Archived 2019 topic: ko’ko’/Guam Rail (Hypotaenidia owstoni): revise global status?

This discussion was first published as part of the 2018 Red List update. At the time a decision regarding its status was pended, but to enable potential reassessment of this species as part of the 2019 Red List update this post remained open and the date of posting has been updated.

The ko’ko’/Guam rail (Hypotaenidia owstoni), a species endemic to Guam, is currently considered Extinct in the Wild due to the introduction of the invasive brown treesnake, Boiga irregularis. Prior to extinction in the wild, 22 individuals were brought into captivity by the Guam Department of Agriculture (GDOA), with the last wild individual documented in 1987 (Witteman et al. 1990). The species has managed to persist at GDOA with the assistance of US mainland zoos. Due to the success of the captive breeding programme, there have been attempts at establishing wild populations of the species. Sixteen individuals were reintroduced to a snake controlled area on Guam in 1998, known as Area 50 (S. Medina in litt. 2018). One bird died within the first week (failure to forage [S. Medina in litt. 2018]) while the rest did remarkably well. Reproduction was documented after six weeks and continued throughout the duration of the project (S. Medina in litt. 2018). However, in 2002, a typhoon destroyed the snake barrier which allowed the birds to disperse from the protected area (S. Medina in litt. 2018) and a lack of reports means persistence there is unlikely (Wenninger in litt. 2007).

Since 1989, >1,200 captive bred birds have been released on various sites on the island of Rota, located 90km north of Guam, in order to establish an experimental population. The first 14 years of releases were met with limited success as release cohorts were small (average 17 birds/cohort) and issues such as cat predation and lack of site fidelity from the release site problematic (S. Medina in litt. 2018). In 1998, the programme was able to overcome these issues when the Guam captive breeding facility increased reproduction by over 400% through intensive management which allowed for larger release cohorts (42-50 birds/release) (S. Medina in litt. 2018). Large numbers of birds are needed for releases to ensure that birds can find one another post release. The amount of continued effort required to manage and sustain the Rota population, however, means that it may not be considered fully self-sustaining yet. Releases continue (the latest being of 49 individuals in September 2017 [S. Medina in litt. 2017]) and the species may become self-sustaining on the island in the future.

An additional release project has occurred on Cocos Island off the southern tip of Guam, after a rat eradication project. Initially, 16 birds were released in 2010, with a further 10 in 2012 (The Lost Bird Project Inc. 2013). Evidence for breeding has been observed, and the bird is now found throughout the island (F. Amidon in litt. 2012, S. Medina in litt. 2017). For a species to be downlisted from Extinct in the Wild as a result of a conservation introduction/translocation, it must have persisted for at least five years and produced viable offspring (IUCN Standards and Petitions Subcommittee 2017). Considering that the last release on Cocos Island was in 2012 and successful breeding has occurred such that the species is now known to occur throughout the island, this species may warrant reassessment. The potential population size is still likely to be extremely small though as the island is roughly only 38 hectares. The species would likely warrant listing as Critically Endangered under criterion D if it were considered no longer Extinct in the Wild.

We therefore request any comments about this potential downlisting of the species from Extinct in the Wild to Critically Endangered.

IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from

The Lost Bird Project Inc. 2013. Highlighting the Guam Rail for endangered species day. Downloaded from

Witteman, G. J.; Beck, R. E.; Pimm, S. L.; Derrickson, S. R. 1990. The decline and restoration of the Guam Rail, Rallus owstoni. Endangered Species Update 7: 36-39.

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4 Responses to Archived 2019 topic: ko’ko’/Guam Rail (Hypotaenidia owstoni): revise global status?

  1. Alan Tye says:

    Given that we only have 5 years’ data for Cocos, with limited evidence of self-sustainability, it might be worth waiting a little longer. Also, there is a definition issue. I am not sure whether the species was originally found on Cocos, but I think not. If it is not “native” to Cocos, then would a population on such a small island as Cocos, where its continued presence depends on conservation management (maintenance of predator-free status), count as a “wild” population, or simply another “captive” population?

  2. James Westrip (BirdLife) says:

    Preliminary proposals

    We would like to highlight that a species does not necessarily need to be introduced to exactly its former ‘native’ range to count towards a Red List assessment. Individuals released for conservation purposes will count towards a Red List assessment as and when other conditions associated with the release are met, as laid out in the IUCN Guidelines. The IUCN Guideline also stipulate that even if there is a certain level of conservation management then a population may be considered wild; one of the examples of such conservation management is control measures against non-native predators. Therefore, these two concerns would not prevent the population on Cocos from counting towards a Red List assessment.

    However, based on available information, our proposal for the 2018 Red List would be to pend the decision on this species and keep this discussion open until 2019, while leaving the current Red List category unchanged in the 2018 update.

    Final 2018 Red List categories will be published on the BirdLife and IUCN websites in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

    IUCN Standards and Petitions Subcommittee. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 13. Prepared by the Standards and Petitions Subcommittee. Downloadable from

  3. Andria Kroner says:

    While working on Rota (studying Mariana Crows) between 2012 and 2018 I observed unbanded Ko’ko’ on multiple occasions, in different locations. This includes one instance in April 2014 of what appeared to be a juvenile with an unbanded parent. I shared video of that observation with Suzanne Medina, who supported my interpretation. This was during a time when I recall few, or no, releases were happening. Unless there is concern that bands of the released birds fall off over time, observations of unbanded individuals would suggest at least some breeding in the wild on Rota, in addition to my observation of a juvenile who may have been 2+ generations wild bred.
    It is unlikely that the Rota population is yet self sustaining, and there are continuing issues with illegal burning in the region that the Ko’ko’ releases occur, as well as non-native predators, which will continue to threaten this species’ progress on Rota, but they appear to be persisting in their current region of north western portion of the island. Based on the criterion that the species has persisted for over 5 years and viable offspring has been produced, from my observations of the species on Rota it seems the Ko’ko’ may qualify for moving out of the “extinct in the wild” category.

  4. Hannah Wheatley (BirdLife) says:

    Preliminary proposal

    Based on available information, our preliminary proposal for the 2019 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline in mid-July, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2019 Red List categories will be published on the BirdLife and IUCN websites in December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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