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. 2017 Jan 6;12(1):e0168880.
doi: 10.1371/journal.pone.0168880. eCollection 2017.

Mitigating Future Avian Malaria Threats to Hawaiian Forest Birds from Climate Change

Affiliations

Mitigating Future Avian Malaria Threats to Hawaiian Forest Birds from Climate Change

Wei Liao et al. PLoS One. .

Abstract

Avian malaria, transmitted by Culex quinquefasciatus mosquitoes in the Hawaiian Islands, has been a primary contributor to population range limitations, declines, and extinctions for many endemic Hawaiian honeycreepers. Avian malaria is strongly influenced by climate; therefore, predicted future changes are expected to expand transmission into higher elevations and intensify and lengthen existing transmission periods at lower elevations, leading to further population declines and potential extinction of highly susceptible honeycreepers in mid- and high-elevation forests. Based on future climate changes and resulting malaria risk, we evaluated the viability of alternative conservation strategies to preserve endemic Hawaiian birds at mid and high elevations through the 21st century. We linked an epidemiological model with three alternative climatic projections from the Coupled Model Intercomparison Project to predict future malaria risk and bird population dynamics for the coming century. Based on climate change predictions, proposed strategies included mosquito population suppression using modified males, release of genetically modified refractory mosquitoes, competition from other introduced mosquitoes that are not competent vectors, evolved malaria-tolerance in native honeycreepers, feral pig control to reduce mosquito larval habitats, and predator control to improve bird demographics. Transmission rates of malaria are predicted to be higher than currently observed and are likely to have larger impacts in high-elevation forests where current low rates of transmission create a refuge for highly-susceptible birds. As a result, several current and proposed conservation strategies will be insufficient to maintain existing forest bird populations. We concluded that mitigating malaria transmission at high elevations should be a primary conservation goal. Conservation strategies that maintain highly susceptible species like Iiwi (Drepanis coccinea) will likely benefit other threatened and endangered Hawai'i species, especially in high-elevation forests. Our results showed that mosquito control strategies offer potential long-term benefits to high elevation Hawaiian honeycreepers. However, combined strategies will likely be needed to preserve endemic birds at mid elevations. Given the delay required to research, develop, evaluate, and improve several of these currently untested conservation strategies we suggest that planning should begin expeditiously.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Predicted total mosquito density (per km2) for sterile/incompatible male mosquitoes under RCP8.5 at mid elevation.
Model baseline (red line) means no release of modified (sterile or incompatible) mosquitoes, other lines show continuous release of 500 modified male mosquitoes per km2 for 9 months with mate competition coefficient (C = 0.5) between modified and wild male mosquito and different magnitudes of egg mortality (EM, blue line for EM = 0.90, and green line for EM = 0.95).
Fig 2
Fig 2. Predicted Iiwi density (per km2) for sterile/incompatible male mosquitoes under RCP8.5, A1B, and RCP4.5 climate projections at mid elevation.
Model baseline (red line) means no release of modified (sterile or incompatible) mosquitoes, other lines show continuous release of 500 modified male mosquitoes per km2 for 9 months with mate competition coefficient (C = 0.5) between modified and wild male mosquito and different magnitudes of egg mortality (EM, blue line for EM = 0.90, and green line for EM = 0.95).
Fig 3
Fig 3. Predicted Iiwi density (per km2) for refractory mosquito strategy under alternative climatic projections at mid elevation.
Model base (red line) means no refractory mosquitoes in the population, others imply a fixed percentage refractory mosquitoes in the population (Ref% = 50%—cyan, 80%—blue, 90%—black, 95%—magnolia and 100%—green, respectively) in alternative climatic projections (RCP8.5, A1B, and RCP4.5) of 21st century.
Fig 4
Fig 4. Predicted Iiwi density (per km2) for refractory mosquito strategy under alternative climatic projections at high elevation.
Model base (red line) means no refractory mosquitoes in the population, others imply a fixed percentage refractory mosquitoes in the population (Ref% = 50%—cyan,80%—blue, 90%—black, 95%—magnolia and 100%—green, respectively) in alternative climatic projections (RCP8.5, A1B, and RCP4.5) of 21st century.

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