Chichijima is a small island in Japan’s Ogasawara archipelago, a UNESCO World Heritage site. In 2010, conservationists started trapping the feral cats that roamed it. Three years and 131 cats later, scientists recorded something they had been hoping for, and genetic tests later revealed an even bigger surprise.
In short
- Between 2010 and 2013, 131 feral cats were removed from Chichijima.
- The island’s red-headed wood pigeon, down to fewer than 80 birds in 2008, then rebounded.
- Observed adults rose from 111 to 966 in three years.
- A 2025 study found the pigeons carry fewer harmful mutations than expected.
A bird on the brink
The red-headed wood pigeon lives only on these islands. By 2008, fewer than 80 birds remained, according to a study published in July 2025 in Communications Biology by Daichi Tsujimoto, Mayo Takayanagi, Jyunko Ishii, Ryouko Sakashita, Kazuo Horikoshi, Hajime Suzuki and Yuji Isagi. Isagi, the corresponding author, works at Kyoto University’s Graduate School of Agriculture.
Introduced predators were a major threat. So in 2010, an intensive trapping program began. By 2013, it had removed 131 feral cats, bringing the island’s cat population down to fewer than 20. The cats were trapped and relocated over those three years, OneGreenPlanet reported.
Three years later
The response was fast. Between 2010 and 2013, observed adult pigeons rose from 111 to 966, and juveniles from 9 to 189. The species “experienced a dramatic population increase three years after the removal of introduced predators,” the researchers write. Cats are wonderful companions at home, as our story of the cat who escaped a shelter to find his rescuer shows, but on fragile islands, feral cats can weigh heavily on wildlife.
The genetic surprise
A population that small should have serious genetic problems. To find out, the team compared the pigeon’s DNA with that of the widespread Japanese wood pigeon. Over 80% of the pigeon’s genome is homozygous, a sign of long-term inbreeding. And yet the birds carry fewer highly harmful mutations than the widespread Japanese wood pigeon.
The researchers’ explanation: “Gradual inbreeding in a historically small population before human impact may have purged part of the mutation load.” In other words, centuries of living in small numbers may have slowly weeded out the worst mutations, which helped the pigeons bounce back once the cats were gone.
Why it matters
“In many endangered species with increased homozygosity, population recovery is limited by expressed deleterious mutations,” the authors write in the journal, part of the Nature Portfolio. Put simply, harmful mutations often show up when populations shrink. Chichijima’s pigeon suggests that, for some island species, removing the main threat can be enough to give them a real second chance. As animal behavior experts like to remind us, cats have their own way of seeing the world.
The limit
The sources we consulted describe the cats as trapped and relocated or removed, without detailing what happened to each animal. The pigeon counts are observations, not a full census. And the genetic findings apply to this pigeon; they don’t mean every species can recover the same way.
That’s the story.
