1 University of Pennsylvania School of Veterinary Medicine, Wheat Ridge Animal Hospital, 3695 Kipling Ave, Wheat Ridge, CO 80033 2* Department of Biology, University of Hawaii at Hilo, 200 West Kawili St., Hilo HI. 96749 3 U.S. Geological Survey, Pacific Island Ecosystems Research Center, P.O. Box 44, Hawaii National Park, HI 96718 PACIFIC CONSERVATION BIOLOGY Vol. 16: 181186. Surrey Beatty & Sons, Sydney. 2010. Can lowland dry forests represent a refuge from avian malaria for native Hawaiian birds? KATHERINE TUCKER-MOHL 1 , PATRICK HART 2 and CARTER T. ATKINSON 3 Hawaii’s native birds have become increasingly threatened over the past century. Introduced mosquito borne diseases such as avian malaria may be responsible for the near absence of endemic Hawaiian forest birds in low-elevation habitats. The recent recognition that some native Hawaiian forest birds may be repopulating moist lowland habitats as a result of evolved resistance to this disease has increased the conservation value of these areas. Here, we investigate whether remnant low elevation dry forests on Hawaii Island provide natural “refuges” from mosquito-transmitted malaria by nature of their low rainfall and absence of suitable natural sources of water for mosquito breeding. Unlike lowland wet forests where high rates of disease transmission may be selecting for disease resistance, lowland dry forests may provide some refuge for native forest birds without natural resistance to malaria. We mistnetted forest birds in two lowland dry forests and tested all native birds by microscopy and serology for avian malaria caused by the Plasmodium relictum parasite. We also conducted surveys for standing water and mosquito larvae. Overall prevalence of infections with Plasmodium relictum in the Hawaii Amakihi Hemignathus virens virens was 15%. Most infected birds had low- level parasitemias, suggesting chronic infections. Although avian malaria is present in these lowland dry forest Amakihi populations, infection rates are significantly lower than in wet forest populations at similar elevations. Sources of breeding mosquitoes in these forests appeared to be largely anthropogenic; thus, there is potential to manage dry forests as mosquito-free habitat for Hawaii Amakihi and other Hawaiian forest birds. Key Words: Amakihi, avian malaria, Hemignatus virens, forest, endangered birds, Hawaii, Plasmodium relictum INTRODUCTION THE Hawaiian honeycreepers (Fringillidae) are an endemic subfamily (Drepanidinae) of birds that have become increasingly threatened over the past century, with some 76% of the 71 endemic avian species present in 1778 currently extinct or endangered (Jacobi and Atkinson 1995). Causes of these declines include habitat destruction, introduced predators and competitors, and disease, particularly avian malaria caused by Plasmodium relictum-(van Riper and Scott 2002, Atkinson and LaPointe 2009). Avian malaria in Hawaiian birds is transmitted primarily by the Southern House Mosquito Culex quinquefasciatus-(LaPointe et al. 2005, van Riper et al. 1986). Although the mosquito was intro- duced to the Hawaiian Islands in 1826, P. relictum likely did not become established in native species until the early 20th Century, following the introduction of non-native bird species that allowed the spread of infection to native birds (van Riper et al. 1986). Hawaiian honeycreepers are extremely susceptible to infection with P. relictum, with mortality ranging from 6390% as a result of the bite of a single infected mosquito under experimental con- ditions (Atkinson et al. 1995; Atkinson et al. 2000). Both high susceptibility of honeycreepers to avian malaria and declines in diversity and abundance of native species at elevations below 1200 m where mosquitoes and disease trans- mission are more common (Ahumada et al. 2004) suggest that this disease has played a major role in the extinction and endangerment of many members of this endemic subfamily (Warner 1968; van Riper et al. 1986). Most field studies of Hawaiian forest birds have focused on mesic to wet forests or dry forests at high (> 1800 m) elevation where the birds are most abundant (Scott et al. 1986). The recent discovery that some lowland populations of Hawaii Amakihi Hemignatus virens virens are expanding and appear to have evolved resistance to this disease has helped to increase the conservation value of remnant patches of lowland native forest (Woodworth et al. 2005; Foster et al. 2007), particularly in wet lowland forests that maintain high populations of mosquitoes. By contrast, lowland (< 700 m) dry forests have received little attention, despite the fact that their value as potential disease refugia was recognized more than 30 years ago (Scott et al. 1986; van Riper 1991). There are two primary reasons for this. First, although lowland dry forests formerly occupied a large proportion of the land on the leeward sides of the main Hawaiian Islands; they are now a highly threatened ecosystem that can be found on less than 10% of their original range (Bruegmann 1996). Second, until recently, it was assumed that native honeycreepers were extremely rare in low elevation forests in Hawaii (Woodworth et al. 2005; Spiegel et al. 2006). This study examines prevalence of P. relictum in two populations of Hawaii Amakihi that have recently been observed in remnant patches of