Last updated: August 29, 2025
Article
How Moloka‘i’s Remarkable Forest Birds Lost Out to Invasive Species
Many of the wondrously unique native birds of the Hawaiian island of Moloka‘i are now extinct or extirpated. National Park Service scientists and partners are trying to help those that remain.
By Seth Judge
About this article

This article was originally published in the "Features" section of Park Science magazine, Volume 39, Number 2, Summer 2025 (August 29, 2025).

NPS / Janice Wei
The Kalaupapa Peninsula juts out from the northern coast of Moloka‘i. It’s a rugged Hawaiian outpost framed by some of the world’s tallest sea cliffs.
Isolated by sheer volcanic walls and battered by ocean winds, this striking landscape has been a place of both refuge and sorrow. For over a century, thousands of Hansen’s disease patients were exiled to Kalaupapa. Separated from their families, they endured the disease in isolation. More than 8,000 people called the peninsula home from the late 19th century until the colony’s official closure in 1969. In 1980, Congress designated Kalaupapa a national historical park.
The park preserves many cultural sites and natural features while honoring the resilience of those who lived and died there. Yet Kalaupapa could become a memorial not only to human history but also to ecological decline. Its native forest birds now fight their own battle against disease, habitat loss, and invasive species. Through long-term surveys and targeted strategies, scientists are working to help them.
Shaped by Isolation
Hawai‘i has some of the world’s most unique and fragile ecosystems. For millions of years, the islands’ extreme isolation shaped their landscapes. The first plants and animals arrived by wind, wings, and waves. Seeds were carried by storms, birds drifted off course, and insects clung to floating debris. Over time, these early colonizers evolved into entirely new species, adapting to the islands in ways seen nowhere else on earth.

NPS / Mark Wasser
Without continental predators or disease, Hawaiian birds lost the need for strong defenses. Some became flightless. Others developed specialized beaks to extract nectar, like the ‘i‘iwi with its long, curved bill. This slow and wondrous evolutionary process created a rich, endemic avian community. It was one uniquely adapted to Hawai‘i’s forests but vulnerable to rapid change.
Humans first arrived on the islands over 1,000 years ago. In a blink of evolutionary time, the islands were overrun by new threats. Early Polynesian settlers hunted flightless geese, ducks, and rails. Introduced dogs and pigs raided seabird burrows and nests. Centuries later, European colonizers brought rats, cats, and mongooses, each highly efficient predators of adult birds and their young. Cattle, goats, deer, and sheep trampled forests, triggering erosion and runoff that degraded upland habitat and damaged nearshore reefs on Molokaʻi.
Native birds, having evolved in the absence of disease, had no immunity.
Most devastating of all, non-native mosquitoes and introduced birds carried avian malaria. Native birds, having evolved in the absence of disease, had no immunity. Species like the Bishop’s ‘ō‘ō, black mamo, and ‘ō‘ū were already extirpated by the late 20th century. The endemic kākāwahie, or Moloka‘i creeper, was last seen in 1963 and was recently declared extinct. The oloma‘o, or Moloka‘i thrush, has not been observed since 1980 and is also feared lost.
Tracking the Decline
To track these declines, U.S. Fish and Wildlife Service researchers initiated systematic surveys of Moloka‘i’s forest birds in 1979 and 1980. This was followed by decades of monitoring by scientists from the National Park Service Pacific Island Inventory and Monitoring Network and its partners. By 2021, surveys in the park and adjacent lands revealed a stark reality—only two native species, ‘apapane and Hawai‘i ‘amakihi, remained. Their continued presence may be because they use a wider range of habitats and resources, including lower-elevation areas, where there are more mosquitoes, hence more malaria. Over time, frequent exposure to avian malaria may have led them to develop immunity or tolerance. As a result, they could survive infections and keep reproducing.

NPS / Janice Wei
In contrast, highly specialized species such as ‘i‘iwi have narrow ecological niches. They’re typically restricted to high-elevation native forests, where they depend on the nectar of specific flowering plants—many of them threatened or endangered. This dependence makes ‘i‘iwi less adaptable to environmental change, including the spread of disease. Having evolved in cooler, mosquito-free zones, they have little resistance to avian malaria. As climate change allows mosquitoes to reach higher elevations, ‘i‘iwi face increasing exposure. Infected birds rarely survive, and populations collapse quickly once the disease becomes established.
Meanwhile, non-native birds have taken over. Species like the warbling white-eye, Japanese bush warbler, and red-billed leiothrix now account for nearly 70 percent of detections at survey stations.
Meanwhile, non-native birds have taken over. Species like the warbling white-eye, Japanese bush warbler, and red-billed leiothrix now account for nearly 70 percent of detections at survey stations. An additional 14 introduced species thrive in both native and non-native forests. Many of these birds originated in Asia or the Americas and have natural resistance to avian malaria. This allows them to persist while Hawaiian honeycreepers disappear. Worse, non-native species serve as reservoirs for the disease. Mosquitoes feeding on infected non-native birds can acquire and then transmit the parasite to vulnerable native species, perpetuating the disease cycle and further accelerating their decline.
Reversing the Trend
Protected status alone is often not sufficient to shield native species. In places like Kalaupapa, non-native plants and animals have already transformed much of the landscape. Active and sustained management is thus essential. Without intervention, invasive plants, animals, and diseases continue to spread. This is true even in designated protected areas. The good news is that Hawai‘i has developed a powerful toolkit for conservation. It’s informed by decades of trial, innovation, and success. Methods like fencing, predator removal, habitat restoration, and mosquito control are helping to protect native species.
Controlling Ungulates
Hawaiʻi has been a leader in large-scale native habitat protection. Through fencing and removal, Hawaiʻi Volcanoes National Park and Haleakalā National Park were able to eradicate goats from more than 200 square miles of park land. Resource managers on Hawaiʻi pioneered the “Judas goat” method, now used worldwide. This method takes advantage of goat social behavior. Because male goats form harems, individual goats can be captured, fitted with radio collars, and released to locate and lead managers to remaining herds. This method isn’t effective for all ungulates. Feral pigs, for example, are particularly challenging. They require a combination of techniques to control, including baited traps, snares, and trained hunting dogs.

NPS / Glauco Puig-Santana
On Moloka‘i, one of the most pressing challenges is the axis deer population. These deer are native to India and other countries, but not Hawai‘i. They were introduced to the island in 1868 as a gift to King Kamehameha V. They have cultural value to residents, including as a subsistence food, but the deer have surged to exceptionally high densities. Moloka‘i, with roughly 7,300 residents, supports an estimated 60,000 axis deer—approximately 8 deer for every person. The deer damage agriculture, degrade forests, and pose a potential threat to the cattle industry through the spread of bovine tuberculosis. To help manage deer populations, the Kalaupapa community and the state coordinate annual multi-day axis deer hunts. The meat goes to community residents. Long-term recovery will depend on consistent efforts to fully remove deer from management units. This will give native habitats a chance to regenerate.
Moloka‘i, with roughly 7,300 residents, supports an estimated 60,000 axis deer—approximately 8 deer for every person.
Curbing Invasive Plants and Protecting Native Ones
A forest’s health depends on the health of its plants. Native forests on Moloka‘i are dominated by ‘ōhi‘a, koa, and other endemic tree species. They support a rich web of life. But in Kalaupapa and across Moloka‘i, invasive species like strawberry guava, Christmas berry, and Koster’s curse outcompete native trees and shrubs. These fast-growing invaders form dense, uniform stands that alter soil chemistry, reduce biodiversity, and provide little food or shelter for native birds. Innovative efforts are underway to control these invasive plants.

NPS / Mark Wasser
Plant disease prevention is a critical component of Moloka‘i forest conservation, especially with the persistent threat of “rapid ʻōhiʻa death.” This disease is caused by a fungus that infects and kills the trees that form the foundation of native rainforests. It isn’t yet on Molokaʻi, but it could ravage the island’s remaining habitat were it to arrive. To avoid this, strict biosecurity measures are critical to have in place for visitors and cargo arriving on the island.
Removing invasive plants and restoring native ones benefit native birds that feed or nest in them. These measures also improve watershed function, support pollinators, and strengthen cultural ties to the land.
Reducing Disease Transmission
Mosquito-borne disease remains the primary threat to Hawai‘i’s forest birds. As the climate warms, mosquitoes expand their range into higher elevations, reaching the last strongholds of vulnerable species. Traditional mosquito control methods are not viable at the landscape scale, but new techniques offer promise. The incompatible insect technique, for example, uses lab-reared male mosquitoes infected with a natural bacterium called Wolbachia. When these males mate with wild females, no viable offspring result. This gradually reduces mosquito populations.
The technique is species-specific and does not involve genetic modification. It is being tested on Maui, where Haleakalā National Park, The Nature Conservancy, the Maui Forest Bird Recovery Project, and other key partners have released incompatible males in core native forest bird habitat. The forests of Molokaʻi may also make a good candidate for future disease suppression efforts. If successful, such strategies could create a disease-free space where native birds can once again thrive.
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Listen to the Park Science Podcast episode on Wolbachia
Birds, Not Mosquitoes project partners Chris Farmer, Luka Zavas, and Ryan Monello discuss a modern mosquito-control technique to save Hawaiʻi’s forest birds from imminent extinction. Hosted by Jeri Stoller.
- Date created:
- 12/29/2023
Looking Ahead
The story of Kalaupapa is one of profound loss but also resilience. The community that once lived here endured in the face of hardship. So too can its native birds if given the chance. Through careful stewardship, scientific innovation, and community collaboration, we can restore the forests of Moloka‘i and protect the species that depend on them. Kalaupapa is more than a place of memory—it is a living landscape, and its future is still being written.

About the author
Seth Judge is an ecologist with the National Park Service’s Pacific Island Inventory and Monitoring Network. Image courtesy of Seth Judge.
Cite this article
Judge, Seth. 2025. "How Moloka‘i’s Remarkable Forest Birds Lost Out to Invasive Species." Park Science 39 (2). August 29, 2025. https://www.nps.gov/articles/000/psv39n2_how-molokais-remarkable-forest-birds-lost-out-to-invasive-species.htm
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- haleakalā national park
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- hawaiian forests
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- monitoring
- avian malaria
- invasive species
- non-native species
- seth judge
- hawaiian birds
- extinction
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