Iriomote Cat

MammalJapan

18 Apr

Prionailurus bengalensis iriomotensis

The Iriomote cat occupies the smallest habitat of any wild cat on Earth — found only on Japan's southern Island of Iriomote — with its current population estimated to be around 100 individuals.

The leopard cat (Prionailurus bengalensis) is a small wild cat about the size of a house cat but sleeker and outfitted with leopard-like spots. It is a forest-dwelling species native to South, Southeast, and East Asia, ranging from northern Pakistan in the west to the Amur region in the Russian Far East, and south to the tip of Peninsular Malaysia — one of the most widespread carnivores in Asia. It has even settled beyond the mainland, on islands like Hainan in southern China, and Taiwan.

A leopard cat (*Prionailurus bengalensis*) from peninsular Malaysia.

If you sail eastwards from northern Taiwan, across the East China Sea, you'd reach the mangrove-lined shores of Iriomote Island. The leopard cat made this same journey over 100,000 years ago. It didn't do it by boat, and it didn't swim either — although leopard cats are good swimmers — but, according to prevailing theory, it walked. During the Last Glacial Maximum, when global sea levels were 120 metres (400 ft) lower than at present, a land bridge spanned the 200-kilometre (125 mi) gulf that, today, separates Taiwan from Iriomote. Some intrepid leopard cats crossed this bridge and settled on the new extension of the mainland. Then, some 10,000–20,000 years ago, the sea levels rose once more and cut off this population, stranding them on what would become Iriomote Island.

Over the millennia, the isolated leopard cats changed, diverging from those on Taiwan and the rest of Asia. The cats of Iriomote became slightly smaller and stockier, with shorter tails. Their fur became darker, as if coated in layers of ash, obscuring the leopard print underneath. They still retain some traits that betray their ancestry, like patterns of dark stripes across their faces, with white rims around their amber-gold eyes, and white markings on the backs of their ears, but you wouldn't mistake a mainland leopard cat — sleek and spotted — for the dark and stocky cat of Iriomote. The stranded felines, remnants of the mainland who adapted to island life, became Iriomote cats (Prionailurus bengalensis iriomotensis).¹

Iriomote-jima

Iriomote Island lies some 200 kilometres (125 mi) to the east of Taiwan.

In contrast to the leopard cat — one of the most geographically widespread felines — the Iriomote cat occupies the smallest habitat of any wild cat on Earth. Iriomote Island, or Iriomote-jima, is not a part of Taiwan, despite its proximity, nor is it part of China, the nearest mainland. The island is the southernmost reach of Japan; a part of the Ryukyu Arc which stretches from Japan's most southern main island, Kyushu, to Taiwan. It's not a particularly large island, only around 284 km² (110 mi²), but it's dense with wilderness. Nearly 90% of Iriomote is covered in forests and mangroves. As such, the Iriomote cat is primarily a forest creature, but it can turn up just about anywhere on the island, from the mountains to the coastlines, in wetlands and even human villages.

Jack of All Trades

Across the fifty-five Ryukyu Islands — from the Ōsumi Islands just below Kyushu, to the large central islands of Amami and Okinawa, and the southernmost Yaeyama Islands (of which Iriomote is one) — there is no larger land predator than the Iriomote cat.²

Cut off from the mainland, the Iriomote cat was forced to adapt to a completely different island ecosystem, where resources were scarcer, but also no large predators to challenge its carnivorous niche. Its hunting skills expanded to fill those uncontested niches, and every venture — into water, trees, and fields — proved rewarding. Bounding up trees, it took fruit bats and birds, plucking the latter of their feathers before eating them. Plunging into streams and lakes, it snatched up fish and crabs and dove in pursuit of water birds.³ It stalked the undergrowth in the dim light of dusk and dawn, pouncing on rodents, frogs, lizards, and snakes. It even took advantage of human settlements and the abundance of "pests" that surround them.

But when it comes to a skill set, wide often means shallow. The Iriomote cat is good at swimming and diving (but not as good as a fishing cat), it's good at climbing trees (but not as good as a margay), and it's good at sneaking up to ambush rodents (but not as good as the black-footed cat). The point is that it's not really an expert at any one hunting style. If the Iriomote cat had a skill tree, it would have invested some points into all the branching arms — swimming, climbing, sneaking — but taken none to their limits. In other words, it is an opportunistic generalist.

This jack-of-all-hunting-styles approach has served the Iriomote cat well. Its diet is among the most diverse of any feline — the cat's "hit list" includes 95 different species, ranging from fish to birds to bats to bugs. Anything that moves and breathes on Iriomote Island is liable to fall prey to this killer. A generalist strategy is also adaptable. If one prey source fails, the cat can turn to another. Alternatively — and especially relevant on an island — if a new predator species somehow arrives, such as a water monitor, for example, and takes over the predatory aquatic niche, the Iriomote cat will still have its other sources of prey. If, however, the invading predator is also a generalist, the Iriomote cat will have to compete on all fronts, for all of its prey. And if the new predator is a better generalist than the Iriomote cat, the Iriomote cat will either have to specialise — invest heavily into one particular niche in which it can outcompete the invader — or face potential extinction.

Master of None

Free-ranging cats are likely the single greatest source of anthropogenic mortality for US birds and mammals.

A domestic cat is a superb generalist predator. In the hours it spends outside the house, it can supplement its kibble diet with birds, rodents, fish, and insects. A feral cat, on the other hand, depends almost entirely on killing to survive. In China alone, free-ranging domestic cats are estimated to kill 26.9–55.2 billion birds and 36.1–98 billion mammals every year.⁴ Wherever humans go, we take with us (intentionally and not) a posse of pets and pests. Our most common companions, rats and cats, have both made it to Iriomote Island.

Iriomote has no native mice or rats, so when the first black rats (a.k.a. ship rats) arrived, they found an island with no rodent competitors. The domestic cats, on the other hand — some of which escaped and went feral — encountered the island natives: dark-coated wild cats that had sparsely populated this island for tens of thousands of years. What followed was an unfair contest between felines.

Iriomote cats had settled into a comfortable generalist niche, one without competition that might have pushed them towards higher efficiency. Then, all of a sudden, they were forced to compete with some of the most proficient, generalist predators on the planet. A study found that the distribution of feral cat scat on Iriomote was closely associated with garbage dumps, with the cats taking advantage of human refuse as a food source — these cats might have been feral, but they still heavily relied on, and benefited from, the presence of humanity. But they didn't just stick to scavenging. Feral cats were found to hunt thirteen species of native animals, ten of which were also a food source for Iriomote cats. The same study also found an apparent negative correlation between the prevalence of feral cats and Iriomote cats — quote, "From 1997 to 2001, the number of observed scats from Iriomote cats declined significantly, while feral cat scat became more common" — and concluded that "the expansion of [feral cats] into habitats of Iriomote cats may increase the competition for prey and habitat resources in the future". The Iriomote cats were being outcompeted.

Some feral cats — primarily breeding males — can have large ranges spanning over 5 km² (2 mi²), but where space is scarce and prey abundant, territories can shrink to as little as 0.01 km² (0.004 mi²). Which is to say, you can squeeze a lot of feral cats onto a small piece of land. Like feral cats, Iriomote cat males hold larger territories that tend to overlap with those of several females with whom they hope to mate. A female iriomote cat holds a stable territory covering 1–3 km² (0.4–1.2 mi²), while a male's range is more transient but also larger, between 2–7 km² (0.8–2.7 mi²). Also like feral cats, Iriomote cats scent mark their home ranges to relay information such as sexual receptivity, and their breeding season yowls sound so similar that it's hard to know whether you're hearing the mating ritual of a rare island endemic or a pair of rooting feral cats. So similar are their breeding behaviours that, despite being different species in different genera, the island natives and invaders began to interbreed. And, as one population (the feral cats) grew, and the other decreased, iriomote cats were less and less likely to find a member of their own species at the end of a scent trail or yowling call, and more and more likely to rendezvous with a member of the "other side". The iriomote cats were in danger of interbreeding to extinction — their unique evolutionary heritage preserved only as scattered remnants in the genomes of feral/Iriomote cat hybrids.⁵

Disease, Hunting, & Traffic

Although no exact records exist before 1982 — when monitoring of the Iriomote cat population began — they were probably never very numerous, with estimates hovering at 100 individuals. Small populations are especially vulnerable to disease, and the colonising cats brought such plagues as feline immunodeficiency virus (also known as FIV or “cat AIDS”). That's not to mention the effects of a small population on the genetic health of a species. The Iriomote cat is believed to have suffered a population bottleneck nearly as extreme as they come, with the current population believed to descend solely from two females and a single male.

That small population was further reduced by direct, though often unintentional, killings. Snares meant for wild boars occasionally caught an Iriomote cat instead. Far from a tragedy, such a twist of fortune meant better eating for some locals who considered the cat's meat a delicacy. In fact, the first scientific survey asking islanders about the endemic cat found that 63% of them had seen it in the wild and that 12% had eaten it before.

Other, less malicious, but no less serious threats endanger the wild cat. While the island is a wild haven of trees, so was much of the world before industrial humans arrived en masse. The human population on Iriomote isn't large (around 2,400), but farms restricted to the lowland coastal plains would welcome any room to expand their yield. Dams are built and roadways increasingly snake their way through once-pristine habitats. Around 10 Iriomote cats are struck down by cars on these roads every year. If the estimates are correct, that's 10% of the total population killed annually, solely by human traffic.

The exact number of Iriomote cats alive today isn't known. The IUCN Red List of Threatened Species stopped tracking its population, citing its subspecies status as the reason (read more in footnotes), with the last assessment labelling it as 'critically endangered', and its population decreasing.

Saving the Iriomote Cat

The Iriomote cat was only formally discovered in 1965, although the locals of Iriomote had long known of its existence (and its taste). Recounting all that the species has faced, it's astounding that this wild cat has survived to the modern day. How did it do it? Much can be ascribed to the tenacity of the Iriomote cat itself — its ability to cling on despite the many threats, and continue to beget new generations — but without assistance, it probably would have perished.

Firstly, the invading felines. Veterinarians set up a program targeting the island's feral cat population with the goal of vaccinating (to prevent disease spread) and sterilizing (to prevent feral cat spread and inbreeding with the Iriomote cat) as many as possible. A pet cat population still persisted inside the homes of the island's human residents. This potential source of new strays had to be accounted for. In the town of Taketomi, for instance, pet cats were registered and vaccinated, and any new cats brought to the island were put under quarantine for a time. These actions seem to have been effective. The feral invaders, the superb generalists that threatened to outcompete and infiltrate the gene pool of the Iriomote cat, were put in check. Since 2018, no feral cats have been seen on Iriomote Island.

Efforts have been made to address the other anthropogenic threats. Part of the cat's habitat was declared a protected area and a research station, the Iriomote Wildlife Centre, now tracks the movements of individual cats to learn more about their still mysterious lifestyles. Additionally, feeding stations have been set up to make up for potential prey scarcity, road signs erected to remind drivers that these cats exist and that they should drive carefully, and expedition tours and school visits are educating more people about this island cat.

The Iriomote cat stands as a symbol of its island's natural uniqueness and richness. Its future is far from secure, but ever since the cat's initial isolation, it probably never was. While it faces perhaps its greatest threats today, it has pulled through before and, with help, can do so again.

¹ The taxonomy of the Iriomote cat has a complicated history and real-world implications in the modern day. Upon its discovery, it was classified as its own species, Mayailurus iriomotensis. Later, it was recognized as a close relative of the leopard cat (Prionailurus bengalensis), and indeed actually was a leopard cat — confirmed by genetic studies despite its physical and behavioural differences — and so it was reclassified as a subspecies, Prionailurus bengalensis iriomotensis.

Clockwise from top left: a crested serpent-eagle (*Spilornis cheela*), Yakushima macaques (*Macaca fuscata*), and Yakushima deer (*Cervus nippon*).

² You could make the case that some predatory birds — such as the crested serpent-eagle, with a max wingspan of 170 cm (5.5 ft) — are larger than the Iriomote cat, although they weigh quite a bit less. There are certainly larger, non-predatory animals on the Ryukyu Islands. On Iriomote itself, there are wild boars, which may be smaller than their mainland counterparts but are still significantly larger than the cat. Up near Kyushu, on Yakushima Island, there are Japanese macaques and sika deer (the latter is also found on Zamami Island off Okinawa, brought there in the 17th century and now considered a subspecies known as the Kerama deer). And, of course, the waters surrounding the islands are rich in large aquatic animals, from hefty fish to migrating sea turtles and whales.

³ As mentioned above, leopard cats are solid swimmers, and that hydrophilia is still evident in their descendants on Iriomote. Unlike domestic cats, many wild felines — tigers, jaguars, ocelots, etc. — are fond of water. Most of these cats live in tropical climates, where a dip in a river or lake offers a nice respite from the heat. In the case of smaller wild cats, water can be used as a means of escaping predators. By fording a river, a cat can also reach new hunting grounds or, for the especially skilled swimmers, water can itself be the best place to hunt.

⁴ In the United States, free-ranging cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually — the majority of murders being committed by unowned cats. Free-ranging cats are, quote, "likely the single greatest source of anthropogenic mortality for US birds and mammals".

⁵ Worrying about the intermingling of genomes — trying to keep a gene pool "pure" — has more than a whiff of eugenics to it. To be sure, eugenics is immoral in the human context, and even in some animal contexts, such as dog breeding. But in the case of the Iriomote cat, it's an inappropriate application of human morality. The thing that makes a species what it is (although 'species' is a necessarily fuzzy concept) is its gene pool. We humans, of course, are one species, and we intra-breed freely, today forming a globe-spanning gene pool with more exchange between populations than ever before.

Every member of a species carries its own unique evolutionary history inside every one of its cells. For one animal species to interbreed with another is for their gene pools to mix. In the case of the Iriomote cat and feral cat, it wouldn't just mean that an endemic island species would gradually be made more and more like the ever-present domestic cat, but that its genetic legacy — from which we could potentially learn more about its history — may be scrambled and lost. That's why we worry about such cases of interbreeding; those that happen between an endangered species and a very common one.

A black stilt (*Himantopus novaezelandiae*)

A Scottish wildcat (*Felis silvestris*).

Other examples include the critically endangered black stilt of New Zealand interbreeding with the common pied stilt, the endangered Ethiopian wolf interbreeding with domestic dogs, and another critically endangered wild cat subspecies/population, the Scottish wildcat, facing the same fate that once threatened the Iriomote cat.

**Where Does It Live?**

⛰️ Forested mountain slopes, open country, and beaches.
📍 Iriomote Island, Ryukyu Islands, Japan

Size // Medium
Length // 71–89 cm (28–35 in)
Weight // 2.9–4.5 kg (6.5–10 lb)
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: 7–8 years in the wild, 8–9 years in captivity
Diet: Carnivore
Favourite Food: Varied palate(95+ different prey species)
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Prionailurus
Species: P. bengalensis
Subspecies: P. b. iriomotensis

The Iriomote cat is thought to be a descendant of leopard cats that arrived from Taiwan over 90,000 years ago, when a land bridge existed between the two islands.

Its sole home is now the small — 284 km² (110 mi²) —but lush island of Iriomote.

With no competition from other predators, the Iriomote cat became an extreme generalist hunter, preying on over 95 different species, ranging from fish to birds to bats to bugs.

Unfortunately, feral cats are even better generalist predators. A study surveying cat scat (poop) found that the presence of feral cats negatively correlated with the prevalence of Iriomote cats.

Both feral and Iriomote cats scent-mark to communicate their sexual receptivity, and their breeding season yowls sound so similar that it's hard to tell them apart. As a result, the two often interbreed — or they used to.

Fortunately, after a registration and sterilisation campaign, no feral cats have been seen on Iriomote Island since 2018.

Roads pose another serious risk. Around 10 Iriomote cats are struck by cars every year. If estimates are correct, that's 10% of the total population killed annually, solely by human traffic.

Although the Iriomote cat has no official status from the IUCN (since it's considered a subspecies), its last evaluation in 2014 listed it as 'critically endangered.' The current population may be as low as 100 cats.