Ecology of Haleakalā National Park
Haleakalā National Park Ecology
Haleakalā, meaning “House of the Sun” in Hawaiian, is known for its beautiful sunrises and sunsets over the edge of one of the world’s largest volcanic craters. Located on the Hawaiian island of Maui, this park extends from the summit of Haleakalā at 10,023 feet to the ocean at the Kīpahulu coast. The park is home to five distinct climate zones that contain a number of plant and animal species found nowhere else in the world.
Animals
A variety of forest birds and seabirds are found within the diverse landscapes of Haleakalā National Park. Although some are very rare, there are six species of Hawaiian honeycreepers that can be found within the forests of the park: ‘akohekohe, ‘apapane, Hawai‘i ‘amakihi, ‘i‘iwi, kiwikiu, and Maui ‘alauahio. These Hawaiian honeycreepers are all endemic to the Hawaiian Islands, meaning they can be found nowhere else in the world, and some are even endemic to just the island of Maui. Forest birds that have been introduced to the Hawaiian Islands are also found within the park, including the Japanese bush-warbler, warbling white-eye, and red-billed leiothrix. Despite their diversity, forest bird populations in Haleakalā, with the exception of native ‘apapane and non-native red-billed leiothrix, are in decline. Additionally, two introduced gamebird species are common in the Park: the ring-necked pheasant and chukar. Ring-necked pheasants were introduced to Hawai‘i for hunting and are seen in pastures and open shrublands. Chukar are found at Haleakalā’s cold, dry summit.
Kiwikiu (maui parrotbill) are endemic to the island of Maui. Kiwikiu can only be found in a small area of high-elevation wet forest on the east side of Maui and are listed as critically endangered by the International Union for the Conservation of Nature. These olive green and yellow birds are identified by their parrot-like curved bill.
‘Ākohekohe (crested honeycreeper) are also critically endangered. This distinctive species has a decorative bushy white head crest and they are the largest honeycreeper remaining on Maui. They are primarily nectarivores but also feed on caterpillars and spiders. They have a variety of vocalizations including guttural clucking gurgles, raspy croaks, and buzzing sounds.
Maui ‘alauahio (Maui creeper) are more common than some of the other honeycreepers on Maui, but their range is still restricted to a portion of its historical distribution. These bright yellow birds reside on forested slopes on east Maui and have songs that consist of repeated whistled phrases.
Nēnē (Hawaiian goose) are Hawai‘i’s state bird and are medium-sized geese. Maui has an estimated population of 600 nēnē with around 200 in Haleakalā National Park. They are found in variety of habitats including high-elevation lava flows, volcanic deserts, grasslands, and shrublands.
Pueo (Hawaiian short-eared owl) are a sub-species of the short-eared owl and are endemic to Hawai‘i, meaning they are found nowhere else. Unlike typical owl behavior, they are active and fly during the day. They often fly over spaces like meadows and shrublands while hunting introduced rodents and mongoose. Prior to the introduction of rodents and mongoose to Hawai‘i, pueo hunted other small birds and insects. Pueo nest on the ground in tall grass, making them vulnerable to predators.
‘Ua‘u (Hawaiian petrel) are endangered seabirds whose historical populations were estimated to be in the hundreds of thousands to millions of birds. The largest nesting colony is located at the top of Haleakalā at elevations of 7,000 to 10,000 feet. Adults spend long durations flying and forging over the ocean, often leaving their chicks alone for many days before returning to their nests. Pairs of ‘ua‘u mate for life and will leave their young in September and stay at sea until the start of the next nesting season in March or April. The decline in ‘ua‘u populations is attributed to habitat loss, degradation of land, and predation by introduced mongooses, feral cats, rats, and dogs.
Current research shows predation and habitat degradation by non-native mammals are threats to Haleakalā’s ‘ua‘u population. Invasive mammal species found in the park that prey on nesting birds and eggs include feral cats, Indian mongoose, black rats, Norway rats, Polynesian rats, and house mice. Actions to solve this issue include predator control, habitat restoration, and population monitoring. In collaboration with Haleakalā National Park, the USGS evaluated seasonal, annual, and environmental patterns and factors that influence small mammal trap events from 2000–2014. The study showed that the probability of predator capture was influenced by ‘ua‘u breeding season, with the highest probability of predator capture during the ‘ua‘u nestling period. These results will assist Haleakalā National Park Endangered Wildlife Management staff to evaluate existing methods for predator control and inform future predator control efforts.
Mosquitos and Avian Disease: Introduced diseases such as avian malaria and pox spread by invasive mosquitoes have led the native honeycreepers that are susceptible to mosquito-borne diseases to near extinction. Cooler temperatures at higher elevations limit mosquitoes and malaria development in these areas, allowing native birds to persist in higher-elevation forests. However, at lower elevations, even in areas where land is preserved, the native birds are not persisting due to avian malaria. With warming temperatures due to climate change, the limited region of mosquito-free habitat at higher elevations is getting smaller as warmer temperatures allow malaria to become more prevalent at higher elevations. Helping the forest bird populations in Haleakalā National Park means controlling mosquito populations. One method scientists are exploring to control mosquito populations is the use of a naturally-occurring bacteria, Wolbachia. These bacteria already exist in Hawai‘i and can be used to infect male mosquitos. The infected mosquitos can mate but can’t produce offspring, resulting in population declines. Other studies are being conducted to determine the prevalence and distribution of avian malaria infections in birds found in various altitudes. This information was also used to identify primary larval habitat for the mosquito vector of the disease.
The Hawaiian monk seal is one of the most endangered seal species in the world. The current population is approximately one-third of historical population levels with an estimated 1,400 seals in the Hawaiian archipelago. These monk seals are endemic to Hawai‘i and are protected by the Endangered Species Act, the Marine Mammal Protection Act, and Hawai‘i's state laws. They eat a wide variety of food including prey that hide in the sand and rocks. The Hawaiian monk seal spends about two thirds of its time at sea but returns to rest on beaches, sometimes for days at a time. The Hawaiian monk seal population exists largely in the remote low-lying Northwestern Hawaiian Islands, where even small increases in sea-level rise may result in the loss of critical habitat affecting species like the Hawaiian monk seal.
Plants
More than 850 plant species are found within Haleakalā National Park. More than 400 of these species are native and over 300 species are endemic to Hawai‘i, found only in these islands. The park contains a high diversity of plants because of the wide variety of elevations and microclimates ranging from mountain peaks to ocean reef habitats.
Geraniums
Haleakalā National Park is home to four species of Hawaiian geraniums that are found nowhere else on Earth.
Geranium cuneatum (silver geranium) is the most common species of geranium in the park. Its small silver leaves are covered in silky hairs that reflect sunlight and preserve moisture. They are found within shrubland ecosystems.
Geranium multiflorum (many flowered geranium) is an endangered geranium found at high-altitude grasslands and forests, and less frequently in shrublands. These flowers are pollinated by the native Hawaiian yellow-faced bee.
Geranium hanaense is a rare geranium found in high-altitude bogs on the eastern slopes of Haleakalā that was first described as a species in 1988.
Geranium arboretum is the rarest of the four species in Haleakalā and is the only bird-pollinated geranium in the world. The red curved flowers are adapted to fit the bill of native honeycreepers that pick up pollen on their foreheads and transfer it to other flowers. Once widespread across the lower slopes of Haleakalā, it is now critically endangered with a population of fewer than 50 individuals.
‘Āhinahina (Haleakalā silversword) is an iconic species that occurs only at the Haleakalā crater and summit, in this tropical alpine ecosystem. ‘Āhinahina live between three and 90 years and flower only once in their lives, then die after flowering and the dead seeds scatter in the wind. ‘Āhinahina are found in hot, dry climates like the aeolian desert alpine zone of the Haleakalā crater.
Current research suggests that ‘āhinahina are sensitive to environmental conditions and are threatened by shifting climate patterns. A shift in weather circulation may make the difference in the survival of silversword populations. In the middle of the twentieth century ‘āhinahina populations were increasing, until 1990 when populations began to sharply decline. In ideal conditions clouds, fog, and rainfall reach higher altitudes bringing water to the plants and providing shade through the disruption of a process called trade wind inversion (TWI). Recent weather patterns have brought less disruption of the TWI, creating drier conditions and reducing the necessary occasional water source for ‘āhinahina that are rare in these harsh environments. Scientists project that the ‘āhinahina habitat will continue to face hotter temperatures and lower rainfall as a result of this process influenced by climate change.
Ecosystems
The extinct volcano Haleakalā stands 10,023 feet tall and is exposed to moist trade winds and drying air masses that contribute to a variety of natural ecosystems. Wind, rain, temperature, and altitude all play a role in shaping each ecological zone.
The alpine aeolian zone seems barren upon first glance. The rocky, dry surface has a wide range of temperatures between day and night. Few species survive in this harsh environment, ‘āhinahina being the most prominent. The plants found in this zone are hardy and adapted to live in this environment but are threatened by increasing temperatures and lower rainfall. The subalpine shrublands cover areas below the alpine zone and contain native shrubs including pūkiawe, māmane, ‘ōhelo, geraniums and pilo. The native fern species laukahi and ‘ama‘u are also found in the subalpine shrubland region along with nēnē, the native Hawaiian goose. Rainforest zones on the slopes of Haleakalā can get 120 to 400 inches of rainfall annually. Sitting above 3,000 feet of elevation native species including ‘ōhi‘a and koa form a dense forest. The native Hawaiian honeycreepers are often found here on native trees and flowers. Dry forest zones are below the shrub zone and get less than 60 inches of rain annually.
Fires and nonnative feral pigs have devastated the majority of Haleakalā’s dry forests. The ‘Ohe‘o stream ecosystem exists within several zones within the park and is one of the few natural riparian habitats in Hawai‘i. Native fish and shrimp are found in this stream environment.
Invasive Species
Although Haleakalā National Park is home to a rich diversity of plant and animal species, many are threatened by non-native predators. There are more than 400 established species of non-native plants in Haleakalā National Park. Several examples of invasive plant species are found at the crater of Haleakalā and threaten the limited populations of native plants that survive in this harsh environment. Cheatgrass, introduced to Maui in the 1880s, spreads easily, rapidly, and is fire resistant. Evening primrose is a common weed found up to 10,000 feet in elevation that and blooms canary-yellow flowers. Rabbit-foot clover grows up to one foot tall and is found above 4,000 feet of elevation. Invasive species found in other zones of the park include Florida blackberry, bull thistle, fireweed, pampas grass, gorse, Koster’s curse (soapbush), kahili ginger, and mule’s foot fern.
Mexican weeping pines outgrow native shrub species, take up water and nutrients, and drop pine needle litter. The pine forests in Haleakalā National Park in the Waikamoi Preserve could expand to cover existing shrubland. The pine needles spread by wind, allowing them to reach even remote areas in the crater.