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