New Study: Nearly All Hawaiian Forest Birds Can Transmit Avian Malaria

A new study led by a University of Hawaiʻi at Mānoa researcher has found that nearly all forest bird species in Hawaiʻi are capable of transmitting avian malaria. This finding helps to explain the disease's widespread presence in areas with mosquitoes across the islands.

Widespread Transmission Confirmed

The research, published on February 10 in Nature Communications, detected avian malaria at 63 out of 64 sites tested statewide, including locations with diverse bird communities. The disease, caused by the generalist parasite Plasmodium relictum, is a significant factor in the population declines and extinctions observed in native Hawaiian honeycreepers.

Christa M. Seidl, mosquito research and control coordinator for the Maui Forest Bird Recovery Project and a lead researcher, stated that the ability of many bird species to sustain quiet transmission narrows options for protecting native birds and makes mosquito control essential.

Unlike diseases typically spread by only a few species, this study found that most bird species in Hawaiʻi, both native and non-native, possess at least a moderate capacity to infect southern house mosquitoes, the primary vector for avian malaria. Even birds carrying very low levels of the parasite were able to transmit the disease to mosquitoes. This indicates that many different bird communities can support ongoing malaria transmission.

Researchers analyzed blood samples from over 4,000 birds across Kauaʻi, Oʻahu, Maui, and Hawaiʻi Island, combining this data with laboratory experiments. The study found that introduced and native birds often had overlapping levels of infectiousness, meaning both groups can contribute to disease spread. The long period during which individual birds can harbor chronic avian malaria infections (months to years) was estimated to drive most disease transmission.

Devastating Impact on Native Honeycreepers

Avian malaria weakens birds by damaging red blood cells, often leading to anemia, organ failure, reduced survival, and in some species, death. For example, reports indicate a 90% mortality rate for infected ʻiʻiwi (scarlet honeycreepers), and the ʻakikiki, a Hawaiian honeycreeper endemic to Kauaʻi, is now considered extinct in the wild, largely due to avian malaria.

Broad Risk and Urgent Need for Control

This broad capacity for infection and spread likely accounts for the disease's widespread nature across the islands. The findings also suggest that few, if any, mosquito-infested habitats are free from transmission risk. Furthermore, warming temperatures are allowing both mosquitoes and avian malaria to develop in formerly mosquito-free refuges, exacerbating the situation.

Seidl and the Maui Forest Bird Recovery Project are participants in Birds, Not Mosquitoes, a collaborative initiative focused on mosquito control for Hawaiian bird conservation.