Scientific Name: Rallus owstoni (Family RALLIDAE)

Common Name: Guam Rail

CHamoru Name: Ko’ko’

Audio sample of the Ko’ko’

Habitat and Natural History: The Ko’ko’ is a large rail, standing 11 to 12 inches or about 28 centimeters tall. It lived in secondary forested areas mixed with grasslands and limestone forest, especially the edges near grassy areas. It nests year round laying one to four eggs in a nest of leaves and grass on the ground. The eggs are tended by both parents. Chicks can run after four days. Considered flightless, the ko’ko’ can only fly very short distances. It is an omnivorous feeder but seems to favor animals. It feeds on seeds and leaves as well as snails, lizards, insects and carrion.

Description: About 12 inches tall with long legs and large feet. The head, neck and eyestripe are brown. The short wings are spotted brown with white bars. The iris is red. The beak is grey.

Range: Guam, where it is endemic.

Current Status: About 70 ko’ko’ live on Dåno’ (Cocos Island) off the coast of Merizo and about 150 live on Luta (Rota). There is a partnership with the American Zoo Association and the Guam Division of Aquatic and Wildlife Resources for the captive rearing program. As of 2019, there are more ko’ko’ in the wild than captive ones. Although there are ko’ko’ living in the wild on Dåno’ and Rota, its status of “extinct in the wild” will not be changed until wild populations are established on Guam.

Threats: Habitat destruction and predation by the brown treesnake as well as feral cats, possibly pigs and hilitai (monitor lizards).

By Gretchen R. Grimm, MS

Visit a Ko’ko’ on Guam
The Cushing Zoo