The Guam rail, or ko’ko’ bird, is a flightless bird endemic to the island of Guam. It is a subspecies of the Guam rail family Rallidae. The Guam rail population faced severe declines in the late 1900s due to predation by the invasive brown tree snake and habitat loss. By the 1980s, the Guam rail was considered extinct in the wild. However, some individuals survived in captivity. Reintroduction efforts began in the 1990s to re-establish wild populations on Guam and other snake-free islands. As of 2023, the Guam rail persists in small captive breeding colonies and tiny wild populations, but its survival remains tenuous.
History and Conservation Status
The Guam rail evolved in the absence of natural predators on the remote Pacific island of Guam. Early accounts described it as abundant and easily observed. However, its population began declining rapidly in the 1970s after the accidental introduction of the brown tree snake. This invasive predator preyed heavily on native forest birds like the Guam rail. Habitat loss from development and feral ungulates also contributed to the Guam rail’s demise.
By 1984, the last confirmed Guam rail sighting on Guam occurred. The Guam rail was listed as endangered by the IUCN in 1994 and believed extinct in the wild since that time. Today, the IUCN Red List categorizes the Guam rail as critically endangered (possibly extinct in the wild).
Captive Breeding and Reintroduction
In the 1980s, biologists captured surviving rails to initiate a captive breeding program. The population bottomed out at just 22 birds held at breeding facilities in Guam and U.S. zoos. Careful captive management enabled some recovery. As of 2019, the captive population stood around 200 individuals.
Beginning in the 1990s, Guam rails have been reintroduced onto snake-free islands within their former range. About 60 have been released on Rota and a similar number on Cocos Island. Small populations persist, but have not thrived. On Guam, a few experimental releases occurred within snake exclusion fences. However, these pilot reintroductions were not deemed successful enough to continue. Predation by feral cats also hinders reintroduction success.
Ongoing threats from invasive species mean Guam rail recovery faces major challenges. Biologists continue working to establish stable wild populations while conserving genetic diversity in the captive flocks.
Characteristics
The Guam rail is a flightless, chicken-like bird with a slender bill and red eyes. Adults reach approximately 12-14 inches long and weigh 5-8 ounces. Their plumage is predominantly dark brown on the head, wings, back and tail. The throat, breast and belly are white with black barring. The legs are yellowish.
Guam rails forage on the forest floor probing for invertebrates, seeds and fruits. They prefer native forest habitat with dense undergrowth. Though flightless, they can run quickly through the brush and even climb vines and tree branches. Guam rails communicate with a series of clucks, kek calls and yelps.
Reasons for Decline
The accidental introduction of the brown tree snake devastated Guam’s native wildlife. Originally from the South Pacific, this venomous, arboreal predator likely stowed away on military transport after World War II. It arrived on Guam by the 1950s.
Lacking natural predators itself, the snake population density exploded. Brown tree snakes preyed heavily on native forest birds like the rail. The snakes could reach rail nests in trees and brush with ease. The Guam rail evolved without snake predators and had no natural defenses against this effective hunter.
The snake also impacted the rail by eliminating other native prey species. Additionally, feral cats and habitat destruction from development, agriculture and invasive plants took their toll. The combined pressures proved catastrophic for the Guam rail. Populations plummeted to unsustainable levels despite conservation efforts.
Current Conservation Strategies
Guam rail conservation today centers on two main strategies:
Captive breeding
Specialized breeding centers aim to maintain genetic diversity and produce surplus birds for reintroduction. Captive flocks exist on Guam and in U.S. zoos. Managers follow scientific recommendations for ideal population size and breeding pairings. Developing standard protocols for successful captive propagation continues.
Reintroduction
Releasing captive-bred rails onto snake-free islands is the only possibility for reestablishing wild populations. Efforts have occurred on Rota, Cocos Island and within fenced enclosures on Guam. Future reintroduction sites are being evaluated. However, reintroduction success has been limited so far, highlighting the difficulties in restoring this species. Ongoing threats from snakes, feral cats and habitat loss remain concerns. Adaptive management and technical improvements to the reintroduction strategy are needed.
Potential Recovery Strategies
Full recovery of the Guam rail will be extremely difficult, but biologists propose additional conservation measures:
- Increase captive breeding output while preserving genetic diversity
- Expand reintroduction sites and improve reintroduction protocols
- Control invasive predators at reintroduction locations
- Restore native forest habitat on potential reintroduction islands
- Consider supplemental feeding and predator aversion conditioning for released rails
- Develop invasive snake control or eradication on Guam
- Establish wild populations on multiple islands to spread risk
Adequate funding and strategic planning will be critical going forward. Because the rail is close to complete extinction, each remaining individual is precious for preserving genetic variability. International cooperation between conservation organizations is also important. Recovery will likely require decades of effort given the substantial obstacles.
Conclusion
While the Guam rail still persists, its future remains uncertain. Once abundant and thriving across Guam, it now exists only in captivity and barely-hanging-on tiny wild populations. Though massive declines drove the species to near extinction, dedicated conservation work has prevented its complete disappearance. Continued intensive management of both captive and wild populations offers some hope of eventual reestablishment. However, the Guam rail will likely depend on human intervention for its survival far into the future. The fate of this unique island bird is a sobering reminder of the devastating effects invasive species can inflict. Its story underscores the immense challenges involved in recovering a species once it reaches such a precarious state.
