Feral Mammals
Water Buffalo (Jarranga / Jarrangini)
Water buffalo (Bubalis bubalis) were introduced by the British to Melville Island from Timor in 1826 for milk, meat, and heavy labour. Although less than 20 animals were introduced, when the Fort Dundas settlement was abandoned they quickly became feral, colonising permanent and semi-permanent swamps, and freshwater springs. Large, uncontrolled herds of feral buffalo have been an environmental disaster for the Tiwi Islands. They trample country, kill plants and leave bare soil resulting in erosion. Their soil disturbance also promotes the spread of invasive weeds such as Mimosa (Mimosa pigra) across floodplains.
Buffalo destroy saltwater crocodile nesting habitat, and eat large volumes of grasses and other plants, removing food sources for native wildlife. On floodplains, buffalo make wallows and trails called swim channels, allowing saltwater to flow into freshwater areas. As a result, large expanses of paperbark forest are killed, and habitat is lost for fish, freshwater turtles and waterbirds. Saltwater intrusion impacts caused by buffalo will be exacerbated by rising sea levels due to climate change.
Buffalo can carry serious diseases of cattle including Lumpy Skin Disease (LSD) and Foot-and-Mouth Disease (FMD) as well as bovine tuberculosis and bovine brucellosis.
Buffalo contribute to climate change through the production of large amounts of methane (CH4), a potent greenhouse gas, as a byproduct of digestion. An individual buffalo belches an average of 76 kilograms of methane each year, which is the equivalent of 2.1 tonnes of CO₂. Over a 25-year lifespan, this equates to the equivalent of more than 50 tonnes of carbon dioxide (CO₂). Buffalo also facilitate the loss of carbon in wetland and floodplain ecosystems through soil damage, erosion, and the removal of vegetation.
Pigs (Rawaturrunga / Pikipiki)
Pigs were introduced by missionaries to Bathurst Island in the early 1900s and have since spread across Bathurst and to western Melville Island. They are responsible for the destruction of habitat, predation of native species, weed dispersal, land degradation, and have detrimental impacts on wetlands, waterways, and water quality. Pigs are major predators of eggs and hatchlings from sea turtle nests and deplete traditional food sources by digging up tubers and destroying vegetation. They are also a serious pest in communities.
Feral pigs pose a significant biosecurity risk – they can host African Swine Fever and Foot-And-Mouth Disease, both of which are present in Indonesia. They are also amplifying hosts of Japanese encephalitis virus (JEV), which is spread to humans by infected mosquitoes. In 2021, a Tiwi Islander was killed by JEV, the first locally acquired human case in Australia since 1998.
Cats (Pujikatuwi)
Feral cats are a serious threat to the conservation of biodiversity on the Tiwi Islands. They prey on a wide range of animals, including invertebrates, frogs, reptiles, birds, and mammals and have been primary contributors to mammal extinctions on the Australian mainland. They are well established on both islands but are in larger numbers on Melville, where frequent fire and feral animal (buffalo and horses) grazing impacts tend to favour them.
Feral cats are the same species as domestic cats and can carry infectious diseases which can be transmitted to native animals, domestic livestock, and humans. Tiwi people generally do not keep cats as pets, and there is overwhelming community support for feral cat control.
Horses (Partirrapartirra / Pika)
Horses were introduced to Melville Island by buffalo hunters in the late 1800s. They became feral when settlements were abandoned and are now commonly seen in the western part of Melville Island, particularly around old forestry plantations and along roadsides.
Feral horses cause damage to natural habitats by trampling vegetation and compacting soils leading to increased erosion. They frequently access water sources, fouling the water, crushing riparian plants and damaging banks. Feral horses contribute to the spread of weeds by carrying seeds in their dung, manes, and tails.