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

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 not 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 http://www.iucnredlist.org/documents/RedListGuidelines.pdf.

The Lost Bird Project Inc. 2013. Highlighting the Guam Rail for endangered species day. Downloaded from http://www.lostbirdfilm.org/highlighting_the_guam_rail_for_endangered_species_day.

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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