A new study reveals that almost every forest bird species in Hawaiʻi can transmit avian malaria, contributing to its widespread presence across the islands. Researchers detected the parasite at 63 of 64 tested sites, highlighting the role of both native and introduced birds in sustaining the disease. The findings underscore the challenges in protecting vulnerable native species like honeycreepers.
A comprehensive study published on February 10 in Nature Communications, led by researchers from the University of Hawaiʻi at Mānoa, has uncovered the extensive reach of avian malaria in Hawaiʻi's forests. The research, conducted by Christa M. Seidl during her PhD at the University of California, Santa Cruz, analyzed blood samples from more than 4,000 birds across Kauaʻi, Oʻahu, Maui, and Hawaiʻi Island. It paired field data with lab experiments to assess how effectively birds infect southern house mosquitoes, the primary vector for the parasite Plasmodium relictum.
The study found avian malaria present at 63 of 64 locations tested, spanning diverse forest environments. Both native honeycreepers and introduced bird species demonstrated the ability to transmit the infection, even with low parasite loads. Birds carrying minimal amounts of the parasite could still infect mosquitoes, and chronic infections persisting for months or years enable ongoing transmission in most mosquito habitats.
"Avian malaria has taken a devastating toll on Hawaiʻi's native forest birds, and this study shows why the disease has been so difficult to contain," said Seidl, now mosquito research and control coordinator for the Maui Forest Bird Recovery Project. "When so many bird species can quietly sustain transmission, it narrows the options for protecting native birds and makes mosquito control not just helpful, but essential."
The disease severely impacts native birds by attacking red blood cells, leading to anemia, organ failure, and high mortality rates. For instance, infected ʻiʻiwi (scarlet honeycreepers) face about a 90 percent mortality rate, while the ʻakikiki on Kauaʻi is now considered extinct in the wild due to avian malaria. Unlike many diseases that rely on few host species, this parasite's broad infectivity across bird communities explains its near-ubiquitous distribution.
Warming temperatures from climate change are exacerbating the issue by allowing mosquitoes to invade higher elevations, once safe refuges for native birds. Seidl's work is part of the Birds, Not Mosquitoes collaboration, involving academic, state, federal, non-profit, and industry partners focused on mosquito control to support bird conservation. All birds were handled under state and federal permits by trained ornithologists.
