Birds, malaria, and climate change

Hawaiˈi’s forest birds are found nowhere else on Earth, and almost all species are threatened or endangered. One of the major threats these birds face is avian malaria, which is spread by a species of introduced mosquito. For some bird species, the death rate from malaria exceeds 90%.

For decades, Hawaiian forest bird conservation has relied on upper mountain forests to protect vulnerable bird populations, because the mosquitoes and disease cannot survive in the cooler temperatures. However, increasing temperatures and rainfall due to climate change could allow mosquitoes and malaria to move to high elevation areas. Infected mosquitos could eventually reach all Hawaiian forest bird habitat, making the disease inescapable. 

Researchers with the Pacific Islands Climate Science Center used climate data and an epidemiological model to understand how Hawaiˈi’s forest birds might fare throughout the remainder of the 21^st century. A new dataset is now available showing predicted changes in climate and the risk of malaria transmission to forest birds during the last years of the 21^st century.

More about the data

Modeling future climate

Three climate models, each describing possible future climate conditions based on different greenhouse gas emissions scenarios, were used to predict potential future temperature and rainfall patterns within different elevation zones on the Island of Hawaiˈi’s Mauna Loa volcano. The following climate scenario models were used:

1. RCP 4.5: In this scenario, emissions are projected to peak around the year 2040. This scenario assumes that climate policies will be introduced in time to reduce emissions by mid-century.

2. RCP 8.5: This “worst-case scenario” predicts climate conditions should emissions continue to rise throughout the 21^st century.

3. A1B: This scenario assumes a future in which human population growth peaks mid-century, then declines, and that a balanced mix of fossil fuel and non-fossil fuel energy sources are used – minimizing, but not eliminating greenhouse gas emissions.

Prior to their use in this study, each climate model was downscaled by climatologists. The downscaling process allows data produced at a large scale (such as global) to be used to make predictions about climate at a small scale (such as for a single mountain).

Modeling malaria transmission

The predicted temperature and precipitation changes were incorporated into an epidemiological model describing the bird-mosquito-malaria relationship. This model integrates information such as mosquito abundance, the density of infected mosquitos, and the rate of malaria parasite development. More details on the model and its parameters can be found here.

The resulting dataset

A dataset showing the predicted daily temperature and rainfall amounts under each climate scenario was produced for low-, mid-, and high-elevation zones on Hawaiˈi’s Mauna Loa volcano, for the years 2098-2100. In addition, the predicted daily risk of avian malaria infection in Hawaiian honeycreepers (a group of forest bird species) was calculated, based on the results of the epidemiological model.

The complete dataset can be downloaded as a .csv file here, under ‘Project Products’, ‘Data’.

What does the data show?

The data shows that without significant intervention, Hawaiian forest birds could suffer major population declines, or even extinction, due to changes in temperature and precipitation. In particular, the hot and dry conditions projected by the RCP8.5 scenario and the warm and wet conditions projected by the A1B scenario would lead to more frequent and intense malaria transmission and severe population reductions. A temperature increase of 2-5°C would enable avian malaria to become established in high-elevation areas. Meanwhile, increases in precipitation would exacerbate malaria transmission and its impacts on birds. Luckily, these effects are unlikely to appear before mid-century, so natural resource managers have time to begin implementing conservation efforts.

This study is an example of how climate data can be used to predict the spread of disease in wildlife. While this study focused on Hawaiian honeycreepers on Mauna Loa, a similar approach could be followed by researchers to predict the future spread of avian malaria and other vector borne diseases to other bird species in Hawaiˈi and elsewhere. Understanding how climate change could impact endemic bird species, particularly those that are threatened or endangered, is critical for long-term conservation planning.

About this series

The Department of the Interior (DOI) Climate Science Centers (CSCs) and their managing organization, the USGS National Climate Change and Wildlife Science Center (NCCWSC), provide scientific information to help natural and cultural resource managers respond to climate change. All data produced from these projects are made publicly available on the project pages of the NCCWSC website. The goal of the Data Announcement series is to highlight the data products generated from these projects and explore their potential applications.