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Vulnerability of Hawaiian Forest Birds to Climate Change

Vulnerability of Hawaiian Forest Birds to Climate Change - Using Models to Link Landscape, Climate, Disease, and Potential Adaptation


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The Hawaiian Islands are home to some of the world’s most culturally valuable but imperiled forest birds, including brightly colored native honeycreepers, many of which are threatened or endangered. One of the major threats these birds face is avian malaria, which is spread by a species of introduced mosquito and can have death rates exceeding 90 percent. For decades, upper mountain forests have provided refuge for Hawaiian forest birds because mosquitoes (and thus the disease) could not survive the cooler temperatures. However, warming associated with climate change could change this. Scientists used climate data and an epidemiological model to evaluate the future impacts of avian malaria on Hawaiian forest birds as a result of climate [...]

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“I'iwi Hawaiian Bird Credit: Robby Kohley”
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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. --- All Hawaiian forest bird species are endemic (found only in Hawai'i), and almost all are listed under the Endangered Species Act. One of the major causes of decline is their extreme sensitivity to introduced avian malaria, which is spread by a species of introduced mosquito. For decades, Hawaiian forest bird conservation has relied on upper mountain forests to protect bird populations, because the mosquitoes and disease cannot survive in the cooler temperatures. However, warming temperatures associated with climate change is threatening the conservation function of these upper forest refugia. With warming, mosquitoes and malaria are able to move up the mountains and are predicted to possibly fill all Hawaiian forest bird habitat with the disease, making it inescapable. Successful conservation of Hawaiian forest birds requires an analysis of climate change and its impact on the future disease risk of native bird populations. This project uses an ecological/epidemiological model to predict future dynamics of the bird-mosquito-malaria system in Hawaii in response to future climatic change. Results will include potential changes in malaria transmission and resulting bird population characteristics (demographics) across the elevation gradient in Hawaii. Because the bird species are highly vulnerable to the disease, resource management is focusing on potential ways to break or reduce the mosquito and malaria cycle, and models produced by this project will be used to evaluate alternative disease mitigation measures. This project will provide the first quantitative assessment of the long-term impact of climate change on bird malaria distribution and on Hawai`i's unique forest birds, and provide a crucial tool to adaptively manage recovery and promote disease resistance among avian populations.

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