Justification of Red List Category
This species is listed as Vulnerable because it has a small and contracting range and, although it is still relatively abundant, surveys have shown that it is undergoing a continuing population decline.
An estimate of more than 350,000 individuals was made in the early 1990s (Jacobi and Atikinson 1995). On Kaua’i, the population estimate has declined greatly since 2000, and is at approximately 2,603 individuals (Paxton et al. in press).
The population is declining (figures still to be published), owing to avian malaria and other factors.
Vestiaria coccinea formerly occurred on all the main islands in the Hawaiian Archipelago (USA) but it is now extinct on Lana'i and relict populations (probably fewer than 50 individuals [J. Lepson in litt. 2000]) remain on O`ahu and Moloka`i (Scott et al. 1986, P. Donaldson in litt. 1999). Recent population estimates are: c.385,000 individuals, excluding birds on O`ahu, during 1976-1983 (Scott et al. 1986) and more than 350,000 individuals in the early 1990s following recent declines in several populations (Jacobi and Atikinson 1995). There is now evidence from monitoring (much of it unpublished) that the species has declined throughout the Hawaiian islands, except on windward Mau`i and at Hakalau, Hawai`i, where the populations appear to be stable (D. Pratt in litt. 2007). The numbers of individuals detected during monitoring have fallen at both mid and low elevations (D. Pratt in litt. 2007). The apparent decline appears to have been most pronounced in western Hawai`i, and on Kaua’i where the population has declined by 86% (D. Pratt in litt. 2007, Paxton et al. in press). Habitat modeling predicts that the species will lose 59.9% of its range across Hawai’I, and 100% of its range on Kaua’i (Fortini et al. 2015).
This species 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 are found at 1,300-1,900 m, and low elevation populations may be sustained primarily by dispersal from mid-elevation populations (Scott et al. 1986). Evidence for hybrization with another honey creeper, the 'Apapane Himatione sanguinea has recently been documented (Knowlton et al. 2014).
The exact causes for the decline are uncertain, although it is known that the species is very susceptible to avian malaria (Jacobi and Atikinson 1995, D. Pratt in litt. 2007). 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). Increased temperatures associated with climate change may influence the prevalence of malaria in this species (Freed et al. 2005). Other factors which are likely to be contributing to its decline include habitat degradation and predation by introduced mammals such as cattle, pigs, cats and rats. Invasive plants degrading habitat include strawberry guava (Psidium cattleianum) (VanderWerf 2012). Observed increases in chewing lice may have impacts on time spent foraging and survival, though further research is needed to fully understand this potential threat (Freed et al. 2008).
Conservation Actions Underway
The species is 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. A habitat suitability map for this species on Kaua’i will also be made following the acquisition of LiDAR in 2016. Actions not directly aimed at the Iiwi will also be benefitting this species, such as ungulate removal and control of alien plant species (VanderWerf 2012).Conservation Actions Proposed
Complete assessment of current population trends. Study the factors driving the decline. Attempt to mitigate against the decline, including efforts to control mosquito populations.
Text account compilers
Benstead, P., Derhé, M., O'Brien, A., Stuart, T., Taylor, J. & North, A.
Camp, R., Donaldson, P., Fretz, J., Lepson, J., Pratt, H., Roberts, P., VanderWerf, E., Hart, P., Costantini, M. & Crampton, L.
BirdLife International (2017) Species factsheet: Drepanis coccinea. Downloaded from http://www.birdlife.org on 19/10/2017. Recommended citation for factsheets for more than one species: BirdLife International (2017) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/10/2017.