A silent reservoir: why Hawaii's birds are failing to stop a plague

Nature · Published 28 October 2026 Swipe more like this →

In short: Avian malaria is systematically dismantling Hawaii’s unique avian biodiversity. While conservationists once focused on the most severely infected native species, new research reveals a far more complex and difficult problem: nearly every bird in the islands—native and introduced alike—is helping keep the disease alive.

The crisis centers on Plasmodium relictum, a generalist parasite that attacks birds' red blood cells. This infection leads to severe physiological damage, including anemia, organ failure (specifically of the liver and spleen), and reduced survival rates. For some iconic species, the impact is catastrophic; the scarlet honeycreeper (ʻiʻiwi) faces a mortality rate of about 90 percent if infected, while the ʻakikiki has already been pushed to extinction in the wild. The disease has already contributed to the loss of over a dozen native bird species. These infections cause birds to suffer from low blood oxygen levels. This pathogen is primarily transmitted through biting mosquitoes.

Recent research led by Christa M. Seidl and A. Marm Kilpatrick at the University of Hawaiʻi at Mānoa and UC Santa Cruz provides a breakthrough in understanding why containment is so difficult. By testing 63 of 64 sites statewide, researchers found that avian malaria is present almost everywhere mosquitoes exist. The reason lies in 'reservoir' dynamics: unlike many diseases spread by only a few high-load hosts, nearly all forest bird species in Hawaii—both native and non-native—are moderately capable of infecting the southern house mosquito. This study was published in Nature Communications on February 10. The research included forests with very different mixes of avian communities. It highlights how the parasite can remain contagious for months or even years.

Crucially, even birds carrying vanishingly small parasite loads can transmit the infection to mosquitoes. This means that any bird community can sustain the disease's lifecycle. Furthermore, certain species like the introduced House Finch and the native ‘Amakihi act as key drivers because mosquitoes feed on them more frequently. This widespread transmission capacity narrows conservation options, making aggressive mosquito control an essential tool for protecting Hawaii’s remaining native honeycreepers. The findings suggest that transmission persists wherever temperatures are warm enough for mosquito development. Consequently, the illness is present throughout most mosquito habitats on these landmasses.

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