|Red List Category & Criteria:
||Camp, R., Fretz, S., Gorresen, M., Roberts, P., VanderWerf, E., Woodworth, B., Morrey, S., Laut, M., Behnke, L., Crampton, L., Paxton, E., Vetter, J. & Pejchar, L.
||Benstead, P., Bird, J., Derhé, M., Harding, M., Isherwood, I., Stuart, T., Symes, A., Wright, L & Ashpole, J
This species qualifies as Critically Endangered because it has an extremely small declining range, confined to one upland area where it is at risk from the effects of hurricanes and exotic taxa, including predators and disease.
|Previously published Red List assessments:|
- 2012 – Critically Endangered (CR)
- 2010 – Critically Endangered (CR)
- 2009 – Critically Endangered (CR)
- 2008 – Critically Endangered (CR)
- 2004 – Critically Endangered (CR)
- 2000 – Critically Endangered (CR)
- 1996 – Endangered (EN)
- 1994 – Endangered (EN)
- 1988 – Threatened (T)
|Range Description:||This species was common and widely distributed in the 1890s on Kaua`i in the Hawaiian Islands (U.S.A.). During 1968-1973, the total population was estimated at 6,832 (±966 standard error), when it was recorded on the Laau ridge and was fairly widespread in Koke'e (USFWS 1983). Since then, the population has declined and the species has retreated from the Koke`e region and the fringes of the Alaka`i region, and is now uncommon to rare in the Alaka`i (Pratt et al. 1987, Pratt 1993, 1994). Recent unpublished survey data indicate dramatic declines (85-89% since 1968-1973) and a decline of c. 64% in its core area in the Alaka`i Swamp from 1970 to 2000 (Anon 2007). The population was estimated to number 1,312 ± 530 birds, based on surveys conducted in April and May 2007 (Hawaii Division of Forestry and Wildlife and USGS, unpublished.data), occupying an area of just 36 km2 (Foster et al. 2004). The most recent estimates from 2012 suggest the population has decreased further to 468 individuals (231-916, 95% CI) (L. Crampton et al. in litt. 2015).|
United States (Hawaiian Is.)
|♦ Continuing decline in area of occupancy (AOO):||Yes|
|♦ Extreme fluctuations in area of occupancy (AOO):||No||♦ Estimated extent of occurrence (EOO) - km2:||90|
|♦ Continuing decline in extent of occurrence (EOO):||Yes||♦ Extreme fluctuations in extent of occurrence (EOO):||No|
|♦ Number of Locations:||1||♦ Continuing decline in number of locations:||Unknown|
|♦ Extreme fluctuations in the number of locations:||No||♦ Lower elevation limit (metres):||1000|
|♦ Upper elevation limit (metres):||1500|
|Range Map:||Click here to open the map viewer and explore range.|
|Habitat and Ecology:||It is found in high-elevation `ohi`a and koa-`ohi`a forest, but the latter is mainly distributed in the Koke`e region, from where it is retreating (USFWS 1983, Scott et al 1986, Pratt 1993). The Alaka`i stronghold is at 1,000-1,600 m. However, the 1968-1973 surveys found the species at lower altitudes in a few areas, and it may not occur above 1,500 m (USFWS 1983, Scott et al 1986). It feeds on invertebrates (Scott et al 1986, Pratt et al. 1987), and has been observed excavating rotting wood from the centre of a twig, presumably for insect larvae (VanderWerf and Roberts 2008). Both parents have been observed bringing food to the nest, with the male providing some food for the female, though the female does also forage independently. A nesting pair in 2007 had a juvenile from a previous nest, indicating the species will attempt to raise two broods (VanderWerf and Roberts 2008). |
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Generation Length (years):||5.7|
|Movement patterns:||Not a Migrant|
Lowland forests have been cleared for timber and agriculture, with feral livestock causing further degradation and destruction (USFWS 1983, Scott et al. 1986). Feral pigs continue to be particularly detrimental, additionally dispersing alien plants and facilitating the spread of introduced mosquitoes which transmit avian malaria and avian pox (Scott et al 1986, Pratt 1994, Loope and Medeiros 1995). Domestic and introduced birds provide reservoirs for these diseases, to which there is little resistance in Hawaiian honeycreeper populations (USFWS 1983, Scott et al 1986, Pratt 1994, Lepson 1997). Predation by introduced animals and competition for arthropod resources by introduced taxa (especially Japanese White-eye Zosterops japonicus, wasps and ants) are additional threats (USFWS 1983, Scott et al 1986, Jacobi and Atkinson 1995, Lepson 1997). Introduced plants such as Kahili Ginger (Hedychium gardnerianum), Blackberry (Rubus argutus), Strawberry Guava (Psidium cattleianum), Australian Tree Fern (Cyathea cooperi) and Firetree (Myrica faya) have degraded much native forest in Koke'e, and threaten the remaining habitat.
Hurricanes have had major impacts on population size in the past; in 1992 Hurricane Iniki devastated forests throughout Kaua`i, and all bird populations on the island appeared to have been drastically reduced (Pratt 1993, 1994), although some have since recovered. Hurricanes are now thought to displace birds from the small area of suitable habitat at altitude and push them into the lowlands where avian malaria is prevalent (Anon. 2007). A growing concern is that rising temperatures could allow mosquitoes to survive at higher altitudes and further transmit avian malaria and avian pox (Anon. 2007) as evidenced by a recent study; over the past two decades there has been a significant increase in the prevalence of avian malaria across the altitudinal range of the Alaka’i Plateau, which coincides with increasing air temperatures and changing patterns of precipitation and streamflow which support increased transmission of the disease (Atkinson et al. 2014) and having a montane distribution that is close to the maximum altitude within its range, this species is potentially susceptible to climate change (BirdLife International unpublished data).