Indonesia's wildlife falls into three groups divided by a line in the sea. West of the Wallace Line, Sumatra, Java and Kalimantan hold Asian animals: three species of orangutan, the Sumatran tiger, the Javan and Sumatran rhinoceroses and Asian elephants. In the middle, the islands of Wallacea, from Sulawesi to Flores, have animals found nowhere else, including the Komodo dragon, the dwarf buffalo called the anoa and the maleo. East of them, Indonesian New Guinea has Australian-type wildlife such as tree-kangaroos, echidnas and birds-of-paradise. The country records 1,809 bird species, 786 of them found only in Indonesia, and its seas sit at the centre of the Coral Triangle, the world's richest reef region.
The Wallace Line: 35 km of Water Between Bali and Lombok
The British naturalist Alfred Russel Wallace drew his boundary in 1859, after years of collecting across the archipelago, and the English biologist Thomas Henry Huxley later gave it Wallace's name. It runs north through the Lombok Strait between Bali and Lombok, then through the Makassar Strait between Kalimantan and Sulawesi. At Lombok the gap is only about 35 km, yet the birds and mammals on either side belong to different worlds.
The explanation lies under the water. Sumatra, Java, Bali and Borneo sit on the Sunda Shelf, a shallow extension of mainland Asia. During the Pleistocene ice ages, when sea levels were up to 120 m lower, that shelf was dry land, and tigers, rhinos and apes walked onto what are now islands. New Guinea and the Aru Islands sit on the Sahul Shelf, which joined them to Australia in the same way. Between the two shelves lies a belt of deep straits that never dried out, so only animals able to cross open water by swimming, flying or rafting could reach the islands there. Naturalists later added two more boundaries: Lydekker's Line, along the edge of the Sahul Shelf, and Weber's Line, where Asian and Australian species are roughly balanced.
Sundaland: Orangutans, Tigers and Rhinos West of the Line
The western islands, known together as Sundaland, hold 381 mammal species, 173 of them endemic to the region, along with about 449 species of reptile and around 1,000 freshwater fish. The animals most closely tied to Indonesia here are its great apes. The Sumatran orangutan survives only in the far north of Sumatra, mostly in Aceh and in Gunung Leuser National Park; a survey published in 2016 estimated 14,613 in the wild, double earlier counts, though the species is still listed as Critically Endangered. In 2017 scientists described a third species, the Tapanuli orangutan, from the Batang Toru forests of South Tapanuli. About 800 survive in roughly 1,000 km², which makes it the rarest of the three orangutans. The Bornean orangutan of Kalimantan, the largest of the three, is also Critically Endangered, mainly because of logging, oil-palm plantations and hunting.
Sumatra is also the last stronghold of the Sunda tiger. Java and Bali once had tigers of their own, but both populations were wiped out between the 1950s and the 1970s. The Sumatran population was estimated at 618 ± 290 animals in 2017, scattered through 27 forest patches from the lowlands of Bukit Barisan Selatan National Park in Lampung to 3,200 m in Gunung Leuser. The tiger as a species is listed as Endangered by the IUCN, and between January 2020 and June 2025 Indonesian authorities seized 127 tigers in 77 cases.
Indonesia's two rhinoceroses are even rarer. The Javan rhinoceros, Critically Endangered, now survives as one wild population of about 74 animals in Ujung Kulon National Park, a UNESCO World Heritage Site at the western tip of Java. The hairy, two-horned Sumatran rhinoceros, the smallest living rhino, has fewer than 80 mature individuals in a handful of populations in Sumatra and Indonesian Borneo. It died out in Malaysia in 2019, and a tiny group was found in East Kalimantan in 2016.
Wallacea: Komodo Dragons, Anoa and the Maleo
Wallacea covers roughly 340,000 km² of land spread over Sulawesi, the Lesser Sunda Islands such as Lombok, Sumbawa, Flores and Timor, and the islands of Maluku. Because big land mammals rarely crossed the straits, the animals that did arrive evolved in isolation. The region has 223 native mammals, but 124 of them are bats, which could fly in; 126 of the mammals are endemic. It also has 222 reptile species, 99 of them endemic, and about 310 freshwater fish, 75 of them endemic, including 53 of the 69 species known from Sulawesi.
The best-known of these island animals is the Komodo dragon, the largest living lizard, with males reaching about 3 m. It lives only on Komodo, Rinca, Flores, Gili Dasami and Gili Motang in the Lesser Sundas. Western scientists first recorded it in 1910, and the American W. Douglas Burden coined the name "Komodo dragon" after his 1926 expedition. Genetic studies show its closest living relative is the lace monitor of Australia, a reminder that Wallacea's reptiles came from both sides. Komodo National Park was created in 1980 to protect it, covers 1,733 km² of which 603 km² is land, and became a UNESCO World Heritage Site in 1991. The wild population was assessed at 3,014 in 2015. The species is listed as Endangered: dragons have already disappeared from Padar, where the last were seen in 1975, and rising seas threaten the low valleys they depend on.
Sulawesi, the largest island in Wallacea, has its own oddities. The two species of anoa, the lowland and mountain anoa, look like miniature water buffalo, weigh up to about 300 kg and 150 kg respectively, and have been classed as endangered since the 1960s; there are probably fewer than 5,000 of each. Babirusas, the "deer-pigs" of Sulawesi, Togian, Sula and Buru, grow upper tusks that pierce the snout and curl back towards the forehead, and every species is listed as threatened. Four Indonesian primates, among them the Siau Island tarsier from the small volcanic island of Siau, have appeared on the list of the world's 25 most endangered primates.
The maleo, a megapode 55 to 60 cm long with a bony black casque, lives only on Sulawesi and nearby Buton. It does not sit on its eggs. Instead, the female buries each egg, about five times the size of a hen's, in sand warmed by the sun or by volcanic heat, and the chicks dig themselves out able to fly. That habit makes the eggs easy to dig up, and only 4 of the 142 known nesting grounds are now considered safe. The maleo has been protected by Indonesian law since 1972, but with an estimated 4,000 to 7,000 breeding pairs in 2005 it is listed as Critically Endangered.
Papua: Tree-Kangaroos, Echidnas and Birds-of-Paradise
Indonesia's provinces on New Guinea belong to the Australian side of the divide, and their mammals include marsupials and egg-laying monotremes rather than apes, tigers or rhinos. Two of the world's long-beaked echidnas, the western long-beaked echidna and Sir David's long-beaked echidna, are found there, and both are listed as Critically Endangered. Tree-kangaroos, kangaroos adapted to climbing, have one of their strangest members in the dingiso, a black-and-white species found only in the Sudirman Range at 3,250 to 4,200 m, which unlike its relatives spends little time in the trees. The Moni people regard it as an ancestral spirit, and the zoologist Tim Flannery gave it the species name mbaiso, "the forbidden animal" in Moni. It was filmed for the first time in 2009 and is listed as Endangered.
The birds-of-paradise are the region's showpiece. The family has 44 species, most of them in New Guinea, and the males carry long plumes and perform elaborate displays. Wilson's bird-of-paradise lives only on Waigeo and Batanta, two islands of Raja Ampat off the Bird's Head Peninsula; the German zoologist Heinrich Agathon Bernstein found its home grounds in 1863, and it is rated Near Threatened. On Halmahera and Bacan in North Maluku, west of the Lydekker Line, the standardwing bird-of-paradise, the westernmost of the true birds-of-paradise, carries long white plumes from the bend of each wing; Wallace himself was the first European to describe it, in 1858. Much of this mountain wildlife is protected in Lorentz National Park, which covers 25,056 km² from mangrove coasts to the glaciers near Puncak Jaya at 4,884 m. It is the largest national park in Southeast Asia and has been a World Heritage Site since 1999.
Raja Ampat and the Coral Triangle
Indonesia's richest wildlife may be underwater. The Coral Triangle, which spans the seas of Indonesia, Malaysia, the Philippines, Timor-Leste, Papua New Guinea and the Solomon Islands, covers about 5.7 million km² of ocean. It holds more than 76% of the world's shallow-water reef-building coral species, 37% of its reef fish species and six of the seven species of sea turtle. Its centre of coral diversity is the Bird's Head Seascape off Indonesian Papua, where 574 coral species, about 72% of the world total, have been recorded.
Raja Ampat lies at the heart of that seascape: more than 1,500 islands, cays and shoals around the main islands of Misool, Salawati, Batanta and Waigeo, now part of Southwest Papua province. Its reefs hold everything from pygmy seahorses to whale sharks, but since 2019 illegal nickel mining on some islands has drawn widespread public criticism in Indonesia.
Back on land, the pressures are plantations and trade. Large oil-palm and timber plantations accounted for more than two-fifths of Indonesia's deforestation between 2001 and 2016, and the wildlife trade has hit rhinos, orangutans, tigers and elephants hardest. Indonesia set up its first national parks in 1980 and now has 554 protected areas covering 27 million hectares, about 14% of its land. The archipelago these animals are split across is mapped island by island in the guide to the islands of Indonesia, the reef belt continues beyond Indonesia's borders in the geography of the Coral Triangle, and Kalimantan's apes get a closer look in where Borneo's orangutans live.