Scientists Evaluate Ways to Save Hawaiian Honeycreeper

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Long distance flights in search of flowering trees threatens the Hawaiian Iiwi as climate change increases the distribution of avian diseases

Man holding red bird.
Iiwi with small radio transmitter attached to help track the bird's movement through the forest(Credit: Eben Paxton, U.S. Geological Survey. Public domain.)

A new study evaluates conservation actions that could save the iconic Hawaiian Honeycreeper bird, also known as the “Iiwi,” providing land managers with guidance on how to save this important pollinator. The study demonstrates how the movement of Iiwi across the slopes of Hawaii’s volcanos in search of nectar from flowers can increase their risk of contracting disease and dying.

Iiwi are highly susceptible to introduced avian malaria, which is transmitted by a tropical mosquito that only occurs at low to mid-elevations of Hawaii. Iiwi breed only in high-elevation forests where the temperatures are too cool for the mosquito to occur, but their flights to find flowering trees can take them to where diseases occur.

Man untangling a little red bird from a net.
Adult Iiwi being removed from a mist net which was used to capture the bird for banding(Credit: Eben Paxton, U.S. Geological Survey. Public domain.)

“Iiwi evolved over millennia to track flowering trees up and down the slopes of Hawaii’s volcanos. Their flights to seek out blooming flowers allowed them to thrive across the Hawaiian Islands in the past,” said Dr. Eben Paxton, co-author of the study and researcher with the U.S. Geological Survey. “Today, however, with avian disease rampant at low and mid-elevations of the islands, these movements could lead to their extinction.”

Warming temperatures are helping mosquitoes and the diseases they carry to move into increasingly higher elevation mountain forests, leading to increased contacts with Iiwi. As a result, Iiwi have gone from being one of the most common native birds in Hawaii over 100 years ago, to now being a species limited to remote forests and in danger of extinction.

Researchers tracked Iiwi movements by attaching small radio transmitters to the birds and followed their signal as they moved across the forests of Hakalau Forest National Wildlife Refuge and beyond. These movements were mapped with the current distribution of avian malaria and future disease distributions under climate change. Researchers were then able to evaluate how the current and future distribution of disease are likely to affect Iiwi populations.

The study showed that after the breeding season, Iiwi leave their disease-free breeding areas in search of blooming trees and travel to lower elevations where disease is present. As disease expands into increasingly higher elevation areas because of increasing temperatures, disease-free areas are projected to vanish and Iiwi rapidly decline. The study indicates that Iiwi may go extinct by 2100 if action is not taken to control avian diseases and secure disease-free habitat.

Man measuring a little red bird.
Measuring the wing length of a banded Iiwi(Credit: Eben Paxton, U.S. Geological Survey. Public domain.)

The study evaluated the benefits of increasing habitat and availability of nectar at high elevations, reducing mosquito numbers, and promoting the evolution of disease resistance. Efforts to reduce disease prevalence through mosquito control could help buy time, but far-ranging movements of Iiwi mean a large-scale reduction in disease would likely be required to save the species. Current efforts to reduce or eliminate mosquitos that transmit avian malaria may be the most effective means of preserving the species. Additionally, habitat restoration efforts to increase native flowering trees at high elevations in parallel with mosquito control efforts may be the most effective conservation plan available to managers at this time. While more resistance to malaria is the best outcome for long-term survival of the species, this may be the most difficult option for managers to directly affect.

“There is nothing more spectacular than seeing the elegant profile of a scarlet Iiwi against a deep blue Hawaiian sky as it feeds in the brilliant red blossoms of Lehua in our native forest. The decline of this magnificent and culturally important bird is an irreplaceable loss to our natural heritage in Hawaii. The Iiwi, as our “canary in the coal mine,” provides a clear warning of the threats moving into Hawaii’s last sanctuaries for not only rare bird species, but our entire island ecosystem. Conservation efforts to save Iiwi are urgently needed to ensure that future generations will continue to see the living legacy of our unique island home. Those efforts will benefit not only Iiwi, but all life in our islands.” said Dr. Samuel M. ‘Ohukani‘ōhi‘a Gon, III, Senior Scientist and Cultural Advisor, The Nature Conservancy of Hawaii.

The journal article “Altitudinal migration and the future of an iconic Hawaiian honeycreeper in response to climate change and management” was published in Ecological Monographs with lead author Alban Guillaumet of the Hawaii Cooperative Studies Unit at the University of Hawaii at Hilo, Wendy Kuntz of Kapiolani Community College, Michael Samuel with the USGS Wisconsin Cooperative Wildlife Research Unit, and Eben Paxton with the USGS Pacific Island Ecosystems Research Center.

A little red bird being handled by scientist
Adult Iiwi being banded at Hakalau Forest National Wildlife Refuge, Hawaii(Credit: Eben Paxton, U.S. Geological Survey. Public domain.)