Mammals introduced to the Tiwi Islands include Black rats, Water buffalo, cattle, pigs, horses, and cats. Reptiles include the Asian house gecko (Hemidactylus frenatus) and the Flowerpot blind snake (Indotyphlops braminus). Six species of pest ants have been recorded.
Feral water buffalo and pigs
Water buffalo were introduced by the British from Timor to Melville Island in 1826 for milk, meat and heavy labour, while pigs were introduced to Bathurst Island for meat in the early 1900s. Buffalo and pigs remain an important food resource for Tiwi people, and buffalo are also valued for their contribution to tourism through trophy hunting and their disease-free status.
However, large, uncontrolled numbers of buffalo have the potential to cause environmental degradation and there is evidence of significant damage to wetlands in remote areas of Melville Island. In 2010, the Tiwi Land Council implemented a Buffalo Management Program to estimate the number and location of animals, and identify areas particularly vulnerable to buffalo impacts. A targeted culling operation was undertaken over a period of seven helicopter aerial shoots in environmentally sensitive areas across Melville Island, with the Tiwi Rangers reducing the total estimated number of buffalo from 6,800 to 5,363.
The rooting and digging behaviour of feral pigs ploughs up vegetation in wetlands and along watercourses, and destroys native ecosystems. They compete with native animals for food, and can spread weed seeds and diseases. Feral pigs have done considerable damage on Bathurst Island, where their numbers are greatest, and a small population has established on Melville Island. The Tiwi Land Council continues to work on the eradication of feral pigs on Melville Island and has banned domestic pigs from communities on Melville Island.
Introduced pest ants are some of the greatest environmental and economic threats to northern Australia. Three of the most serious pest ant species occurring in the Northern Territory are on the Tiwi Islands, including Tropical fire ants (Solenopsis geminata), Singapore ants (Monomorium destructor) and African big-headed ants (Pheidole megacephala). The ants most likely arrived on the Tiwi Islands in barge cargo from Darwin.
The Tiwi Tropical Fire Ant Project, a collaboration between the Tiwi Land Council, CSIRO and the Tiwi Plantations Corporation, has achieved some of the world’s largest pest ant eradications. Two of the three areas where Tropical fire ants have been eradicated on Melville Island are the second and fourth largest ant eradications ever achieved. In 2015, the project won the Biodiversity category of the United Nations Association of Australia World Environment Day Awards. It was also a finalist in the Indigenous Leadership Category of the 2015 Banksia Sustainability Award.
Although there has been considerable success in eradicating Tropical fire ants on the Tiwi Islands, two infestations persist on Melville Island. Singapore ants are present in the main communities while African big-headed ants have been eradicated from both islands. Management of pest ants is an ongoing consideration for the Tiwi Land Council. Greater awareness of the importance of quarantine on the Tiwi Islands aims to reduce new introductions of pest ants, and visitors are asked to help Tiwi people fight pest ant infestations by carefully checking luggage, vehicles and freight.
The Tiwi Islands are special because they are one of the last refuges for small mammals that are regionally extinct in many parts of mainland Australia, but research has shown that some of these mammals may be in decline.
Tiwi landowners are very concerned about the destructive impacts feral cats may be having on their animals, and for many years the Tiwi Land Council has been proactive in promoting a cat-free Tiwi Islands. The Tiwi Land Council has been working with Animal Management in Rural and Remote Indigenous Communities, the University of New England and The Ark Animal Hospital, with support from the Australian Government’s Threatened Species Commissioner, to deliver a community education and cat desexing program. In contrast to many other Aboriginal communities, Tiwi people generally do not keep cats as pets, and there is overwhelming community support for feral cat control. Permission must be sought from the Tiwi Land Council to transport cats to the islands, and only desexed animals will be considered for approval. Research on the impacts of feral cats on small mammals has been conducted on Bathurst and Melville Islands.