Ogasawara Pigeon Recovers After 131 Feral Cats Are Removed

Far out in the Pacific, more than 1,000 kilometres south of Tokyo, the red-headed Ogasawara pigeon, a rare forest bird, was considered all but lost. Human intervention then changed the picture: a small number of voracious predators were deliberately removed from the ecosystem, and the trend suddenly reversed. Yet what appears to be a straightforward conservation success story also reveals a remarkable genetic advantage.

An isolated paradise falls out of balance

Often called the “Galápagos of Japan”, the Ogasawara Islands are volcanic outcrops in the open ocean. Their isolation has shaped a distinct range of plants and animals over thousands of years, including the red-headed Ogasawara pigeon, an endemic subspecies found only in these dense evergreen forests.

Everything changed when settlers arrived during the 19th century. Forests gave way to farmland, roads and settlements. People also brought domestic cats, pigs and goats, triggering a pattern well known to island ecologists: pets escape, become feral and begin hunting native wildlife.

Cats, in particular, became a serious threat on Chichijima, one of the main islands. They preyed on ground-nesting birds, raided nests, caught young birds and further weakened an already small population. By the early 2000s, researchers counted only around 80 red-headed Ogasawara pigeons. Forecasts suggested that the species could disappear within a few decades.

“What began as a side effect of keeping pets developed into an existential threat to one of Japan’s rarest birds.”

The turning point: 131 cats are removed and the Ogasawara pigeon returns

In 2010, Japanese authorities decided that the situation could not continue. Rather than relying on isolated, half-hearted measures, they launched a systematic programme targeting stray and feral cats. Its aim was to reduce pressure on the key breeding areas of native birds.

Over just three years, specialists trapped 131 cats and removed them from sensitive areas. It may sound like a plain statistic, but on a small island it represents a major intervention in the ecosystem’s web of relationships.

The Ogasawara pigeon responded with striking speed. By the end of 2013, researchers reported 966 adult birds and 189 young birds. A population that had numbered only a few dozen had rapidly become stable and growing. For a species that had been close to extinction, this was exceptional.

• Early 2000s: around 80 known birds
• 2010–2013: 131 feral cats trapped
• End of 2013: nearly 1,150 birds (adults + young)

Recoveries of this kind are more commonly associated with resilient species such as wild boar or crows, rather than highly specialised island birds. This raised an obvious question: how could this bird withstand so much when its genetic base was so narrow?

Genetic puzzle: highly inbred, yet remarkably healthy

A research team at Kyoto University examined the genetic material of several wild and captive birds. The findings surprised even geneticists: more than 80 per cent of the genome is homozygous, meaning it is essentially identical across both chromosomes. Put simply, the birds show extremely high relatedness and very little variation.

Normally, this would be a warning sign. Small, isolated populations frequently suffer from inbreeding depression, including congenital defects, reduced fertility and weakened immune systems. However, researchers did not observe these problems in the Ogasawara pigeon.

A study published in Communications Biology in 2025 offers one possible explanation. It appears that the species has eliminated harmful mutations over many generations. This process is known as genetic purging. A moderate degree of breeding between relatives over a long period may have gradually removed the most damaging genetic faults from the population.

“The Ogasawara pigeon carries remarkably few harmful mutations, despite centuries of isolation and severe inbreeding.”

Tests involving captive birds showed that individuals with a higher degree of relatedness did not have shorter lives, were not markedly less healthy and did not produce fewer offspring than genetically more “varied” birds. That runs counter to many conventional assumptions in conservation.

When evolutionary history makes the difference

The researchers interpret the case as follows: the species experienced a “bottleneck” long ago, a period when very few birds remained. Many harmful variants disappeared at that point because the individuals carrying them either did not survive or failed to reproduce successfully. What remained was a small but relatively robust genetic foundation.

When the cats were removed, the bird was therefore, in a sense, ready to recover. It retained sufficient genetic health to reproduce quickly, while having so little variation that newly arising dangerous mutations had little impact.

What this case means for conservation

For a long time, conservationists have relied on simple principles: a small population means high risk, and low genetic diversity means poor prospects. The Ogasawara Islands now demonstrate that such formulas can sometimes be too crude.

Other cases support this view. Island species, including some fox species and certain Seychelles songbirds, show similar patterns: small populations, extensive inbreeding and yet unexpectedly stable numbers. Conversely, species with what appears to be a “good” genetic starting point, such as the Mauritius pink pigeon, have struggled to survive for decades despite intensive conservation programmes.

The implication is that conservation requires closer examination. Rather than comparing only population figures and broad genetic measures, programmes should give greater weight to the individual history of each species:

• How long has it been isolated?
• Were there previous bottlenecks that may already have “filtered” its genetic material?
• What role do introduced predators or diseases play?
• Can a small but stable population be maintained rather than forcing “more diversity” at all costs?

Lessons from the Ogasawara Islands: sensitive intervention

The bird’s rapid recovery did not result from huge budgets or complex breeding schemes. Three factors mattered most: the right timing, a clearly defined intervention and a genetic make-up that was already reasonably resilient.

“Sometimes removing one dominant stress factor is enough for a weakened ecosystem to help itself.”

For other places facing comparable problems, such as those dealing with feral cats in Australia or on Mediterranean islands, the Japanese case could provide a model. Restricting major predators in a targeted way can give endemic species breathing space. The ethical and practical question of how to deal with feral pets remains important: culling programmes are controversial, while relocation or consistent neutering costs money and requires public support.

Why feral cats transform islands so profoundly

Cats are among the animal kingdom’s most efficient hunters. On islands where birds often have no experience of terrestrial predators, cats encounter prey that is unprepared. Many species nest on the ground, flee slowly or have no fear of mammals. For a roaming cat, this is an easy hunting ground.

Cats also do not hunt only when they are hungry. They are driven by a powerful prey instinct. Even well-fed animals regularly bring birds home to their owners. On small islands, this persistent hunting pressure can cause entire populations to collapse within a few years.

Anyone seeking to protect island ecosystems therefore finds it difficult to avoid managing cats, whether through consistent neutering, preventing further abandonment or, in sensitive conservation areas, fully removing feral animals.

What non-specialists can take from this story

The Ogasawara Islands case is not aimed solely at experts. It clearly illustrates how everyday human actions can affect ecosystems far away. Every unneutered outdoor cat and every pet abandoned on a holiday island can eventually become part of a much wider problem.

At the same time, the story offers hope. Even species that have almost disappeared from public attention can recover if their main threats are kept away and the particular features of their evolution are understood. Not every species is as genetically robust as the red-headed bird from Japan. However, its return shows that well-planned, limited interventions can often achieve more than spectacular large-scale projects that overlook the details.