Recent research published on February 10 in Nature Communications reveals that avian malaria has been detected in 63 of 64 locations tested across Hawaiʻi. This extensive study spans forests with diverse bird species, highlighting the widespread impact of the disease. The illness is caused by the parasite Plasmodium relictum, which has significantly contributed to the alarming decline and extinction of native Hawaiian honeycreepers.
Christa M. Seidl, the mosquito research and control coordinator for the Maui Forest Bird Recovery Project, emphasizes the seriousness of the situation: "Avian malaria has severely affected Hawaiʻi's native forest birds, and this research illustrates the challenges in controlling the disease." Conducted as part of her PhD at the University of California, Santa Cruz, Seidl's study underscores the urgent need for effective mosquito control measures to protect native avian species.
The Impact of Avian Malaria on Native Birds
This parasitic infection targets red blood cells, leading to anemia, organ failure, and reduced survival rates among affected birds. The consequences are particularly dire for iconic species in Hawaiʻi. For instance, studies indicate that the mortality rate for the ʻiʻiwi, or scarlet honeycreeper, can reach up to 90 percent upon infection. The ʻakikiki, a honeycreeper endemic to Kauaʻi, is now considered extinct in the wild primarily due to this disease.
Unlike many infectious diseases that depend on a few species for transmission, avian malaria behaves differently in Hawaiʻi. Most forest birds, whether native or introduced, can effectively infect southern house mosquitoes, the primary carriers of the disease. Even birds with minimal parasite loads can infect mosquitoes, allowing for ongoing transmission across diverse bird populations.
"While it's natural to focus on the birds when discussing avian malaria, it's crucial to remember that the parasite relies on mosquitoes for reproduction," Seidl notes. "Our findings reveal how effectively it has adapted to infecting mosquitoes through various bird species."
Chronic Infections and Continuous Transmission
The research team analyzed blood samples from over 4,000 birds across Kauaʻi, Oʻahu, Maui, and Hawaiʻi Island. By combining field data with laboratory studies, they found that both native and introduced birds exhibited similar levels of infectiousness, contributing equally to the spread of the parasite.
Moreover, the study discovered that birds can harbor chronic infections for extended periods, ranging from months to years. During these times, birds may show only mild symptoms yet remain capable of transmitting the parasite to mosquitoes. Researchers estimate that this prolonged infectious phase is responsible for the majority of statewide transmission.
Climate Change and Habitat Loss
The parasite's ability to infect a wide range of bird species likely accounts for the extensive prevalence of avian malaria in Hawaiʻi. The findings indicate that few areas remain free from transmission risk, and climate change is exacerbating the situation. Rising temperatures are enabling mosquitoes and avian malaria to invade higher elevations, which previously served as safe havens for vulnerable native birds.
Seidl and the Maui Forest Bird Recovery Project are part of the Birds, Not Mosquitoes initiative, a collaborative effort among academic, state, federal, non-profit, and industry partners aimed at enhancing mosquito control to support the conservation of Hawaiian birds.
The Maui Forest Bird Recovery Project operates under the Pacific Cooperative Studies Unit within the College of Natural Sciences. All birds involved in this study were handled by trained ornithologists in compliance with state and federal regulations.