Love them or Hate them , Cane Toads are Here to Stay ( continued )
ARTICLES
Love them or Hate them , Cane Toads are Here to Stay ( continued )
Toads spread westwards across northern Australia reaching the Northern Territory in 1985 . The toad front now moves at about 40 to 60 km per year , and our radio-tracking shows that this is because individual toads at the front travel long distances ( sometimes more than a kilometre ) each night – and do so every night . This is an incredible rate for an amphibian : cane toads at the Aussie invasion front travel much much faster and further than any other frogs or toads that have been studied elsewhere in the world . By 2008 , they had reached the Western Australian border . They have now reached the Kimberleys .
Toads also moved south into New South Wales . The rate of spread was much slower than that recorded in northern Australia . Toads were first recorded in northern NSW in 1968 , near Byron Bay . From there they spread north and south , the northern group quickly linking up with the main Queensland invasion front . The southern group spread slowly southwards .
Why are the toads moving faster and faster ? It ’ s probably a direct result of the pressures that flow from being an invader . For every generation , there is a continuing “ selection pressure ” – each cane toad that reached the leading edge of the invasion front got the most food . There was great selection pressure for the fastestmoving animals . Over successive generations , the only animals at the invasion front were the fastest-moving offspring of those fastest-moving toads . The cumulative result of this selection was that the toads at the front are the ones who have evolved to be quicker and quicker . The result of this process is that the toads are moving faster – from 10 km per year in the early years , through to 50 km or more per year today .
One of the most amazing recent developments in the cane toad invasion is their spread into the very dry parts of western Queensland . Toads are now firmly established around the Longreach area , and one population ( deliberately introduced – some people never learn !) is all the way into the desert around Windorah . The toads are also moving into desert regions along the Victoria River in the Northern Territory . There is clear evidence that cane toads are rapidly adapting to harsh Australian conditions .
Cane Toad Stowaways
Cane toad populations sometimes appear is isolated locations . These populations are not founded by super-fast toads ; rather , they are founded by stowaway toads . Toads often find themselves being accidentally transported across the country in the back of trucks or on trains , in containers of produce or building materials , in bundles of pipes or satchels of woodchips . Stowaways are reaching new and unprecedented parts of Australia .
Several attributes of toad behaviour make them good at hitchhiking . First , cane toads are most abundant in places where people live – they are basically a “ weed ” species . Even in their native range in South and Central America , there ’ s no point looking for cane toads in the thick forest – they are mostly in cleared areas around farms and near towns . Living close to people makes it more likely that toads will end up inside vehicles .
Second , toads love to squeeze into tight hidey-holes , and so will often end up inside material and equipment that is about to be transported . Some situations make this particularly likely . For example , many landscape suppliers keep piles of woodchip and similar material in large open bins . Toads are attracted to such places to hide out during the daytime , and thus picked up with a load of woodchip when the truck is loaded . A few days later , when the woodchip is dumped out , the stowaway toad has a new home .
Third , cane toads are tough ! Adult toads are so large that they can tolerate fairly extreme conditions during transport – including a wide range of temperatures and moisture levels . So they are likely to arrive alive , after trips that would kill many other types of animals .
The Frog and Tadpole Study Group of New South Wales ( FATS ) has been gathering information about the transport of toads into Greater Sydney for more than 20 years . Toads most often arrive from southern Queensland in consignments of landscaping supplies , such as composts , mulches and garden soils . It was often thought that toads would not survive the cold winters of Sydney , and that they would not breed here . Unfortunately , toads are very adaptable , and breeding populations have been found in Sydney . In 2010 , a colony of toads was found in Taren Pont , to the south of Botany Bay . It became clear that the toads had been present at the site for several years before they were discovered , and several generations of toads were present . FATS and Sutherland Shire Council then undertook a six-year toad extermination campaign that ultimately succeeded in getting rid of the toads . But don ’ t be fooled . Toads still come into Sydney ( and elsewhere ) as stowaways on a regular basis . Without constant vigilance , they could become as common in Sydney as they are in parts of Queensland .
The Taren Point outbreak provided a great opportunity to trial new methods of dealing with toads . Toad-trained sniffer dogs were initially used to locate toads in thick bush or difficult places . Dogs such as these had been used with great success in the first eradication of toads ever conducted , at Port Macquarie , in 1998 . The Shine Lab at Sydney University also came up with new tools to combat toads . Radio-transmitters were attached to gravid ( egg-bound ) female toads and they were tracked to find the egglaying sites that were being used by the toads . Toad tadpole baits were developed ; these baits will attract only toad tadpoles and so confined waterways can be cleared of toads even after breeding has occurred .
30 SCIENCE EDUCATIONAL NEWS VOL 67 NO 2