Ecology of Hawai'i Volcanoes National Park
Learn more about the ecology of Hawai'i Volcanoes National Park.
Well known for its active volcanoes and geological significance, Hawai‘i Volcanoes National Park is also one of the most ecologically diverse landscapes in the world. Located more than 2,000 miles from the nearest continent, the Hawaiian Islands are the most geographically isolated group of islands on Earth. Being almost in complete isolation, Hawai‘i has more endemic species, meaning species that are not found anywhere else, than nearly any other place on Earth. Hawai‘i Volcanoes National Park has a large range of elevation from sea level to the summit of Mauna Loa at 13,678 feet, resulting in a variety of landscapes and ecosystems. There are seven ecological zones within the park including seacoast, lowland forest, mid-elevation woodland, rain forest, upland forest, subalpine, and alpine. The introduction of invasive species and diseases have resulted in many of Hawai‘i’s endemic species becoming threatened or endangered.
Hawai‘i Volcanoes National Park became a U.S. National Park in 1916, making it the 13th national park and the first in a U.S. Territory (Hawai'i became a state in 1959). Although the park was first designed for visitors to experience the active volcanoes, it now highlights the unique animal and plant species and variety of ecological features as well. The USGS and the National Park Service work to understand the endemic plant and animal species that exist within the park. Hawai‘i Volcanoes National Park was designated an International Biosphere Reserve in 1980 and a World Heritage Site in 1987.
Animals
Hawai‘i Volcanoes National Park is famous for its abundant land birds and seabirds. However, Hawai‘i’s birds have shown significant population declines in the past 200 years, resulting in a growing number of species being listed as threatened or endangered. Threats to these birds include disease, invasive species, habitat loss, and decreasing survivorship and productivity due to predators.
Six species of birds in the honeycreeper family are found within Hawai‘i Volcanoes National Park. Honeycreepers are endemic to the Hawaiian Islands, have brightly colored feathers, and sing canary-like songs. Having evolved with a wide range of bill shapes and eating behaviors from sparrow-like birds that arrived in Hawai‘i 4-5 million years ago, the Hawaiian honeycreepers are a great example of adaptive radiation. Because of their diversity, some consider the Hawaiian honeycreepers as an even better example of adaptive radiation than Darwin’s famous Galapagos finches.
Within Hawai‘i Volcanoes National Park, the Hawaiian Honeycreepers are most commonly found in the high elevation forests of Kahuku near Mauna Loa. ‘Akaiapōlā‘au, Hawai‘i Ākepa, and Hawai‘i Creeper are listed as endangered, and the ‘I‘iwi are threatened.
Nēnē evolved from the Canada Goose, and are flying birds that have short wings, long legs, and webbed toes. When Captain Cook arrived, there were an estimated 25,000 Nēnē in existence where, by 1952 as few as 30 remained. The birds were hunted by humans and introduced predators as settlers brought new species into the islands. To combat the declining population, Hawai‘i Volcanoes National Park became a breeding and reintroduction area for the state bird in 1970. There are currently research programs and protection measures instilled in the park to improve their breeding success and survival rate. Biologists in the park are involved in banding and monitoring specific birds to learn about their behavior, biology, and habitat.
‘Io are widespread on the Island of Hawai‘i and are commonly seen throughout the park in low and high elevations. They have been nicknamed the Hawaiian Hawk and are the only species of hawk native to Hawai‘i. The ‘Io was first listed as endangered on March 11th, 1967, and was recently removed from the Federal List of Endangered and Threatened Wildlife because of stable populations on February 3rd, 2020.
The ‘Ua‘u, also known as the Hawaiian Petrel, is an endangered native seabird that biologists estimate there are only 50 to 60 breeding pairs left within Hawai‘i Volcanoes National Park. The ‘Ua‘u spends most of its life at sea, returning to Mauna Loa to nest and take care of young in high elevation underground burrows. It is estimated that historical populations of the ‘Ua‘u were in the hundreds of thousands to millions of birds. Factors that have contributed to their decline include historic hunting by humans, non-native predators such as feral cats, and habitat loss. Current National Park Service actions to protect the species from non-native predators includes the construction of a five-mile fence surrounding ‘Ua‘u habitat on Mauna Loa.
Current Research
Avian Pathogens and Vectors
Demographic and ecological studies are being conducted to determine the health of Hawai‘i’s bird populations. Current threats to the bird populations in the park include climate change, invasive species, residential development near the park, and introduced pathogens and vectors. Recent and ongoing research aims to understand the potential effects of growing threats, monitor trends in disease, and develop strategies to control disease.
The Kahuku forest of Hawai‘i Volcanoes National Park is the only National Park lands where the endangered Akiapōlāʻau, Hawai‘i ‘Akepa, and Hawai‘i Creeper are still found. Recent USGS projects aimed to provide resource managers at Hawai‘i Volcanoes National Park and endangered species biologists at Pacific Islands U.S. Fish and Wildlife Service with baseline data for the Kahuku forests on the prevalence of avian disease and the distribution of introduced mosquitoes that are a vector of avian diseases. Specifically, researchers documented the prevalence of avian malaria, avian pox, and knemidokpotic mange (a parasite transmitted disease). Of the mosquitos caught in the park during the study, 20% were found to have avian malaria (9). Researchers predict that avian disease may serve as a constraint to the existing populations and limit restoration attempts. Additional mosquito monitoring research projects are being conducted in Kaloko Honokōhau and Pu‘uhonua O Hōnaunau National Historical Parks on the island of Hawai‘i. There are six species of biting mosquitoes that have been introduced to the Hawaiian Islands since Western contact.
Cooler temperatures at higher elevations prevent mosquitoes from existing in these areas and native birds that are susceptible to mosquito-borne diseases have persisted in higher-elevations forests. Expanding mosquito populations and climate change are two potentially important factors affecting the birds of Hawai‘i Volcanoes National Park. With warming temperatures, the small envelope of mosquito-free habitat at higher elevations is decreasing and increasing birds’ exposure to mosquitos and the avian diseases they carry. Because of this, the topic is widely studied in Hawai‘i Volcanoes National Park and throughout Hawai‘i, as it has great potential to be devastating to the bird populations in the future.
Hawaiian Honeycreeper Elevational Movement
Hawai‘i Volcanoes National Park has a variety of unique ecosystems because of its variation in elevation that extends from reef to ridge. Within the park, documentation of elevational movement of endemic birds is important to understanding disease transmission as birds may move in and out of areas with variable disease risk. This information can be used to better understand effective strategies for species conservation, preservation of high elevation habitats, and habitat management. Researchers recently found evidence that the endemic Hawaiian honeycreepers may be elevational migrants and are currently researching this topic. They observed the bird’s diets to see if they are eating foods found at higher elevations and measured the level stable isotopes (hydrogen, carbon, and nitrogen) in the bird’s active tissue samples.
Hawaiian honeycreepers are highly susceptible to avian malaria, which is currently minimal in high-elevation forests. Understanding which honeycreepers visit low-elevation forests may be critical in predicting and mitigating the impacts of avian malaria on these populations.
‘Ōpe‘ape‘a (Hawaiian Hoary Bat)
The Hawaiian hoary bat is the only native terrestrial mammal in the Hawaiian Islands. Unlike the normal image of bats, Hawaiian hoary bats do not live in caves, they roost in the foliage of trees. Around sunset, the bats leave the trees to eat insects, primarily moths. They have been spotted from sea level to as high as the summit of Mauna Loa. Potential threats to this endangered species include habitat loss, wind turbine collisions, barbed wire fences, and other structures. There is limited knowledge of the Hawaiian hoary bat distribution, abundance, and habitat needs; however, the USGS is working to better understand their diet, roosting ecology, movements and population genetics.
Honou‘ea (Hawksbill Turtle)
Honu‘ea are endangered sea turtles that live in the water near many of the Hawaiian Islands. The turtles are known to nest on beaches in Hawai‘i Volcanoes National Park. They can be differentiated from the more common green sea turtle by their sharper, pointed beaks. The turtle populations have reduced in this area because of loss of nesting habitat, predation, and poaching.
Plants
From the coastal plains to the endless lava flows, Hawai‘i Volcanoes National Park hosts a wide variety of plant species in the unique landscape they inhabit. The volcanoes, forests, and plants within the park hold importance to Native Hawaiian history. Despite the rich biodiversity of plant species, they are facing threats from invasive species, disease, introduced predators, and climate change.
Ferns
Two hundred fern species can be found across the Hawaiian Islands and 65% of those are considered endemic. ‘Ae is a pioneer species and one of the first to be found sprouting from the cracks of lava. ‘Ama‘u ferns are a distinct red color and turn green as they mature. Hāpu‘u are the largest tree ferns in Hawai‘i and can reach up to 35 feet in height. The Asian Sword Fern is highly invasive and commonly found near the summit of Kīlauea and is dominant in certain areas of the forest.
‘Āhinahina (Mauna Loa Silversword) only survive at high altitudes on Mauna Loa and are named for their sword-like leaves. They share a common ancestor with species found on Mauna Kea and Haleakalā but are distinct from the other species. Only once in the plant’s life, after 10 to 30 years of maturity, they send up a fragrant flower stalk that can grow up to nine feet tall. After a few weeks of blooming the entire plant dies. Animals like cattle, sheep, and goats eat silversword and have contributed to its endangered status. Recovery efforts for the Mauna Loa silversword include fencing areas to exclude introduced grazers and the collection of seeds for germinating and replanting in the wild. Since 2007, more than 32,000 Mauna Loa silversword seedlings have been reintroduced with a survival rate of over 70 percent.
Ōhelo grow only a few feet tall and are recognized for their brightly-colored berries. The berries are used in foods like jams and pies, and are an important food source for Nēnē, the threatened state bird of Hawai‘i. ‘Ōhelo are a pioneer species, meaning they are one of the first plants to colonize new lava flows. The plant has cultural significance in the islands and was considered sacred to the Hawaiian volcano deity Pele. There are two species of ‘Ōhelo in Hawai‘i Volcanoes National Park.
Trees
‘Ōlapa trees are known for their small dark blue fruits that are commonly consumed by Hawaiian honeycreepers. Native Hawaiians traditionally used these fruits to create dark-colored dyes. Feral pigs often eat tiny ‘Ōlapa saplings.
Koa trees are another endemic native tree that are prominent and stand out reaching up to 100 feet tall. Koa is a keystone species with other species in the ecosystem such as insects, birds and understory plants influenced by or dependent on them. There is a prominent koa forest near Mauna Loa in Hawai‘i Volcanoes National Park and the tree can be seen in many areas of the park. Within the park the trees are guarded and protected from grazing and harvesting. Koa wood is prized for canoe making and other woodworking and building materials.
Hau kuahiwi are only found on the Island of Hawai‘i and currently listed as critically endangered. The original tree died in 1930, and cuttings were collected and propagated. The population of these cuttings have been reduced to a single tree at least three times. Hundreds of trees were planted in the early 2000s but the current population is unknown. Threats to this tree include consumption of the bark, flower, and fruit by rats, leaf damage from native insects, and competition from foreign grasses. Efforts to conserve the species include establishing new populations in safe areas.
‘Ōhi‘a Lehua, commonly called ‘Ōhi‘a, is the most abundant native Hawaiian tree and arguably the most recognized with its bright red blossoms. These trees are adapted to live in Hawai‘i’s volcanic landscape by having stomata (pores in leaves that allow plants to breathe) that close in the presence of harmful volcanic gases. The ‘Ōhi‘a Lehua tree is deeply rooted in Hawaiian culture and history and are keystone species in the National Park and throughout the Hawaiian Islands. The ‘Ōhi‘a in Hawai‘i Volcanoes National Park and are an important source of food for native birds such as the honeycreepers.
Current Research
Rapid ‘Ōhi‘a Death (ROD)
Rapid ‘Ōhi‘a Death is a fungal disease of the ‘Ōhi‘a Lehua tree that threatens Hawai‘i’s native forests. The disease was named because of its rapid progression once disease symptoms are present. The Hawai‘i Volcanoes National Park resources managers have responded to the disease by cutting and covering infected trees in tarps to reduce the potential spread. The USGS is working with the National Park Service to measure the rate of spread in the Kahuku forests, identify pathways for natural and human-mediated dispersal of the fungus, and evaluate the potential effectiveness of management actions. Research to prevent the disease and contain its impacts are ongoing, and work to date has been largely focused on developing a better understanding of how the fungus is spread.
Invasive Plants and Animals
The introduction of invasive plant and animal species results in direct competition with native species. This can alter the function of an ecosystem, fire patterns, soil nutrients, food webs, and pollinator visitation, which reduces native plant survival. In Hawai‘i Volcanoes National Park, USGS researchers monitor the species present to attempt to track the spread of invasive species. To execute restoration projects, researchers must first understand the role of invasive species and potential ecosystem impacts.
Pigs have been a part of Hawaiian culture and history as they were one of the first animals introduced to the Hawaiian Islands by Polynesians. Decades later, European settlers also brought feral pigs that were larger, more aggressive, and roamed free compared to the Polynesian pigs. They eat native and invasive plant species, which has reduced the number of native plants and spread invasive plants. Pigs also push over plants, destroy sections of the forest, and create areas of standing water, which are breeding grounds for harmful mosquitos. Cats and mongooses have had a severe impact on native species, specifically declining bird populations. Kalij pheasants are a game bird that was introduced to Hawai‘i from Asia and can be found in Hawai’i Volcanoes National Park. They distribute seeds through their droppings, which increases the spread of invasive plant species such as guava.
Strawberry guava, although it produces desirable fruit, is one of the most invasive species in Hawai‘i. Native to southeastern Brazil, the plant was brought to Hawai‘i for its fruit. Strawberry guava can crowd out native plant species, break up natural areas, disrupt native animal communities, alter water systems, and provide refuge for nonnative pests such as fruit flies. The plant is easily spread by nonnative birds and pigs that consume the fruit. It has spread throughout Hawai‘i because the tree grows aggressively and has limited predators and diseases on the islands. Another invasive species, Kāhili ginger, also called Himalayan ginger, can dominate the forest understory and crowd out native species such as ferns and prevent the regeneration of native trees. Kāhili ginger is spread by birds eating and spreading the seeds to remote parts of forests.
Rats
Among invasive species in Hawai‘i, black rats are one of the most damaging to native forest bird populations and habitats. Rats are harmful to bird populations because they target adult birds in nests and remove intact eggs. Recent research in Hawai‘i Volcanoes National Park assessed forest bird survival and nesting success after the reduction of rat populations. Results showed that reducing rat predation immediately improved the nesting success of bird species. Rats also have been identified to be harmful to native plant species through consumption of the fruit and seeds of native plants, including the critically endangered hau kuahiwi. There is limited knowledge on the role that rats play in affecting seed dispersal, germination, and seedling establishment in forest ecosystems.
Climate Change
Climate change is expected to alter the seasonal and annual patterns of rainfall and temperature in the Hawaiian Islands. Likewise, warming temperatures and altered precipitation are expected to affect Hawai‘i Volcanoes National Park’s unique ecological systems. Temperatures have been increasing in Hawai‘i over the past 40 years, especially affecting higher elevations where populations of native birds and plants have persisted. Along with increasing temperatures, there has been an increase in the frequency of drought across the Hawaiian Islands. The climatic changes could have a significant impact on the plants and animals, making current habitats no longer suitable and allowing invasive species to spread into new areas.
To help national park managers prepare for climate change, USGS researchers combined climate modeling for the state of Hawai‘i with plant ranges to estimate projected suitable habitat. This study focused on Special Ecological Areas, sites of critical importance configured to protect plant communities and important species by controlling invasive plants and animals. The study identified native species that are projected to have a reduced elevation habitat range under climate change scenarios and the footprint of these ranges relative to the park’s Special Ecological Areas so that managers can assess if boundaries should to be adjusted to accommodate future plant migration.