Expansion of deadly, mosquito-borne bird diseases such as avian malaria into Hawaiʽi’s high elevation forests as a result of global warming is one of the most significant threats facing the state’s rare native forest birds. Few practical options for control of disease-carrying mosquitoes over large landscapes are available, however. The best hope for remaining species of native birds may be the development of tolerance or resistance to this introduced disease. Therefore, understanding how tolerance and resistance evolve and developing ways to speed this process may be good proactive strategies for addressing impacts of climate change. We evaluated ways to rapidly measure a bird’s natural immunity with the hope that they can predict survival from avian malaria. We evaluated cell-mediated immune responses, measured levels of natural antibodies (NAb) in the blood plasma, and measured plasma antioxidant capacity with the hypothesis that these tests may be able to distinguish disease-tolerant low-elevation populations of Hawaiʽi ʽAmakihi (Hemignathus virens) from disease-susceptible high-elevation populations. We found no significant differences in amount of wing web swelling associated with cellular immune responses and no significant differences in plasma antioxidant capacity between low- and high-elevation ʽAmakihi. We observed significant differences in levels of NAb from high- and low-elevation birds in an assay that measured complement-mediated lysis of rabbit erythrocytes. This assay is rapid, not affected by malarial infection status, relatively inexpensive, and works for a wide range of species, making it particularly attractive as a management tool for distinguishing malaria-tolerant and susceptible individuals. Additional work is needed to determine whether high levels of NAb correlate with ability to recover from avian malaria in ʽAmakihi and other native honeycreepers and whether this assay can be used to map geographic populations of native forest birds that are tolerant of this disease.
