Brief Summary

The Guam Rail (Gallirallus owstoni) is a flightless bird, endemic only to the United States territory of Guam.  In the Chamoru language, used on Guam, it is known as Ko'ko'.  Before 1960 it was common, though it has a secretive lifestyle living in scrubby secondary growth or mixed forest.  The Guam Rail disappeared from southern Guam in the early 1970’s and was extirpated from the entire island by 1987 due to the accidental late-1940’s introduction of the brown tree snake Boiga irregularis.  Department of Agriculture biologist Bob Beck found that Guam rails breed well in captivity and established a breeding program which keeps birds at the Division of Aquatic and Wildlife Resources on Guam and at 15 mainland U.S. zoos.  Captive grown rails were reintroduced to Guam in 1998 with no long-term success, and subsequently introduced to the snake-free island of Rota (Northern Mariana Islands), where two small breeding populations were able to persist despite hunting pressure from feral cats.  In 2011 birds were also introduced to the island of Cocos, where they appear to be breeding.

The Guam rail is a medium-sized rail about 28 cm (11 in) in total length. The body is elongated and laterally compressed, particularly in the neck and breast regions, allowing the birds to move rapidly through dense vegetation. Males are slightly larger than females but have similar appearance with brown head and back, a dark breast barred with white, grey eye stripe and dark brown legs and beak. Gallirallus owstoni are generalists; they eat slugs, snails, lizards, insects, carrion and plant matter such as seeds, leaves, flowers and grasses.  They nest year-round on the ground, with a usual clutch size of 3-4 eggs.  They are territorial, usually silent but will give a loud whistle or series of whistles in response to the call of another bird or a disturbance.  (BirdLife International 2012; Fritts and Leasman-Tanner 2001; Wikipedia 2013)

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Historic Range:
Western Pacific Ocean_U.S.A. (Guam)


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Forests of Guam (s Mariana Islands). On verge of extinction.
  • Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/


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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Gallirallus owstoni

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 4
Species With Barcodes: 1
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© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)


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Conservation Status

Current Listing Status Summary

Status: Endangered
Date Listed: 04/11/1984
Lead Region:   Pacific Region (Region 1)   
Where Listed: except Rota

Status: Experimental Population, Non-Essential
Date Listed: 10/30/1989
Lead Region:   Pacific Region (Region 1)   
Where Listed: Rota

Population detail:

Population location: Entire, except Rota
Listing status: E

Population location: Rota
Listing status: EXPN

For most current information and documents related to the conservation status and management of Gallirallus owstoni, see its USFWS Species Profile


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Guam rail

The Guam rail (Gallirallus owstoni) (Chamorro name: ko'ko' [2]) is a flightless bird, endemic to the United States territory of Guam. The Guam rail disappeared from southern Guam in the early 1970s and was extirpated from the entire island by the late 1980s. This species is now being bred in captivity by the Division of Aquatic and Wildlife Resources on Guam and at some mainland U.S. zoos. Since 1995, more than 100 rails have been introduced on the island of Rota in the Commonwealth of the Northern Mariana Islands in an attempt to establish a wild breeding colony. Although at least one chick resulted from these efforts, predation (largely by feral cats) and accidental deaths have been extremely high. A small number of birds potentially persists.


Nine of the 11 species of native forest-dwelling birds have been extirpated from Guam. Five of these were endemic at the species or subspecies level and are now extinct on Guam. Two of these species, the Guam rail and the Micronesian kingfisher, are being captively bred in zoos in the hope that they can eventually be released back into the wild. Several other native species exist in precariously small numbers, and their future on Guam is perilous. Most native forest species, including the Guam rail, were virtually extinct when they were listed as threatened or endangered by the U.S. Fish and Wildlife Service in 1984.


The Guam rail is a flightless species endemic or unique and only found in the island of Guam. It is a medium sized rail about 28 cm in total length. The body is elongated and laterally compressed, particularly in the neck and breast regions, allowing the birds to move rapidly through dense vegetation. The plumage or feather color and pattern of both sexes is similar, however males can often be distinguished by their larger size. The head and back are brown. It has a grey eye stripe and throat and a dark blackish breast with white barring. The legs and beak are dark brown. This species is a generalist, preferring animal over vegetable matter.

Behavior and habitat[edit]

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

It is a year-round ground nester making it highly susceptible to predators, such as monitor lizards and rats. It lays 2-4 eggs and both parents share in the construction of a shallow nest of leaves and grass. They mature at six months of age and have been known to produce up to 10 clutches per year in captivity.


The Guam rail 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 Guam rail was abundant on the island with a population estimated to be around 70,000 before the 1960s. It evolved in the absence of predators such as snakes and rats. It was so common that it was hunted for food. After the end of World War II, the brown tree snake was accidentally transported from its native range in Papua New Guinea to Guam, probably as a stowaway in military ship cargo. Beginning in the 1960s, the snake became well established as numbers began to grow exponentially and the rail populations plummeted along with the rest of Guam's native avifauna. The Guam rail had no experience with such a predator and lacked protective behaviors against the snake. Consequently, it was an easy prey for this efficient, nocturnal predator.

Appreciable losses of the Guam rail was not evident until the mid 1960s. By 1963, several formerly abundant rails had disappeared from the central part of the island where snakes were most populous. By the late 1960s, it had begun to decline in the central and southern parts of the island and remained abundant only in isolated patches of forest on the northern end of the island. Snakes began affecting the rail in the north-central and extreme northern parts of the island in the 1970s and 1980s, respectively. The population declined severely from 1969 to 1973 and continued to decline until the mid 1980s. It was last seen in the wild in 1987.

Conservation efforts[edit]

Ceremonial statue of a Guam rail (Ko'ko), presented as a gift by the Government of Guam.

Zoologist Bob Beck, a Guam Department of Agriculture Division of Aquatic and Wildlife Resources wildlife supervisor, is credited with leading the efforts to capture the remaining wild Guam rails, Micronesian kingfishers and other native birds to save them from extinction.[2] His efforts to save the Guam rail began in 1982 and lasted more than 20 years.[2] Beck was considered to be instrumental in capturing the remaining population of Guam rails and establishing captive breeding programs for the species on Guam.[2] He later established a release site and an introduced breeding population of Guam rails on the neighboring island of Rota in the Northern Mariana Islands.[2]

Beck was also a driving force in establishing Guam rail breeding programs in zoos throughout the mainland United States.[2] Beck's Guam rail breeding program initially began with just three zoos in the U.S. - the Bronx Zoo, the Philadelphia Zoo and the National Zoo in Washington, D.C.[2] The program proved to be successful and was soon expanded to include other zoos. Seventeen zoos now participate in the Guam rail breeding program, as of 2008,[2] including the Audubon Zoo in New Orleans, the San Diego Zoo, the Santa Fe College Teaching Zoo, and zoos in Chicago, Houston and San Antonio.[2]

The efforts by Beck, and others, to save the Guam rail have been promising. There are now approximately 120 Guam rails in captivity in Guam and approximately 35 birds in captive breeding programs throughout the United States.[2] Biologist Gary Wiles, who worked on the Guam rail breeding program from 1981 through 2000, said of Beck's efforts to save the Guam rail, "Bob was one of the first to begin organizing catching the birds so they could be brought into captivity, held there and bred. He started a captive population. We still have Guam rails today because of his efforts."[2] Suzanne Medina, a wildlife biologist, also credited Beck with saving the Guam rail, "Bob Beck was the ko'ko' champion, was Guam's champion at the time for preventing the extinction of these birds."[2]

A recent effort to introduce rails on Guam in a 22 hectare forested area concentrated on protecting the rails by limiting snakes using a combination of trapping and a perimeter barrier to reduce re-invasion by snakes. This endeavor allowed the tentative survival of several pairs of rails released into the area. Reproduction by the rails was reported in this control area on the basis of sounds attributed to chicks. The preliminary success constitutes one of the few bright spots in the conservation of Guam's native fauna in recent years and speaks to future opportunities to recover wildlife. [1]

In November 2010, 16 Guam rails were released on Cocos Island, a 33 hectare small atoll 1 mile off the coast of the southern tip of Guam as part of its reintroduction two decades after its extinction in the wild. It was an effort to provide safe nesting areas for the rails, as well as a place for the public to see them in the wild. Before the reintroduction, rats were eradicated off the island and the forest was further enhanced with native trees. A native lizard survey was conducted to make sure that the rails had enough food to eat. Monitor lizard populations were reduced to minimize their impacts of the newly released rails. The reintroduction proved to be successful as evidence of breeding have been observed. This will provide a model environment to develop strategies for future reintroductions as well as expertise in rodent and snake detection, eradication, and bio-security measures.[3]


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