Ogasawara Red-headed Pigeon: How 131 Cats Changed Its Fate

Far south of Tokyo, on a remote island archipelago, a rare pigeon appeared to be beyond saving. Researchers and public authorities then intervened, systematically removing feral cats - and something few people expected happened: the bird’s numbers surged. Its return was not simply the result of sound management, but also of a remarkable genetic advantage.

A remote paradise falls out of balance

The Ogasawara Islands sit in the Pacific, more than 1,000 kilometres south of Tokyo. Their isolation has earned them the description “the Galápagos of Japan”: they contain numerous endemic species, ancient forests and a fragile ecosystem.

One of these special species is the Red-headed Pigeon, a rare subspecies of the Japanese wood pigeon group that is endemic to the islands, meaning it occurs nowhere else. For millennia, it lived comparatively safely in the islands’ dense forests, without significant predators on the ground.

That situation gradually changed after settlement began in the 19th century:

• Woodland was cleared
• Domestic animals, including dogs and cats, were brought to the islands
• Some cats became feral and began hunting birds

Feral cats, in particular, became a serious threat. They climbed into shrubs, waited on the ground, raided nests and caught adult birds. The Red-headed Pigeon was an ideal target: it stays close to the ground, is not especially wary and had little adaptation to natural predators.

Near extinction - then a turnaround after 131 cats were removed

Ornithologists raised the alarm in the early 2000s. On Chichijima, one of its principal habitats, researchers counted only around 80 Red-headed Pigeons. Conservationists were already referring to the “last chapter” of the species.

The authorities decided that inaction was no longer an option. In 2010, they introduced a determined programme to control the cat population. Traps were deployed, animals were captured, and some were rehomed while others were euthanised - an emotionally contentious approach, but one with a firm scientific basis.

Within only three years, 131 feral cats were removed from the Ogasawara Islands - eliminating the decisive threat to the Red-headed Pigeon.

The impact was immediately evident in the figures. According to a study published in the Japanese Journal of Ornithology, by the end of 2013 Chichijima was home to:

• 966 adult Red-headed Pigeons
• 189 juvenile birds

In just a few years, a tiny population on the edge of extinction had become a stable bird population again. Such a rapid rise is highly unusual for a species facing this level of threat, and it drew the attention of geneticists.

The Red-headed Pigeon’s unexpected genetic strength

Researchers at Kyoto University took a closer look at the birds’ genetic make-up. Their expectation was that such a small, isolated population would show clear harmful effects of inbreeding, such as greater susceptibility to disease, reduced fertility or shorter lifespans.

Instead, they found the opposite. Genetic analyses revealed that more than 80 per cent of the Red-headed Pigeon’s genome is homozygous. Put simply, many sections of its genes occur in identical versions, indicating close relatedness in its ancestry.

Ordinarily, this would be a warning sign. Harmful mutations often accumulate in small populations because limited genetic diversity cannot keep them “diluted”. Yet a 2025 study in Communications Biology reached a different conclusion: the Red-headed Pigeon carries strikingly few of these damaging changes, considerably fewer than closely related pigeon species with wider distributions.

A genetic “clean-up” over many generations

The researchers describe this as a genetic “purge”, effectively a clean-up of the genome. Across long periods of limited mate choice and moderate inbreeding, especially harmful mutations were repeatedly removed because affected animals had lower chances of survival.

The resulting population is therefore genetically relatively uniform, but appears unexpectedly resilient. Even long-term observations of birds kept in captivity found no link between the degree of relatedness and life expectancy.

The Red-headed Pigeon demonstrates that a small population does not necessarily have to be genetically fragile - if the species has a long history of adaptation behind it.

What the Japanese case means for conservation

Many textbooks still state that small populations are automatically at genetic risk, that inbreeding is almost always harmful, and that greater diversity is inherently better. The Red-headed Pigeon case requires experts to take a more nuanced view of this broad assumption.

Evolutionary processes on islands such as Ogasawara differ from those on the mainland. For thousands of years, a species there may consist of only a few hundred or a few thousand animals. These populations are accustomed to fluctuations and have repeatedly survived periods of extreme scarcity.

Researchers have already documented similar patterns in other species:

• California island foxes, which appear remarkably healthy despite low diversity
• Seychelles warbler populations, which recovered from a tiny surviving remnant
• By contrast, the Mauritius pink pigeon, which has struggled to become stable despite greater genetic diversity

These examples show that meaningful conservation cannot rely on field counts alone. Genome data are becoming enormously important. Only by understanding which mutations have accumulated and how extensively a population has already been “purged” can effective decisions be planned.

Targeted intervention rather than indiscriminate action

The Ogasawara Red-headed Pigeon also illustrates an unpopular but effective measure: removing invasive predators. Cats provoke strong emotions, especially in Western countries, and conservation schemes that involve reducing their numbers regularly face protests.

At the same time, feral cats are among the major drivers of bird deaths on islands worldwide. They hunt not only for survival but also from play instinct, often killing far more than they consume. For isolated species that have never encountered such hunters, the consequences can be devastating.

A growing view among specialists is that a combination is required:

• Genetic analysis of the threatened species, including resilience and hidden weaknesses
• Ecological assessment of the main threats, such as predators, habitat loss and disease
• Targeted interventions addressing precisely those threats, rather than attempting everything at once

That is exactly what happened on Ogasawara. Science showed that, despite its low number of individuals, the Red-headed Pigeon remained sufficiently viable. Attention could therefore focus on cats as its primary enemy. This single, clearly defined lever was enough to put the species back into recovery.

What non-specialists can learn from this case

This story carries several messages that extend far beyond a small island group. It demonstrates how powerfully human intervention - whether poorly conceived or well intended - can disrupt or stabilise natural systems. Several lessons can readily be applied elsewhere:

• Pets in sensitive areas should be neutered and not allowed to roam freely
• The introduction of non-native species must be controlled extremely strictly on islands
• Conservation can begin with a relatively small, clearly defined project

The case also highlights how complex the debate around inbreeding and genetic diversity is. Not every small population is automatically doomed. Some species already carry a kind of “emergency package” in their genes, shaped by many generations of natural selection.

For future projects, this could mean that, rather than reflexively demanding “more animals, more genes, more releases”, it is worth examining the population’s actual genetic quality closely. In some cases, introducing animals from other regions may help. In others, it could disrupt a functioning genetic package that is already well adapted.

The Ogasawara Red-headed Pigeon therefore remains a prime example of the delicate relationship between people, predator and prey. It also shows that a seemingly small step - the systematic removal of 131 cats - can be enough to return a supposedly lost species to the treetops.