Justification of Red List Category
This species is classified as Endangered because it has a very small, severely fragmented range, and is experiencing continuing declines in range, habitat quality and population, largely owing to the effects of introduced species. It is projected that the extirpation of small subpopulations will continue.
In 1990-1995, surveys estimated a population of 1,163 individuals. This is rounded to an estimate of 1,200 individuals, roughly equivalent to 800 mature individuals.
Surveys in 1990-1995 suggested a decline of c.22.5% over the previous 13 years (Fancy et al. 1996). The Mauna Kea population became extinct in 2002 and the species has not been seen in Kona since the late 1990s (L. Pejchar in litt. 2007). 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).
Hemignathus munroi is endemic to Hawai`i in the Hawaiian Islands (USA), where it was formerly widespread. 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, representing a decline of c.22.5% over 13 years, with 1,105 in Hamakua (fragmented into two, possibly four, distinct subpopulations at Keauhou-Kulani, c.312 birds, and north Hamakua, c.793 birds), 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 Mauna Kea population became extinct in 2002 and the species has not been seen in Kona since the late 1990s (L. Pejchar in litt. 2007). 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). The species's 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).
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). Recent 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 chief threats are thought to be habitat modification through grazing and logging (particularly of koa), predation by introduced rats, feral cats and native raptors, and avian diseases spread by introduced mosquitoes, which restrict it to high altitude (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). Due to its low reproductive rate this species may be particularly vulnerable to these threats and slow to recover (USFWS 2003).
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 sheep and mouflon from Mauna Kea has permitted regeneration of mamane forest habitat (USFWS 2003). However, the species is now extinct there (L. Pejchar in litt. 2007, T. Pratt in litt. 2007). 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 2003). 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).
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
Stattersfield, A., Isherwood, I., Stuart, T., Benstead, P., Harding, M., Taylor, J.
Pratt, T., Gorresen, M., Camp, R., Pejchar, L., Morin, M., Fretz, S., Woodworth, B., VanderWerf, E., Lepson, J.
BirdLife International (2021) Species factsheet: Hemignathus wilsoni. Downloaded from http://www.birdlife.org on 16/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/10/2021.