VU
Iiwi Drepanis coccinea



Justification

Justification of Red List Category
This species has experienced rapid declines in some parts of its range, and is projected to decline substantially by 2100 as a result of climate change and the resultant increased prevalance of avian malaria. The newly-introduced tree disease known as Rapid 'Öhi'a Death may also cause declines. Overall, a population reduction of 30-49% is suspected to occur over the next ten years and so the species is listed as Vulnerable.

Population justification

It has a male-biased sex ratio of 1.44:1 (Fancy et al. 1993).

During 1976-1983, the population size was estimated at c.385,000 individuals, excluding birds on O`ahu (Scott et al. 1986). In the early 1990s, the total population was estimated to be more than 350,000 individuals (Jacobi and Atikinson 1995)Based on data from surveys up to 2012, using distance sampling and by multiplying density estimates by areas of habitat. the total population size was estimated to be 605,418 individuals (550,972–659,864 95% C. I.; Paxton et al. 2013). It was noted that surveys were carried out during the breeding season, when most juveniles had not fledged, so the individuals counted were mostly adults. The earlier population estimates are thought to have been understimates due to the time of year that the surveys took place (Paxton et al. 2013). 

The main population on Hawai‘i Island was estimated at 340,000 ± 12,000 individuals based on surveys in 1976-1983 (Scott et al. 1986). In 2012, the population on the island was estimated at 543,009 individuals (516,312–569,706 95% C.I.; Paxton et al. 2013). This included 277,055 birds in the northeastern part of the island (at Hakalau), 71,524 birds in the central eastern part of the island, 28,325 birds in the southeastern part of the island, 3,489 birds in south Kona, western Hawai‘i, 139,829 birds in central Kona, 22,787 birds in north Kona, and 802 individuals in the Kohala Mountains (based on surveys in 1976-1983; Scott et al. 1986). The 1976-1983 population in the Kohala Mountains was later re-estimated at 690 (Burnett 2020). Following further surveys in 2017, the Kohala Mountains population was estimated at 4,928 (2,910 - 8,345) individuals (Burnett 2020), although differences in survey timing may have affected the comparability of the results. At Mauna Kea, the population was estimated to number 802 birds in 1979-1983 (Scott et al.1986). 

During 1976-1983, the population on east Maui was estimated at 19,000 ± 2,000 individuals (Scott et al. 1986). In 2001, the population on east Maui was estimated at 107,744 individuals (Camp et al. 2009). Based on surveys in 2011 and 2012, the population on east Maui was estimated at 59,859 individuals (54,569–65,148 95% C. I; Paxton et al. 2013). The difference between the 2001 and 2011-12 estimates may be partly attributed to a decline, and partly attributed to survey error (Paxton et al. 2013). Following further surveys in 2017, the 2011-2012 population size was re-estimated at 37,574 individuals, and the 2017 east Maui population size was estimated at 50,252 (43,908–57,146 95% C. I.) individuals (Judge et al. 2019).

There is a small population on west Maui. A total of 5, 2 and 11 individuals were recorded in 1980, 1997, and 2010, respectively (Paxton et al. 2013). In 1980, the population on west Maui was estimated at 180 ± 150 individuals (Scott et al. 1986).

At Alaka‘i Plateau on Kaua‘i, the population numbered 7,800 ± 2,300 individuals in 1968-1973, with the total Kaui population estimated at the time to be 26,000 ±6,000 individuals (Sincock et al. 1984). 5,400 ± 500 individuals were estimated at the Alaka‘i Plateau in 1981 (Fancy and Ralph 2020). By 2004, the Kaua‘i population was estimated at 9,985 ±960 individuals (Foster et al. 2004), and in 2012, at 2,603 individuals (1,789–3,520 95% C. I.; Paxton et al. 2016).

Eight individuals were recorded during surveys on O`ahu from 1994-1996 (Vanderwerf and Rohrer 1996), with the total population there suspected to be less than 50 individuals. Only a small proportion of the area of suitable elevation on the island has been surveyed (Paxton et al. 2013). The current population on O`ahu is likely to be extremely small, and perhaps no more than ten individuals (USFW 2017).

On Moloka`i, 12 individuals were recorded during 120 counts in 1979-1980, and the population was estimated at 80 ± 65 (Scott et al. 1986). There have been very few records since (Paxton et al. 2013, eBird 2020). During 148 counts in 1988, only two individuals were detected (T. Pratt unpubl. data, in Fancy and Ralph 1998). Any remaining population on the island is likely to be extremely small.

Based on the range of estimates, the total population size is therefore estimated at 350,000 - 601,470 individuals. Assuming that most recorded individuals were adults, and taking into account the male-biased sex ratio, the total number of mature individuals may be placed at approximately 280,000 - 481,176, and is here placed in the band 250,000 - 500,000 mature individuals.

There are up to seven subpopulations: one or two on Hawai‘i Island (Scott et al. 1986), and one on each of east Maui, Kaua‘i, O`ahu, west Maui and Moloka`i (Paxton et al. 2013).

Trend justification

Data from surveys indicates that populations have declined in Kaua‘i and parts of east Hawai‘i island, and suggests population increases in west Hawai‘i island, although it is noted that data from here is sparse (Paxton et al. 2013). Models of the impact of climate change and the resulting increased prevalence of avian malaria projected that the species will undergo severe declines by the end of the century (Fortini et al. 2015, Guillaumet et al. 2017). The species's population size is therefore projected to be undergoing a decline.

In the northeastern part of Hawai‘i island, at Hakalau, the population was estimated at 277,055 birds in 2012, and the population was estimated to be stable or declining slowly between 1999 and 2012, with a projected 20% decrease over 25 years (Paxton et al. 2013). In the central eastern part of the island, the 2012 population was estimated at 71,524 birds, with a decreasing trend over 1995-2012, with projected reductions of 48% over 25 years at Keauhou, and 29% over 25 years at Mauna Loa (Paxton et al. 2013). In the southeastern part of the island, the population was estimated to number 28,325 birds in 2004-2010 (Paxton et al. 2013). Density estimates were two-to-three times lower in 2004-2008 than in 1976, and the species had disappeared at another site in the region, but the differences may reflect survey error (Paxton et al. 2013). 

In south Kona, western Hawai‘i, the population was estimated at 3,489 birds, based on surveys conducted in 2003, 2009 and 2010 (Paxton et al. 2013). Population densities indicated a 96% decrease from 1978 to 2009, and a 43% decrease from 2005 to 2010 at higher elevations (Paxton et al. 2013). In central Kona, the population was estimated at 139,829 birds, based on the densities observed in 2009 and 2010 (Paxton et al. 2013). The population density was estimated to have increased over 1995-2012, with 71% and 97% increases projected over 25 years from lower and upper elevations, respectively (Paxton et al. 2013). In north Kona, the population was estimated at 22,787 birds, based on survey results from 2003 and 2009 (Paxton et al. 2013). The population density in the Pu'u Wa'awa'a region was estimated to have increased over 1990-2009, with a projected 147% increase over 25 years (Paxton et al. 2013). However, the apparent increases in the western part of the island may be an artefact of small sample sizes (Paxton et al. 2013). The Kohala Mountains were estimated to hold 802 individuals in 1976-1983 (Scott et al. 1986), later revised to 690 (Burnett 2020), and 4,928 individuals in 2017 (Burnett 2020), although differences in survey timing may have affected the comparability of the results. At Mauna Kea, the population was estimated to number 802 birds in 1979-1983 (Scott et al.1986). Species abundance declined from 0.0039 birds per station (bps) in 1998-2002 to 0.007 bps in 2003-2007, and 0.002 bps in 2008-2012 (Paxton et al. 2013).

Based on surveys in 2011 and 2012, the population on east Maui was estimated at 59,859 individuals (Paxton et al. 2013). Densities in the northeast of east Maui declined between 1980 and 2011, with a projected decline of 34% over 25 years (Paxton et al. 2013). However, densities in the southeast showed a stable or moderately increasing trend, with a projected 22% increase over 25 years (Paxton et al. 2013). Following further surveys in 2017, the 2011-2012 population size was re-estimated at 37,574 individuals, and the 2017 east Maui population size was estimated at 50,252 individuals, representing a density increase of 110 individuals/km2 (Judge et al. 2019).

There is a small population on west Maui. In 1980, the population on west Maui was estimated at 180 ± 150 individuals (Scott et al. 1986). The sample sizes here have been too small to infer a trend (Paxton et al. 2013).

The population on Kaua‘i is rapidly declining (Paxton et al. 2013, 2016). In 2004, the Kaua‘i population was estimated at 9,985 ±960 individuals (Foster et al. 2004), and in 2012, at 2,603 individuals (Paxton et al. 2016). The species's range on the island declined from c.10,064 ha in 2000 (Foster et al. 2004) to 5,436 ha in 2012 (Paxton et al. 2013). Densities at the Alaki'i Plateau significantly declined from 2000 to 2012, with a projected decline 92% over 25 years (Paxton et al. 2013).

On Moloka`i, 12 individuals were recorded during 120 counts in 1979-1980, and the population was estimated at 80 ± 65 (Scott et al. 1986). There have been very few records since (Paxton et al. 2013, eBird 2020), and any remaining population on the island is likely to be extremely small.

By scaling and projecting the trends described above to the period 2010-2020, and scaling by the proportion of the total population to which they refer, the total population size is inferred to have been approximately stable, or to have undergone a reduction of up to around 11%, over the past decade, depending on whether increasing trends based on limited data are included in the estimate. These estimates assume that trends projected in 2012 (Paxton et al. 2013) continued. The species is therefore inferred to have undergone a reduction of 0-11% over the past ten years.

A model of the impact of climate change predicted that the species will lose 59.9% of its range between 1990–2010 and 2080–2100 (Fortini et al. 2015). This rate of decline is equivalent to a reduction of 10% over ten years. A model of the impact of malaria under climate change projected that the species's abundance in the Hamakua region may decline from 43.3% of estimated carrying capacity in 2003-2004 to 15% (0.3–24.6%) by 2100 (Guillaumet et al. 2017). This rate of decline is also equivalent to a reduction of 10% (6-40%) over ten years. However, it is unlikely that declines caused by climate change and its impact on malaria will occur at a constant rate, and the species's range may decline sharply when a climate 'tipping point' is reached (see Paxton et al. 2016).

Rapid 'öhi'a Death (R.O.D.; Ceratocystis sp.), has recently spread rapidly across the Hawaiian Islands and has caused extensive mortality of 'öhi'a (Keith et al. 2015, Fortini et al. 2019). In 2016, it was estimated that approximately 200 km2 of forest on Hawai‘i had been affected (Hughes 2016, in USFWS 2017b), including some areas within the range of the Iiwi (Hughes 2016 and Keith 2016, in USFWS 2017b), and by 2019, more than 600 km2 of forest were affected (Fortini et al. 2019). Based on a model of the potential range of C. lukuohia across the Hawaiian islands under current climatic conditions (Fortini et al. 2019), it has a high chance of infecting up to around 40% of the tree cover within the Iiwi's range. Surveys in an infected area of forest found that the density of another Hawaiian honeycreeper, the Hawaii Amakihi (Chlorodrepanis virens), declined by 79% between 2003-2004 and 2016, following the infection of the forest with R.O.D. (Camp et al. 2019). Assuming that 40% of the Iiwi's range is affected over the next decade, and that density declines similar to those seen in Chlorodrepanis virens occur, R.O.D. could cause a reduction of up to 33% over the next three generations. However, R.O.D. is more prevalent at higher temperatures at lower elevations, and the Iiwi is more numerous at higher elevations, so it may be expected to be affected less severely.

Taking into account the projected decline of up to 11% over the past decade, the projected future declines of around 10% (6-40%) per decade due to climate change and malaria (Fortini et al. 2015, Guillaumet et al. 2017), and the potential additional future decline of up to 33% caused by R.O.D., the species is suspected to undergo a reduction in the range of 6-73% over the next decade, with a best estimate placed in the band 30-49%.

Distribution and population

Drepanis coccinea formerly occurred on all the main islands in the Hawaiian Archipelago (USA). It is now largely restricted to the islands of Hawai‘i, Maui, and Kaua‘i, with relict populations remaining on O`ahu and Moloka`i (Scott et al. 1986). On Hawai‘i, it forms a band around much of the island, with the majority of the population at Hamakua, with a separate range area at Kohala Mountain (Scott et al. 1986). On Kaua‘i, it is now restricted to a small, remote area of the Alaka‘i Plateau (Paxton et al. 2016). On Maui, the majority of the population is found at East Maui, with a small population remaining on West Maui (Scott et al. 1986). On Moloka`i, a small relict population is distributed at two areas: Olokui Plateau and Kamakou Preserve (Scott et al. 1986). On O`ahu, it occurs in three small isolated populations in the Wai‘anae and Ko‘olau Ranges (Vanderwerf and Rohrer 1996). It was extinct on Lana'i by 1929 (Munro 1944).

Ecology

It occurs primarily in mesic and wet forests dominated by ‘öhi‘a and koa (Scott et al. 1986). It was formerly found in forests at any elevation, and still occurs in a variety of native, disturbed and unnatural habitats from 300 to 2,900 m (Berger 1972, Scott et al. 1986). The greatest densities (and approximately 90% of the population) are found at 1,300-1,900 m, with much lower densities below 1,000 m, except in dry areas of Kona, Hawai‘i, where moderate densities have been recorded down to 300 m (Scott et al. 1986, Paxton et al. 2013). It is nectarivorous, with nectar from 'öhi'a (Metrosideros polymorpha) and mämane (Sophora chrysophylla) forming a major part of the diet, and also feeds on foliage insects and spiders (Ralph & Fancy 1995, 2020). It makes long flights to locate nectar sources and makes seasonal movements to lower altitudes in response to 'öhi'a and mämane flowering events (Ralph and Fancy 1995, Guillaumet et al. 2017). Evidence for hybrization with another honey creeper, the 'Apapane Himatione sanguinea has been documented (Knowlton et al. 2014).

Threats

The species is very susceptible to avian malaria (Plasmodium relictum) (Scott et al. 1986, Jacobi and Atikinson 1995). Malaria is transmitted by the introduced southern house mosquito Culex quinquefasciatus. Nine of ten individuals bitten by a single mosquito infected with avian malaria died within 37 days (Atkinson et al. 1995). Research on the Alaka‘i Plateau found the species to have very low malaria prevalence, with just one infected individual detected in 1994 and none in the period 2007-2013, whilst research at Hakalau found an increase in malaria prevalence from 0% in 1988-1992 to 8% in 2001-2002 (VanderWerf 2012). A study on Hawai‘i island from 1992–1998 and from 2001–2005 found an overall infection rate of 2.6%, with an infection rate of 2.2% at higher elevations, and an infection rate of 20% at mid elevations (Samuel et al. 2015). The annual risk of an adult individual becoming infected with malaria was estimated at 0.23, and the mortality rate for all infected individuals was estimated at 0.93 (Samuel et al. 2015).

Both the Culex quinquefasciatus mosquito and the Plasmodium relictum parasite develop more easily at higher temperatures, and the resultant prevalence of malaria at lower elevations is thought to explain the Iiwi's current concentration at higher elevations (LaPointe et al. 2010). Increased temperatures associated with climate change may increase the prevalence of malaria at higher altitudes in the future (Freed et al. 2005, Paxton et al. 2016). Research suggests that temperatures at higher elevations may now be high enough to allow mosquitoes and hence malaria to spread throughout the species's range (Atkinson et al. 2014, Paxton et al. 2016). The Iiwi's seasonal movements to lower altitudes to track floral resources also place them at increased risk from malaria (Guillaumet et al. 2017). A model of the impact of climate change predicted that the species will lose 59.9% of its range between 1990–2010 and 2080–2100 (Fortini et al. 2015). Another model of the impact of malaria under climate change projected that the species may be close to extinction by 2100 (Guillaumet et al. 2017).

Recently introduced pathogens, Ceratocystis lukuohia and C. huliohia, both of which cause Rapid 'Öhi'a Death (R.O.D.), or 'Öhi'a Wilt, have spread rapidly across the Hawaiian islands and caused extensive mortality of 'öhi'a (Keith et al. 2015), which is an important food and nesting plant for Iiwi. The effects of R.O.D. were noticed on Hawai‘i by 2012, the disease was first identified in 2014 (Keith et al. 2015) and the Ceratocystis species involved were confirmed in 2018 (Barnes et al.). Ceratocystis sp. have now spread across much of the lowland forests on Hawai‘i island, as well as on Kauaʻi and Oʻahu (Mortenson et al. 2016, College of Tropical Agriculture and Human Resources 2020). In 2016, it was estimated that approximately 200 km2 of forest on Hawai‘i had been affected (Hughes 2016, in USFWS 2017a), including in some areas within the range of the Iiwi (Hughes 2016 and Keith 2016, in USFWS 2017b), and by 2019, more than 600 km2 of forest were affected (Fortini et al. 2019). Surveys of infected forest have found that an average of 25% of 'öhi'a trees were dead (Camp et al. 2019). Surveys in an infected area of forest found that the density of another Hawaiian honeycreeper, the Hawaii Amakihi (Chlorodrepanis virens), declined by 79% between 2003-2004 and 2016, following the infection of the forest with R.O.D. (Camp et al. 2019). If R.O.D. spreads into forest at higher elevations, if could cause rapid declines in Iiwi populations (Camp et al. 2019). Based on a model of the potential range of C. lukuohia across Hawaii under current climatic conditions (Fortini et al. 2019), it has a high chance of infecting up to around 40% of the Iiwi's range. C. lukuohia appears to be associated with higher temperatures (Fortini et al. 2019), so climate change could facilitate its spread into higher elevations.

Feral ungulates, including cattle (Bos taurus), feral sheep (Ovis aries), mouflon sheep (Ovis gmelini), feral goats (Capra hircus), and Axis deer (Axis axis) have degraded habitat quality by browsing, causing soil erosion, disrupting forest regeneration, spreading alien plant seeds, and facilitating the invasion of alien plants. Feral pigs (Sus domesticus) destroy understory vegetation and provide breeding sites for mosquitoes. Invasive plants including strawberry guava (Psidium cattleianum) degrade habitat (VanderWerf 2012), and their invasion is likely to be facilitated by climate change (Vorsino et al. 2014). Introduced rats (Rattus sp.) may predate on the species, although there is little direct evidence for this. The species is affected by avian pox (Avipoxvirus sp.), but it is not known whether this impacts on the population size. 

Forests have been cleared for agriculture, cattle-ranching and development (Fancy and Ralph 2020). Historically, the species was harvested for its feathers, for use in traditional cloaks and helmets.

Conservation actions

Conservation Actions Underway
The species was listed as Threatened under the Endangered Species Act in 2017 (USFWS 2017b).

The species has been the subject of population trend analysis and detailed studies into the effects of avian malaria by the U.S. Geological Survey Pacific Island Ecosystems Research Centre. Research has been underway on methods to control mosquitoes, and on the genetic basis for malaria immunity (Paxton et al. 2018).

Government and private protected areas have been established, many of which are fenced to exclude ungulates (Fancy and Ralph 2020). Alien plant species have been controlled at forest reserves (VanderWerf 2012). Forest restoration has been carried out at deforested areas (Paxton et al. 2018). Rats have been controlled in localised areas. Groups have been established to coordinate mosquito control (Paxton et al. 2018). A website has been created to disseminate information on how to prevent the spread of R.O.D., and regulations have been introduced to control the movement of 'öhi'a trees and parts (USFWS 2017a).

Conservation Actions Proposed
Carry out demographic studies to better understand the causes of declines. Study techniques for promoting the evolution of resistence to avian malaria. Develop techniques for controlling mosquitoes and rats. Improve monitoring of population trends at a range of elevations. Research the potential impact of R.O.D. on the species.

Protect and restore native forests, especially at higher elevations. Control mosquito populations, for example, by releasing sterile males (Liao et al. 2017). Fence areas of forest to control grazing and browsing and to prevent transmission of R.O.D. by feral ungulates. Control feral pigs, particularly at higher elevations (Liao et al. 2017). Continue to control invasive alien plants. Increase public awareness of the need for mosquito control (Paxton et al. 2018). Consider providing supplementary nectar via feeders at higher elevations to discourage birds from tracking flowering events at lower elevations where they are more at risk from malaria (Guillaumet et al. 2017).

Acknowledgements

Text account compilers
Wheatley, H.

Contributors
Benstead, P., Camp, R., Camp, R., Costantini, M., Crampton, L., Derhé, M., Donaldson, P., Farmer, C., Fretz, J., Hart, P., Lepson, J., North, A., O'Brien, A., Pratt, H.D., Roberts, P., Stuart, T., Taylor, J., VanderWerf, E. & Wu, J.


Recommended citation
BirdLife International (2022) Species factsheet: Drepanis coccinea. Downloaded from http://www.birdlife.org on 10/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 10/08/2022.