Cat heaven is a place on Earth — and it’s just 20 minutes by ferry from Fukuoka.

To go there, catch a boat from Shingu Port in Fukuoka to Ainoshima Island. It is a small island, some 1¼ sq. km in size, inhabited by around 500 people, most of whom make their living by fishing.

You will immediately notice the cats. There are hundreds of them, roaming freely. Almost all are feral, wild-living and battle-hardened. For cat lovers, the place is becoming a tourist attraction. The photographer known as Fubirai has spent several years documenting the cats of the island on his blog, and in 2012 his photos went viral on Buzzfeed. A steady trickle of feline enthusiasts are now making the crossing from Fukuoka — the residents of Ainoshima might soon supplement their income catering to the cat-watchers.

Akihiro Yamane has also spent time on the island — seven years. Now a curator at Kitakyushu Museum of Natural History and Human History, Yamane was for many years a leading cat scientist, first at Kyushu University, and then at the Laboratory for Wildlife Conservation at the National Institute for Environmental Studies in Tsukuba — where I met him.

Ainoshima has gained the nickname Cat Heaven Island, but while it may be a great place for scientists — and it has taught us a surprising amount about so familiar an animal — it is not perhaps the ideal place for cats. Feral cats are tough, and have tough lives. They live for just three to five years, compared with around 15 years for the average house cat. Yamane studied the cats in a six-hectare area on the south tip of the island, where there were six garbage patches. The cats arrange themselves in groups, based around ownership and control of the garbage patches. There is a strict hierarchy.

“Male cats fight rivals to secure priority access to females in estrous (on heat),” Yamane says. “That ensures the males are more successful in mating and reproducing.”

By trapping and tagging all the cats, Yamane found that the bigger and heavier a male in a group, the more access to females he secured. Big males also risked incursions into enemy territory — they visited other garbage heaps in attempts to mate with other females. “But these males were beaten there by smaller males of the other group, just like away supporters in a football game.” Very few “away team” copulations were observed.

However, Yamane also took DNA samples of cats and kittens. The analysis showed that despite seeing few copulations between intruding males and females, there were actually far more kittens fathered from outside the group than expected.

Females have more control over who fathers their kittens than you might think from the male-dominated structure of their society. Yamane says he often saw females dash away from their dominant males while the males were snoozing. “In many trials, females failed to escape, because males noticed the movement, but some attempts were successful,” he says.

The reason for this, Yamane suspects, is to reduce the effects of inbreeding.

When he started the study, Yamane says he had no special affection for cats. If anything, he had negative feelings about them, because some birds he kept when he was a child had been killed by cats. But he started to change his mind. He saw how different the life of a feral cat is to that of a house cat.

Female cats had to compete to get enough food to feed their kittens. Life was tough and many kittens died through starvation, disease and even infanticide, as seen in lions. Male cats had to endure dangerous and damaging fights to get the chance to mate. “I found myself respecting them,” Yamane says. “After a while I grew to love them.”

Yamane also observed many instances of male-on-male homosexual behavior. Often this would occur when a fertile female ran away from a courting male; sometimes the male would bite and mount a nearby immature male cat. It is hard to read this as “frustrated” actions on the part of the male — although Yamane says it is not yet fully understood.

Yamane has just written a book drawing together his research on cats. “Neko no Himitsu” (“Secrets of the Cat”) was published this weekend by Bunshun Shinsho. Yamane says the book describes the life of both feral and household cats, from birth to death. One of the issues he considers is how to control the spread of feral cats.

“Feral cats kill and eat endangered endemic wildlife,” he says, “and may even contribute to extinction.”

There are some reports in Japan of feral cats reducing the population of wild birds, and they are suspected of spreading disease to the endemic wildcat, the Iriomote yamaneko. Japan deals with the issue by euthanizing kittens. In 2012 in Japan, some 120,000 cats were euthanized. In some European countries, the problem is tackled by trapping and neutering cats, and then releasing them, but while some local governments have recommended this in Japan, it hasn’t caught on. For Yamane the issue encapsulates other societal problems in Japan.

In the olden days, he says — in the Edo Period (1603-1867) and Showa Era (1926-89) — people did not have enough surplus food to feed stray cats. Now they do, and they feed feral cats. We can’t go back to the olden days, but it is easy to stop feeding cats, he says.

“A problem is that aged people living alone tend to constantly feed feral cats, because they have little contact with other people and feel lonely,” Yamane says. One of the consequences of a society where older people are lonely is that cats are overfed and reproduce at high rates, and their kittens have to be euthanized.

For my part, I love cats, because despite the millenniums of domestic life, they retain impressive predatory characteristics. They are only a whisker away from being wild animals.

Yamane feels the same. In his book, he outlines the characteristics of cats that we find so attractive: beauty, adaptability, a capricious nature, a sense of mystery, independence. Each of them, he says, are byproducts of evolution, the force of natural selection that created an efficient killer.

Rowan Hooper (@rowhoop on Twitter) is the news editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha at ¥1,500. The title is “Hito wa Ima mo Shinka Shiteru (The Evolving Human).”

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