The Guam rail is a flightless but fast-running bird with a narrow body, native to Guam in the western Pacific Ocean, where it is also known as Ko’Ko, in Chamorro, an Austronesian language spoken by some of the people of the island. However, the bird completely disappeared from the entire island by the late 1980s.It is believed that apart from the feral cats, their population was wiped out by the brown tree-snakes, which were possibly transported to the island unknowingly as a stowaway in military ship cargo from its native range in Papua New Guinea, after World War II.

Fortunately, their populations were established through breeding programs in captivity and currently they survive in the wild by introduced population, only on the islands of Rota, located in the north of Guam, part of the Commonwealth of the Northern Mariana Islands and the uninhabited, small island of Cocos, about a mile off the southern tip of Guam.

The body of Guam rail, about eleven inches in total length and weighing 200 to 350 grams, is elongated and laterally compressed. Although females are slightly smaller than males, their plumage is the same. They have chocolate-brown heads and necks, a plain grey stripe just above the eyes and medium length grey bills. While their lower necks and upper breasts are also grey, they have white stripes, called bars, beneath a mantle of light brown shading to buff on the neck. However, the lower parts of their breast, abdomen, under tail coverts and tail are black with white bars.

Their short wings are dark with brown spots and barred with white, but they have strong, medium-length legs and long toes that help them walk over grasses and soft marsh mud. They cannot fly, but they can swim, dive, and even sink, using their wings underwater. The Guam rail is a secretive, territorial species and is generally silent. But its call is a loud, piercing whistle or series of short whistles, usually given by two or more birds in response to a sudden loud noise or other disturbances.

The Guam rail is an omnivorous species foraging along field edges and roadsides, never far from cover and mostly at dawn and dusk. Although the bird eats seeds, flowers and palm leaves from low grasses and shrubs, it appears to have a preference for non-veg items like geckos, snails, various insects, even low-flying butterflies.

The flightless Guam Rails, listed as critically endangered by the International Union for Conservation of Nature, attain sexual maturity rather early, at about five months and breed throughout the year, especially from July to November. Both the male and female build their shallow ground nest on dry ground with grass and leaves, hidden in dense grasses. After the incubation period that lasts 19 to 21 days, females lay two to four eggs in a clutch and both the parents share to care and feed the chicks. The soft and dark chicks, covered with silky plumage, grow very quickly, getting their juvenile feathers at four weeks and reaching their adult weight in just seven weeks.

Although both the parents continue to feed the chicks, they are actually precocial and become capable to leave the nest to forage with their parents within a very short span of time. It is observed that in captivity, the female Guam Rails live around five to seven years, while the male species has a life expectancy of about nine to ten years.