Iiwi (Drepanis coccinea) Species Status Report Pacific Islands Fish and Wildlife Office U.S. Fish and Wildlife Service, Region 1 December 2016 ● Final v1.0 Introduction The U.S. Fish and Wildlife Service was petitioned to list the Iiwi (Vestiaria coccinea) [now Drepanis coccinea] as an endangered or threatened species on August 24, 2010. On January 24, 2012, we published a finding that the petition presented substantial information indicating the listing of the species under the Endangered Species Act may be warranted; this finding initiated a status review of the species (77 FR 3423). We have prepared this summary document to help inform that status review. Here we present a review of the conservation status of the Iiwi, including: species abundance, distribution, and trends; stressors that may affect the Iiwi; conservation measures or regulations that may ameliorate those stressors; and projected future conditions for the species. We reviewed a large number of references to compile this report; however, for the discussion of population status and trend, we primarily draw upon a thorough and recent peer-reviewed report published by the U.S. Geological Survey (USGS), “Abundance, Distribution, and Population Trends of the Iconic Hawaiian Honeycreeper, the Iiwi (Vestiaria coccinea) throughout the Hawaiian Islands” (Paxton et al. 2013). For the climate change analysis portion of this status report, we relied particularly on two recently published papers, “Large-Scale Range Collapse of Hawaiian Forest Birds under Climate Change and the Need [for] 21st Century Conservation Options” (Fortini et al. 2015), and “Will a warmer and wetter future cause extinction of native Hawaiian forest birds?” (Liao et al. 2015). This document is not intended to be an exhaustive review of all published scientific literature relevant to the Iiwi; rather, it is intended to capture and summarize the key points from the best scientific and commercial data available relevant to our evaluation of the current and future conservation status of the species. This species status report was prepared by the staff of the U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, Honolulu, Hawaii; and the U.S. Fish and Wildlife Service, Pacific Region, Portland, Oregon. Executive Summary Executive Summary The Iiwi is an Hawaiian forest bird in the endemic honeycreeper subfamily of the Fringillidae (finch family). It is found primarily in closed canopy, montane wet or montane mesic forests of tall stature, dominated by native ohia trees (Metrosideros polymorpha) or both ohia and koa trees (Acacia koa). Iiwi are nectarivorus and feed primarily on flowering ohia; ohia trees are also used for nesting. Abundance, Distribution and Trend Although historical abundance estimates are not available, the Iiwi was considered one of the most common of the native forest birds in Hawaii by early naturalists, described as “ubiquitous” and found from sea level to the tree line across all the major islands. In the late 1800s, Iiwi began to disappear from low elevation forests, and by the mid-1900s, the species was largely absent from sea level to mid-elevation forests. Today Iiwi are no longer found on Lanai and only a few individuals may be found on Oahu, Molokai, and west Maui. Remaining populations of Iiwi are restricted to high-elevation forests on Hawaii Island, east Maui, and Kauai. The current population size of Iiwi rangewide is estimated as a mean of 605,418 individuals (range 550,972 to 659,864). Ninety percent of all Iiwi now occur on Hawaii Island, followed by east Maui (about 10 percent), and Kauai (less than 1 percent). Iiwi population trends vary across the islands. The population on Kauai is in steep decline. Trends on Maui are mixed but generally appear to be in decline. On Hawaii Island, there is evidence for stable or declining populations on the windward side of the island. Apparent trends of increase have been documented on the leeward (Kona) side of Hawaii Islands, but these trends were inferred from a limited data set. Of the nine regions for which sufficient information is available for quantitative inference, five show strong or very strong evidence of declining populations; one, a stable to declining population; one, a stable to increasing population; and two, strong evidence for increasing populations. Four of the nine regions show evidence of range contraction. Overall, based on the most recent surveys (up to 2012), approximately 90 percent of remaining Iiwi are restricted to a narrow band of habitat between elevations of roughly 4,265 and 6,234 feet (ft) (1,300 and 1,900 meters (m)). Stressors For the purposes of our evaluation, we look for evidence that a stressor, acting either singly or in concert with other factors, may be resulting in population-level impacts to the species. We evaluated many potential stressors to Iiwi and their habitat, including: stressors that may affect the extent or quality of their ohia forest habitat (ohia dieback, ohia rust, rapid ohia death, drought, fires, volcanic eruptions, nonnative plants, and feral ungulates), introduced diseases, predation by introduced mammals, competition with nonnative birds, ectoparasites, climate change, and the effects of small population size. Based on our assessment, disease is the primary driver in the ongoing declines in abundance and range of Iiwi, and climate change substantially exacerbates the impact of disease on the species. Some of the other stressors may i Executive Summary have contributed to past declines in Iiwi, or may even have some negative effect on the species or its habitat today; however, of the additional stressors listed above, we found no information to suggest that any is currently a key factor in the ongoing declines in abundance and range of Iiwi. We did, however, identify rapid ohia death (ROD), a type of Ceratosystis wilt fungal disease, as a potentially significant emerging habitat stressor. Based upon the most recent research, ROD-infected stands of ohia often show greater than 50 percent mortality initially and nearly 100 percent of trees in a stand succumb to the disease within 2 to 3 years. Rapid ohia death is presently reported only from the island of Hawaii; however, over roughly the last 5 years it has spread across the island, which is home to 90 percent of the Iiwi population, and in some areas, affected trees have been observed within the range of Iiwi. As of January 2016, ROD is estimated to have infected approximately 34,000 ac (13,759 ha), which is a 100 percent increase in affected area since 2015. The best scientific data available consistently identifies introduced mosquito-borne avian diseases, including avian malaria and avian pox, —as the primary stressors driving the declines in abundance and distribution of Iiwi observed since the turn of the 20th century. Avian malaria is a disease caused by a blood parasite, and avian pox is caused by a virus; both are transmitted by the bite of the nonnative mosquito Culex quinquefasciatus, and both have serious impacts on native forest birds, including Iiwi. The two diseases often co-occur, and although avian malaria has received greater study, avian pox is likely also an important factor in Iiwi declines based on field observations and limited experimental studies in other native forest birds. Iiwi exhibit an extremely high mortality rate in response to avian malaria (95 percent) and are absent at low elevations where malaria is prevalent, despite the availability of otherwise suitable habitat. Both the life cycle of the mosquito vector and the development and transmission of the malaria parasite are temperature-limited; neither can be completed at cool temperatures, which prevail at high elevations. Iiwi are now found primarily in high elevation forests above 3,937 ft (1,200 m) that provide disease-free refugia, where malaria prevalence and transmission is only brief and episodic, or nonexistent, under current conditions. The Iiwi has not demonstrated any sign of developing resistance to avian malaria to date. Although there has been less research on the effects of avian pox virus, the limited results to date suggest it may also be a source of significant mortality. The fact that avian malaria and avian pox often infect the same individual simultaneously complicates the ability to discern the effects of each disease, as the two diseases may be acting both individually and synergistically. Climate change is a stressor with potentially significant impacts on Iiwi when considered in conjunction with avian malaria. Air temperature in Hawaii has increased in the past century and particularly since the 1970s, with greater increases at high elevation. Increases are currently documented in (a) the elevation where the avian malaria parasite and its mosquito vector can survive and reproduce, and (b) the prevalence of avian malaria in forest birds at high elevation sites, where Iiwi are declining (e.g., on Kauai). The projections for future climate conditions in Hawaii describe a continued warming trend, especially at high elevations. The temperature barrier to the development and transmission of avian malaria will continue to move up in elevation in response to warmer conditions, resulting in the curtailment or loss of disease-free habitats for Iiwi. Three studies specifically address the future of native Hawaiian forest birds, ii Executive Summary including Iiwi, in the face of the synergistic interactions between climate change and avian malaria: • Benning et al. (2002) conclude that under optimistic assumptions (i.e., 3.6°F (2°C) increase by 2100), malaria-susceptible Hawaiian forest birds, including Iiwi, lose most of their low-risk habitat in the three areas considered in their projection of climate change impacts. For example, current disease-free habitat (below the 55°F (13°C) isotherm) at Hakalau Forest National Wildlife Refuge is reduced by 96 percent. • Fortini et al. (2015) conducted a vulnerability assessment for 20 species of Hawaiian forest birds, based on an increase of 6.1°F (3.4°C) at higher elevations by 2100.