Data Zone
Justification of Red List category
This species has a very small population size that is inferred to be declining primarily owing to nest predation by Black Rats, with no subpopulation exceeding 1,000 mature individuals. It is therefore assessed as Vulnerable.
Population justification
The total population was estimated at 1,261 mature individuals (95% CI=1,205-1,317) following surveys conducted from 2011-2012 (VanderWerf et al. 2013), consisting of about 477 breeding pairs and 307 single males. This total includes 592 males (95% CI= 554-630) and 369 females in the Ko'olau Mountains and 192 males and 84 females in the Wai' anae Mountains (VanderWerf et al. 2011a, 2013). The genetically effective population size may be even lower because of the fragmented distribution (VanderWerf et al. 2001, 2013).
The largest subpopulations are in the central (523 mature individuals) and southeastern Ko’olau (403 mature individuals) Mountains, with smaller subpopulations in ‘Ekahanui (100 mature individuals), Schofield Barracks West Range (104 mature individuals), Palehua (41 mature individuals), Waikane and Kahana Valleys (24 mature individuals), and several tiny fragments containing 1-5 mature individuals each (VanderWerf 2012a).
Trend justification
Surveys conducted in the 1990s produced evidence that the species had declined by more than 75% since 1975 and by approximately 96% since the arrival of humans (VanderWerf et al. 2001). The species has continued to decline over much of its range, particularly in the Wai`anae mountains, where only 300 birds were found in 2006-2010 (VanderWerf et al. 2011a), and overall has declined in abundance by about 50% since the 1990s, when the population was estimated to be about 1,974 birds (VanderWerf et al. 2001). Numbers have been shown to remain stable or increase in areas where rats are controlled (VanderWerf et al. 2013). The overall trend of the species in the O?ahu Army Natural Resources Program (OANRP) recovery areas (Schofield Barracks Military Reservation, ?kahanui Gulch in Honouliuli Forest Reserve, Palehua and Moanalua Valley) has remained somewhat stable between 2013-2018, likely due to effective predator control in these areas (USFWS 2019). In 2017 the number of ‘elepaios in the area where rats had been controlled in Pia Valley had declined somewhat since 2007, which was the last year of rodent control (VanderWerf 2017). Between 2013 and 2018, the number of pairs appears to have declined in Wailupe Valley (USFWS 2019). Little is known on the status of O?ahu ?Elepaio outside of the OANRP recovery areas and Wailupe Valley, although populations continue to be limited by habitat loss, modification and avian disease and predation (USFWS 2019). It is likely that areas where rats are controlled serve as sources of emigrants that help to support adjacent areas where declines are ongoing due to high levels of predation (VanderWerf et al. 2013). Given that stability of populations is heavily reliant on rodent control and that rats are not sufficiently controlled throughout the range (USFWS 2019), the population is inferred to be declining overall.
Chasiempis ibidis is endemic to O'ahu in the Hawaiian Islands (USA).
The species is most abundant in mesic forest in valleys (VanderWerf et al. 2001), preferring mixed-species forest with a tall canopy and well-developed understorey, at 200-800 m (VanderWerf et al. 2001). The species is less common in drier forest (Vanderwerf 1998). It feeds on insects and other invertebrates (VanderWerf 1998).
Habitat loss to development has been extensive, with 56% of its former range lost to agricultural or urban development (VanderWerf et al. 2001), though most areas where the species still occurs are zoned for conservation and are protected from development. The primary threats responsible for the decline of the species are nest predation by alien Black Rats (Rattus rattus) and mosquito-borne diseases (VanderWerf et al. 2013).
Nest-predation by black rats is the most serious current problem (VanderWerf et al. 1997, 2001; VanderWerf 1998, 2009), leading to a male-biased sex ratio (VanderWerf et al. 2001). Feral cats Felis catus and mongooses Herpestes auropunctatus are additional predators. Invasive alien plants promote high rat abundance because many alien trees bear fruit or nuts that are attractive to rats (VanderWerf 2009). Fires are known to destroy key habitat and promote the spread of alien plants on O'ahu (USFWS 2006), with negative consequences for nest success (VanderWerf 2009). Feral pigs Sus scrofa also facilitate the spread of invasive alien plants.
Diseases such as avian pox and malaria are a problem throughout its range given that there are no high elevation refugia, increasing mortality of adults by c.10-25% and possibly preventing birds from nesting (E. VanderWerf in litt. 1999, VanderWerf et al. 2006). However, ‘elepaios have greater immunity to introduced mosquito-borne diseases than most of the Hawaiian honeycreepers and the species has persisted despite high disease prevalence (VanderWerf 2012a). Malaria prevalence in the species has been recorded at 87%, with 36% of birds showing signs of avian pox (VanderWerf et al. 2006). High prevalence of mosquito-borne diseases and local declines in the species' population are associated with high rainfall (USFWS 2006, VanderWerf et al. 2006).
Conservation Actions Underway
Critical habitat has been designated on O'ahu (USFWS 2001). The species has benefitted from conservation measures targeted at endangered honeycreepers on the island, including fencing, ungulate control and forest restoration. Rat control in 1996-2008 resulted in a 25% increase in survival of breeding females and a 100% increase in reproductive success, stabilising studied populations (VanderWerf and Smith 2002, VanderWerf 2009). Further rat control has taken place at other populations, but efficacy has been variable (VanderWerf et al. 2011b). Captive breeding has been suggested but is unlikely to be effective unless threats in the wild are adequately managed (E. VanderWerf in litt. 2016). Recent research has shown that nesting height of Oahu Elepaios is increasing through evolution by selection from rat predation, which has lead to an overall increase in nest success in at least one population (VanderWerf 2012b). Rat control is ongoing and in 2014, installing and maintaining large-scale trapping grids of Goodnature A24 traps were added to control measures (USFWS 2019). The use of aerial broadcast methods to control rats over a larger scale has begun in certain recovery areas (USFWS 2019).
14 cm. Small monarch flycatcher that often cocks its tail. Adults have white tips to tail feathers, white rump, and white wing bars. Immatures have buffy or rufous wingbars (VanderWerf 2001). Adult brown above, white below with brownish streaks on breast, and with black chin irregularly blending into white throat. Similar spp. Introduced Japanese Bush-warbler Horornis diphone duller with prominent eyebrow and no white markings. Introduced juvenile White-rumped Shama Copsychus malabaricus larger, darker above, with dark spots on breast. Voice Song a lively whistled eh-leh-PYE-o, often given in series (del Hoyo et al. 2006); calls include sharp chup, two-note squeak-it like dog's toy, and raspy chatter.
Text account compilers
Vine, J.
Contributors
Camp, R. & VanderWerf, E.
Recommended citation
BirdLife International (2024) Species factsheet: Oahu Elepaio Chasiempis ibidis. Downloaded from
https://datazone.birdlife.org/species/factsheet/oahu-elepaio-chasiempis-ibidis on 22/12/2024.
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 22/12/2024.