Data Zone
Justification of Red List category
This species is listed as Critically Endangered because of its extremely small and contracting range where it is considered to be restricted to a single location. The population is small and declining primarily owing to avian malaria and rat predation. The species is highly susceptible to avian malaria, with climate change causing an increase in the elevation below which regular transmission occurs.
Population justification
During 1976-1983, it was estimated to number c.500 individuals, of which 71% (c. 355) occurred above 1,500 m (Scott et al. 1986). Density surveys in 1997 and 2001 suggested similar numbers in the 35 km2 of remaining suitable habitat above 1,525 m (Simon et al. 1997, D. Leonard in litt. 2012). The total population size was estimated to number 513 ± 143 individuals in 1980, 447 ± 157 in 1992, 544 ± 153 in 2001 and 291 ± 69 in 2011 (Judge et al. 2021). Overall density was even lower in 2017 (0.05 ± 0.02 birds/ha), with an estimated total abundance of 157 ± 67 (95% CI 44–312) individuals in their 2,992 ha range (Judge et al. 2021). This is roughly equivalent to 105 mature individuals.
Trend justification
Since 2001 the population has declined by approximately 71% to 157 ± 67 individuals in 2017 (Judge et al. 2021). Surveys suggest a c.46% decline in the period 2011-2017, roughly equivalent to 64% in ten years (Judge et al. 2021), and this is thought to be continuing given that the threats are ongoing. The current rate of decline is therefore placed in the band 60-70% in ten years. The current estimated range is projected to decline by >75% by 2100 according to climate-based models (Fortini et al. 2015), although the population is likely to become functionally extinct in as few as ten years if current population trajectories continue (Mounce et al. 2018).
This species is endemic to Maui in the Hawaiian Islands (U.S.A.), where it is found on the north-eastern slopes of Haleakala, although fossil evidence indicates that it once occurred in the lowlands and on Moloka'i.
It is now restricted to montane mesic and wet forest at 1,200-2,350 m (mainly 1,500-2,100 m), and is absent from adjacent areas dominated by exotic trees (Mountainspring 1987, T. Pratt in litt. 1999, D. Leonard in litt. 2012). This habitat is probably marginal, as heavy rainfall leads to drastic losses during the breeding season (Simon et al. 2000). It feeds mainly on the larvae and pupae of wood- and fruit-boring beetles, moths and other invertebrates (Mountainspring 1987, Simon et al. 1997). Range size is 9.29 ha and territories are defended year-round (Pratt et al. 2001, Warren et al. 2015). The nest is cup-shaped and placed in the outer canopy forks of mature ohia (Metrosideros polymorpha), a situation that may afford some protection from introduced predators (Simon et al. 2000). During the breeding season (between November and June), one chick is usually raised per year and young are dependent on parents for 5-8 months (Lockwood et al. 1994, T. Pratt in litt. 1999, J. C. Simon in litt. 1999, Simon et al. 2000). Studies in the Hanawi Natural Area Reserve (NAR) in east Maui in 2006-2011 found nest success probability of 19 % (n=30) and seasonal nest success of 46 %, with 49 of 106 breeding pairs monitored successfully producing one fledgling (Mounce et al. 2013).
The primary threat to this species is introduced avian disease to which it is highly susceptible, particularly avian malaria (Plasmodium relictum), causing it to have a limited distribution at higher elevations (Atkinson et al. 2014, Judge et al. 2021). Climate change is increasing the elevation below which regular transmission of avian malaria occurs and climate modelling has suggested a possible range contraction of c. 75% by 2100 (Fortini et al. 2015) although the species is likely to become functionally extinct in as little as 10 years (Mounce et al. 2018). Avian pox virus is an additional threat (USFWS 2019). From 1945-1995, the invasion of feral pigs on Haleakala caused chronic habitat degradation (Loope and Medeiros 1995) and facilitated the spread of disease-carrying mosquitoes into remote rainforests (Pratt 1994). The species continues to be threatened by invasive ungulates, however the entire range is now fenced and mostly ungulate free (Warren et al. 2021). Weather influences the survival of young and thus potential recruitment rates (Simon et al. 1997, Becker et al. 2010), with nest failures frequently occurring after heavy rainfall (Warren et al. 2021). Other limiting factors include logging, cattle ranching and silviculture (VanderWerf 2012) and predation and competition from exotic bird and insect species (Mountainspring 1987, Simon et al. 1997). Rats have been observed high in native 'olapa trees and are both a potential predator of eggs and young and a potential source of competition for berries. Although they have not been documented as predators of parrotbill nests, rats have been documented predating Akohekohe nests at similar heights. Mounce et al. (2013) found no significant difference in reproductive success between birds in an area with predator control (bait stations loaded with rodenticide and snap traps) and those in an area without, suggesting that current control efforts may not be sufficient. Nest predation by Short-eared Owl (Asio flammeus) has been observed, though its extent and effect is unknown. Removal of small mammal nest predators may result in owl populations switching to a greater proportion of birds in their diet (Mounce 2008). Cats (Felis catus) and the small Indian mongoose (Herpestes auropunctatus) are also likely predators of the species (Simon et al. 2020). Invasive plants represent a threat to habitat and require constant monitoring (D. Leonard in litt. 2012). Given its slow life-history traits and heavy reliance on adult survival, the species is particularly at risk and less likely to recover from declines (Mounce et al. 2018).
Conservation and Research Actions Underway
Life history and demographic studies have been ongoing since 2005 (D. Leonard in litt. 2012), with genetic studies ongoing since 1996 (Mounce et al. 2015). The East Maui watershed is cooperatively managed with fencing at c.1,070 m and removal of feral ungulates (Loope and Medeiros 1995, P. Baker in litt. 1999). In the Waikamoi Preserve, Hanawi Natural Area Reserve and Haleakala National Park, conservation practices additionally combat the establishment of alien plants and, since the late 1980s, feral pigs have been controlled (Loope and Medeiros 1995, Simon et al. 1997). As a result, the forest understory has recovered well and non-native plant invasions have slowed (Loope and Medeiros 1995, T. Pratt in litt. 1999). The entire range is now fenced and mostly ungulate free (Warren et al. 2021). Intensive control of rats (Rattus spp.) is underway in a portion of Hanawī Natural Area Reserve, Waikamoi Preserve, and Kahikinui’s Nakula Natural Area Reserve (USFWS 2019). A small population exists in captivity, having bred for the first time in 2000 (Maxfield 2000), and numbering 12 individuals in 2015. However, the captive population numbered just 2 non-breeding individuals in 2022 (Paxton et al. 2022). The Leeward Haleakala Watershed Restoration Partnership has been established to help restore the south side of Maui's forests in partnership with State agencies (H. Mounce in litt. 2008) and 1,100 ha of mesic koa forest is currently being restored on leeward east Maui (Mounce et al. 2014). In 2019, seven individuals from Hanawī Natural Area Reserve and seven from the captive population managed by San Diego Zoo Global were translocated to the Nakula Natural Area Reserve on the leeward slope of Haleakalā in an attempt to establish a second population (Warren et al. 2021). However, all birds either died or disappeared, with necropsies indicating avian malaria as the primary cause of death (Warren et al. 2021). Development of genetic tools to reduce transmission of avian malaria is ongoing. This includes transgenic or genetically modified mosquitoes that have reduced ability to transmit pathogens and also incompatible insect techniques, for example using a different strain of Wolbachia bacteria to produce males that cannot produce viable offspring (Judge et al. 2021, Miranda Paez et al. 2022).
Conservation and Research Actions Proposed
Carry out surveys to obtain an up-to-date estimate of the population size. Continue to study life history and ecology (D. Leonard in litt. 2012). Continue genetic research in disease immunity in Hawaiian honeycreepers (Paxton et al. 2018). Conduct research to assess the impact of ungulate exclusion. Evaluate the effect of rodent control on the species’ reproduction and survival (USFWS 2019). Continue research in the fields of genomic technologies and genetically modified mosquitoes for disease control and their field application (Paxton et al. 2018). Monitor population trends through regular surveys.
Control alien plants, including outside the three wildlife protection areas (Loope and Medeiros 1995, Simon et al. 1997). Initiate landscape-scale control of predators (Judge et al. 2021). Implement a landscape-level mosquito control programme (Paxton et al. 2018). Continue habitat restoration efforts and replant koa forest in areas adjacent to its current distribution (Simon et al. 1997, Mounce et al. 2014, Judge et al. 2021). Supplementary feeding may also aid species recovery (Mounce et al. 2014). Improve techniques for successful captive breeding and reintroduction (Warren et al. 2021). Given the imminent risk of extinction, bringing birds into captivity and holding them for just long enough for the Wolbachia incompatible insect technique to break the disease cycle has been proposed as a management action (Paxton et al. 2022).Begin public outreach concerning the importance and benefits of controlling rodents (D. Leonard in litt. 2012).
14 cm. Chunky, short-tailed, big-headed passerine with huge parrot-like bill. Male olive-green above, yellow below with dark streak through eye and bold, sharply defined yellow superciliary. Two-toned bill, upper third of maxilla dark, remainder pale yellowish-pink. Female duller with much smaller bill. Similar spp. Nukupuu Hemignathus lucidus has yellow head without dark eye-line and bold superciliary, and much thinner bill. Voice Song a plaintive series of short whistles descending in pitch chwee-chwee-chwee-chwee-chwee. Calls include short warble, upslurred whistle, and loud chewp uttered by dependent juveniles, all similar to calls of Akiapolaau Hemignathus munroi of Big Island. Hints Only accessible site for observers is Waikamoi Preserve, where rare but regular. Best located by voice.
Text account compilers
Vine, J.
Contributors
Baker, H.C., Baker, P.E., Camp, R., Leonard, D., Mounce, H., Pratt, T. & Simon, J.C.
Recommended citation
BirdLife International (2024) Species factsheet: Maui Parrotbill Pseudonestor xanthophrys. Downloaded from
https://datazone.birdlife.org/species/factsheet/maui-parrotbill-pseudonestor-xanthophrys on 23/11/2024.
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 23/11/2024.