Guam rail (ko'ko')

How it was counted

The estimate was drawn from a mix of survey methods on Cocos Island, the only confirmed wild site, and it is a figure for birds, not nests. The 100 birds in captivity (at the Guam Division of Aquatic and Wildlife Resources facility and in zoos in the United States) are given separately and are not part of the wild figure.

An estimate with a range: surveys on Cocos Island put the wild birds at about 22 to 48, so it is not an exact count.

What moves it

The U.S. Fish and Wildlife Service names limited breeding and the small number of birds among the primary threats, and reports brown treesnakes back on Cocos Island, where fires also affected ko'ko' habitat and encroached on nests. In captivity, the Service reports breeding stalled by little fire ants and Typhoon Mawar, and no way to fly birds between zoos in the United States and Guam. On Rota, where recent surveys by the Guam Division of Aquatic and Wildlife Resources found no birds and the ko'ko' has likely declined or gone from the island, the Service names wildfire and feral cats as the primary threat.

• brown treesnakes back on Cocos Island, the only confirmed wild site. Since the 2020 review, brown treesnakes have re-invaded Cocos Island and were officially documented in 2020. Source: U.S. Fish and Wildlife Service.
• wildfire and feral cats on Rota. Increasing wildfire and feral cats remain the primary threat to ko’ko’ persistence on Rota. Source: U.S. Fish and Wildlife Service.
• wildfire on Cocos Island, where fires in March and April 2024 affected ko'ko' habitat and encroached on nests. Fires also occurred on Cocos Island in March and April 2024, impacting ko’ko’ habitat on the island and encroaching on ko’ko’ nests Source: U.S. Fish and Wildlife Service.
• limited reproduction and small population size, which the review lists first among the primary threats. The primary threats to ko’ko’ include limited reproduction and small population size Source: U.S. Fish and Wildlife Service.
• captive breeding stalled by little fire ants and Typhoon Mawar. A little fire ant (LFA; Wasmannia auropuncta) infestation that began in 2021 and Typhoon Mawar in 2023 resulted in little to no breeding Source: U.S. Fish and Wildlife Service.
• no way to fly birds between US zoos and Guam. the only airline with a direct flight to Guam from the continental United States has stopped carrying birds in cargo Source: U.S. Fish and Wildlife Service.

Who is helping

The Guam Division of Aquatic and Wildlife Resources (DAWR) and Association of Zoos and Aquariums (AZA) zoos are behind the captive breeding programme, begun in 1983 with 22 birds moved to AZA zoos in the mainland United States and to DAWR. The USDA National Wildlife Research Center (NWRC) and USGS study brown treesnakes on Cocos Island and work to clear them from it, with community removal work by Friends of Islan Dåno’.

The next count

The count is expected to be updated every 5 years; no date for the next count is known.

Sources

• U.S. Fish and Wildlife Service Last checked 12 November 2026.

What changed

• 12 November 2026 Added to Live Species, on the wall (1,000 or fewer): 22 to 48 (Estimate, with range, 2025).

Every change on the site