The Micronesian Region

The Micronesian Region is comprised of thousands of small islands scattered across the western Pacific Ocean, north of the equator and west of the International Date Line. Major groups include the Mariana Islands in the north-west, the Caroline Islands in the centre, the Marshall Islands to the west, and the islands of Kiribati in the south-west. Geologically these islands are mainly coral atolls and the climate is entirely tropical with very little seasonal variation. Fauna generally consists of bats, birds, and a few reptiles.


Species and subspecies

The Mariana flying fox (Pteropus mariannus) is confined to the Mariana Islands and to Ulithi, an atoll in the Caroline Islands, where it is threatened mainly by habitat destruction and hunting for food.

Bannerman’s shearwater (Puffinus bannermani) is a small seabird that breeds only on Higashijima and perhaps Chichi Jima, as well as on Minami-Iwoto in the Volcano Islands.

The Micronesian imperial pigeon (Ducula oceanica) is, as a species, found in the Caroline Islands, Marshall Islands, and Nauru. Its various subspecies will be discussed below.

The Micronesian saw-tailed gecko (Perochirus ateles) was historically found throughout the Micronesian Region and remains fairly common despite have been extirpated from some islands, such as Guam. It is threatened mainly by competition from introduced Pacific house geckos (Hemidactylus frenatus) and by predation from feral cats.

Boettger’s emo skink (Emoia boettgeri) is found primarily in the Caroline Islands, where it has been recorded from Pohnpei, Sapwuahfik Atoll, and the Mortlock Islands. The species also occurs marginally in the Marshall Islands, where it known from three small islets within Arno Atoll and historically from Majuro Atoll as well. It is everywhere experiencing declines due to forest loss and degradation as well as from predation by invasive mammalian predators.

The Bonin Islands

Also known as the Ogasawara Islands (Ogasawara Gunto in Japanese), the Bonin Islands are a group of over 30 subtropical and tropical islands of volcanic origin about 1300 km southeast of Japan. Because they have never been connected to a continent, many of the animals and plants here have undergone unique evolutionary processes. This has led to the islands’ nickname of the ‘The Galápagos of the Orient’.

The Bonin sambar deer (Rusa unicolor boninensis) is known only from the remains of two specimens collected in the early twentieth century.

The Bonin flying fox (Pteropus pselaphon) is confined to a few islands in the archipelago, where the total population is thought to be less than 300.

Chichi Jima

Chichi Jima is the largest island in the Bonin Islands group. At least four species have been driven to extinction on this island owing to enormous forest destruction and introduced pigs and rats.

The Bonin wood pigeon (Columba versicolor) is known to have existed only on Chichi Jima and Nakondoshima. It was last recorded in 1889.

The Bonin rufous night heron (Nycticorax caledonicus crassirostris) was last observed in 1889.

The Bonin thrush (Zoothera terrestris) is known only from four specimens collected in 1828. It became extinct during the nineteenth century.

The Bonin grosbeak (Carpodacus ferreorostris) is known only from two specimens collected in 1828. It became extinct during the nineteenth century.

Haha Jima

Haha Jima is the second largest of the Bonin Islands.

Sturdee’s pipistrelle bat (Pipistrellus sturdeei) is a small species known from only a single specimen collected in 1915. It was said to have come from Haha Jima, but there is the possibility that it may have originated elsewhere.

The Volcano Islands

The Volcano Islands (Kazan Retto in Japanese; also known as the Iwo Islands) are a group of three actively volcanic islands located south of the Bonin Islands.

Matsudaira’s storm petrel (Hydrobates matsudairae) is fairly widespread throughout the eastern Pacific and central Indian oceans, but is only known to breed for certain in the Volcano Islands (Minami and perhaps formerly on Kita). In 2004 the total population was estimated at around 20,000.

Iwo Jima

Iwo Jima is unusually flat and featureless for a volcanic island, apart from Mount Suribachi on its southern tip.

The Iwo Jima white-browed crake (Amaurornis cinerea brevipes) was wiped out by introduced cats and rats. It was last collected in 1911 and last seen in 1924.

The Mariana Islands

The Mariana Islands are a crescent-shaped arc of 10 uninhabited and mostly dormant volcanic peaks and 5 limestone and coral islands located about 2000 km east of the Philippines. Once covered by dense forests, all but one of the latter islands have been inhabited by Europeans for 350 years and are intensively cultivated. Cattle and pigs were introduced early. Probably several species of birds were extirpated before zoological exploration began in 1822, which may explain why there are far fewer species of bats, birds, and reptiles on the large Marianas than on the smaller islands of Caroline Islands group, many of which are highly threatened.

The Mariana sheath-tailed bat (Emballonura semicaudata rotensis) was historically found on Guam, Rota, Tinian, Saipan, and Aguigan. It is now entirely confined to the latter island, where the total population of around 500 is known to roost in just three caves.

The Micronesian scrubfowl (Megapodius laperouse) is a chicken-like bird divided into two subspecies. The Mariana scrubfowl (M. l. laperouse) has been exterminated on four of the Mariana Islands, including Guam, owing to habitat destruction and predation by rats, cats, and dogs, and barely survives on only five islands.

Owston’s rail (Hypotaenidia owstoni) is a flightless species that was historically endemic to Guam, where it was extirpated by the late 1980s due to feral cat predation. Fortunately, a captive breeding programme was established, and populations have been introduced onto Rota and Cocos Island.

The Mariana fruit dove (Ptilinopus roseicapilla) is still fairly common on four of the Northern Mariana Islands (Saipan, Tinian, Aguijan, and Rota). It has become extirpated from Guam owing to predation by the introduced brown tree snake (Boiga irregularis), although vagrants originating from Rota are reported on occasion. Threats include habitat destruction, hunting, and introduced predators.

The Mariana swiftlet (Aerodramus bartschi) is a bat-like bird that was historically found on Guam, Saipan, Tinian, Rota, and Aguigan. Invasive species, pesticides and disturbance of its nesting caves all contributed to a significant decline during the mid-twentieth century, and the species has long been extirpated from Tinian and Rota. A small breeding colony was successfully introduced to the Hawaiian Island of Oahu in the 1960s, and a reintroduction is planned for Rota.

The Mariana crow (Corvus kubaryi) is a very rare species confined to northern Guam and Rota in the Northern Mariana Islands, where it has declined steadily since the 1960s. It has nearly been extirpated on Guam, where it has been decimated by the introduction of the brown tree snake (Boiga irregularis). On Rota the primary threat is loss of habitat. A small number of birds from the latter island have been relocated to the Guam National Wildlife Refuge. The total world population is thought to be less than 250.

The golden white-eye (Cleptornis marchei) is a type of passerine bird now confined to Saipan, Aguigan, and Sarigan (where it was successfully translocated in 2011–12), but which appears to have formerly occurred on Tinian and Rota as well. It is threatened by habitat destruction and by predation from introduced brown tree snakes (Boiga irregularis).

The Northern Mariana white-eye (Zosterops saypani) is confined to Tinian, Saipan, and Aguijan, where it is fairly common.

The Mariana emo skink (Emoia slevini) was historically found throughout the Mariana Islands, but has been extirpated from many of them due to introduced tree snakes. It apparently still survives on Guguan, Alamagan, Asuncion, Sarigan, and Maug.


Pagan is a double island consisting of two stratovolcanoes joined by a narrow strip of land, located about 320 km north of Saipan. The inhabitants were all evacuated due to eruptions in 1981.

The Pagan reed warbler (Acrocephalus yamashinae) likely became extinct in the early 1970s owing to human development and introduced feral ungulates. The volcanic eruption on the island in 1981 destroyed any lingering hope of its survival.


Saipan is the second largest of the Mariana Islands, after Guam. The western side is lined with sandy beaches and a large lagoon, while the eastern shore is composed primarily of rugged rocky cliffs. The highest point is a limestone mountain called Mount Tapochau. Remaining native forest occurs in small, isolated fragments on steep slopes.

The Saipan reed warbler (Acrocephalus hiwae) is confined to Saipan and Alamagan, where it is seriously threatened on the former island by introduced brown tree snakes (Boiga irregularis).


Aguigan (also known as Aguihan, Aguiguan, and Aguijan) is a small, uninhabited coralline island located 8 km north-west of Tinian. Feral goats have destroyed much of the native vegetation.

The Aguigan reed warbler (Acrocephalus nijoi) has not been reported since 1995 despite extensive surveys, and is now believed to be extinct.


Tinian is located about 10 km south-west of Saipan.

The Tinian monarch (Metabolus takatsukasae) is a type of passerine bird that had been reduced to about 40 individuals by the late 1960s, but has made a remarkable recovery since then and now numbers in the tens of thousands. Nevertheless, it remains vulnerable to typhoons and the potential introduction of the brown tree snake (Boiga irregularis) from nearby Guam. In 2015–16 it was successfully translocated to Guguan in the Northern Marianas.


Rota is a small island located north of Guam.

The Rota white-eye (Zosterops rotensis) is a type of passerine bird endemic to the island, where it was formerly common and widespread but now largely confined to the upper escarpments of a single plateau.


The southernmost of the Mariana Islands, Guam is the largest island in Micronesia. From the seventeenth to the nineteenth centuries the Spanish introduced pigs, dogs, chickens, Philippine deer (Rusa marianna), and water buffalo (Bubalus bubalis). Later introductions included cane toads, the East African giant land snail, and various frog species. However, it was the accidental introduction of the brown tree snake (Boiga irregularis) near the end of World War II that has really devastated the endemic wildlife. During the twentieth century much of the island’s once-dense forests were replaced by thick tangan-tangan brush (Leucaena leucocephala).

The Guam flying fox (Pteropus tokudae) is only known from three specimens, the last having been shot by hunters in 1968. There was a possible sighting in the late 1970s, but nothing since.

The Guam kingfisher (Todiramphus cinnamominus) remains extinct in the wild, but is well-established in captivity.

The Guam flycatcher (Myiagra freycineti) was considered common up until the 1970s, but quickly went extinct in 1983 along with most of the island’s endemic birds.

The bridled white-eye (Zosterops conspicullatus) was a type of passerine bird endemic to Guam that is believed to have gone extinct in 1983 due to predation by introduced brown tree snakes (Boiga irregularis).

The Guam reed warbler (Acrocephalus luscinius) was last seen in the Agana Swamp in 1969, despite having been reported as fairly common there just a year or two before.

The Caroline Islands

The Caroline Islands number about 500 tiny, widely scattered islands extending some 2600 km across the Pacific Ocean to the north of New Guinea. Most of them are low, flat coral atolls, but a few are mountainous and of volcanic origin. Several have become infested by rats brought long ago by whalers.

The pelagic flying fox (Pteropus pelagicus), as a species, is found on the Chuuk and Nomoi islands, where it is seriously threatened by rising sea levels due to climate change. The Chuuk flying fox (P. p. insularis) was historically known from the Chuuk Islands and Namonuito Atoll, although the latter population may now be extirpated.

The Caroline Islands sheath-tailed bat (Emballonura semicaudata sulcata) is confined to the islands of Chuuk and Pohnpei.

The Palau imperial pigeon (Ducula oceanica monacha) is confined to Yap and the Palau Islands.

The Caroline ground dove (Pampusana kubaryi) is confined to the islands of Pohnpei, Chuuk, and Ant Atoll.

The Caroline lorikeet (Trichoglossus rubiginosus) is nowadays confined to Pohnpei and nearby Ahnd Atoll, but is thought to have formerly had a wider distribution within the Caroline Islands.

The Caroline goby (Sicyopterus eudentatus) is confined to a few streams on Pohnpei and Kosrae.


Located in the eastern Caroline Islands, Pohnpei (formerly known as Ponape Island) is the largest and highest island in Micronesia and one of the few islands within the region to maintain its central volcano. The invasive introduction of the brown tree snake (Boiga irregularis) has had a devastating effect on avian populations in recent decades, as has habitat destruction.

The Pohnpei flying fox (Pteropus molossinus) is known for certain only from Pohnpei as well as Ant and Pakin atolls. Reports from the Nomoi Islands appear to be erroneous.

The Pohnpei imperial pigeon (Ducula oceanica townsendi) is confined to Pohnpei.

The Pohnpei starling (Aplonis pelzelni) is (or was) endemic to Pohnpei. The species declined dramatically sometime after 1930, when about 60 specimens were collected in a 3-month period. It was not located during a survey conducted in 1983 and is considered extinct by some authorities. However, since the 1970s there been several possible sightings, including a specimen collected in 1995.

The Pohnpei kingfisher (Todiramphus reichenbachii) is confined to the lowland forests of Pohnpei, where it remains relatively common but declining.

The Pohnpei cicadabird (Edolisoma insperatum) is confined to Pohnpei.

The Pohnpei emo skink (Emoia ponapea) is confined to the forests of Pohnpei.


Kosrae (formerly known as Kusaie) is the easternmost of the Caroline Islands. It is mountainous and still largely unspoiled.

The Kosrae flying fox (Pteropus ualanus) declined rapidly in 1927 owing to a disease epidemic. A few colonies of 100–400 bats were reported in 1983, after which significant numbers were harvested for export to Guam as food (it is not locally hunted). The species was reported to be uncommon in 1989 but relatively stable.

The Kosrae crake (Zapornia monasa) was a flightless species known only from two specimens collected from coastal swamps in 1827–28. It is believed to have gone extinct within half a century due to introduced rats.

The Kosrae imperial pigeon (Ducula oceanica oceanica) is confined to Kosrae.

The Kosrae starling (Aplonis corvina) is known only from two specimens collected from mountain forests in 1828. It was extinct by 1880 due to introduced rats.

Yap Island

Yap Island is actually made up of four contiguous (although separated by water) islands surrounded by a common coral reef.

The Yap flying fox (Pteropus yapensis) is confined to the four adjacent main islands of Yap, where it is seriously threatened by hunting.

The Yap reed warbler (Acrocephalus astrolabii) is known only from specimens collected in 1838 or 1839, the precise origins of which remain unclear.

The Yap cicadabird (Edolisoma nesiotis) is fairly widespread on Yap, but in very low numbers.

The Palau Islands

Located about 900 km east of Mindanao, the Palau Islands are an archipelago of about 340 coral-reef islands forming the western chain of the Caroline Islands.

The large Palau flying fox (Pteropus pilosus) is known only from two specimens collected prior to 1874, and extensive surveys over the years since have failed to locate it. The precise causes of its presumed extinction are unknown, although hunting for food by local people along with forest degradation seems most likely. The small Palau flying fox (P. pelewensis) is found on the main islands of Palau as well as on a few more distant islets, where it is seriously threatened by hunting.

The Palau sheath-tailed bat (Emballonura semicaudata palauensis) is found on the islands of Koror, Peleliu, Babelthuap, and Anguar, where it is reasonably common.

The Palau scrubfowl (Megapodius laperouse senex) has been exterminated on two islands and barely survives on four others.

The Palau ground dove (Pampusana canifrons) occurs throughout the Palau Archipelago but is rare on most islands. Surveys in the late 1970s estimated a total population of around 500. However, there have been very few records in recent years, in part because of the inaccessibility of the bird’s habitat along with their secretive nature. Cats and rats are known to be present on at least some of the islands.

The Rock Islands

The Rock Islands are a collection of limestone and coral uprises located in Palau’s Southern Lagoon. They were declared a world heritage site in 2012.

The Seventy Islands scaly-toed gecko (Lepidodactylus paurolepis) is known only from five specimens collected from three small islands in the Ngerukeuid Islands Wildlife Preserve.


Anguar is the southernmost of the Palau Islands.

The Palau forest dragon (Hypsilurus godeffroyi) is known only from two specimens of uncertain provenance collected in 1867. Subfossil remains of an agamid lizard here considered to be conspecific have been discovered on Anguar.

The Chuuk Islands

The Chuuk Islands (formerly known as the Truk Islands, and also known as Chuuk Lagoon) are a group of 11 major islands and dozens of smaller ones centred around a central lagoon with a common fringing coral reef. The islands have been heavily deforested.

The Chuuk imperial pigeon (Ducula oceanica teraokai) is confined to Chuuk.

The Chuuk monarch (Metabolus rugensis) is a type of passerine bird widely but sparsely distributed on all, or nearly all, of the high lagoon islands as well as some of the outer reef islets.

The Faichuk Islands

The Faichuk Islands are located in western Chuuk Lagoon.

The teardrop white-eye (Rukia ruki) is a type of passerine bird confined to four tiny islands in the Faichuk group. In 1984 the total population was estimated at 530.

Namoluk Atoll

Namoluk is a small atoll located about 185 km south-east of Chuuk.

The Toimon scaly-toed gecko (Lepidodactylus oligoporus) is known only from a few specimens collected on Toimon Island, part of Namoluk Atoll.

The Nomoi Islands

The Nomoi Islands (also known as the Mortlock Islands) are a group of three large atolls located about 250 km south-east of the Chuuk Islands.

The Nomoi flying fox (Pteropus pelagicus pelagicus) is confined to the Nomoi Islands, where it has been extirpated from at least two islands.

The Marshall Islands

The Marshall Islands, located near the equator and slightly west of the International Date Line, are spread out over 29 coral atolls and comprise 1156 individual islands and islets. During the mid-twentieth century they were the setting for much nuclear testing on the part of the Americans. The latter began in 1946 on Bikini Atoll after residents were evacuated. Over the years, 67 weapon tests were conducted, including the 15-megaton Castle Bravo hydrogen bomb test, which produced significant fallout in the region. The testing concluded in 1958. Over the years, just one of over 60 islands were cleaned by the U.S. government, and many of the islanders and their descendants still live in exile as their islands remain contaminated with high levels of radiation. Many other low-lying islands are additionally threatened now by rising sea levels due to global warming, which threaten to submerge them entirely.

The Marshall Islands imperial pigeon (Ducula oceanica ratakensis) is confined to the Marshall Islands.

Wake Island

Wake Island is an isolated low atoll in the central Pacific between the Marianas and Hawaii. With limited freshwater resources, no harbour, and no plans for development, it remained uninhabited during the early twentieth century. It did, however, boast a large seabird population, which unfortunately attracted Japanese feather poachers.

The Wake Island rail (Hypotaenidia wakensis) was a nearly flightless species that was the only native land bird on the island. It was exterminated during its occupation by Japanese troops in World War II, probably in 1945.


Nauru is a tiny, isolated atoll located in the south-western Pacific. Once heavily vegetated, its environment was largely destroyed by strip-mining for its phosphorous deposits and introduced species.

The Nauru reed warbler (Acrocephalus rehsei) is confined to the island, where it remains relatively common.

The Gilbert Islands

The Gilbert Islands (formerly known as the Kingsmill Islands) are a chain of 16 coral atolls located about 1500 km north of Fiji.

The islands have no known endemic species, although it is possible that a now-extinct population of Micronesian imperial pigeon (Ducula oceanica) represented a distinct subspecies. In addition, three species of threatened petrel (Pterodroma) as well as the bristle-thighed curlew (Numenius tahitiensis) are found on the islands.


Anthropogenic effects on the flora and fauna

Modern human settlement of the Micronesian Region began several thousand years ago, although there are competing theories about where these people came from and when they first arrived. The Marianas were the first islands in all of Oceania to be colonized by Austronesian peoples, having been settled by voyagers from the Philippines in approximately 1500 bc. These populations gradually moved southwards until they reached the Bismarck Archipelago, the Solomons and coastal New Guinea by 1300 bc. By 1200 bc they were once more crossing open seas beyond inter-island visibility, reaching Vanuatu, Fiji, and New Caledonia before continuing eastward to become the ancestors of the Polynesian people. Further migrations by other Austronesians also followed, most likely from Sulawesi, settling Palau and Yap by around 1000 bc.

The earliest known contact between these Micronesian indigenous peoples and Europeans was in 1521, when a Spanish expedition under Ferdinand Magellan reached the Mariana Islands. Further contact was made during the sixteenth century, although initial encounters between Europeans and natives were often very brief. In the early seventeenth century Spain colonized Guam, parts of the Marianas, and the Caroline Islands, creating the Spanish East Indies. During the early nineteenth century American missionaries began to have an influence, and thereafter the colonies would be shared among American, German, and British interests until most achieved independence during the twentieth century. Today, most of Micronesia consists of independent states with the exception of the Northern Mariana Islands, Guam, and Wake Islands, all of which continue to be U.S. territories.

In recent historical time (i.e. since ad 1500), the Micronesian Region has lost at least 15 species/2 subspecies of vertebrates. Among the extinct forms 2 species are mammals, 12 species/2 subspecies are birds, and 1 species is a reptile. One other species is possibly extinct, and 1 species is currently extinct in the wild.

In addition, there are 37 species/11 subspecies currently threatened with extinction (that is to say, either Critically Endangered, Endangered, or Vulnerable according to the IUCN Red List, as well as certain forms either listed as Data Deficient or Not Assessed but which are clearly at some risk of extinction). Of these, 8 species/6 subspecies are mammals, 23 species/5 subspecies are birds, 5 species are reptiles, and 1 species is a freshwater fish.


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