Data Zone
Justification of Red List category
This species was extirpated from its native range in 1987 following catastrophic declines owing to predation by the introduced brown tree-snake. A captive population survived and individuals have been released on the islands of Rota and Cocos. Only the Cocos island population is considered to be self-sustaining; the area of this island is tiny, so the population must be extremely small. For this reason, the species is listed as Critically Endangered.
Population justification
Although individuals have been released on Guam and on Rota, there are unlikely to be any wild individuals remaining on Guam and the population on Rota is not yet considered to be self-sustaining. Sixteen birds were released on Cocos Island 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, where it is considered to be self-sustaining. The population size on Cocos has not been estimated, but the area of the island is only c.38 hectares so the population size is likely to be extremely small (F. Amidon in litt. 2012, S. Medina in litt. 2017). The population is therefore placed in the band 1-49 mature individuals.
Trend justification
The species was formerly extinct in the wild and an introduced population has now been established on Cocos, where 16 individuals were released in 2010 and a further 10 in 2012 (The Lost Bird Project Inc. 2013). Although there are no population data from which to estimate a trend, evidence for breeding has been observed and the bird is now found throughout the island, so the population size is suspected to be increasing.
Hypotaenidia owstoni is endemic to Guam (to USA), where it was widely distributed until 1968 when, along with most other indigenous species, it started to decline (Jaffe 1994). In 1981, the population was estimated at c.2,000, in 1983 it was reckoned to number fewer than 100 and, by 1987, it was extirpated from the wild (Witteman et al. 1990). Prior to extinction in the wild, 22 individuals were brought into captivity by the Guam Department of Agriculture (GDOA). It survives in captive-breeding facilities in Guam and in the USA (Ross et al. 2011).
In 1998, 16 individuals were reintroduced to a snake-controlled area on Guam, known as Area 50 (S. Medina in litt. 2018). 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 (P. Wenninger in litt. 2007).
Since 1989, over 1,200 captive-bred birds have been released on various sites on the island of Rota, Northern Mariana Islands (to USA), 90 km north of Guam, in order to establish a reintroduced population. The first 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 were 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). Evidence for breeding on Rota has been observed and the population size was estimated at 125 individuals in 2013 (USFWS 2014), but the amount of continued effort required to sustain the population through further releases of large cohorts means that it may not be considered fully self-sustaining yet (A. Kroner in litt. 2019). Releases continue (S. Medina in litt. 2017).
An additional release project has occurred on Cocos Island off the southern tip of Guam, after a rodent eradication project. Initially, 16 birds were released in 2010, with a further 10 in 2012 (The Lost Bird Project Inc. 2013). Evidence for breeding was observed by 2014 and the bird is now found throughout the island (USFWS 2014). It is now considered that this population is self-sustaining and that the species is no longer extinct in the wild. The population size is still likely to be extremely small as the area of the island is only c.38 hectares (F. Amidon in litt. 2012, S. Medina in litt. 2017).
This flightless species was widely distributed in most habitats on Guam, including forest, savanna, scrub, secondary grassland, fern thickets and agricultural areas (Pratt et al. 1987) (but not in freshwater wetland habitats [Taylor and van Perlo 1998]). Birds released on Rota have been found to prefer open habitats (grassland, scrub, coconut groves and cattle fields) and edge habitats rather than the interiors of forest (USFWS 2014, S. Medina in litt. 2017). It forages along field edges and roadsides (never far from cover) for snails, slugs, insects, geckos, vegetable matter, seeds and flowers from low grasses and shrubs, and also the introduced giant African snail Achatina fulica which became an important part of the diet (Taylor 1996). It breeds throughout the year (birds attaining sexual maturity at four months) with a peak period during the rains in July-November (Haig et al. 1993). Nests are located on dry ground in dense grass, and clutch-size is 1-4, usually 3-4 (Taylor 1996).
Its decline and previous extinction in the wild was the result of predation by the introduced Brown Tree Snake Boiga irregularis (Savidge 1987). Predation by feral cats was responsible for the failure of the reintroduction attempts on Guam and has affected the reintroduced population on Rota (P. Wenninger in litt. 2007, A. Kroner in litt. 2019). Illegal burning has also affected the reintroduced population on Rota (A. Kroner in litt. 2019). Habitat loss on Guam through agricultural and urban development may affect the area and quality of habitat available on Guam, which could affect future reintroduced populations on the island, although the species favours edge habitats so it may not be greatly affected (USFWS 2014). Typhoons may also pose a threat (USFWS 2014).
Conservation Actions Underway
Listed as Endangered by the USFWS. An Action Recovery Plan was published in 1990 (USFWS 1990). Captive breeding started in 1984 and captive populations are maintained in Guam and in the USA mainland (USFWS 2014).
Since 1987, efforts have been under way to establish a reintroduced population on the nearby snake-free island of Rota (Haig et al. 1993). Over 1,200 individuals had been released on the island by 2018. The first years of releases were met with limited success, but intensive management at the Guam captive breeding facility increased reproduction, allowing for larger release cohorts, and birds bred on Rota for the first time in 1999 (K. Brock per G. Wiles in litt. 1999, S. Medina in litt. 2018). The Rota population is dependent on continued releases of large cohorts for its persistence and is not currently considered to be self-sustaining (A. Kroner in litt. 2019). Releases continue (S. Medina in litt. 2017) and the species may become self-sustaining on the island in the future. Control of feral cats is underway on the island (M. O'Brien et. al. 2017). The population is surveyed annually (S. Medina in litt. 2017).
Sixteen individuals were reintroduced to a 24 ha snake-controlled area on Guam, known as Area 50, in 1998 (S. Medina in litt. 2018). Although these birds initially bred (K. Brock per G. Wiles in litt. 1999), this population is now extinct (P. Wenninger in litt. 2007). Research has been underway on methods to control B. irregularis on the island (Engeman et al. 2018b).
An additional release project has occurred on Cocos Island off the southern tip of Guam, following the eradication of Rattus exulans and Mus musculus in 2009 (Engeman et al. 2018a). 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. It is now considered that this population is self-sustaining and that the species is no longer extinct in the wild. The population size is still likely to be extremely small as the area of the island is only c.38 hectares (F. Amidon in litt. 2012, S. Medina in litt. 2017). B. irregularis monitoring and biosecurity efforts are underway on the island to prevent invasion by this species (Engeman et al. 2018a).
28 cm. Medium-sized, flightless, but fast-running rail. Chocolate-brown above. Plain grey eyebrow, lower neck and upper breast. Remaining underparts and remiges boldly barred black and white. Yellow-brown legs and feet. Brown iris. Medium-length bill. Similar spp. Domestic chicken Gallus gallus much larger, chunkier, without barring. Juvenile Common Moorhen Gallinula chloropus plain grey throughout. Voice Loud, screeching kee-yu and short series of kip notes.
Text account compilers
Shutes, S., Ekstrom, J., Stattersfield, A., Westrip, J., Wheatley, H., Dutson, G., Mahood, S., Derhé, M., North, A.
Contributors
Amidon, F.A., Kroner, A., Lepson, J., Wenninger, P. & Wiles, G.
Recommended citation
BirdLife International (2024) Species factsheet: Guam Rail Hypotaenidia owstoni. Downloaded from
https://datazone.birdlife.org/species/factsheet/guam-rail-hypotaenidia-owstoni on 24/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/11/2024.