Why the Amami Rabbit Is a "Living Fossil" — and Recovered 8x After Mongoose Eradication

What is the Amami rabbit? A solitary species with no living relatives

The Amami rabbit (scientific name Pentalagus furnessi) belongs to the genus Pentalagus within the rabbit family (Leporidae). Today, this genus contains only this one species. It occupies an extremely unusual position even among rabbits worldwide, and Japan's Ministry of the Environment describes it as "an academically important species with unique, primitive traits."

The word "primitive" here does not mean inferior. Rather, it means the species has retained, almost unchanged to this day, a body shape close to that of its ancestors — from before many rabbit species evolved longer hind legs and powerful jumping ability. Combined with the fossil record discussed in the next chapter, the Amami rabbit can be described as a living snapshot of evolution, a natural history specimen that is still alive today.

A medium-sized rabbit: 41–51cm long, 1.3–2.7kg

According to Ministry of the Environment materials, the Amami rabbit weighs 1,300–2,700g and has a head-and-body length of 41–51cm. Its digits carry well-developed claws suited to digging, and it lives by digging burrows for rest and birthing in tree hollows, rock caves, and at the base of large trees. Its lifespan in captivity is thought to be around 15 years, and it is believed to breed year-round rather than in a fixed season.

A nocturnal rabbit with short ears that walks instead of hops

Unlike the common image of a hare bounding across open grassland, the Amami rabbit has short ears and relatively short hind legs. It moves through the forest at a slow walk rather than by hopping. It is nocturnal, spending most of the daytime in its burrow, and lives a solitary life in subtropical evergreen broadleaf ("laurel") forest, secondary forest, and coastal woodland dominated by chinquapin and oak species. Its home range is thought to be on the order of a few hundred meters across.

Another notable trait is that breeding activity is not confined to a particular season but is believed to occur throughout the year. Separately from its resting burrow, it digs a dedicated burrow in a tree hollow, rock cave, or the base of a large tree to raise its young — a strategy of hiding underground. This "burrowing" ecology was originally well adapted to an island environment with few predators, but as we will see, it offered no reliable defense against an invasive predator, the mongoose, that could follow it into its burrow.

A varied, largely plant-based diet that shifts with the seasons

According to a blog post from the Ministry of the Environment's Okinawa Regional Environment Office, the Amami rabbit is entirely herbivorous, eating a wide range of plants: grasses such as Japanese silver grass and Peucedanum japonicum, the leaves of woody plants such as Clerodendrum trichotomum and Styrax japonica, the bark of trees such as cedar and citrus, the fruit of Castanopsis sieboldii, and even bamboo shoots. In the food-scarce autumn and winter months, it turns to harder-to-eat items such as young tree buds, bark, and acorns. This flexible, season-by-season diet is itself evidence of how the species has sustained itself within the limited environment of a subtropical laurel forest.

• Scientific name: Pentalagus furnessi (Leporidae, genus Pentalagus)
• Range: Amami-Oshima and Tokunoshima islands, Kagoshima Prefecture — nowhere else on Earth
• Size: head-and-body length 41–51cm, weight 1,300–2,700g
• Traits: short ears, short hind legs, long claws; a solitary, nocturnal walker rather than a hopper
• Protection status: Critically Endangered (Ministry of the Environment's 4th Red List), Japanese Special Natural Monument (designated 1963)

Its ancestor, Pliopentalagus: a "living fossil" lineage nearly five million years old

The reason the Amami rabbit is called a "living fossil" lies in the age of its lineage. According to research explained by Japan's National Museum of Nature and Science, the ancestor of the genus Pentalagus, known as Pliopentalagus, was a rabbit-like animal that lived on the continent around five million years ago, during the Pliocene epoch of the Neogene period. For a long time only fragmentary fossils had been found, and its evolutionary history remained largely a mystery.

Fossils in China's Anhui province revealed the evolutionary path

The turning point came with the discovery of a large number of fossils from multiple sites of different ages at Dajushan in Anhui province, China. These finds made it possible to reconstruct the evolution of Pliopentalagus in concrete detail, and also revealed that related rabbit species once found in North America were descendants of Pliopentalagus populations that had migrated from Asia.

Every mainland relative died out; only the two island species survived

However, the genus Pentalagus (as Pliopentalagus), once widespread across the continent, eventually disappeared entirely amid environmental change. The only population to survive was the one isolated on Amami-Oshima and Tokunoshima after separation from the continent. As a result, the genus Pentalagus today comprises just one species — a lineage that endured on an isolated island even after its continental relatives vanished, earning it the "living fossil" designation.

This evolutionary history illustrates just how special Amami-Oshima and Tokunoshima are — islands where, in a sense, time stood still. A lineage that would otherwise have been driven to extinction by continental environmental change or by more adaptable rivals was able to survive thanks to its isolated island environment. The flip side of that isolation, however, is that such ecosystems are extremely vulnerable to new competitors or predators introduced from outside. That vulnerability became a real threat with the arrival of the invasive mongoose, discussed in the next chapter.

Because the mainland members of the genus Pentalagus are extinct, the genus today comprises only a single species.

— National Museum of Nature and Science, "Tracing the Ancestry and Evolution of the Amami Rabbit"

Few endangered species anywhere in the world have their phylogenetic relationships backed by fossil evidence this concrete. An evolutionary history that, in an era when only fragmentary tooth fossils were available, remained purely speculative has only recently become something that can be told with hard evidence — thanks in part to the chance discovery of a large fossil deposit in China. Research on the Amami rabbit thus holds academic value that extends beyond conserving a single living species; it also offers clues to a much larger evolutionary story that includes its extinct relatives.

Why did it survive only on Amami-Oshima and Tokunoshima?

Amami-Oshima and Tokunoshima are islands with an oceanic-island character, having separated from the continent relatively early, allowing a unique ecosystem to persist for a long time. For the Amami rabbit, which lives in old-growth forest (mature stands spared from logging) and adjacent food-rich areas, these two islands — with little development and few large predators — are thought to have become the last refuge where it could survive even after its continental relatives had gone extinct.

Even among the islands of the Amami and greater Ryukyu chains, the Amami rabbit occurs naturally only on Amami-Oshima and Tokunoshima; it is absent from Okinawa Island, Yoron Island, and others. Even the World Natural Heritage site that lumps together "Amami-Oshima, Tokunoshima, Northern part of Okinawa Island, and Iriomote Island" is, in reality, made up of different combinations of endemic species on each island, each forming its own distinct biodiversity — a reminder of how differently each island's origins have shaped the distribution of its wildlife.

This kind of island-by-island difference echoes a theme found in the endemic species of the Ogasawara Islands as well. On islands separated by ocean, the broad-scale interbreeding and selective pressures typical of continents operate far less, so unique evolution proceeds more readily within a limited population. The flip side is that, precisely because the population itself is small, it can quickly be pushed toward extinction by even a modest environmental change or an outside influence — such as the arrival of an invasive species.

Critically Endangered status, and a Japanese Special Natural Monument

The Amami rabbit is listed as Critically Endangered (Category IB) on the Ministry of the Environment's 4th Red List, and in 1963 it was designated a Japanese Special Natural Monument under the Act on Protection of Cultural Properties. Part of its habitat is protected as the nationally designated Yuwandake Wildlife Protection Area and the Kamiya/Yuwandake Natural Monument Forest, and in Yamato Village on Amami-Oshima, a village ordinance in effect since 2001 bans capturing the species within village limits.

In terms of protecting the habitat as a whole, another major milestone came on March 7, 2017, when Amami Islands National Park was designated as Japan's 34th national park. Much of the laurel forest where the Amami rabbit lives falls within this national park's boundaries, establishing a framework that protects the entire forest ecosystem as a landscape, not just a single species. This national park designation also helped lay the groundwork for the 2021 World Natural Heritage listing discussed later.

The 2004 conservation plan, and four threats to survival

In 2004, the species was designated a Nationally Endangered Species of Wild Fauna and Flora, and a conservation and propagation plan was formulated jointly by the Ministry of the Environment, the Ministry of Agriculture, Forestry and Fisheries, and the Ministry of Education, Culture, Sports, Science and Technology (with a 10-year implementation plan added in 2014). The Ministry of the Environment lists four factors threatening the species: ① the decline and fragmentation of old-growth forest, ② predation by the mongoose, ③ predation by cats and dogs, and ④ traffic accidents. As the following chapters show, factor ② — the invasive species problem — was by far the most serious threat.

The creeping threat of the invasive mongoose

The single greatest threat to the Amami rabbit's survival was the invasive small Indian mongoose (Urva auropunctata), introduced by humans. According to records from the Japan Wildlife Research Center and the Ministry of the Environment, the mongoose was introduced as a countermeasure against habu snakes and rodents — to Okinawa Island in 1910, and to Amami-Oshima around 1979. Interviews with those involved confirm that around 30 mongooses were brought from Okinawa Island and released near Asakuraki, Naze City, on Amami-Oshima.

A population explosion on an island with no natural predator

Amami-Oshima originally had no large native predator capable of controlling the mongoose. The released mongooses spread and multiplied, reaching an estimated population of about 10,000 by 2000 (an estimated 6,000 at the end of fiscal 1999, plus natural growth), according to the Ministry of the Environment. Mongooses prey on a wide range of animals, from small invertebrates such as grasshoppers and crickets to vertebrates such as frogs, rats, and rabbits, and they had a major impact on rare species endemic to Amami, including the Amami rabbit and the Ryukyu long-haired rat.

Shrinking native ranges, and initial countermeasures that fell behind

Local municipalities began culling the mongoose as a harmful wildlife species in 1993, and the Ministry of the Environment (then the Environment Agency) and Kagoshima Prefecture launched a four-year pilot project in 1996 to survey its distribution and population and study capture methods. However, because the mongoose's home range is small, trapping only along roadsides failed to curb the spread of its distribution — and by the time officials judged that more thorough measures, including inside the forest interior, were needed, the ranges of many native species had already shrunk considerably.

According to the Ministry of the Environment, the pilot project produced concrete data showing that the ranges of many native species, including the Amami rabbit, were shrinking in step with the mongoose's expanding distribution. That evidence was the deciding factor in shifting strategy from partial trapping along roadsides to a full-scale eradication program across the entire island, including its forest interior. Conversely, it also shows just how long a period of observation and patience was required before the effects of countermeasures showed up in the numbers.

The mongoose is originally a member of the family Herpestidae, native to a wide range spanning the Middle East, southern China, and South Asia. It is roughly 60cm long in males and 50cm in females — somewhat larger than a Japanese weasel. It gives birth about once a year, averaging 2.26 young per litter, with the breeding season on Amami-Oshima running mainly from March to September. With no natural predator on the island to check this reproductive capacity, the roughly 30 individuals introduced in 1979 exploded into an estimated population of about 10,000 by 2000, twenty years later.

Thanks to its slender body, the mongoose can squeeze into narrow gaps and burrows in the ground, and it preys on everything from small invertebrates such as grasshoppers and crickets to frogs, rats, and rabbits. As noted in the previous chapter, the Amami rabbit digs burrows in tree hollows, rock caves, and the base of large trees to hide while resting or raising young — but this strategy of "hiding underground," while effective in an era with no large island predators, is thought to have instead become a weakness that left it with nowhere to flee once a small, agile predator like the mongoose could follow it into its burrow.

A world first: eradicating the mongoose from an inhabited island

In 2000, the Ministry of the Environment (then the Environment Agency) and Kagoshima Prefecture launched a full-scale eradication program with a bounty system tied to the number captured (run solely by the Ministry of the Environment from 2001 onward). In 2005, the small Indian mongoose was designated an Invasive Alien Species under Japan's Invasive Alien Species Act, and that same year a dedicated team, the "Amami Mongoose Busters," was formed.

30,000-plus traps, detection dogs, and 124 specialists

According to records from the Japan Wildlife Research Center, the Amami Mongoose Busters began with 12 members and have involved 124 people in total over the years in mongoose eradication work. They set up and managed more than 30,000 traps and over 300 camera traps across nearly the entire island, including forest interiors, and from fiscal 2007 also deployed mongoose detection dogs imported from New Zealand (17 dogs trained and used to date). Traps and detection dogs together caught 20,961 mongooses; combined with harmful-wildlife culling and other methods, the total capture count reaches 32,647.

According to a Ministry of the Environment press release, the eradication process involved repeated improvements to traps to avoid "bycatch" of other animals, as well as the development of individual capture techniques through coordination between detection dogs and their handlers — every available method was mobilized. In particular, in the final, hardest-to-treat areas, rodenticide-based measures were also employed. Because the difficulty of finding a single remaining individual rises sharply as the capture count approaches zero, this combination and continual refinement of methods is credited with ultimately achieving eradication.

September 3, 2024: a science-based declaration of eradication

After the last capture in April 2018, no mongoose sign was confirmed by traps, detection dogs, or camera traps for years afterward. Because it is inherently difficult to prove directly that a species has completely disappeared from an area, the Ministry of the Environment evaluated eradication using two models: an area-based model called HBM (Harvest-Based Model) and an individual-based model called REA (Rapid Eradication Assessment). Based on finalized data through the end of fiscal 2023, these models showed eradication probabilities of 99.7% (HBM) and 98.9% (REA). On the strength of these results, the Ministry of the Environment declared the mongoose eradicated from Amami-Oshima on September 3, 2024.

In general, invasive species control faces a wall: capture can sharply reduce numbers while the population is large, but the difficulty of finding a single remaining individual rises steeply as density falls. Maintaining the same level of trapping and search effort through fiscal 2023, even after the capture count reached zero, is what enabled this high level of confidence from the eradication-probability models. The work of the Amami Mongoose Busters can be described as a steady accumulation of monitoring aimed at scientifically proving an absence.

Eradication across Amami-Oshima's 71,200 hectares (712 km²) is exceptional by world standards. According to the Ministry of the Environment, nine islands worldwide had previously achieved mongoose eradication, but the largest island where a long-established, breeding population had been eradicated through planned control was just 115 hectares (Fajou Island, a French territory). The Amami-Oshima case, on an island far larger than that, is regarded as a world-first achievement in biodiversity conservation.

Tackling feral cats alongside the mongoose

The mongoose was not the only threat to the Amami rabbit. According to Ministry of the Environment materials on the population estimate, feral cat control began on Amami-Oshima in fiscal 2018, and on Tokunoshima — where the mongoose had never been present — in fiscal 2014. Recent population growth on Amami-Oshima is attributed partly to this feral cat control, while the increase on Tokunoshima, which never had a mongoose problem, is attributed mainly to feral cat control. This accumulation of complementary measures alongside mongoose control is what led to the population recovery discussed below.

How much has the population recovered?

As mongoose control progressed, the Amami rabbit population steadily recovered. The long-standing benchmark had been a researcher's paper published in 2003, which estimated 2,000–4,800 individuals on Amami-Oshima and about 200 on Tokunoshima.

The 2021 estimate, revised using camera traps and statistical modeling

The 2003 estimate was based on a "fecal pellet count survey" — counting droppings along streams across the island — combined with information such as how much an individual defecates per day and how long droppings take to disappear from the environment. Experts pointed out, however, that this method carried significant variability and a risk of overestimation, so the Ministry of the Environment carried out an additional camera-trap survey (the REST method) during the winters of fiscal 2020–2021 to revise the estimation method itself.

In fiscal 2022, the Ministry of the Environment combined the traditional fecal pellet survey with camera-trap density surveys (REST method), field surveys, and route-census sighting counts, using a time-series analysis technique called a "state-space model" to re-estimate the population over the 19 years from 2003 to 2021. The result: the estimated population as of fiscal 2021, combined for Amami-Oshima and Tokunoshima, was between 11,549 and 39,162. Compared simply with the 2003 estimate (roughly 2,200–5,000 for both islands combined), the upper bound represents an increase of roughly 5 to 8 times.

The Ministry of the Environment states that both islands show a long-term recovery trend, with the increase on Amami-Oshima attributed mainly to the mongoose capture program that began in fiscal 2000, and the recent increase common to both islands attributed to the effects of feral cat control. The same survey also produced a population estimate for the Amami woodcock: it showed a similar increasing trend on Amami-Oshima, but remained flat over the long term on Kakeromajima and Tokunoshima — showing that the degree of recovery differs by species.

Given this substantial recovery, some local news reports say the Ministry of the Environment is considering lowering the species' threat category. However, this remains only a matter under discussion — as of this writing, the Amami rabbit's classification on the Ministry of the Environment's Red List (Critically Endangered, Category IB) has not actually changed. A larger population does not mean every threat has disappeared; as the roadkill problem discussed in the next chapter shows, recovery itself has also created new challenges.

Recovery has not been limited to the Amami rabbit

According to a Ministry of the Environment press release, as mongoose control progressed, recovery trends also became evident in amphibians such as the Amami tip-nosed frog, the Otton frog, and the Amami Ishikawa's frog, and in rare rodent species such as the Amami spiny rat and the Ryukyu long-haired rat. Improvements in the range of bird species such as the Amami thrush and the Amami woodcock have also been reported, suggesting that mongoose control and eradication contributed to the recovery of Amami-Oshima's ecosystem as a whole.

• Amami rabbit (mammal): estimated population increased substantially
• Amami tip-nosed frog, Otton frog, Amami Ishikawa's frog (amphibians): recovery trend
• Amami spiny rat, Ryukyu long-haired rat (mammals): recovery trend
• Amami thrush, Amami woodcock (birds): improved range

The Ministry of the Environment also cites trends in camera-trap capture frequency (images per 1,000 camera-days) as further evidence supporting this recovery trend. However, it notes that species such as the Ryukyu long-haired rat and Okinawa woodpecker are less often captured by cameras placed on the ground, so how easily change can be tracked varies by species. This stance — never judging the whole ecosystem from a single indicator, but combining multiple surveys — is something that has been cultivated over these 30 years of control efforts.

The cost of recovery: a worsening roadkill problem

While the population recovery is welcome, it has created a new problem. As the population has grown and its range has expanded closer to roads, deaths of Amami rabbits from traffic accidents have increased. The Ministry of the Environment's Okinawa Regional Environment Office continuously collects data on the carcasses of rare wildlife and compiles a breakdown of causes of death.

2022: a record high on both islands

According to a Ministry of the Environment press release (November 2022), the number of confirmed traffic accidents as of the end of September 2022 stood at 68 on Amami-Oshima and 21 on Tokunoshima — both record highs. Accidents are concentrated on National Route 58, Prefectural Route 85, and forest roads; the analysis found that on Amami-Oshima accidents are increasing at previously identified hotspots, while on Tokunoshima they are increasing at the edges of the species' range.

Local newspapers, including the Nankai Nichinichi Shimbun, report that the number of accidents on Amami-Oshima has continued to rise year after year since then, with record highs being set repeatedly over multiple years. Given the pace of population recovery, this rise in accident numbers over a certain period is, in a sense, the flip side of the population coming back. But because each of these deaths represents an individual life lost, strengthening countermeasures remains an urgent, ongoing task.

Countermeasures led by the Ministry of the Environment and JAF

Countermeasures include installing warning signs at accident hotspots, raising public awareness through leaflet distribution, and verifying the effectiveness of entry-deterrent fencing. The Amami Wildlife Conservation Center urges drivers at night to slow down to a speed that allows them to stop safely if wildlife suddenly darts out, and joint efforts continue with the Japan Automobile Federation's (JAF) Kagoshima branch, including publishing awareness videos — a public-private effort that continues on multiple fronts. The damage extends beyond the Amami rabbit to other rare species such as the Ryukyu long-haired rat and the Amami spiny rat.

Around one of Amami-Oshima's mountain roads, the Santaro Pass, a set of rules governing nighttime vehicle use is also in effect. The Ministry of the Environment says it will make necessary improvements to these rules based on future usage patterns and roadkill trends, and, together with verifying the effectiveness of entry-deterrent fencing, continues to examine new measures aimed at helping roads and wildlife coexist. Causes of death are inferred from the condition of the carcass, the discovery site, and necropsy results; because traffic accidents are especially likely to be discovered on roads where they are easily spotted, the Ministry itself cautions that these surveys alone cannot capture the full picture of causes of death.

Its value as a World Natural Heritage site, and what we can do

Amami-Oshima and Tokunoshima, together with the northern part of Okinawa Island and Iriomote Island, were inscribed as a UNESCO World Natural Heritage site — "Amami-Oshima, Tokunoshima, Northern part of Okinawa Island, and Iriomote Island" — on July 26, 2021. The listing recognized the region's rich biodiversity, symbolized by rare endemic species found nowhere else, including the Amami rabbit and the Amami woodcock. The Ministry of the Environment states that the recovery of native species following mongoose eradication contributed significantly to this World Heritage listing and to the conservation of Amami Islands National Park.

Tourism value, and the difficulty of coexistence

With the mongoose eradicated, damage to agriculture and livestock has disappeared; meanwhile, night tours to observe wildlife have become one of the major pillars of tourism on Amami-Oshima. The recovery of native species is thought to be benefiting the local economy as well, but as we have seen, the road network essential to tourism and daily life is also generating friction — traffic accidents — with the wildlife that has recovered. Balancing conservation with local livelihoods within the framework of a World Natural Heritage site remains an ongoing challenge.

The Ministry of the Environment states that successfully eradicating the mongoose from a large, topographically complex island like Amami-Oshima could serve as a valuable reference case for invasive species control efforts in Japan and abroad going forward. The patient, sustained work of the Amami Mongoose Busters and other agencies and local residents over more than a quarter-century has left a lesson for biodiversity conservation efforts worldwide.

What we can do when we engage with Amami-Oshima and Tokunoshima

When visiting these islands, slowing down while driving at night and following the rules for designated trails and forest roads are direct forms of conservation action. There is also much to learn from stories of rare-species conservation elsewhere in Japan — such as the effort toward zero traffic fatalities for the Iriomote cat, or the recovery of the crested ibis on Sado Island, a species once on the very brink of extinction that recovered through community-wide effort. As with the endemic species of the Ogasawara Islands, understanding just how vulnerable a closed island ecosystem is to invasive species is itself a first step toward preventing the next "mongoose."

The story of the Amami rabbit brings together three timelines: an evolutionary history stretching back roughly five million years, a crisis caused by a human-introduced invasive species, and a recovery achieved through more than three decades of patient eradication work. The world-first achievement of mongoose eradication did not happen naturally — it is the result of the persistent effort of the Amami Mongoose Busters and everyone else involved. And now, as the islands face the new challenge of traffic accidents, how this "living fossil" and people will coexist continues to be tested.

• When traveling, keep nighttime driving to a minimum and follow designated routes and rules
• If you find an injured or dead animal, contact a wildlife conservation center promptly
• Keep the Three Principles for Preventing Invasive Species Damage — "don't bring them in, don't release them, don't let them spread" — in mind in daily life too
• Support local conservation work through hometown tax donations (furusato nozei) or contributions to conservation organizations