Species information
Scientific name: Hypotaenidia okinawae
Japanese name: ヤンバルクイナ
Chinese name: 沖繩秧雞、山原秧雞
English name: Okinawa rail
Origin: Northern Okinawajima (endemic)
Ecology and description
1. Appearance
The Okinawa rail has a total length of approximately 35 cm and weighs about 450 g. The plumage from the crown to the tail is deep olive-green, the face is black, and a white line runs from behind the eye to the neck. The legs and bill are bright red, and the underbelly features a black-and-white barred pattern. There is no significant difference in appearance between males and females.
The Okinawa rail was described as a new species in 1981. Before that, locals called it “Agachaa,” meaning the flustered bird, or “Yamadui,” meaning the bird of the mountains. The Japanese common name, Yambaru Kuina, emphasizes that it is endemic to the Yambaru region.
The Okinawa rail is the official bird of Kunigami Village. It is designated as a National Natural Monument (Law for the Protection of Cultural Properties), a Nationally Endangered Species of Wild Fauna and Flora (Act on Conservation of Endangered Species of Wild Fauna and Flora), and is an endangered species.
2. Habits
The Okinawa rail is primarily diurnal, searching for food in the forest or bathing by the water during the day. At night, it sleeps in trees to avoid predators such as the Habu viper. It has sturdy legs and powerful claws that allow it to grip bark and walk up into trees. Consequently, giant trees with deeply fissured bark, such as Ryukyu Pine (Pinus luchuensis) or Castanopsis sieboldii, are its favorite sleeping spots.
The species is omnivorous, feeding on earthworms, lizards, acorns, snails, and various plant seeds. If you find large snail shells broken in the middle in the forest, those are traces of the Okinawa rail feeding. They have favorite “snail-hammering stones”; research shows that an individual rail will repeatedly bring snails to the same stone to crack them, leaving scattered shells nearby.
Okinawa rails nest on the ground and breed from late March to June. They lay 3 to 5 eggs per clutch, which hatch after about three weeks. Newly hatched chicks are entirely black. Both parents share the brooding duties. After about two months, the chicks develop the same coloration as adults and become independent.
3. Evolution
Evolution Close relatives of the Okinawa rail are distributed across various Pacific islands. This suggests that the ancestor of the Okinawa rail was likely a flighted rail species that dispersed to different islands. In the absence of terrestrial mammalian predators on small islands, they evolved into flightless forms. The flightless rails found on various islands are likely results of multiple independent events of convergent evolution. (Source: Lecture slides)
The skeletal specimen displayed at the Yambaru Wildlife Conservation Center shows that, unlike typical birds, the Okinawa rail lacks a well-developed sternum and keel. The sternum is where breast muscles attach, and the ridge-like projection in the middle is called the keel, which supports the large muscles required for flight. In birds that fly long distances, such as pigeons, the keel is highly developed. However, observing the Okinawa rail skeleton reveals a small sternum, a non-protruding keel, wings that are small relative to the body, and very long legs. This structure demonstrates its adaptation to a flightless life, walking on the ground and climbing into trees.
Most extinct rail species on Pacific islands vanished due to the intrusion of human civilization, as flightless rails were easily caught for food. Fossils of the Okinawa rail have been found in caves in southern Okinawa in strata dating back approximately 20,000 years. The extinction of the species in central and southern Okinawa today is likely due to the development of human habitats, which led to a massive decline in their population.
Threats to the Okinawa Rail
1. Invasive Small Indian Mongoose
The Small Indian Mongoose was introduced to Okinawa in the past with the hope of reducing the Habu viper population. However, after spreading to northern Okinawa, they began preying on the Okinawa rail, causing a rapid decline in the rail’s population. Thanks to the efforts of the “Mongoose Busters” (anti-mongoose task force), the mongoose population in the Yambaru region has significantly decreased, and the number of Okinawa rails is currently recovering.
2. Invasive Feral Cats and Dogs
Abandoned pet cats and dogs in the Yambaru region can become feral and prey on local wildlife, including the Okinawa rail. The Okinawa government is actively promoting measures such as microchipping and neutering/spaying for pets. If stray cats or dogs are spotted in the mountains, they are captured using traps and announced on the Kunigami Village website. If no owner is found, they are put up for adoption.
3. Roadkill
Historical data indicates that the peak month for Okinawa rail traffic accidents is during the brooding season in May and June. During this period, adults frequently forage by the roadside to feed their chicks, increasing the risk of being hit by vehicles. Furthermore, accidents occur most frequently between 6:00 AM and 8:00 AM, which is the peak foraging time for the rails. Drive carefully at all times in the Yambaru region to avoid roadkill.
Data source: 1995-2023 Roadkill Statistics
If you find an injured Okinawa rail (or accidentally hit one), please immediately contact the Yambaru Wildlife Conservation Center (0980-50-1025) or the NPO Animal Hospital Okinawa (090-6857-8917). Tell the conservation staff your location. If you are on a prefectural road, look for the blue road sign indicating the road number (e.g., Prefectural Road 70), the location name (e.g., Sosu), and the kilometer marker.
Field photographs taken during our tours, with observation dates
Observation Records and Photos from Tours During the 【Night Birding】 tour, we can frequently observe Okinawa rails roosting in trees at night. Based on past experience, during periods of low winter temperatures or during the incubation period starting in April, the rails often do not choose to stay in trees overnight; thus, observation chances are relatively lower during these times.
The best season to observe roosting Okinawa rails at night is usually August and September, when the chicks are learning to climb trees. During this time, there is a chance to see juveniles perched on lower branches. On the night of August 17, 2025, we observed 14 Okinawa rails, and on September 16, 2025, we observed 18.
Additionally, during the 【Morning Birding】 tour between April and July, there is a chance to observe Okinawa rails brooding their young during the day.
