ʻIʻiwi have gone from being one of the most common native birds in Hawaiʻi over 100 years ago, to now being a species limited to remote forests and in danger of extinction.
A new study evaluates conservation actions that could save the ʻiʻiwi or Hawaiian honeycreeper bird. The study, headed by Alban Guillaumet of the Hawaiʻi Cooperative Studies Unit at the University of Hawaiʻi at Hilo, provides land managers with guidance on how to save this important pollinator. The study demonstrates how the movement of ʻiʻiwi across the slopes of Hawaiʻi volcanos in search of nectar from flowers can increase their risk of contracting disease and dying.
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 Guillaumet, Wendy Kuntz of Kapiʻolani Community College, Michael Samuel with the USGS Wisconsin Cooperative Wildlife Research Unit, and Eben Paxton, a researcher with the USGS Pacific Island Ecosystems Research Center.
ʻIʻiwi are highly susceptible to introduced avian malaria, which is transmitted by a tropical mosquito that only occurs at low to mid-elevations of Hawaiʻi. The birds 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.
“ʻIʻiwi evolved over millennia to track flowering trees up and down the slopes of Hawaii’s volcanoes,” says Paxton. “Their flights to seek out blooming flowers allowed them to thrive across the Hawaiian Islands in the past. Today, however, with avian disease rampant at low and mid-elevations of the islands, these movements could lead to their extinction.”
Future disease distributions under climate change
Warming temperatures are helping mosquitoes and the diseases they carry to move into increasingly higher elevation mountain forests, leading to increased contacts with ʻiʻiwi . As a result, ʻiʻiwi have gone from being one of the most common native birds in Hawaiʻi over 100 years ago, to now being a species limited to remote forests and in danger of extinction.
Researchers tracked ʻiʻiwi 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 ʻiʻiwi populations.
The study showed that after the breeding season, ʻiʻiwi 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 ʻiʻiwi rapidly decline. The study indicates the species may go extinct by 2100 if action is not taken to control avian diseases and secure disease-free habitat.
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 ʻiʻiwi mean a large-scale reduction in disease would likely be required to save the species. Current efforts to reduce or eliminate mosquitoes 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.