These cool, high-elevation above 4,000 feet (1,200 meters) -- mountains not only provided habitats that mosquitoes didn't thrive in, but they also had habitat that honeycreepers liked, wrote the authors. While birds in those areas find refuge from the diseases dispersing juvenile birds and adults that follow seasonal flowering of native plants to lower elevations are exposed to disease.
"Unfortunately," said study co-author, USGS scientist Dr. Dennis LaPointe, "this seasonal movement happens at the same time that mosquito populations soar at mid-elevations, which fuels high disease-transmission rates there. There's a continuous source of disease-susceptible birds each fall."
Although most disease transmission now occurs in these mid-elevation forests, this will change if the projected 3.6 degrees Fahrenheit (2 degrees Centigrade) raise in temperature occurs.
"With this kind of temperature change, about 60 to 96 percent of the high-elevation disease refuges would disappear," said Atkinson. For example, available high-elevation forest habitat in the low-risk disease zone would likely decline by nearly 60 percent at Hanawi Natural Area Reserve on Maui to as much as 96 percent at Hakalau Forest National Wildlife Refuge on Hawaii Island. On other islands, such as Kauai, with lower elevations and no low-risk zones even now, predicted temperature changes would likely be catastrophic for remaining honeycreeper species.
"Right now, disease transmission in the mountains of Kaui is highly seasonal, but with temperature increases, disease would be able to be transmitted throughout most of the year," said Atkinson.
In addition, the tropical inversion layer often visible as a thin cloud layer around high peaks -- may play a more significant role than temperature in determining tree line and the upper extent of forest bird habitat, the authors wrote. The inversion layer forms as cool, dry air meets warm, moist air, creat
|Contact: Carter Atkinson|
United States Geological Survey