Although Tiwi people have long held a deep knowledge of the animals of their lands, western scientific knowledge of Tiwi fauna has only been documented since the 1990s.
A total of 222 species of bird have been recorded on the Tiwi Islands. The islands have been identified as an Important Bird Area by BirdLife International because they support relatively high densities of Red Goshawks, Partridge Pigeons and Bush Stone-curlews and up to 40,000 shorebirds on tidal flats, particularly on the south-east of Melville Island. A record number of 12,000 Great Knots, more than one per cent of the global population, have been recorded as well as Red-necked Stints, Greater and Lesser Sand Plovers, and Bar-tailed Godwits. Pirripatiriyi (Seagull Island), off the north-western tip of Melville Island, supports a breeding colony of about 60,000 Crested Tern (Sterna bergii), the largest known colony in the world. Three colonies of Little Terns on the islands are considered of national significance. Thirteen threatened bird species occur on the Tiwi Islands, including the endemic subspecies Tiwi Masked Owl (Tyto novaehollandiae melvillensis), Tiwi Hooded Robin (Melanodryas cucullata melvillensis) and Horsfield’s Bushlark (Mirafra javanica melvillensis).
There are 36 native mammal species on the Tiwi Islands, which is exceptional compared to other Australian islands. The islands have substantial populations of native mammal species that have undergone dramatic recent decline on the Northern Territory mainland. There are seven threatened mammal species, including healthy populations of species such as Brush-tailed Rabbit-rat (Conilurus penicillatus) which have declined close to local extinction on the NT mainland.
The waters around the islands support a number of marine mammal species including dugongs, dolphins and whales.
Feral mammals on the islands include black rats, cats, pigs, water buffalos, horses, and cattle. Water buffalos are common on Melville Island but not on Bathurst Island. 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 is implementing a Buffalo Management Program and continues to work on the eradication of feral pigs.
Tiwi people have strong cultural and subsistence links to sea turtles and the sandy beaches on the west coast of Bathurst Island and the north coast of Melville Island are very important for sea turtle nesting. Nesting is dominated by Flatback (Natator depressus) and Olive Ridley turtles (Lepidochelys olivacea), but Green turtles (Chelonia mydas), and Hawksbill turtles (Eretmochelys imbricate) also nest on Tiwi beaches. Each of these marine turtle species is listed as threatened.
Green turtles are the main turtles harvested in the water while eggs of all sea turtle species are collected. Traditional hunting mainly takes place close to communities, leaving most of the islands free from harvest pressure. The Tiwi Island rookeries at Pirripatiriyi (Seagull Island) and the north-west coast of Melville Island are among the largest in Australia for Olive Ridley turtles. Ensuring turtle populations remain healthy in the long-term is very important to Traditional Owners and since 2003 the Tiwi Land Council has partnered with a range of organisations to study Olive Ridley turtles. This important research, which has been conducted at Imalu Beach at Cape Van Diemen on the north-west coast of Melville Island, has made a significant contribution to knowledge about the ecology of Olive Ridley turtles in Australia.
Sea turtles are expected to be particularly threatened by rapid climate warming and rising sea levels. The Tiwi Land Council is partnering with scientists to investigate the effects of increased temperatures and nest inundation on hatchling sex ratios and turtle hatchling performance. Research will continue to inform future turtle management work undertaken by the Tiwi Land Council.
The Tiwi ant fauna has high national significance, with many species occurring nowhere else in the world. More than 200 species of ants have been recorded to-date on the Tiwi islands and Tiwi rainforests have especially high levels of endemism. The Tiwi ant fauna includes several genera and species-groups that do not occur on the NT mainland. Two dragonfly species are restricted to the Tiwi Islands and a skipper butterfly is only known from Bathurst Island. Other invertebrates, however are not as well known. Four invertebrate species on the Tiwi Islands are listed as threatened in the Northern Territory including two Land snails (Amphidromus cognatus and Trochomorpha melvillensis), Dodd’s Azure Butterfly (Ogyris iphis doddi), and the Atlas Moth (Attacus wardi).
Three of the most serious pest ant species occurring in the Northern Territory are found on the Tiwi Islands, including Tropical fire ants (Solenopsis geminata) Singapore ants (Monomorium destructor) and African big-headed ants (Pheidole megacephala).