Native species need our help!
Who can we help?
Cane toads do not pose a direct threat for most native species. However, for the large frog-eating predators, Cane toads spell disaster. Predator populations decline substantially when toads arrive and they can even become locally extinct. Because these predators are at the top of food webs, their declines throw entire ecosystems into disarray by tripping 'trophic cascades', flow on imbalances in predator/prey dynamics. This two-fold impact (direct and indirect) of Cane toads means that we need to focus on preserving the large species that are hit the hardest. By preserving these species, we can also maintain ecosystem structure and stability.
Below are the main predator species for which we aim to buffer the direct impact of Cane toads:
Yellow-spotted Monitor
(Varanus panoptes)
Yellow-spotted Monitors are the giants of floodplains, forests and savannahs across Northern Australia. They have interesting mating strategies, rapid rates of growth, complex behavioural ecology and a reputation for being smart! They are common, generalist predators attaining high densities where resources are abundant. Because of this, Yellow-spotted Monitors arguably suffer the largest Cane toad impacts by magnitude. Once toads move through an area, populations decline substantially (90% to local extinction); the impact is twofold. By documenting the cascading effects of these declines on lower levels in the food chain, multiple studies have demonstrated that Yellow-spotted Monitors maintain stable ecosystem function when their populations are healthy.
Yellow spotted Monitors are also extremely important to aboriginal cultures in Northern Australia. They are a traditional bush tucker and associated with unique language, hunting practices, ceremony and beliefs. The loss of these animals from the landscape is devastating in this respect.
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Georgia Ward-Fear trialled CTA in the wild with this charismatic species for her PhD with Rick Shine. In the East Kimberley Georgia worked with the Balanggarra people to train wild lizards; when the cane toad invasion passed through all untrained animals had died within three months, whereas more than half of the trained animals were still surviving at the end of the study (3 years). Georgia also discovered that lizards possess individual personalities and this influences how well animals learn.
Northern blue tongue lizard
(Tiliqua scincoides intermedia)
Gondwana Reptile Productions
Species description: Across most of the continent, people recognise Bluetongue lizards as iconic Australians. These skinks are distinctive for their large size, short stumpy legs, and bright blue tongues that they poke out of their mouths as a defensive display. Although currently classified as a subspecies of the wide-ranging Bluetongue lizard of eastern Australia, genetic data conclusively show that the northern Bluetongue is a separate species in its own right. Sadly, that means that an entire species is now at risk of extinction due to the Cane toad invasion.
Northern Bluetongues have very broad diets and are happy to eat plant material as well as small animals. They are very sensitive to the poisons of Cane toads, and die if they eat even a medium-sized toad. Very common across the tropics prior to toad invasion, Northern Bluetongues are now very rare animals behind the toad invasion front.
For her Ph D with Rick Shine, Samantha Price-Rees radio-tracked dozens of Northern Bluetongues in Western Australia, as the toad invasion arrived. Almost all of her lizards were killed as soon as the toads invaded her study sites. They ate the first toad they met, and died of a heart attack. But Sam trained some of her lizards not to eat toads, and those animals survived.
Merten's Water Monitor
(Varanus mertensii)
Australian Reptile Park
Merten's water monitors are conspicuous, amphibious lizards. They live around the edges of waterbodies and are active for most of the year. They are generalist predators feeding on aquatic animals (such as fishes and crabs) as well as terrestrial animals (such as lizards, frogs and beetles).
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Like larger goanna species, these water-loving lizards are badly affected by the Cane toad invasion. We’re not sure why, but the impact of Cane toads has not been quite as awful in some areas for Merten’s Water Monitors as for land-dwelling goannas. Perhaps being in the water enables a goanna to wash the poison out of its mouth after it seizes a toad?
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Freshwater crocodile
(Crocodylus johnstoni)
Australian Reptile Park
Found throughout billabongs, rivers and wetlands of Northern Australia, Freshwater Crocodiles are all adapted to an amphibious life. They can hold their breath underwater for up to an hour and swim rapidly by means of their powerful tails. On land, they move very quickly over short distances and can propel themselves at great speed down sloping river banks into the water. Smaller than the famous Saltwater Crocodile, the “freshie” can grow to more than two metres in length but (almost) never causes problems for people.
However, freshies love to eat frogs, and they readily attack Cane toads when the toxic invaders first arrive. In some areas, that results in massive mortality of crocodiles – up to 90% or so of some size classes. But in other areas, freshies don’t seem to be affected. We still don’t know why those differences occur, but clearly we need to take the problem seriously. We have shown, with laboratory studies, that young freshies are very smart – they can learn to avoid Cane toads after only a single nausea-inducing meal. Our project will give the crocs a chance to learn from their first encounter with a toad, rather than die.
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Northern Quoll
(Dasyurus hallucatus)
Brad Leue photography
Northern Quolls are nocturnal predators of invertebrates, but they also eat small mammals, reptiles, birds, carrion and fruit. Quolls have interesting breeding biology. They become sexually mature at one year of age; during the mating season, males expend considerable energy fighting other males, and do not survive to breed a second year! Females den in tree hollows, logs and rock crevices, raising a litter of up to eight young. At the end of the breeding season, the Northern Quoll population is comprised almost entirely of mature females and their young. Females may live for two or three years.
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These cat-sized, spotted marsupial predators were once abundant in tropical Australia, but their numbers have been declining for decades. The causes probably involve predation by cats, dogs and dingoes, and loss of forested habitat through fire and land-clearing – but the arrival of the Cane toad was the death knell for some populations that had managed to persist through all of the other challenges. Fortunately, we have shown that quolls are quick learners, and that taste-aversion training can enable a quoll to survive even in toad-infested areas. Even better, the offspring of those quolls learn to avoid toads as well.