They’ve metamorphosed into small frogs and they’re waiting for their own parotid glands to develop so they can start making their own toxins.”

The study’s success means they are one step closer to developing a strategy requiring minimal human input.

Balingarra Rangers coordinator Thomas Grounds says the ranger’s knowledge of the goannas, which are a key part of Aboriginal culture, was vital to the study’s success.

He says they would help train other Indigenous Ranger groups if juvenile toads were released into other parts of the Kimberley.

Notes:

The study took place near Oombulgurri/Forrest River, north of Wyndham in the East Kimberley.

The old scientific name for cane toads was Bufo marinus which appears in some earlier SNWA stories. It has recently been reclassified Rhinella marina.

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