The Guam rail (Gallirallus owstoni), called ko'ko' in the Chamorro language, is a small bird that lives on the ground and is found only in Guam. It belongs to the Rallidae family and is one of the few bird species native to the island. In the early 1980s, the species disappeared from the wild because scientists captured the last remaining birds to start a breeding program. Since then, they have been reintroduced to nearby Rota and Cocos Islands. In 2019, the International Union for the Conservation of Nature changed the bird’s status from "Extinct in the Wild" to "Critically Endangered."
Adult male and female Guam rails have mostly brown feathers with black-and-white stripes on their underparts. Their heads are brown with a grey stripe above the eye and a medium-length grey beak. They have strong legs and long toes that help them walk on wet, marshy ground. Their main sounds are short "kip" calls, and they make loud screeches during the breeding season.
The number of Guam rails dropped sharply because of attacks by invasive brown tree snakes. Today, the birds are bred in captivity by the Division of Aquatic and Wildlife Resources on Guam and in some U.S. zoos. Since 1995, more than 100 rails have been released on Rota Island in the Commonwealth of the Northern Mariana Islands to create a wild population. In 2010, 16 birds were released on Cocos Island, and 12 more were added in 2012.
Taxonomy and etymology
The Guam rail was first named Hypotaenidia owstoni in 1895 by Lord Walter Rothschild. Rothschild explained that the name owstoni honors Mr. Alan Owston of Yokohama, whose workers helped collect specimens on the Marianne Islands. The name Hypotaenidia comes from Ancient Greek words: hypo, meaning "under," and tainia, meaning "stripe" or "band." This refers to the striped feathers found on the bird's underside and wings, a feature common to many rail species. Today, the Guam rail is classified in the genus Gallirallus, which was first introduced in 1841 by Frédéric de Lafresnaye.
Description
Guam rails are medium-sized birds that grow to about 11 inches (28 cm) in total length. Adult Guam rails weigh about 7 to 12 ounces (200 to 350 grams). They have a long body, small wings, and medium-length legs. Guam rails have weak wing muscles and cannot fly well, though they can fly short distances of 3 to 10 feet (1 to 3 meters). Their strong legs allow them to run quickly instead.
Male and female Guam rails look the same and have the same features. They are mainly brown, with a grey beak and tan-colored legs. The head and back are brown. They have a grey stripe across the eyes and throat, a dark blackish chest with white stripes, and dark brown legs and beak.
Distribution and habitat
Historically, the rail was only found on Guam. The island covers about 132,230 acres. A 2013 survey found that about 53% of the island is covered by forests. Rails once lived in many different habitats on the island, such as mixed forests, savannas, grasslands, fern thickets, and agricultural areas. Individuals observed by the Guam Division of Aquatic and Wildlife Resources were noted as preferring edge habitats that provided good cover.
Today, the rail is still found on Guam, but only in captivity. Wild populations have been introduced to Rota and Cocos Islands. Since 1985, the rails have only lived in captivity on Guam at the Guam Department of Agriculture.
Ecology and behavior
Guam rails are shy, fast birds. Although they can fly short distances, they rarely do. They are more often found in savannas and scrubby mixed forests than in large areas of old-growth forest. They usually stay in thick vegetation but have also been seen bathing or feeding near roadsides or forest edges. Their call is a loud, sharp whistle or a series of whistles, often made by two or more birds when they hear a loud noise, another rail’s call, or other disturbances. While individual birds usually respond to another rail’s call, the species is generally quiet.
Guam rails nest on the ground all year and lay 2–4 eggs in each nest. Both parents help build a shallow nest made of leaves and grass. They reach maturity at six months of age and can lay up to 10 nests per year in captivity.
Their nesting habits make them vulnerable to predators, including the native Mariana monitor and invasive animals like feral pigs, feral cats, feral dogs, mangrove monitors, brown tree snakes, black rats, and Norway rats.
Guam rails are omnivores that eat snails, insects, geckos, seeds, and plant material. A significant part of their diet includes giant African snails, which were introduced to Guam around 1945 and became an easy food source. Snail shells and coral have been found in the stomachs of Guam rails, suggesting they use these materials as grit.
Guam rails have been seen foraging and hunting. When foraging, they peck food from the ground and eat seeds and flowers from grasses. They have also been observed hunting insects, especially butterflies.
The species once had a unique louse, Rallicola guami, which likely went extinct due to conservation efforts. When Guam rails were taken into captivity, they were treated to help them survive, which probably caused the louse to disappear.
The brown tree snake (Boiga irregularis) is a major threat to the survival of the Guam rail. The snake was likely brought to Guam accidentally on a military ship after World War II. Once on the island, the snakes thrived because there were many prey animals with no natural predators. Brown tree snakes eat lizards, birds, eggs, insects, small mammals, and human trash. They are active at night, live in trees, and hunt birds and their young that nest on the ground.
Over time, the snake greatly reduced the number of native birds in Guam’s forests. With fewer prey in trees, the snakes began targeting the nests of the Guam rail, which are on the forest floor. It is unlikely the snakes can hunt adult rails, but they often eat their eggs and young.
Invasive animals, such as feral pigs and Philippine deer, harm native forests and the habitat of the Guam rail. These animals damage vegetation by trampling plants and digging for food. Feral pigs also wallow in mud, and deer thin the tree canopy, which disrupts the ecosystem. These actions have changed soil properties, forest ecology, and reduced ground cover.
Feral cats have also made it difficult to reintroduce the species to Guam. After Guam rails were brought back to Andersen Air Force Base in 2006, feral cats killed all the reintroduced birds within eight weeks.
Conservation
The species was once very common, with an estimated population of between 60,000 and 80,000 in the late 1960s and early 1970s. Nine of the eleven types of birds that live in the forests of Guam are no longer found in the wild. Five of these birds were only found on Guam and are now extinct. The Guam rail and the Guam kingfisher are being raised in captivity with the hope that they can one day be released back into the wild. Many other native birds exist in very small numbers, and their future on Guam is uncertain. Most native forest birds, including the Guam rail, were nearly gone when they were listed as threatened or endangered by the U.S. Fish and Wildlife Service in 1984.
Significant declines in the number of Guam rails were not noticed until the mid-1960s. By 1963, many rails that were once common had disappeared from the central part of the island, where snakes were most common. By the late 1960s, the rail population had started to drop in the central and southern parts of the island, and only remained in small, isolated forest areas on the northern end. Snakes began to affect the rail population in the north-central and extreme northern parts of the island in the 1970s and 1980s. The rail population dropped sharply from 1969 to 1973 and continued to decline until the mid-1980s. The last known wild Guam rail was seen in 1987.
Zoologist Bob Beck, a wildlife supervisor with the Guam Department of Agriculture’s Division of Aquatic and Wildlife Resources, led efforts to capture the remaining wild Guam rails, Guam kingfishers, and other native birds to save them from extinction. His work to save the Guam rail began in 1982 and lasted more than 20 years. Beck was important in capturing the last wild Guam rails and starting captive breeding programs for the species on Guam. He later created a release site and introduced a breeding population of Guam rails on the nearby island of Rota in the Northern Mariana Islands.
Beck also helped establish Guam rail breeding programs in zoos across the mainland United States. These programs started with three zoos in the U.S.—the Bronx Zoo, the Philadelphia Zoo, and the National Zoo in Washington, D.C.—and later expanded to other zoos.
The efforts by Beck and others to save the species were successful. By the time Beck died in 2008, there were about 120 Guam rails in captivity on Guam, and another 35 birds were in breeding programs in 17 zoos across the U.S., 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.
By 2019, the number of Guam rails surviving in habitats near Guam had grown to 200 birds on Rota and another 60 to 80 birds on Cocos Island, where 16 birds were released in late 2010.
Biologist Gary Wiles, who worked on the Guam rail breeding program from 1981 to 2000, said of Beck’s work: “Bob was one of the first to organize capturing the birds so they could be brought into captivity, kept there, and bred. He started a captive population. We still have Guam rails today because of his efforts.” Suzanne Medina, a wildlife biologist, also credited Beck with saving the Guam rail, saying, “Bob Beck was the ko’ko’ champion; [he] was Guam’s champion at the time for preventing the extinction of these birds.”
The U.S. Geological Survey and U.S. Fish & Wildlife Service have worked with the Department of Defense and the territorial government since the 1990s to control the brown tree snake population and help reintroduce the rail and other bird species to Guam.
In November 2010, 16 Guam rails were released on Cocos Island, a 33-hectare atoll located 1 mile off the southern tip of Guam, as part of the species’ reintroduction two decades after its extinction in the wild. This effort aimed to provide safe nesting areas for the rails and a place for the public to see them in the wild. Before the reintroduction, rats were removed from the island, and native trees were planted to improve the forest. A survey of native lizards was conducted to ensure the rails had enough food. Monitor lizard populations were reduced to protect the newly released rails. The reintroduction was successful, as evidence of breeding has been observed. This project has provided a model for future reintroductions and has helped develop strategies for detecting and removing rodents and snakes, as well as improving biosecurity measures.
In culture
Guam's official bird is the Ko'ko'.
Every year, the Ko'ko' Road Race Weekend takes place on Guam. This event helps people learn about the Ko'ko' and supports efforts to protect the bird and its habitat.