• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Justification of Red List category
This species is classified as Endangered owing to its very small and contracting range where habitat degradation is ongoing, and it is projected that the extirpation of small subpopulations will continue. The population is highly susceptible to avian malaria, with climate change projected to cause an increase in the elevation below which regular transmission occurs.

Population justification
In 1976-1979 and 1983, surveys estimated c.1,500 birds, with 900 in Hamakua, 500 in Ka`u, 50 on Mauna Kea, and 20 in central Kona (Scott et al. 1986). In 1990-1995, surveys estimated 1,163, with 1,105 in Hamakua, c.44 in Ka`u, fewer than 10 on Mauna Kea (and only a few males by 1999 [T. Pratt in litt. 1999]), and perhaps fewer than 10 in Kona (Fancy et al. 1996). The population on western Mauna Kea has since been extirpated (VanderWerf 2012). The species' population in Ka`u was estimated at 1,073 individuals (95% CI: 616-1,869) in 2005 (Gorresen et al. 2007). It should be noted that this higher population estimate in Ka`u does not represent a genuine population increase, but an improvement in survey methodology. Surveys conducted during 2003-2004 in the Kapapala Forest Reserve reported 35 individuals (including 14 families) in c. 650 ha of the reserve (Pratt et al. 2009). The population at the Kona Forest National Wildlife Refuge may also now be extirpated (Fancy et al. 1996, Camp et al. 2009). The global population was estimated at 1,900 birds in 2009 (Gorreson et al. 2009), roughly equivalent to 1,300 mature individuals overall, with 1,163 birds (95% CI: 507-2,401) occurring in Hakalau Forest National Wildlife Refuge (Kendall et al. 2022).

Trend justification
Surveys in 1990-1995 suggested a decline of c.22.5% over the previous 13 years (Fancy et al. 1996). The species is extirpated from subalpine Mauna Kea and likely Kona districts (Gorresen et al. 2009). Surveys from 1977 to 2003 indicate that the species may have declined in the Keauhou-Kulani area (Gorresen et al. 2005). In the Ka`u District of Hawai`i, surveys from 1976 to 2005 indicate that the species has been extirpated from habitat below 1,500 m, with no change in the density of populations at high elevations (Gorresen et al. 2007). Trends at Hakalau Forest National Wildlife Refuge and in the upper portions of the Ka‘? Forest Reserve were previously thought to be increasing and stable, respectively (Camp et al. 2009, 2010). In a recent analysis of annual population density estimates in Hakalau Forest National Wildlife Refuge, which supports c.61% of the population, trends were negative in the closed-forest stratum in the period 1987-2019. In the most recent decade 2010-2019, density declined by more than 10% in the closed-forest stratum, although the trend was inconclusive for open-forest and increasing in restored pasture (Kendall et al. 2022). Trends are unknown in central windward Hawai‘i and Ka‘? regions (USFWS 2020). The population is inferred to be declining overall given ongoing range contraction, and this is predicted to continue given that the threats are ongoing. Given that the species is highly susceptible to avian malaria, climate change is likely to reduce the area of suitable remaining habitat and drive further declines through causing an increase in the elevation below which regular transmission occurs (USWFS 2020).

This species is endemic to Hawai`i in the Hawaiian Islands (U.S.A.), where it was formerly widespread but now occurs as two distinct subpopulations (USFWS 2020).

It occurs mainly in old-growth mesic and wet koa Acacia koa and `ohi`a Metrosideros polymorpha forest between 1,300 and 2,100 m in Ka`u, Hamakua and perhaps still in Kona (Ralph and Fancy 1996). It formerly occupied dry mamane and naio woodlands from 1,900 to 2,900 m on Mauna Kea (Ralph and Fancy 1996, L. Pejchar in litt. 2007). Research suggests that it occurs in high densities and forages and nests successfully in secondary growth koa in regenerating forests (T. Pratt in litt. 1999, Pejchar et al. 2005). The species is found at its highest densities in koa plantations and forests with a high percentage of koa trees (Pejchar et al. 2005). It is the only species on Hawai`i to exploit the woodpecker niche, but is rare despite the lack of competition (Ralph and Fancy 1996). It feeds primarily on lepidopteran and cerambicid larvae under the bark of koa trees, and it only occasionally feeds on nectar (Pejchar and Jeffrey 2004). Its preference for koa trees is evident despite the relative scarcity of this tree species in the environment (Pejchar et al. 2005). As an apparent alternative to nectar the species regularly feeds on sap from `ohi`a trees all year round, perhaps to supplement insect larvae, whose populations fluctuate. The species acquires sap by drilling 3-5 mm deep holes into the phloem of suitable trees and drinking the sap that emerges. The preferred trees (known as "Aki trees") are rare (2 ha^-1), spatially clustered and defended by the species. Selected trees are probably used by successive generations (Pejchar and Jeffrey 2004). Pairs occupy very large home ranges (0.25-0.30 km² [E. VanderWerf in litt. 1999]) and produce only one chick per year (T. Pratt in litt. 2007), which has a long dependency period (Ralph and Fancy 1996).

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. 1995, 2000; Banko and Banko 2009). Climate change is projected to cause an increase in the elevation below which regular transmission of avian malaria occurs, reducing the area of suitable habitat and exacerbating declines (USFWS 2020). According to climate projections, due to increased rainfall and temperatures, high elevation areas for Hawaiian bird populations will only remain free of mosquitos to mid-century (Liao et al. 2015) and GIS simulation has shown that a 2 degrees Celsius increase would cause a c.100% decline in the land area where transmission is currently only periodic (Benning et al. 2002). Avian poxvirus is an additional threat, also transmitted by the non-native southern house mosquito (Culex quinquefasciatus) (VanderWerf 2012). The species may have declined in the past owing to habitat loss and degradation through grazing and logging (Ralph and Fancy 1994, VanderWerf 1998), although may be less limited by habitat loss than other Hawaiian honeycreepers because it will forage in relatively young koa (Pejchar et al. 2005). Predation by introduced rats, feral cats and native raptors are additional threats (Ralph and Fancy 1996). Predators may have been the primary threat to the now extinct Mauna Kea population, while disease may be responsible for declines in protected areas (Fancy et al. 1996). Feral ungulates, particularly pigs, have severely degraded native forests and facilitate the spread of alien plants and disease-carrying mosquitoes (Scott et al. 1986, Pratt 1994). Chewing lice may be an additional threat (Freed et al. 2008). In addition to exacerbating the threat of introduced diseases, climate change is predicted to increase the geographic extent and intensity of habitat loss, invasive plants and non-native predators (Paxton et al. 2018). Due to its low reproductive rate this species may be particularly vulnerable to these threats and slow to recover (USFWS 2006).

Conservation Actions Underway
Populations occur within Ka`u Forest Reserve, the Keauhou Ranch, Olaa/Kilauea partnership area, Kapapala Forest Reserve, Hakalau Forest National Wildlife Refuge (Fancy et al. 1996, J. Lepson in litt. 1999, L. Pejchar in litt. 2007, T. Pratt in litt. 2007) and the Kahuku Unit of Hawai`i Volcanoes National Park (acquired in 2003) (Tweed et al. 2007). Habitat restoration work is underway for this species (S. Fretz, E. Vanderwerf, R. Camp, M. Gorresen and B. Woodworth in litt. 2003). Removal of cattle and fencing of the Kapapala Forest Reserve and the Pu`u Wa`awa`a Forest Bird Sanctuary has occurred; although the species does not occur in the latter reserve, it could serve as a site for reintroduction (USFWS 2006). The removal of cattle, mouflon sheep and pigs from the Kahuku Unit of the national park is expected to benefit the species (T. Pratt in litt. 2007). Extensive replanting of koa has occurred at Hakalau Forest National Wildlife Refuge (~ 4,000 ha) and on Keauhou Ranch (Pejchar et al. 2005, L. Pejchar in litt. 2007, T. Pratt in litt. 2007). Both sites have been fenced and ungulates have been removed from significant portions of each site (L. Pejchar in litt. 2007). 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 (Miranda Paez et al. 2022).

Conservation Actions Proposed
Carry out further surveys to obtain an up-to-date estimate of the species' total population size and determine trends. Conduct studies to further examine habitat selection and foraging ecology, particularly in regenerating koa forests (VanderWerf 2012). Continue genetic research in disease immunity in Hawaiian honeycreepers (Paxton et al. 2018). Monitor the species' populations in new koa plantations that are replacing exotic grasslands in Hakalau Forest National Wildlife Refuge (Pejchar et al. 2005). Continue research in the fields of genomic technologies and genetically modified mosquitoes for disease control and their field application (USFWS 2020). Investigate how to protect and restore habitat effectively at a landscape level, connecting fragmented populations, and publish the results as an action plan. Preserve remaining old-growth `ohi`a and koa forests above the zone where mosquitoes occur (Ralph and Fancy 1996). Secure deforested and pasture lands on Hawai‘i at high elevations adjacent to protected refugia and manage these areas for forest growth to provide suitable habitat (USFWS 2020). Continue habitat management in areas where the species currently exists (USFWS 2020). Ensure that protected areas include an adequate number of preferred sap trees ("Aki trees") (Pejchar and Jeffrey 2004). Expand the programme for fencing and control of feral ungulates in native forests. Implement a landscape-level mosquito control programme (Paxton et al. 2018). Replant koa on exotic grasslands, such as extensive pastures in protected areas, at high elevations (above the disease line) (Pejchar et al. 2005, T. Pratt in litt. 2007). Incorporate the need for a supply of suitable sap trees (Pejchar and Jeffrey 2004) into long-term habitat restoration efforts. Determine feasibility of translocations to managed areas in their former range (VanderWerf 2012). Develop captive propagation techniques to help speed recovery (USFWS 2006). Work with land-owners to combine habitat restoration and the commercial growing of koa trees (Pejchar et al. 2005).

14 cm. Stocky, bull-headed honeycreeper with peculiar mismatched bill. Long and decurved maxilla, straight mandible half the length of maxilla, leaving small diastema in closed bill. Male yellow-green dorsally, yellow ventrally, with orange tinge to face and upper breast, whitish tinge to undertail-coverts. Similar spp. Hawai`i `Amakihi H. virens similarly coloured but much smaller with proportionally smaller bill. Voice Song a short, rapid warble. Calls include an upslurred whistle, a very short warble cheedle-ee, and a short sweet. Juveniles utter loud chewp as sound beacon to attendant adults. Hints Can still be found in forest tracts off Saddle Road and Hakalau Forest National Wildlife Refuge. Usually in small family groups.

Text account compilers
Vine, J.

Contributors
Camp, R., Fretz, S., Gorresen, M., Lepson, J., Pejchar, L., Pratt, T., VanderWerf, E. & Woodworth, B.

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Recommended citation
BirdLife International (2024) Species factsheet: Akiapolaau Hemignathus wilsoni. Downloaded from https://datazone.birdlife.org/species/factsheet/akiapolaau-hemignathus-wilsoni on 24/12/2024.
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 24/12/2024.