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There are a very few places where natural surface water persists. Using both publicly available maps, and ground-truthing with pastoralists and traditional owners, we are pretty sure we mapped all of these. They have been taken into account.
In the Northern Territory, at the top of the Tanami Desert, trials were run that exclude toads from turkey nest water impoundments. The presence of goanna burrows, fresh cow pats, made little difference. All the toads at these locations perished. More recently, we radio-tracked male toads on Wallal station, just north of the Pilbara. They were very good at finding goanna burrows and shelter, but again, conditions were simply too hot and dry in the late dry season; they all perished.
Undoubtedly. But human assisted dispersal would almost certainly have to be a deliberate act. There are now billions of toads on the continent, and along the eastern seaboard tens of millions of people create huge flows of traffic. Hitch-hiker toads regularly turn up as far afield as Sydney and Perth. Despite this, there have been only three accidental colonisation events recorded ahead of the mainland invasion front. All of these have been at the southern front in New South Wales.
Accidental transportation events typically involve only a single animal, and so cannot establish a population (toads have external fertilisation, so pregnant females cannot produce offspring without a male to fertilise eggs as they are laid). Where transportation involves multiple animals, the natural tendency of toads to segregate by sex means that these multiple animals are very often the same sex. But of course, any containment strategy requires vigilant monitoring and a plan for rapid eradication if a small population is detected. It is also critical that the community is behind this idea.
True, it rains hard in this part of the world. There are very few drainage lines, and those there are, run east to west (perpendicular to the toad invasion) so are unlikely to raft animals across the waterless barrier.
There is some uncertainty around the future of water use in the area of the TCZ. Intensification of cropping in the region could make the TCZ substantially more expensive to implement. We need to work together to manage this intensification for both agriculture and toads.
Cane toads cannot jump higher than about 70cm, so it is possible to design a cattle trough that excludes them. The much bigger risk is leaking pipes. These provide a steady source of water onto the soil, and this is enough to support many hundreds of toads. Tanks and troughs that are not leaking will not support toads.
The waterpoints will be designed to exclude toads but allow cattle and native animals that rely on the water (e.g. wallabies, dingos, and birds) to drink. Most other native species found across the TCZ zone, such as bilbies, goannas, snakes, and desert frogs, are adapted to desert conditions and do not require permanent waterbodies for survival.
This strategy will be important for stopping the invasion front as it first hits the TCZ, and it can be maintained for many years. The TCZ can, however, be made smaller after some time. As time passes, the toad population at the edge of the TCZ will rapidly evolve lower rates of dispersal and will become less likely to disperse into it, making the TCZ more effective.
We acknowledge the Traditional Owners of the lands on which this project is conducted.
These lands always were, and always will be, the lands of Aboriginal and Torres Strait Islander People.
All images provided by Judy Dunlop, Ben Phillips and Tim Dempster.
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