Changes in prevalence of avian malaria on the Alakaii Plateau, Kauai. Hawaii

June 30, 2010

We determined prevalence of malarial infections in samples of native and non-native forest birds that were sampled at three locations on the Alakai Plateau between 1994-1997 and again between 2007-2009. The three sites spanned the elevational range of the plateau and were located at Kawaikōī Stream (1100 m), the upper drainage of Mōhihi Stream (1250 m) and the vicinity of Halepaakai Stream near Sincock’s Bog (1350 m). We detected a dramatic and significant increase in prevalence of avian malaria both at the lower (Kawaikōī) and upper (Halepaakai) ends of the Alakai Plateau during the past decade. Overall prevalence of infection increased threefold from 11% to 30% at Kawaikōī Stream and tenfold from 2% to 20% at Halepaakai Stream. Much of this increase is likely a result of local transmission, since two sedentary native species, Elepaio and Kauai Amakihi, have experienced some of the largest increases in prevalence. Curiously, prevalence has not changed significantly at Mōhihi Stream and remains at approximately 10%. We also detected avian trypanosomes (Trypanosoma sp.) in both recent and historic blood samples from Nutmeg Mannikins (Lonchura punctulata) that were captured on the plateau. This is the first report of this mosquito-transmitted blood protozoan from the Hawaiian Islands and evidence indicates that it has been a previously undetected blood parasite in the islands for at least 15 years and likely longer. We found no evidence to indicate that the parasite has spread to native Hawaiian forest birds, but our sample sizes are limited. While our study was not designed to detect the specific factors responsible for the changes in prevalence of malaria at lower and upper portions of the plateau, the results are consistent with predicted increases in prevalence that might be expected in a warming climate and clearly show that environmental conditions necessary to support transmission of malaria now exist throughout major portions of the Alakai Plateau. Additional field work to identify larval habitat for mosquitoes, adult mosquito distribution and density, and the relative role of human activity, feral ungulates, and interactions between changing climatic conditions and the deeply dissected topography of the plateau may help to identify why some areas have experienced significant increases in malarial prevalence.

• USGS Source: Publications Warehouse (indexId: 70175421)