Native Animals
The Territory is rich in wildlife, in part because it spans a substantial environmental range from the deserts to the monsoonal tropics. Documentation of the Territory's biodiversity is relatively recent, although Aboriginal Territorians have long held a profound knowledge of their environments. The bird and mammal fauna is now close to comprehensively described, but new species of fish, frogs, reptiles, invertebrates and plants continue to be discovered. Knowledge of invertebrates is particularly sketchy.
The Territory's vertebrate fauna includes about 400 species of birds, 150 species of mammals, 300 species of reptiles, 50 species of frogs, 60 species of freshwater fish and several hundred species of marine fish. A listing of these species can be viewed at link to lists. In most groups, the richness declines from high rainfall areas in the north to lower rainfall areas in the south. There are relatively few exotic (introduced) species in this fauna, but these do include some serious pest species, such as the cane toad, rock dove (feral pigeon), rabbit, fox, cat, donkey, goat and water buffalo.
Among the birds, there are few endemic (that is, restricted to the Territory) species: the white-throated grass-wren, banded fruit-dove and chestnut-quilled rock-pigeon from the stone country of western Arnhem Land. Threatened birds include the gouldian finch, night parrot, masked owl, and white-throated grass-wren. Birds provide some of the Territory's most notable nature experiences - such as the massive aggregations of magpie geese and other waterfowl in the billabongs and floodplains of the north; flocks of budgerigars, cockatoos and other parrots in central Australia; stately brolgas and jabirus (the Australian crane and stork); and, for the lucky or the dedicated, flocks of the beautiful gouldian finch, or waterholes visited by hundreds of other finches, doves, parrots and honeyeaters. Most Territory cities have extremely rich birdlife, and offer the opportunity to observe much of the Territory's bird life in comfort.
Some of the Territory's birds only spend part of their life in the Territory. The Territory coastlines, swamps and waterbodies support large numbers of many species of waders (shorebirds), most of which breed in the northern hemisphere in their summer. For many of these, the Territory offers a stop-over for a more distant destination in southern Australia. Other Territory birds have less extensive migrations. The koel, dollarbird, rainbow bee-eater, channel-billed cuckoo, and pied imperial-pigeon (or Torres Strait pigeon) make annual migrations to Indonesia and other parts of south-eastern Australia, although bothe the rainbow bee-eater and pied imperial-pigeons also include some year-round residents, with this proportion apparently growing for the latter, possibly bacuse of the increases in dry season food availability due to rnamental plantings around Darwin.
The mammals include a higher number of endemic species, such as the Arnhem rock-rat, black wallaroo, central rock-rat, carpentarian rock-rat, kakadu dunnart, central pebble-mound mouse and kakadu pebble-mound mouse, as well as the bats Taphozous kapalgensis and Hipposideros diadema inornatus. As their names imply, many of these are restricted to the western Arnhem Land plateau, including parts of Kakadu National Park. The tally of mammals includes about 35 bat species and about 25 marine mammals. Among the latter, the dugong and Irawaddy dolphin are locally abundant. A high proportion of the Territory's threatened species are mammals, and, sadly, many Territory mammal species have become extinct (entirely, or within the Territory) over the last 100 years. These include the western quoll Dasyurus geoffroii, numbat Myrmecobius fasciatus, desert bandicoot Perameles eremiana, pig-footed bandicoot Chaeropus ecaudatus, lesser bilby Macrotis leucura, brush-tailed bettong Bettongia penicillata, burrowing bettong B. lesueur, central hare-wallaby Lagorchestes asomatus, crescent nailtail wallaby Onychogalea lunata, and lesser stick-nest rat Leporillus apicalis. Threatened mammal species that exist still in the Territory include the golden bandicoot, marsupial mole, bilby, mulgara and butler's dunnart. Much of the Territory's mammal fauna is nocturnal and/or inconspicuous. The red kangaroo in central Australia and the agile wallaby in the north are notable exceptions, generally being common and readily observed. Much of the rest may be seen only with careful study: but, especially in the north, bandicoots, quolls (native cats) and some other species may come and feed among campers in the bush at night.
Lizards, particularly skinks (with more than 100 species), dominate the reptile fauna, but there are many other notable features. Five species of marine turtle (the green, flatback, olive (or pacific) ridley, hawksbill, and loggerhead) are common, and the leatherback turtle occurs occasionally. Territory beaches are very significant breeding sites for the pacific ridley, flatback, hawksbill and green turtles. There is also a diverse freshwater tortoise fauna, with between 5 and 10 species. The saltwater (estuarine) and freshwater crocodiles are a feature of the north of the Territory. Other notable reptiles include the goannas (especially the huge perentie of central Australia), the frilled lizard (in woodlands of the north), and the thorny devil (in central Australia). Snakes are also common and diverse, with about 90 species (including 20 sea-snakes) recorded from the Territory. These include the endemic Oenpelli python, an extremely large snake restricted to the western Arnhem Land massif; the water python (which can be seen commonly at night at Fogg Dam); the closely-related black-headed python and woma, beautifully marked snakes that prey largely on other snakes; and some highly dangerous snakes such as the king brown, western brown, taipan (which is relatively rare in the Territory) and death adder.
The most notable of the Territory's frogs include the green tree frog, which is a common and generally much-loved inhabitant of many Territory houses, the related but far more spectacular magnificent tree-frog (restricted in the Territory to the Gregory and Keep River areas), and a host of burrowing frogs, many of which appear in central Australia only after heavy rainfalls.
The Territory's insect fauna is poorly known. However there is an extraordinary abundance and diversity in some forms. For example, more than 100 ant species may be found within any hectare of the eucalypt forests of northern Australia.
Some parts of the Territory are particularly important for wildlife in that they harbour unusual richness of species, or particular concentrations of endemic or threatened species. The most important area is the sandstone massif (the "stone country") of western Arnhem Land, which is home to far more endemic and threatened plants and animals than anywhere else in the Territory. This is largely because it is extremely dissected (with numerous deep gorges, caves, sheer escarpments and rugged boulder-strewn slopes), which provides some protection from predators, hostile fire regimes and climatic change). Hence, the area now supports many relict species, either entirely restricted to this area, or with highly disjunct distributions: many of these relict species are hangovers from periods of far warmer or wetter climates. Some of the ranges in central Australia also support large numbers of restricted and endemic species: Palm Valley is one such place. Other parts of the Territory are important because they support exceptional abundances of wildlife. The most obvious of these are the lowlands and floodplains of northern Australia, which support massive aggregations of waterfowl, dense populations of fish and crocodiles, and many other species. One example is Fogg Dam, where the population of water pythons is considered to represent the greatest biomass density for any terrestrial predator system in the world, and the abundance of their main prey item, the dusky rat 15,000 individuals (about 1 tonne) per km2. Massive aggregations of wildlife may be a more transient feature elsewhere in the Territory - for example the long-haired rat undergoes irruptions ("plagues") from the mitchell grasslands and chenopod shrublands of the Barkly Tablelands at about 10-20 year intervals, then supporting similar irruptions of its main predators, the letter-winged kite and barn owl. The flock bronzewing is another mitchell grassland species that may occasionally occur in very large numbers - early explorers described vast flocks of this pigeon darkening the sky for hours as they passed overhead.