Abstract

The Hawaiian Islands are home to some of the world’s most imperiled forest birds. Introduction of mosquitoes and vector-borne avian malaria are important factors in the historic decline and extinction of many endemic Hawaiian honeycreepers which are particularly susceptible to avian malaria.

We used a model of forest birds, mosquitoes, and avian malaria to evaluate future impacts of avian malaria on these Hawaiian birds as a result of climate change. As climate warms during the 21st Century temperatures will favor increased mosquito populations and much higher transmission of malaria to endangered honeycreepers existing in high-elevation forests. We conclude that without significant intervention many native Hawaiian honeycreepers will suffer major population declines and/or extinction due to this increasing risk from avian malaria.

Proposed strategies to mitigate the problem include mosquito population suppression using sterile males or incompatible males, release of mosquitoes which are genetically modified to prevent malaria transmission to birds (e.g., refractory mosquitoes), competition from other introduced mosquitoes, evolved malaria-tolerance in native honeycreepers, feral pig control to reduce mosquito larval habitats, and predator control to improve bird demographics. Because predicted transmission rates of malaria will be higher than currently observed, several conservation strategies including predator removal, competing vectors, and feral pig control were insufficient to maintain these important bird populations at current levels. In contrast, mosquito control strategies offer potential long-term benefits to high-elevation Hawaiian honeycreepers.

The predicted higher rate of future disease transmission means that combined strategies will likely be needed to preserve endemic birds at mid elevation. The predicted climate changes are likely to have enormous impacts in high-elevation forests where current low rates of transmission create a refuge for highly-susceptible birds, mitigating malaria transmission should be a primary avian conservation goal. Strategies that maintain highly-susceptible honeycreepers (such as the Iiwi) in high-elevation forests will likely benefit many other endangered Hawaiian birds.