Pacific Islands Fish and Wildlife Office
Pacific Region

Endangered Species in the Pacific Islands

Guam Rail / Gallirallus owstoni  / Ko‘ko‘

Photo of Guam rail The Guam rail has a brown head, neck and eye stripe; near gray throat and upper breast; short wings that are dark with brownish spots and barred with white; lower breast, abdomen, under tail coverts, and tail are blackish with white barrings; gray bill, long legs and dark brown feet; and red iris. Females are similar but slightly smaller than male.
Guam rail - Photo credit Suzanne Medina/Guam Department of Agriculture

Habitat & Behavior: The Guam rail is a secretive, flightless, territorial species that is most easily observed as it bathes or feeds along roadsides or field edges. The call is a loud, piercing whistle or series of whistles, usually given by two or more birds in response to a loud noise, the call of another rail, or other disturbances. Though individuals will respond almost invariably to the call of another rail, the species is generally silent.

The rail is one of the few native birds of Guam that is found more frequently in scrubby second growth or mixed forest than in uniform tracts of mature forest, and might have been more abundant after the arrival of humans than before.

It is omnivorous but appears to prefer animal over vegetable food. It is known to eat gastropods, skinks, geckos, insects, and carrion as well as seeds and palm leaves.

The rail is a year-round ground nester making it highly susceptible to predators, such as the monitor lizard and the rat. It lays 2-4 four eggs and both parents share in the construction of a shallow nest of leaves and grass. A far more efficient predator was introduced in the 1950s, the brown treesnake. The brown treesnake is generally considered to be the primary cause of the disappearance of most of Guam's native birds.

Past & Present:
Before the 1970s, the Guam rail occurred island-wide and distributed in all habitats except wetlands. The population declined severely from 1969-1973, and the rail disappeared from southern Guam in the mid 1970s. The decline of the rail continued until in 1980, only 10 rails were recorded. In a desperate move, 21 birds were caught in the wild in the mid-1980s and placed in captive breeding both in the continental United States and on Guam.

Conservation Efforts:
The U.S. Fish and Wildlife Service began conducting systematic forest bird surveys in Micronesia in 1981. The majority of forest birds were protected on Guam by the turn of the century with such acts as Guam Public Law 6-87 which prohibited the taking, buying or selling of wild birds or their eggs and the Endangered Species Act of Guam (Guam Public Law 15-36), which protects both locally and federally listed endangered species on Guam. The Government of Guam also established four conservation reserves that provided protected habitat for many native species, at least until the brown tree snake invaded.

A brown treesnake barrier was erected around a 60-acre parcel known as Area 50 on Andersen Air Force Base in 1998, and 16 Guam rails were released into the area in November 1998 - the first Guam rails to exist in the wild on the island since the mid-1980s. Breeding was documented, however, the small population was believed to have been extirpated by feral cats and other predators. A second release of 44 Guam rails was undertaken in a snake controlled area of Anderson Air Force Base in 2003. Due to predatory feral cats, it is believed that no Guam rails exist on Guam at this time.

The Cocos Island Resort, Guam Department of Agriculture, and US Fish and Wildlife Service entered into an agreement to create a safe harbor for the Guam rail on Cocos Island in 2009. Rats were eradicated prior to release. On November 15, 2010, sixteen captive bred ko'ko birds were released into the wild on Cocos Island. Guam rails also have been introduced on Rota, an adjacent island that has not been invaded by brown treesnakes. Every year about 100 ko'ko birds are released on the island of Rota in an effort to preserve the species.


Last updated: September 20, 2012
Pacific Islands Fish and Wildlife Office
Pacific Region Home

U.S. Fish and Wildlife Service Home Page | Department of the Interior  |  | About the U.S. Fish and Wildlife Service  | Accessibility  | Privacy  | Notices  | Disclaimer  | FOIA