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 )
Native Animal Responses to Toads
As the highly toxic toads disperse across northern Australia , many native animals perish . Predators of frogs such as certain birds , quolls , goannas and most snakes , are often eliminated from an area after the arrival of toads . Even crocodiles are not immune to their toxins . Many parts of Queensland and the Northern territory have suffered local extinctions of species at the hands of toads . older crocodiles have become older because they have had a non-lethal encounter with toads and have remembered the experience .
Toads have been present in Queensland for almost 80 years and in that time some native animals have learned that toads are deadly and should be treated with care . Crows and currawongs have learnt how to eat toads by avoiding the most toxic parts and pecking out the belly parts of the toad ( Figure 4 ). Other species have simply learned to avoid toads and not to eat them at all .
Figure 5 Young crocodiles still fall victim to the toads
Birds may be more tolerant to toad toxins than reptiles and marsupials . It has been suggested that this tolerance may be due to historic genetic exchange between Australian and Asian birds that have co-evolved with toads .
The Future
Figure 4 Torresian Crow preying on a Cane Toad . Rhinella marina , Lake Kurwongbah Qld . S . Wilson
The problem with developing a learned response to toads is that you have to survive your first ( and perhaps second ) encounter with toads . If you die as a result of the encounter , nothing is learned . However , if you survive ( perhaps feeling sick in the tummy ), you may be able to associate the sick feeling with toads and so learn to avoid them . If you are a species that has high parental care , you may be able to teach your offspring to avoid toads also .
But what if you don ’ t have parental care of the young – how does the next generation learn of the dangers of eating toads ? Consider freshwater crocodiles ; they will eat a range of aquatic animals , including frogs . They also lay large eggs that are incubated in a nest that is guarded by the female crocodile . But the female does not teach the young about who or what to hunt . For a young crocodile it is trial and error . The result is that in areas where toads are present there is a high death rate of young crocodiles ,
Toads are a highly adaptable species and they are here to stay . How our fauna ultimately respond to the presence of toads in unclear – some species will be lost , others will become more uncommon , others will be able to adapt and perhaps recover to former numbers . At present we seemed to have halted the spread of toads along the New South Wales coast through community vigilance and quick responses to the appearance of toads in a new area . Toads may still be able to spread southwards along the Darling River to Victoria . As there are fewer people and towns along the way , toads could easily go undetected and reach plague proportions .
In Western Australia , toads are currently raiding the Kimberleys . The invasion front will soon turn southwards where it will confront a dry barrier of about 100 kilometres before it can enter the Pilbarra ( where toads will be able to survive and spread out ). The WA government is considering a program of removing all dams and waterpoints in this 100 kilometre zone in an attempt to halt toads and keep the Pilbarra free of toads . Even if this tactic is adopted , stowaway toads are an ever-present threat to any area , and so surveys and checks will still be required to limit the spread of toads .
31 SCIENCE EDUCATIONAL NEWS VOL 67 NO 2