The Kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys) is a critically endangered Hawaiian honeycreeper endemic to the island of Maui. Once found across much of the islands of Maui and Molokai, the Kiwikiu is now limited to 30 km2 of wet rainforest on windward east Maui. This historic range covered multiple forested habitat types from high elevation wet forests to lowland dry forests. The current range of the species is constrained by the combination of the distribution of high quality native forest and disease vectors. Like many other native forest bird species, Kiwikiu are primarily threatened by non-native species, loss and/or alteration of habitat, and climate change.
As is the case for nearly all extant native Hawaiian bird species, Maui Parrotbill or Kiwikiu (Pseudonestor xanthophrys) have undergone a significant reduction in range and population size since human contact with Hawai‘i. Although apparently never among the most widespread of Hawaiian passerine species, subfossil evidence shows that Kiwikiu formerly occupied a large proportion of the islands of Maui and Moloka‘i. Some of these subfossils have been found down to 200 m in elevation in the Kahikinui region and the fossil sites on Moloka‘i are coastal dunes. This historic range covered multiple forested habitat types from high elevation wet forests to lowland dry forests. No modern observations were made of the species outside of its current range, but Maui was historically under-sampled by early naturalists. All historic specimens come from the same area of forest at Ukulele near the present day Waikamoi Preserve of The Nature Conservancy. However, observations made in the late 19th century indicated a preference for koa (Acacia koa) as a foraging substrate in the limited areas that Kiwikiu were historically observed. Thus, although not present in large numbers throughout the current range, koa may have played an important role in the historical distribution of Kiwikiu.
The current range of the species may be in large part an artifact of the extent of the last remaining large tracts of high elevation native forest instead of a result of forest preference. Wide-scale deforestation for agriculture and livestock grazing has reduced the amount of forest cover on the island of Maui to a fraction of prehistoric levels. The subsequent addition of invasive plant and animal species further eroded the extent of native forest and reduced forest quality throughout the island. Furthermore, introduced avian diseases restrict Kiwikiu to forests above 1200 m in elevation, above the elevational range of disease vectors; i.e. mosquitoes. As such, the current range of the species is constrained by the combination of the distribution of high quality native forest and disease vectors. These factors have resulted in a species range of approximately 30 km2 on Maui; the species was extirpated on Moloka‘i. The current range of the species is located on the windward slopes of Haleakalā Volcano from The Nature Conservancy’s (TNC) Waikamoi Preserve in the east to the Manawainui planeze in Haleakalā National Park.
Current Kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys) species range (Total area = 29.92 km2) and land management areas. Also shown are the genetic sampling locations, including showing collection sites of initial captive individuals (east). Subpopulations, east and west, are based on analysis of genetic population structure by Mounce et al. (2015).
Endangered. The first comprehensive population survey for Kiwikiu was done in 1980 as part of Hawaii Forest Bird Surveys. The population estimate at that time was 502 ± 116 individuals. While subsequent surveys have shown densities in certain portions of their range as similar to 1980, none have been able to conclusively show that the population is stable across its range. The recent 2017 range-wide study estimated Kiwikiu abundance at between 44 – 312 (95% CI; mean 157) individuals (analysis still in prep, not peer reviewed). While alarming, abundance estimates for the species have historically shown significant variability and the low precision of each estimate should not be ignored. However, overall abundance is realistically fewer than 312 and the population may be declining. Regardless of exact numbers, recent distribution surveys have suggested that their current habitat is “full”, with no room to expand.
Data show a species in decline. Current rates of reproduction and survival will not sustain the population into the future. Population viability analysis predicts extinction of the species within 25 years. The forests that the Kiwikiu currently exists in are well protected: habitat management already includes removing ungulates and invasive species. Managers do not currently have the tools necessary to be able to mitigate the remaining threats in their current range (avian disease and vector control on a landscape scale, predator control at a landscape scale, weather). Since we are unable to increase the Kiwikiu population in its current range, we need to expand it.
Reducing predation risks to these birds would perhaps increase survival. However, the native habitat is too mountainous, fragile, and remote to make wide-scale rodent reduction a viable option for managers. Increasing nest success may also increase productivity. However, with nests failing in heavy weather, there are no management options to counteract the storm patterns in this habitat. Furthermore, the birds have not responded to supplemental feeding to try to increase survival and/or productivity. Lastly, climate change models predict that Kiwikiu habitat could decrease to 7 km2 on the windward slope by 2080-2100, making all of the habitat in Waikamoi inhospitable due to avian disease. The combination of all these factors and limitations make moving these birds to a new habitat the most immediately viable option to secure their survival.
The US Fish and Wildlife Service (USFWS) Recovery Plan (2006) calls for the creation of a second population of Kiwikiu. According to USFWS, the recovery strategy for the Kiwikiu centers on protection, restoration, and management of native high elevation forests on East Maui (Haleakala), West Maui, and East Molokai. This includes ungulate monitoring and control, predator control, disease monitoring and control, captive propagation, and habitat restoration. Habitat restoration and reestablishment of a population on leeward East Maui is needed to promote natural demographic and evolutionary processes. Habitat restoration should eventually relink the remnant Kahikinui forest to other forests on East Maui. There is historically occupied habitat currently being restored on leeward east Maui for the benefit of Kiwikiu and other imperiled Hawaiian biota on Maui. This habitat is a mesic forest that appreciates lower annual rainfall forest than the habitat in the birds’ current range.
There are many reasons for using reintroduction as a conservation tool in a given species, but put in its simplest form, restoring a species to an area where it has been extirpated will increase the total number of individuals for that given species over time and reduce extinction risk. The release of such organisms back into historical habitats is known as a reintroduction. When moving threatened and endangered species where conservation is the main objective, these reintroductions are also considered conservation translocations.
Reintroductions have been widely used throughout conservation programs worldwide and the number of such efforts is growing exponentially each year. The increasing use of reintroductions is not unexpected due to the accelerating rate of global ecological change and the corresponding pressure on biodiversity.
Many of these reintroductions have been on islands, which is not unexpected given that islands hold a large percentage of our global diversity (Stattersfield et al. 1998). Due to the inherent nature of island populations, these species do not have the luxury of large numbers of individuals that continental conservation programs might have and often rely on small numbers of founding individuals. There are many examples of successful and well-known island reintroductions around the world that started from low numbers of individuals. Some examples of these include but are not limited to:
The Kiwikiu captive population was initiated in 1997 and founding individuals were collected from the eastern population in 1999, 2001, and 2005. The San Diego Zoo Global at the Maui Bird Conservation Center and Keahou Bird Conservation Center runs the conservation-breeding program. Five genetic founders have composed the captive population. There are only 8-9 individuals that may be released into the wild. The relatively small number of breeding females and the unique life history characteristics (pair bonding, one egg per clutch, long juvenile dependency) of the Kiwikiu limits current breeding potential in captivity. Because of the low numbers and low genetic diversity of Kiwikiu in captivity, wild Kiwikiu will need to be used in the reintroduction.
The creation of an additional population of Kiwikiu is a critical management action that is necessary to improve the long-term population viability of the species and is a high-priority action listed in the species’ recovery plan, and for USFWS, DOFAW, and MFBRP. This action will be a conservation translocation and is classified as a reintroduction by the IUCN standards because it is releasing Kiwikiu into an area of its indigenous range from which it has disappeared. This plan is focused on the actions needed for reintroduction to succeed over the short-term and to begin the process of achieving long-term success for the population in Nakula. The initial Kiwikiu responses and results from the initial reintroduction are unknown. Planning how to achieve the long-term objective and determining if any modifications or improvements are needed can only occur after assessing the first introductions.
The short-term goal of this reintroduction is to create a disjunct population of Kiwikiu, separate from the main source population, which survives through multiple years. This plan details the steps necessary to accomplish this objective, and start the leeward Haleakalā population on the trajectory to achieve the long-term objective.
The long-term objective of the overall reintroduction effort is for the newly established population of Kiwikiu to be self-sustaining, successfully breeding, and to achieve sufficient size to provide significant protection from extinction in case the source population is threatened or extirpated. All of the actions described here work towards accomplishing this objective, but achieving this goal will require substantial resources, committed over a long period, so a detailed strategy is beyond the scope of this plan’s recommendations. One of the keys in confidently assessing population establishment is determining the long-term status and fates of the released birds. We believe the management and monitoring actions should be adaptively extended into the future to collect these data.
Selection of a suitable reintroduction site was based on a number of factors, including historical distribution of Kiwikiu, the need to promote natural demographic and evolutionary processes, establishment of a disjunct population to reduce extinction risk, and to increase the ecological breadth of the species to help buffer against climatic fluctuations. Based on these factors, the Revised Recovery Plan for Hawaiian Forest Birds delineated 470.27 km2 as recovery habitat for the species on East Maui (315.24 km2), West Maui (90.58 km2), and Moloka‘i (64.45 km2). This recovery plan identifies reintroduction to leeward Haleakalā as one of the high priority actions for Kiwikiu.
The reintroduction plan prioritizes evaluating, selecting, and preparing sites for releases and/or translocation of endangered birds to ensure long-term persistence of reintroduced populations, including potentially suitable habitat outside the species’ known historic range. The goal is to select and restore habitat that fulfills the year-round requirements for the species to ensure that birds remain in the managed habitat (e.g., sufficient seasonal food resources, nesting and roosting sites). Site selection and subsequent management should include the evaluation of the species’ natural history requirements, vegetative analysis, physical qualities (area), elevation, elevational gradient, topography, soil characteristics, prevailing weather patterns, corridor potential, proximity to other conspecific populations, biological limiting factors (e.g., diseases, mosquitoes, predators, food availability, feral ungulates, alien competitors), anthropogenic threats, historical habitat modification and cultural practices of pre-contact Hawaiians, and current level of management and landowner cooperation and integration (habitat conservations plans, safe harbor agreements, etc.). Methods also should consider prevalence of threats identified, and the species’ likely response to novel habitat and threats. If areas available for releases do not provide all requirements during some periods of the year but logistical or other concerns necessitate release in these areas, then technologies must be available to support released birds during periods when essential niche characteristics are temporarily absent. Species and areas currently in need of habitat evaluation and selection for releases of endangered birds include:
Kiwikiu currently occupy roughly 20% of the identified recovery habitat on East Maui on the northern and eastern slopes of Haleakalā. It is hoped that fencing and ungulate removal below the current range on these aspects of the mountain will allow regeneration of a complex subcanopy and reduce mosquito densities to allow expansion of the population into these areas and increase densities in currently occupied habitat.
The recovery habitat on West Maui and Moloka‘i is predominately fenced and ungulate-free currently, but much of the habitat lies below the 1,400 m elevation where mosquitoes become more plentiful and Plasmodium is able to complete its life-cycle. While the long-term goal for the recovery of the Kiwikiu may be dependent on establishing a second viable population in one or both of these areas, more work is needed to assess the current mosquito abundance and disease prevalence in the areas and potentially develop methods to reduce or eliminate this limiting factor before reintroductions can begin. A study of disease prevalence in Nakula NAR and TNC Waikamoi Preserve conducted by MFBRP found higher prevalence of Culex quinquefasciatus mosquitoes in Nakula than windward sites at similar elevations. However, this study also indicated comparable rates of Plasmodium infections in the bird populations in Nakula compared to other sites at similar elevations on Hawai‘i Island, including areas containing ‘Akiapōla‘au (Hemignathus wilsoni), the closest living relative to Kiwikiu. Particularly, given the higher than expected mosquito densities in Nakula, more work is needed to map the distribution of both the vector and parasite across the recovery area.
The western and southern slopes of Haleakalā offer the most immediate opportunity to create a disjunct second population and expand the range and population of Kiwikiu in the near term. The original mesic forests on these slopes were destroyed or severely degraded by ranching and feral ungulates over the past few centuries, which caused the local extinction of Kiwikiu. As previously mentioned, some remnant forest exists on state-owned land within the Kahikinui Forest Reserve and Nakula Natural Area Reserve and on land owned by the Department of Hawaiian Homelands. Restoration of this area has begun by the State of Hawaii, MFBRP, LHWRP and partner agencies and when restored, these areas will support a mature mesic koa-‘ōhi‘a forest, which historical observations suggest was a prime habitat for Kiwikiu.
Initial restoration has focused within a 170 ha area of the Nakula NAR (Wailaulau Unit), which represents some of the most intact portions of this forest, especially in gulches inaccessible to ungulates. Peck et al. from USGS did work in the area in 2014/2015 and found the “total arthropod biomass and caterpillar biomass at Nakula was as great or greater than that observed at Hanawi and Waikamoi”, however their results were limited to the scale of the individual branch or tree – the vegetation density and quality still need to be compared across these sites but overall woody plant density is almost certainly lower in Nakula. This area is sufficiently separated from the current population and creating an additional population would improve the conservation status of Kiwikiu by reducing the risk of extinction from demographic or environmental stochasticity. It would also serve as the founding population for an eventual connection to the current population through National Park owned lands to the east. Finally, the reintroduction site is under state control and work can begin immediately when planning is complete.