Australian Native Animals and the Destructive Cane Toad
Establishing 'safe havens' for our native animals
Introduced pests have been responsible for the disappearance of some of Australia's unique mammals and have brought many to the brink of extinction. Efforts to curb the devastation have had random results and limited success. Now, in Western Australia, a new idea is taking shape as the biggest threat ever to our native wildlife makes its insidious way down the west coast from the northern parts of the state.
The new threat comes in the shape of a large, terrestrial toad which averages 10 to 15cm in length The largest recorded specimen measured 38cm in length and weighed 2.65kg. That is one big toad! The toad has poison glands and even the tadpoles can be highly toxic if eaten by animals.
The cane toad (Bufo marinus) was introduced in 1935 by the Bureau of Sugar Experiment Stations in an attempt to control the native cane beetle (Dermolepida albohirtum). It multiplied rapidly and was soon migrating well beyond its intended area, playing havoc with the local biodiversity. By 1978 the cane toad had reached the New South Wales border and by 1984 it was into the Northern Territory. Not content with migrating across the north, the toads on the western fringes of its range have developed larger legs and a larger body, enabling it to travel even more efficiently. Migration is estimated to be 25 miles (40kms) per annum.
It has found its way across the top end of the continent and is now in Western Australia and working its way south. The cane toad is highly poisonous when eaten by carnivorous animals such as freshwater crocodiles, quolls, goannas and snakes. It is having an greater negative impact on Australia's native fauna than did the introduction of the fox and rabbit so many years ago.
Until settlement by Europeans, Australia had a complex interdependent ecology. Hence, when new species were introduced there were often no natural predators.
The first cane toad to enter Western Australia was discovered in February 2009. Since then a bumper wet season has seen them poised to enter the World Heritage-listed Purnululu National Park. They are already in residence 110km south of Kununurra at the Argyle diamond mine and are all set to invade El Questro Wilderness Park.
Scientists concede it is a losing battle trying to stop the advance of these odious creatures but the Department of Environment and Conservation (DEC) has taken a lateral approach and is now looking at establishing colonies of endangered species on the various islands that dot our western coastline.
Once established, these modern day Noah's Arks will be home to dozens of species at risk with the advance of the cane toad. A four-year survey of the largest Kimberley islands will cost $7 million and will determine which of the islands are most suitable for threatened species such as the northern quoll. The islands range from an unnamed 620 hectare island to the 19,000 hectare Augustus Island. Twenty-two islands are being investigated stretching from Derby to Kalumburu. These islands have not been subjected to population by introduced species such as the fox, rabbit, and goat. There are also no feral cats or wild dogs.
The Kimberley Land Council, WA Museum and Australian Museum are assisting with the survey, which has already uncovered a treasure trove of species on the islands. The presence of these native animals was hitherto unknown to the scientists. The red-cheeked dunnart, western chestnut mouse and agile wallaby are some of these species. Northern quolls, on the brink of extinction in the east Kimberley, were found on Adolphos Island in the mouth of the Ord River. The golden bandicoot is found on Augustus, Barrow and Middle Islands.
Although there have been no known mammal extinctions in the Kimberleys to date, the arrival of the cane toad has everyone holding their breath. The DEC has already 'translocated' threatened species from the mainland to islands in Shark Bay and the Exmouth Gulf.
The largest population of golden bandicoots is found on Barrow Island which is located north of Onslow and to the west of Karratha. Population numbers are believed to be between 90,000 and 130,000. Because of the absence of cats and foxes the only predators are birds. Barrow Island became a nature reserve in 1910. The island is also home to Australia's largest onshore oilfield. Due to stringent environmental policies, mining coexists with the native wildlife and golden bandicoots have found the mining camps an easy source of food.
As well as the golden bandicoot, Barrow Island is home to boodies, bandicoots, brushtail possums and spectacled hare-wallabies.
The northern quoll (Dasyurus hallucatus) (above) was once widespread across northern Australia. It measures between 12 and 45cm in length and the tail is a similar length. It is the smallest of the quolls weighing between 0.4 and 1.2kg for males. The pelage is brown or grey-brown with large white spots. Males often die after mating, especially if they inhabit flat, open grassland. The average litter size is six. These are born between June and September and carried for around two months before being weaned at about five months. Quolls regard the cane toad as an ideal size snack but the poisonous glands of the toad make the meal a fatal one.
The red-cheeked dunnart (Sminthopsis virginiae) has distinctive red hair on the cheek hence the name. It is 16 to 27cm in length, of which 8 to 13.5cm is the body with the rest being the tail. It has large ears and a thin, pale pink tail. The breeding season is from October to March with litters following each other in quick succession.
The western chestnut mouse (Pseudomys nanus) is a rodent from the Muridae family. It is only found in Australia and is listed as 'near threatened' on the IUCN Red List of threatened species.
The agile wallaby (above) is a mid-sized species of the marsupial family. Males weigh in the vicinity of 27kg and females are lighter and around 15kg. They are also known as the sandy wallaby because of the sandy brown colouring of the back. This can appear red in some localities. The underside is much lighter. The agile wallaby is distinctive because of the dark stripe down the midline of the head from ears to eyes. They also have a light coloured cheek stripe and a light stripe on the thighs. The edges of the ears and the tip of the tail are black. While the agile wallaby is not directly threatened by the cane toad, its habitat is fast disappearing and establishing breeding colonies on safe islands is a great way to guard against its extinction.
As soon as there is evidence that the native animal population is being affected by the advance of the cane toads, it is envisaged that mass relocations will take place.