Population estimates and trends of three Maui Island‐endemic Hawaiian Honeycreepers

Abstract

Population monitoring is critical for informing the management and conservation of rare Hawaiian forest birds. In 2017, we used point-transect distance sampling methods to estimate population densities of birds on Haleakalā Volcano on east Maui island. We estimated the populations and ranges of three island-endemic Hawaiian honeycreepers, including the endangered ‘Ākohekohe (Palmeria dolei), the endangered Kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys), and the Maui ʻAlauahio (Paroreomyza montana newtoni). We examined population trends back to 1980, and our 2017 density estimates were the lowest ever recorded for each species. Most concerning was the status of Kiwikiu, with a 71% decline in population since 2001 to a current population of 157 (95% CI 44–312) birds. The population of ‘Ākohekohe similarly decreased by 78% to a current population of 1768 (1193–2411) birds. For both species, population declines were due to declines in density and contraction of ranges from lower elevations. Both species are now restricted to ranges of less than 3000 ha. We surveyed ~ 91% of the range of Maui ‘Alauahio and estimated a population of 99,060 (88,502–106,954) birds, a 41% decrease since the highest estimate in 1992. Contraction of ranges to higher elevations is consistent with evidence that the impacts of avian malaria are being exacerbated by global warming trends. Our results indicate that the landscape control of either avian malaria transmission or its vector (Culex mosquitoes) will be a pre-requisite to preventing the extinction of endemic forest birds in Hawaii. Estimaciones y tendencias poblacionales de tres especies endémicas de trepadores de miel hawaianos en la isla de Maui El monitoreo poblacional es fundamental para informar sobre la gestión y la conservación de aves forestales raras aves de Hawai. En 2017, utilizamos métodos de muestreo de distancia de transectos puntuales para estimar las densidades de población de aves en el volcán Haleakalā en la isla este de Maui. Estimamos las poblaciones y áreas de distribución de tres trepadores de miel hawaianos endémicos de la isla, incluido la especie en peligro de extinción ‘Ākohekohe (Palmeria dolei), la especie en peligro de extición Kiwikiu (Pico de loro de Maui; Pseudonestor xanthophrys) y el Alauahio de Maui (Paroreomyza montana newtoni). Examinamos las tendencias de la población desde 1980, y nuestras estimaciones de densidad de 2017 fueron las más bajas jamás registradas para cada especie. Lo más preocupante fue el estado de Kiwikiu, con una disminución del 71% en la población desde 2001 a una población actual de 157 (IC del 95%: 44–312) aves. La población de ‘Ākohekohe disminuyó de manera similar en un 78% a una población actual de 1768 (1193–2411) aves. Para ambas especies, la disminución de la población se debió a la disminución de la densidad y la contracción de los rangos de las elevaciones más bajas. Ambas especies están ahora restringidas a áreas de distribución de menos de 3000 ha. Muestreamos ~ 91% del rango del Alauahio Maui y estimamos una población de 99,060 (88,502-106,954) aves, una disminución del 41% desde la estimación más alta en 1992. La contracción de rangos hacia elevaciones más altas son consistentes con evidencia de que los impactos de la malaria aviar se ve agravada por las tendencias del calentamiento global. Nuestros resultados indican que el control del paisaje de la transmisión de la malaria aviar o de su vector (mosquitos Culex) será un prerrequisito para prevenir la extinción de l. The avifauna of Hawaiʻi is characterized by a high level of endemism resulting from adaptive radiation (Fleischer et al. 1998, Pratt 2005, Lerner et al. 2011). Since human colonization of the Hawaiian Islands, the introduction of alien flora and fauna has caused the biota to become more continental in composition and ecology, almost invariably to the detriment of native species. The decline in populations of Hawaiian birds is often explained as the non-adaptive response of ecologically constrained or behaviorally naïve species to the arrival of new diseases, parasites, predators, and competitors (Atkinson 1977, Pratt 1994, van Riper and Scott 2001, Pratt and Jacobi 2009). Only 43 of 113 native forest bird species persist in the islands (Pyle and Pyle 2017), with 36 considered threatened or endangered and 11 not seen in the last 45 years (Banko and Banko 2009, Elphick et al. 2010). Haleakalā Volcano encompasses all of Haleakalā National Park (NP), several state-managed Forest Reserves (FR) and Natural Area Reserves (NAR), and private lands, most of which were included in the 2017 East Maui Island forest bird survey area (hereafter, East Maui). The area contains habitat for several honeycreepers, including three species endemic to East Maui: ‘Ākohekohe (Palmeria dolei), Kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys), and Maui ʻAlauahio (Paroreomyza montana newtoni) (Scott et al. 1986). Disease, habitat conversion, and introduced plants and animals have had negative effects on populations of these birds. Species of honeycreepers that have fared better on East Maui include the Hawai‘i ‘Amakihi (Chlorodrepanis virens wilsoni) and ‘Apapane (Himatione sanguinea). These species have broad distributions across the main Hawaiian Islands (Gorresen et al. 2009) and have even demonstrated some localized resistance to avian malaria (Atkinson et al. 2000, Foster et al. 2007). There have also been dynamic shifts in the avian community in Hawaiʻi as populations of native species decline and non-native species expand into new habitats. Over 170 species of birds have been introduced to the islands, and 54 have become naturalized (Foster 2009, Pyle and Pyle 2017). Species such as Japanese Bush-Warblers (Horornis diphone), Warbling White-eyes (Zosterops japonicus), and Red-billed Leiothrixes (Leiothrix lutea) have expanded their ranges into native forests on East Maui (Judge et al. 2013). Introduced ungulates and anthropogenic impacts have contributed to the conversion of more than 50% of lowland native forests to non-native habitat (Leopold and Hess 2017, Gon et al. 2018). Additionally, the encroachment of weedy shrubs into mesic- and wet-montane habitat threatens the unique ecological niches occupied by honeycreepers (Loope and Mueller-Dombois 1989, Pratt and Jacobi 2009). Control of invasive species has been the most challenging and critical management action for preserving habitat that supports honeycreepers (Loope and Medeiros 1995, USFWS 2006). This includes managing invasive predators such as cats (Felis catus), rats (Rattus sp.), and mongooses (Herpestes javanicus) as well as introduced disease spread by non-native mosquitoes. In some areas relatively free from disease-related impacts, habitat management (e.g., predator, ungulate, and weed control) has resulted in stable or increasing populations of native landbirds (Camp et al. 2010). Methods for long-term forest bird population monitoring in Hawaiʻi were established by the Hawaiʻi Forest Bird Survey of 1976 to 1983 (HFBS; Scott et al. 1986) and were implemented on East Maui in 1980. Subsequently, HFBS transects have been surveyed using the same methods, and additional transects were added by private, state, and federal agency natural-resource managers. Recent surveys have been conducted by personnel from the Hawaiʻi State Division of Forestry and Wildlife (DOFAW), Maui Forest Bird Recovery Project (MFBRP), Haleakalā NP resource management, and the National Park Service (NPS) Pacific Island Inventory and Monitoring Network (PACN). In 2017, DOFAW, MFBRP, Haleakalā NP, and PACN collaboratively conducted surveys on almost all East Maui transects for the first time since 1980 to provide an updated status of native and non-native forest bird species for the entire region. Survey findings were reported in the NPS National Resource Report Series in Judge et al. (2019). Here we provide occurrence, density, and trend data from East Maui to examine the short- and long-term trajectories of populations of ‘Ākohekohe, Kiwikiu, and Maui ʻAlauahio from 1980 to 2017. The East Maui forest bird survey was conducted in a 146 km2 inference area of Haleakalā Volcano (3055 m asl). The area was divided into four regions, including Haleakalā NP, Windward, Leeward, and Kula (Fig. 1). The Haleakalā NP Region primarily includes the eastern portion of the Kīpahulu District. The northern Windward Region is contiguous with Haleakalā NP and includes areas managed by DOFAW and The Nature Conservancy (TNC). The Kula and Leeward Regions are disjunct units from the climatically wet Haleakalā NP and Windward regions, occurring on the drier southern and western slopes of Haleakalā Volcano. The Haleakalā NP region inference area included 29 km2 of the upper portions of the Kīpahulu Valley Biological Reserve (Fig. 1). Bird monitoring stations range from 1500 to 2100 m in elevation. Habitat was dominated by a canopy of native ‘ōhi‘a (Metrosideros polymorpha) and koa (Acacia koa) forest and predominantly native understory. Feral pigs (Sus scrofa) and goats (Capra hircus) occurred at low and mid-elevation areas where they negatively affect the native understory and spread seeds of invasive plants such as Clidemia hirta, Psidium cattleainum, and Cyathea cooperi. Typical northeast tradewinds pervade Kīpahulu Valley, and annual mean rainfall from weather stations in the area ranges from 5600 to 10,270 mm (Giambelluca et al. 2013). The Windward region inference area covered 67 km2 jointly managed by TNC and DOFAW. The region includes TNC’s Waikamoi Preserve, Hanawī NAR, Ko‘olau FR, Makawao FR, and Hāna FR (Fig. 1). Transects range from 600 to 2300 m elevation. The habitat varied from wet ‘ōhi‘a-dominated forests in the eastern portion to transitional wet-mesic forests with a mixed koa and ‘ōhi‘a canopy along the western edge. Mean annual rainfall in the area ranged from 6600 to 10,270 mm (Giambelluca et al. 2013). The Leeward region encompassed 26 km2 on the south-facing slope of Haleakalā (Fig. 1). DOFAW manages Nakula NAR and Kahikinui FR in the central portion of the region. The Haleakalā NP Nuʻu Unit is located east of Kahikinui FR. The state of Hawai‘i Department of Hawaiian Home Lands (DHHL) manages the western portion of the region and the privately owned Nu‘u Mauka Ranch manages the land on the eastern end (Fig. 1). Forest quality in this region generally declines from west to east. In DHHL and Nakula NAR, there are large intact patches of koa and ‘ōhi‘a woodland and savanna in the west, whereas only scattered ‘ōhi‘a and severely eroded, non-native grass-covered slopes remain in the east. Thus, most of the remaining habitat for forest birds is in the western portion of the Leeward region. Transects ranged from 1100 to 2000 m elevation and the region experiences dry conditions, with a mean annual rainfall ranging from 720 to 1000 mm (Giambelluca et al. 2013). The Kula region encompassed 24 km2 on the east- and northeast-facing slopes of Haleakalā. Most of the region is managed by DOFAW, which includes the Kula FR and a portion of Kahikinui FR. Privately owned Ka‘ono‘ulu and Ulupalakua ranches own smaller areas in the region (Fig. 1). The region is dominated by non-native tree species (conifers, eucalyptus, and Acacia spp.), with a mix of native tree and shrub species. Upper-elevation areas are dominated by native shrubland. Transects ranged from 1700 to 2700 m in elevation. Mean annual rainfall ranges from 800 to 920 mm (Giambelluca et al. 2013). Surveys were conducted from 13 March to 28 June 2017. We surveyed for birds at 570 stations along 32 transects in the four regions (Fig. 1). Transects were 350 to 3500 m apart and ranged from eight to 72 stations long. Stations were ~ 150 m apart and surveyed using point-transect distance sampling methods lasting 8 min. Surveys began soon after dawn and concluded by 11:00 in Haleakalā NP and by 12:00 in the Leeward, Kula, and Windward regions. We recorded species, horizontal distance in from to each bird and or were also recorded at each distance sampling methods for by a to estimate using methods et al. sampling for that and estimates are the critical that all birds are with at the birds are and are of Hawaiian forest bird sampling be in et al. are from the National Park Service We used and the current and of species to the inference area for Methods for area and inference of occurring species are in by Judge et al. (2019). We used survey and conducted from to 2017 to the and occupied by each species. only since that inference areas the current range of each species. The lower of each range the lowest where each species was in each region and varied regions. were using management or (e.g., The upper for the range of each species was using habitat or management The ranges of ‘Ākohekohe and Kiwikiu were smaller than the survey inference we were to provide global population estimates for species. ‘Ākohekohe and Kiwikiu in habitat dominated by native forests in Haleakalā NP and the Windward We used habitat for native all native and to the upper of their ranges et al. ranges using the same methods, a of from surveys conducted from 1980 Scott et al. the ranges of ‘Ākohekohe and Kiwikiu to be and more survey et al. the ‘Ākohekohe range to and the Kiwikiu range to ha. We the in species ranges the and current Maui ʻAlauahio native some non-native and habitat in the Haleakalā NP, Windward, and Kula For this species, we primarily used as the upper of the inference This generally the same upper as the inference on habitat and we that portions of their range the 2017 inference area we provide an inference area for surveyed areas and an updated range for the species by including and habitat on surveys conducted in 1980, Scott et al. estimated the range for the species to be ha. more et al. reported a range contraction to a density estimates were for ‘Ākohekohe, Kiwikiu, and Maui were and densities were estimated using et al. 2010). we had relatively of ‘Ākohekohe and Kiwikiu, than the et al. their were with data from all surveys to and additional to to a of than was for a and we used the global to estimate densities using This is for densities of rare species where are and are by et al. of Maui ʻAlauahio data of our 2017 data were with data from all surveys additional The were to and with an of et al. by et al. the was with and and the was with and was by sampling in the distance sampling of et al. 2010). included and time of and were as a time of was as a time of as a varied the a bird first was with both and and of was used to and the of for survey and were also for all three species of in the was and the was that with the lowest for et al. 2001, and were with the most to the with the lowest to of were not were at a distance where the was ~ This by and the of to the and were by methods in from et al. from a global using by region and species was as mean density by in estimated densities our 2017 survey and the most survey for Haleakalā NP or for the Windward were using by region. was to for and an region (Camp et al. to where there was trend an to a trend and 2005, et al. were to a in the population or a and annual of in population density, or were as stable or trend occurred the in density estimates was than the region. trend occurred the the region. occurred densities were and results and We long-term trends using to in population that the trend not in densities with and used to the population of the time We and only eight Kiwikiu 1). were m elevation in wet-mesic and ‘ōhi‘a-dominated in Haleakalā NP and on Windward transects in Hanawī NAR and TNC’s Waikamoi and There were on Windward transects in eastern Waikamoi Preserve, FR, and Kīpahulu Valley, areas that included portions of the and current estimated ranges of each species and species was in the Kula or Leeward regions. For ‘Ākohekohe, we estimated a density of and an of 1768 (95% CI in their For Kiwikiu, we estimated a density of and a of 157 67 (95% CI 44–312) in their We had of Maui ʻAlauahio that were in native and non-native forest at elevations ranging from to 2300 m in Haleakalā NP, Windward, and Kula regions, in the Leeward region (Fig. Population density of Maui ʻAlauahio was and we estimated an of 99,060 (95% CI in the inference on habitat and our estimates not include of their range We a contraction in the ‘Ākohekohe range to estimates reported by et al. from surveys conducted from 1980 2001 The range of Kiwikiu by an estimated 41% for ‘Ākohekohe and Kiwikiu were due to a of at lower elevations in surveys conducted from 2017. We estimated the species range of Maui ʻAlauahio to be a from the range reported by et al. The our estimates and of et al. was our of additional areas in the Kula region and TNC’s Waikamoi where the species is to We not this a in the in portions of the Maui ʻAlauahio range on additional et al. 2007). We trends of ‘Ākohekohe, Kiwikiu, and Maui ʻAlauahio by the 2017 densities to estimated densities on surveys conducted in and were for each species of relatively in densities and large in the of population trajectories of ‘Ākohekohe, Kiwikiu, and Maui ʻAlauahio have since 1980 (Fig. their densities to in the and for ‘Ākohekohe and Kiwikiu in 2001 (Fig. densities of ‘Ākohekohe decreased by 78% in both density and to our 2017 estimates (Fig. the of in the CI of density estimates of the most surveys surveys also that this species has declines in population the last (Fig. densities and of Kiwikiu decreased and since 2001 (Fig. The highest estimated density and of Maui ʻAlauahio were in with estimates by 41% in density and in to our 2017 estimates (Fig. We declines in the density and of the three Maui island-endemic honeycreepers, with a more than decline in of and Kiwikiu since 2001 and a decline in Maui ʻAlauahio since 1992. The of Kiwikiu in 2017 was with an estimated to remaining in the also with an estimated of to in populations of Kiwikiu and have been exacerbated by range of more than since 1980, by the of in the range of the area to years 2017. The of Maui ʻAlauahio was higher than that of the Maui with an estimate and in density were more in Maui ʻAlauahio than range contraction this species in some drier areas in mixed native and non-native Scott et al. reported in Maui ʻAlauahio densities and m whereas our results indicate that the entire range of the species is 1500 m declines in in of each species that are native avian on East Maui. Since 1980, most of and Kiwikiu have been 1500 m where disease has to be avian malaria has a for Riper et al. and 2009, et al. et al. native species of Hawaiian birds to persist in a as higher mean global and in both the disease and its the southern (Culex higher into native forest (Atkinson et al. a of of the current estimated range of and Kiwikiu by 2100 et al. population trajectories Kiwikiu is to persist years and will become in as as years et al. 2018). The species is on high and by low have from the of et al. 2018). The and decline of Maui to the current decline of populations in populations of four forest bird species have by ~ et al. The is even smaller there and of native forest birds are in the of the in range of avian malaria and its vector et al. on East Maui are than that avian malaria was first in of Kiwikiu to years et al. and 2009). be to a the elevation ranges of malaria and species, including transmission of malaria in and forests due to or annual et al. some of which in large population impacts, and by birds in or forests that or their to malaria due to in or of birds and of birds that disease in birds that most of their time in habitat et al. or in response to avian The of these the of in the of endemic birds on East and the of avian malaria in Hawaiian birds that the or for the populations of each species be challenging even with and habitat also be to declines in populations on East Maui. the or impacts of these is not forest habitat has relatively intact in the current range of endemic species and effects of are to have been in the last years new predators have been introduced to East Maui the last This is not to that these are not critical to bird that they are either not for the declines or that the impacts of these the of will be In an ecological time to Kiwikiu and a of on where to and a of the of declines with and management for the not be et al. that in an adaptive the of management This provide a of to the and the of a of response to management action provide and our of to these species. control of both avian malaria and predators be the management most to the native Hawaiian bird community in East Maui. habitat is also habitat have been in for and we they will landscape control of malaria and either a of species and better and the of The most to malaria is by or the only vector of this disease in the invasive this have the to are et al. 2017). control be in Hawaiʻi 2001, Banko et al. landscape have been implemented in on the main Hawaiian Islands due to and The most to landscape control of is the of the ranges of endemic Maui species et al. control of malaria and will be and are a of evidence they are the only with the to or the long-term decline of of native Hawaiian birds et al. 2018). to the of this is the that to new populations or Kiwikiu in have had and et al. 2018). have concluded that now is the time to even with et al. et al. to State of Hawai‘i Department of and Natural of Forestry and and Natural Area Reserve and to the East Maui and Leeward Haleakalā to The Nature and Wildlife Maui Species East Maui Haleakalā Ulupalakua Department of Hawaiian Mauka and to Windward for to and from to of the Pacific Island Network Inventory and Monitoring the Maui Forest Bird Recovery and to all conducted surveys in 2017. of or is for only and not by the This was by the National Park Pacific Island Inventory and Monitoring with of Hawaiʻi at and with the Survey and the of Hawaiʻi at The Maui Forest Bird Recovery the of Pacific Unit of Hawaiʻi at conducted surveys on state and private land with by the Division of Forestry and Wildlife and their The is not for the or of by the than be to the for the

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