The Guam rail, known locally and in Chamorro as ko'ko', is a small, terrestrial bird endemic to Guam in the Rallidae family. They are one of the island's few remaining endemic bird species. The species became extinct in the wild in the early 1980s when biologists captured the remaining wild population to establish a breeding program. They have since been successfully introduced to the nearby Rota and Cocos islands. In 2019, they became the second bird species to be reclassified by the International Union for the Conservation of Nature from Extinct in the Wild to Critically Endangered.
Region
Micronesia (Mariana Islands)
Typical Environment
Historically restricted to Guam, it now persists through reintroduced populations on Cocos Island (off southern Guam) and Rota in the Northern Mariana Islands. It occupies dense grasslands, coastal scrub, forest edges, and secondary growth where ground cover is abundant. The species forages almost exclusively on the ground and uses thickets and tangantangan stands for cover and nesting. On managed sites, it favors mosaic habitats with nearby open patches for foraging and dense vegetation for concealment. Continued expansion depends on predator-free refuges and snake-exclusion areas on Guam.
Altitude Range
Sea level to 400 m
Climate Zone
Tropical
Ease of Keeping
Beginner friendly: 2/5
Known locally as ko'ko', the Guam rail is a mostly flightless, terrestrial rail that once vanished from the wild due to predation by the invasive brown tree snake. Intensive captive breeding and releases have established populations on nearby snake-free islets such as Cocos Island and on Rota. In 2019 it became only the second species ever downlisted by the IUCN from Extinct in the Wild to Critically Endangered, reflecting reintroduction successes. It remains closely managed with predator control and biosecurity.
A brown tree snake on a barbed wire fence.
Ceremonial statue of a Guam rail (ko'ko), presented as a gift by the Government of Guam.
Temperament
secretive and territorial
Flight Pattern
flightless; runs swiftly through cover
Social Behavior
Typically found singly or in monogamous pairs that defend small territories. Nests are concealed on the ground in dense vegetation, with both parents sharing incubation and chick-rearing. Clutches are small to moderate, and pairs may raise multiple broods under favorable conditions.
Migratory Pattern
Resident
Song Description
Vocalizations include sharp, repetitive kik-kik or kek-kek calls and chattering duets, often at dawn and dusk. Alarm calls are harsher and more rasping when predators or intruders approach.
Plumage
Rich chestnut to dark brown head and upperparts with a gray face and throat; underparts show bold black-and-white barring, especially on the flanks and belly.
Diet
An opportunistic omnivore that takes insects, snails, slugs, spiders, and other invertebrates from leaf litter. It also consumes seeds, fallen fruits, and tender plant shoots. On occasion it may take small vertebrates such as skinks or geckos. Foraging is done by probing and flicking aside leaf litter with the bill.
Preferred Environment
Feeds on the ground in dense grass, scrub edges, and secondary forest margins where cover is close to open foraging patches. Often uses paths, clearings, and the edges of thickets to search for prey while remaining near cover.
