Christmas Island is an Australian external territory comprising the island of the same name. It is located in the Indian Ocean, around 350 kilometres south of Java and Sumatra and around 1,550 km north-west of the closest point on the Australian mainland. It lies 2,600 km northwest of Perth and 1,327 km south of Singapore. It has an area of 135 square kilometres,
Two species of native rats, the Maclear's and bulldog rats, have become extinct since the island was settled, while the Javan rusa deer has been introduced. The endemic Christmas Island shrew has not been seen since the mid-1980s and may be already extinct, while the Christmas Island pipistrelle is presumed to be extinct.
The fruit bat species Pteropus natalis is only found on Christmas Island; its epithet natalis is a reference to that name. The species is probably the last native mammal, and an important pollinator and rainforest seed-disperser; the population is also in decline and under increasing pressure from land clearing and introduced pest species. The flying fox's low rate of reproduction and high infant mortality rate makes it especially vulnerable and the conservation status is as critically endangered. Flying foxes are an 'umbrella' species helping forests regenerate and other species survive in stressed environments.
The land crabs and seabirds are the most noticeable fauna on the island. Christmas Island has been identified by BirdLife International as both an Endemic Bird Area and an Important Bird Area because it supports five endemic species and five subspecies as well as over one per cent of the world populations of five other seabirds.
Twenty terrestrial and intertidal species of crab have been described here, of which thirteen are regarded as true land crabs, being dependent on the ocean only for larval development. Robber crabs, known elsewhere as coconut crabs, also exist in large numbers on the island. The annual red crab mass migration to the sea to spawn has been called one of the wonders of the natural world. This takes place each year around November – after the start of the wet season and in synchronisation with the cycle of the moon. Once at the ocean, the mothers release the embryos where they can survive and grow until they are able to live on land.
The island is a focal point for seabirds of various species. Eight species or subspecies of seabirds nest on it. The most numerous is the red-footed booby, which nests in colonies, using trees on many parts of the shore terrace. The widespread brown booby nests on the ground near the edge of the seacliff and inland cliffs. Abbott's booby nests on tall emergent trees of the western, northern and southern plateau rainforest, the only remaining nesting habitat for this bird in the world.
Another endangered and endemic bird, the Christmas frigatebird, has nesting areas on the northeastern shore terraces. The more widespread great frigatebirds nest in semi-deciduous trees on the shore terrace, with the greatest concentrations being in the North West and South Point areas. The common noddy and two species of bosun or tropicbirds also nest on the island, including the golden bosun, a subspecies of the white-tailed tropicbird that is endemic to the island.
Of the ten native land birds and shorebirds, seven are endemic species or subspecies. This includes the Christmas thrush and the Christmas imperial pigeon. Some 86 migrant bird species have been recorded as visitors to the island.
Six species of butterfly are known to occur on Christmas Island. These are the Christmas swallowtail, striped albatross, Christmas emperor, king cerulean, lesser grass-blue, and Papuan grass-yellow,
Insect species include the yellow crazy ant, introduced to the island and since subjected to attempts to destroy the supercolonies that emerged with aerial spraying of the insecticide Fipronil.