The small Japanese island of Ōkunoshima, located in the Seto Inland Sea near Hiroshima, is internationally famous for one reason. It is colloquially known as “Rabbit Island” (Usagi Shima) because it is overrun by a large, free-roaming population of wild rabbits. This phenomenon attracts thousands of visitors annually, eager to experience the sight of friendly animals approaching humans without hesitation. The island’s transformation from a place of wartime secrecy to a modern animal sanctuary involves history, ecology, and tourism.
Current Population Estimates and Counting Challenges
Determining the exact number of rabbits on Ōkunoshima is an ongoing challenge, as a precise census is nearly impossible to conduct due to the animals’ behavior. The population is generally estimated to fluctuate between 500 and 1,000 individuals, depending on the season and tourism levels. Prior to the 2020 global travel disruption, surveys confirmed at least 920 rabbits, with local authorities suggesting the true number was likely over a thousand.
More recent observations and surveys, however, have indicated a reduction, with estimates falling to a range of 400 to 600 rabbits in some years. The difficulties in obtaining a stable count stem from the rabbits’ reproductive speed, their small size, and their tendency to hide or be active nocturnally. Researchers often rely on transect counts, a method where visible individuals are counted along a specific path, meaning many animals concealed in burrows are missed.
The population size is highly responsive to external factors, making any single number a temporary snapshot. Since the rabbits are feral and spread across the 0.7 square-kilometer island, obtaining a consistent, accurate census requires resources that are not always available. This constant fluctuation means the island is best described as having a large, dynamic population.
The Unique History of Ōkunoshima and Rabbit Origins
The island’s current reputation as a rabbit haven stands in stark contrast to its dark military past. In 1929, the Japanese Imperial Army established a secretive chemical weapons production facility on Ōkunoshima, producing over six kilotons of mustard gas and tear gas. The island was intentionally erased from unclassified maps to maintain secrecy, earning it the nickname “Poison Gas Island.”
The facility operated until the end of World War II, with workers often suffering from severe health problems due to toxic exposure. Following Japan’s surrender, the Allied Occupation Forces dismantled the factory. Today, the island retains a Poison Gas Museum and the ruins of military structures as a reminder of its history.
The rabbits are not descendants of the animals used for chemical testing during the war. Historical records indicate that the laboratory rabbits were euthanized when the factory was decommissioned. The accepted theory is that the current population originated around 1971, when a small group of domestic rabbits was released onto the island by schoolchildren.
Managing the Rabbit Population Dynamics
The explosive growth of the rabbit population is attributed to the island’s unique ecological conditions, namely the complete absence of natural predators. Regulations strictly prohibit bringing domestic animals like dogs and cats onto the island, and native predators are not present in the small, isolated ecosystem. This allows the rabbits to breed without the typical predation pressures that regulate populations elsewhere.
The population is not without checks, which often come in the form of resource scarcity and disease. The number of animals frequently exceeds the island’s natural carrying capacity, leading to overgrazing and a depletion of natural forage. This dependency on outside resources means fluctuations in tourism directly impact the health and size of the colony.
When tourism is high, the abundance of food leads to a population boom, but the reliance on visitor-provided food can cause health problems. The rabbits have been observed to have a shortened lifespan, partially due to consuming inappropriate foods. When visitor numbers drop, competition increases, and the population naturally declines.
Visitor Guidelines for Interacting with the Wildlife
Visitors to Ōkunoshima are encouraged to interact with the wildlife, but specific guidelines are in place to ensure the safety and health of the rabbits. Despite their friendly demeanor, these are feral animals whose diet must be carefully controlled. Visitors should never feed the rabbits human food, such as bread or sweets, which can cause severe digestive issues like fatal bloat.
The best practice is to purchase approved rabbit pellets, which are typically available at the ferry terminal on the mainland before crossing to the island. Guests should always be mindful of where the rabbits are and avoid feeding them on roads or near building entrances to prevent accidents. Visitors are prohibited from chasing, hugging, or picking up the rabbits, as these actions cause extreme stress and can lead to injury.