Hawaiian stilt population improves from 200 to in 40s to 1,500 today, recovery documented in UH study

The US Fish and Wildlife Service announced the reclassification of the Aeʻo, or Hawaiian stilt (Himantopus mexicanus knudseni), from endangered to threatened under the Endangered Species Act, a rare and hopeful milestone for a native Hawaiian species.

The change, published in the Federal Register alongside a species-specific 4(d) rule, reflects more than 50 years of conservation work that has brought the long-legged waterbird back from the brink.

The recovery is documented in a new study led by researchers from the University of Hawaiʻi at Mānoa’s College of Tropical Agriculture and Human Resilience (CTAHR) and their partners, published in Ornithological Applications. 

Once abundant across the Hawaiian Islands, the Aeʻo dwindled to roughly 200 birds in the 1940s after decades of overhunting, the loss of wetlands to agriculture and development, and the spread of invasive predators. Following its listing as endangered in 1973 and sustained conservation efforts, the population has since climbed to more than 1,500 birds today.

Community partnering with conservation managers

The team analyzed more than five decades of data, representing more than 2,000 nests across nine wetlands on Oʻahu from 1963 to 2020. They found that nesting success and chick fledging success improved measurably over time, providing evidence that management actions such as predator control and habitat restoration are working.

“This is a bright spot story,” said Melissa Price, associate professor in CTAHR’s Department of Natural Resources and Environmental Management. “So many species across Hawaiʻi are in decline. The ae‘o demonstrates how community can work in partnership with conservation managers to achieve recovery and rebuild relationships with our native species.”

A promising path

Expanding managed wetland habitat is the key to increasing the Ae‘o population. Ae‘o readily colonize restored and managed wetlands, and recent work has documented the birds nesting in restored Indigenous wetland agro-ecosystems. As sea-level rise threatens existing coastal wetlands, these community- and culturally-grounded restoration efforts offer both new habitat and a model for stewardship.

The new rule accompanying the reclassification is designed to keep the momentum going. It allows certain activities that benefit the Aeʻo to continue, including habitat management and restoration work, even where such activities would otherwise be restricted under the Act. This flexibility is intended to sustain the partnerships and on-the-ground care that the species still depends on as it progresses toward full recovery.

The authors are careful to call the Ae‘o a “conservation success story in progress.” Like many native Hawaiian species, it remains conservation-reliant: dependent on ongoing predator control, water management and habitat protection. 

“Downlisting doesn’t mean the work is done,” said lead author Jessica Idle, a manager with the UH Mānoa Pacific Cooperative Studies Unit. “It means the work is paying off. Continued monitoring and management, especially expanding protected wetland habitat, will be essential to keep the population growing.”

The research was a collaboration among UH Mānoa, the US Fish and Wildlife Service, the Hawaiʻi Department of Land and Natural Resources, Tufts University and other partners, reflecting the coordinated, cross-agency effort behind the bird’s recovery.