ABSTRACT Protected areas are vital to the recovery of endangered species. Of the 24 remaining endemic passerines in Hawaiʻi, 16 species are endangered or critically endangered. Yet protected areas in the archipelago are changing as a result of climate change and biological invasions. For example, the non-native southern house mosquito ( Culex quinquefasciatus ), the primary vector of avian malaria ( Plasmodium relictum ), has been encroaching upward as higher elevations warm. How the ranges of endemic birds have also shifted their range upward in the Kaʻū Rainforest, the largest native forest on the Island of Hawaiʻi, is not well understood. We used hierarchical distance sampling to characterize how population density has changed from 2002 to 2024 for eight endemic bird species in the Kaʻū Rainforest. For five species, the most parsimonious model included an interaction between year and a quadratic elevation effect. Species that were most common at lower elevations in 2002, e.g., ʻApapane ( Himatione sanguinea ), tended to be most common at mid- elevations by 2024. Species that were already most common at higher elevations, such as ʻIʻiwi ( Drepanis coccinea ) and Hawaiʻi ʻĀkepa ( Loxops coccineus ), tended to decline in density. For example, ʻIʻiwi density at 1,530 m declined from 3.31 birds per ha (95% confidence interval [CI]: 2.67-4.11) to 1.34 birds per ha (95% CI: 1.05-1.71), and Hawaiʻi ʻĀkepa were completely extirpated from elevations below 1,530 m by 2024. Our results demonstrate how the elevational ranges of endemic species have shifted in response to climate change, biological invasions, and habitat degradation. Translating these results into conservation measures may require a more thorough investigation of the causal mechanisms of these range shifts with finer scale habitat data, under the same hierarchical modeling framework. LAY SUMMARY Protected areas such as National Parks, private lands managed for conservation, and state managed reserves have been essential to conserving Hawaiʻi’s native forest birds. Climate change and the cold-intolerant, invasive southern house mosquito, the primary vector of avian malaria, both threaten protected areas in Hawaiʻi. As the climate warms, avian malaria has been encroaching upwards to higher elevations. We found evidence that five of eight native forest bird species were shifting upward in elevation, perhaps in response to these dual threats, in Kaʻū Rainforest, the largest native forest in the Hawaiian Islands. The endangered Hawaiʻi ʻĀkepa has been extirpated from elevations below 1530m. Further, the vulnerable ‘I‘iwi has been extirpated from elevations below 1200m, and their density has declined by half at 1530m. Although more research could enhance understanding the mechanisms of this shift, our study supports wildlife managers in decisions related reducing the impact of mosquitos and climate change on native forest bird species within Hawaiʻi’s protected areas.

Hawai'i's avifauna has undergone profound changes over the past 1,000 years, with many endemic bird species driven to extinction and non-native introductions reshaping forest ecosystems. On the island of Moloka'i, habitat degradation and the introduction of mosquito-borne disease, mainly avian malaria (Plasmodium relictum), have caused extinctions and severe declines in native forest bird populations. To assess these changes, point-transect distance sampling surveys were initiated in 1979 and 1980 and repeated six times, most recently in 2021, covering a 3,527 ha area. This study analyzes species composition, population densities, abundances, and long-term trends for species with sufficient detections using log-linear regression. Since 1979-1980, a total of 17 non-native and 3 native species were detected across all six surveys. The non-native Warbling White-eye (Zosterops japonicus) had the highest density and abundance in every survey, while abundance of Red-billed Leiothrix (Leiothrix lutea) significantly trended upward. The Japanese Bush Warbler (Horornis diphone) irrupted in the survey area, increasing in abundance by more than 99% since 1979-1980. Among native species, 'Apapane (Himatione sanguinea) populations increased by 33%, while Hawai'i 'Amakihi (Chlorodrepanis virens) declined by 78% from their peak in 1995. Federally threatened 'I'iwi (Drepanis coccinea), highly susceptible to avian malaria, have not been recorded on Moloka'i since 2010, and the endemic Oloma'o (Myadestes lanaiensis) has not been detected since 1980 and is possibly extinct. Our results underscore the ongoing conservation crisis for Moloka'i's forest birds and the continued vulnerability of native birds to disease and habitat loss.

Federal, state, and non-governmental partners resurveyed landbirds in the Ka?? Rainforest on the Island of Hawai?i in 2019. Point-transect distance sampling was conducted in Hawai?i Volcanoes National Park, Ka?? Forest Reserve, Kap?pala Forest Reserve, and Kap?pala Cooperative Game Management Area. This is the first comprehensive survey of the region since 2008. Through a collaborative effort, monitoring transects were consolidated to provide a consistent, repeatable sampling frame for future surveys. We estimated landbird distribution, density, and abundance for eight surveys since 1976. Changes in species-specific densities were assessed using a log-linear regression to determine trends of the six most recent surveys since 2002. Trends were assessed in three strata: low elevation (<1,500 m), high elevation (?1,500 m), and total survey area. We detected 23 species and there were sufficient detections of 11 species to estimate density and abundance. We provided indices of relative occurrence for the remaining 12 species detected. Native birds vulnerable to avian malaria (Plasmodium relictum) were absent or trended downward in the low elevation stratum. The federally endangered ?Akiap?l??au (Hemignathus wilsoni), ?Alaw? (Hawai?i Creeper, Loxops mana) and Hawai?i ??kepa (Loxops coccineus) were restricted to areas above 1,500 m elevation, likely due to the low prevalence of the cold-intolerant vector of avian malaria, the southern house mosquito (Culex quinquefasciatus), in this high elevation stratum. However, downward trends of the federally threatened ?I?iwi (Drepanis coccinea) above 1,500 m elevation may indicate an expansion in range of mosquitoes due to warming trends. Thought to be more resilient to avian malaria, the ?Apapane (Himatione sanguinea) and Hawai?i ?Amakihi (Chlorodrepanis virens virens) trended upward in all three strata. The Hawai?i ?Elepaio (Chasiempis sandwichensis) trended downward in each stratum. The ??ma?o (Myadestes obscurus) trended upward in the low stratum and downward in high. Trends were inconclusive for Hawai?i ??kepa, but favorable for ?Alaw?, which trended upward in its restricted range. There were insufficient detections of ?Akiap?l??au in 2019 to estimate density, but the 2008 abundance estimate of 691 ? 410 (SE) birds was the lowest since 1976. Trends were mixed for the non-native Warbling White-eye (Zosterops japonicus), Red-billed Leiothrix (Leiothrix lutea), and Northern Cardinal (Cardinalis cardinalis). Overall, upward trends of ?Apapane and Hawai?i ?Amakihi throughout the survey area, ??ma?o in the low stratum, and ?Alaw? in the high stratum, suggests management actions to protect native forest bird habitat are having a positive benefit. Nevertheless, avian malaria is predicted to have an increasing impact on vulnerable species as mosquitoes expand into higher elevations.

The National Park of American Samoa (NPSA) was surveyed in 2011 and 2018 using point-transect distance sampling to estimate trends in landbird distribution, composition, population density, and abundance. Surveys were conducted within the Tau-Unit and Tutuila Unit, each on separate islands of American Samoa. We detected a total of 14 species during surveys and there were sufficient detections of seven species to allow for density estimation and abundance within each unit. We assessed differences in density between surveys with a two-sample z-test and found significant declines of Blue-crowned Lorikeets (Vini australis) in the Tau-Unit, and of Samoan Starlings (Aplonis atrifusca) in the Tutuila Unit. Density estimates of the Crimson-crowned Fruit Dove (Ptilinopus porphyraceus), Pacific Kingfisher (Todiramphus sacer), Polynesian Wattled Honeyeater (Foulehaio carunculatus), and Samoan Starling (in the Tau-Unit) were also lower in 2018 than 2011, but differences were inconclusive because of relatively large variance estimates. Densities of the Polynesian Starling (Aplonis tabuensis) and Pacific Imperial Pigeon (Ducula pacifica) in the Tau-Unit were higher in 2018 than 2011, but differences were similarly inconclusive. Lower 2018 densities could be due to Tropical Cyclone Gita that struck the islands just four months before the surveys. We provide indices of relative occurrence and abundance for the remaining seven species detected, which include the Many-colored Fruit Dove (Ptilinopus perousii) and the rarely detected Spotless Crake (Zapornia tabuensis)-both of which are species of concern in American Samoa.

Abstract: Axis deer (Axis axis) are invasive species that threaten native ecosystems and agriculture on Maui Island. To mitigate negative effects, it is necessary to understand current abundance, population trajectory, and how to most effectively reduce the population. Our objectives were to examine the population history of Maui axis deer, estimate observed population growth, and use species-specific demographic parameters in a VORTEX population viability analysis to examine removal scenarios that would most effectively reduce the population. Only nine deer were introduced in 1959, but recent estimates of >10,000 deer suggest population growth rates (r) ranging between 0.147 and 0.160 even though >11,200 have been removed by hunters and resource managers. In VORTEX simulations, we evaluated an initial population size of 6,000 females and 4,000 males, reflecting the probable 3F:2M sex ratio, with annual removal rates of 10%, 20%, and 30% over a 10-year period. A removal rate of 10% resulted in a positive growth rate of 0.103 ± 0.001. A 20% removal rate resulted in only a slightly negative growth, while a 30% removal rate resulted in –0.130 ± 0.004. By increasing the ratio of females removed to 4F:1M in the 30% harvest scenario, the decline nearly doubled, resulting in –0.223 ± 0.004. Effectively reducing axis deer will most likely require an annual removal of approximately 20–30% of the population and with a greater proportion of females to increase the population decline. Selective removal of males may not only be inefficient, but also counterproductive to population reduction goals.

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 Haleakala Volcano on east Maui island. We estimated the populations and ranges of three island-endemic Hawaiian honeycreepers, including the endangered 'Akohekohe (Palmeria dolez), the endangered Kiwikiu (Maui Parrotbill; Pseudonestor xanthophrys), and the Maui 'Alauahio (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 'Akohekohe 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 similar to 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.

Endangered Hawai'i. 'Akepas (Loxops coccineus) are endemic to Hawai'i island, where they occur in five spatially distinct populations. Data concerning the status and population trends of these unique Hawaiian honeycreepers are crucial for assessing the effectiveness of recovery and management actions. In 2016, we used point-transect distance sampling to estimate the abundance of Hawai'i. 'Akepas in portions of Hawai'i Volcanoes National Park (HAVO) and the Ka'u Forest Reserve (KFR) on Mauna Loa volcano. We then compiled the survey data from four other populations to provide a global population estimate. In our HAVO and KFR study area, we mapped habitat classes to determine the population densities in each habitat. Densities were highest (1.03 birds/ha) in open-canopy montane 'ohi'a (Metrosideros polymorpha) woodland. In contrast, densities of the largest. 'Akepa population on Mauna Kea volcano were highest in closed-canopy 'ohi'a and koa (Acacia koa) forest where the species is dependent on nest cavities in tall (> 15 m), large (> 50-cm diameter at breast height) trees. We surveyed potential nesting habitat in HAVO and KFR and found only one cavity in the short-stature montane 'ohi'a woodland and five cavities in the tall-stature forest. Differences in densities between the Mauna Kea and Mauna Loa populations suggest that Hawai'i. 'Akepas may exhibit different foraging and nesting behaviors in the two habitats. The estimated overall population density in the HAVO and KFR study area was 0.52 birds/ha, which equates to 3663 (95% CI 1725-6961) birds in their 11,377-ha population range. We calculated a global population of 16,428 (95% CI 10,065-25,198) birds, which is similar to an estimate of 13,892 (95% CI 10,315-17,469) birds made in 1986. Our results suggest that populations are stable to increasing in the two largest populations, but the three other populations are smaller (range = 77-1443 birds) and trends for those populations are unknown.

European mouflon (Ovis gmelini musimon), the world's smallest wild sheep, have proliferated and degraded fragile native ecosystems in the Hawaiian Islands through browsing, bark stripping, and trampling, including native forests within Hawai'i Volcanoes National Park (HAVO). HAVO resource managers initiated ungulate control efforts in the 469 km(2) Kahuku Unit after it was acquired in 2003. We tracked control effort and used aerial surveys in a 64.7 km(2) area from 2004 to 2017 and more intensive ground surveys and camera-trap monitoring to detect the last remaining animals within a 25.9 km(2) subunit after it was enclosed by fence in 2012. Aerial shooting yielded the most removals per unit effort (3.2 animals/hour), resulting in 261 animals. However, ground-based methods yielded 4,607 removals overall, 3,038 of which resulted from assistance of volunteers. Ground shooting with dogs, intensive aerial shooting, ground sweeps, and forward-looking infrared (FLIR)-assisted shooting were necessary to find and remove the last remaining mouflon. The Judas technique, baiting, and trapping were not successful in attracting or detecting small numbers of remaining individuals. Effort expended to remove each mouflon increased nearly 15-fold during the last 3 yr of eradication effort from 2013 to 2016. Complementary active and passive monitoring techniques allowed us to track the effectiveness of control effort and reveal locations of small groups to staff. The effort and variety of methods required to eradicate mouflon from an enclosed unit of moderate size illustrates the difficulty of scaling up to entire populations of wild ungulates from unenclosed areas.

European mouflon sheep (Ovis gmelini musimon) were introduced to Kahuku Ranch on Hawai‘i Island in 1968 and 1974 for trophy hunting and have been detrimental to the native ecosystem by trampling, bark stripping, and browsing vegetation. In 2003, Hawai‘i Volcanoes National Park acquired Kahuku Ranch and managers began removing mouflon. The objective of this project was to determine whether hunting has changed the distribution of mouflon in Kahuku, to better understand mouflon behaviour and to expedite eradication efforts. Locations from hunting and GPS telemetry data during 2007–14 were used to determine the effect of hunting on mouflon distribution by examining distance to roads and habitat use. Mouflon seemed to avoid roads after hunting pressure increased and their distribution within vegetation types changed over time. Mouflon without hunting pressure were detected in native shrub habitat in 68% of all observations. Hunted mouflon were encountered less in native shrub habitat and more in other habitats including open forest, closed forest, and areas with no vegetation. These changes suggest that hunting has influenced the distribution of mouflon over time away from native shrub and into other vegetation types where they may be more difficult to control.

Hawaiian Petrels Pterodroma sandwichensis nest on the main Hawaiian Islands. Island colonies are small in geographic area relative to the foraging range of this long-distance flier (Adams and Flora 2009). The species belongs to the order Procellariiformes and is characterized among the “gadfly” petrels because of the birds’ erratic flight behavior. Like many other seabirds, Hawaiian Petrels are regarded as highly philopatric to natal breeding sites (Harris 1984, Warham 1990, Hamer 2001). Philopatry and the resulting reduced dispersal can contribute to population differentiation of seabirds (Greenwood 1980, Shields 1982, Clobert et al. 2001). Thus, philopatry may lead to the genetic isolation of island colonies. Evidence of subsequent differentiation may be apparent in behavior, breeding phenology and morphology.

The endemic solitaire, 'Oma'o (Myadestes obscurus), is common in windward forests of Hawaii Island, but has been historically extirpated from leeward forests. The last detections of Oma'o on the leeward side of the island were in woodland habitat on the western flank of Mauna Loa in 1978. Oma'o were detected in woodland habitat in relatively low densities during a 2010 forest bird survey of Hawaii Volcanoes National Park. The source of the population is unknown. It is probable they originated from a documented but unsurveyed population of 'Oma'o in scrub alpine lava. Alternatively, the birds may have persisted undetected for nearly 35 years, or expanded from windward mesic forests on southeast Mauna Loa. There is no evidence 'Oma'o recolonized the wet mesic forests of leeward Mauna Loa. The 'Oma'o can occupy diverse native habitats compared to other species in the Hawai'i Myadestes genus, of which most species are now extinct. The connectivity of each population is not understood but we assume there are significant geographic, physiological, and behavioral barriers for scrub alpine and wet mesic forest populations. The expansion of 'Oma'o to leeward woodlands is encouraging as the species is Hawaii Island's last native frugivore capable of dispersing small and medium sized seeds of rare angiosperms, and could have an important role in re-establishing ecosystem function. Received 27 February 2012. Accepted 28 June 2012.