Nowhere to fly: Avian malaria is ubiquitous from ocean to summit on a Hawaiian island

Climate change, habitat degradation and invasive species are key threats to biodiversity globally. Avian malaria in Hawaiʻi is a model system for understanding environmental effects on host, vector, and parasite dynamics and is where all these threats to biodiversity combine to impact bird populations. Previous research in Hawaiʻi has shown a clear decrease in malaria infection with increasing elevation, due to lower temperatures thermally constraining the vector and parasite. Over the last decade, however, avian malaria infections have increased at higher elevations. The island of Oʻahu, with a maximum elevation of ~1200 m, offers a glimpse into what transmission may look like across mid-elevation forests in the Hawaiian Islands in a warming world. We tested hypotheses about the effects of elevation, temperature, and precipitation on spatial patterns of avian malaria infection, and evaluated correlations between site host diversity and infection patterns. We collected 1194 blood samples from 16 bird species from seven sites across Oʻahu at elevations from 105 to 1209 m and tested for Plasmodium relictum infection using qPCR. Malaria infection was widespread across all sites. Prevalence varied four-fold among the three years and differed among species. Prevalence in red-billed leiothrix increased with maximum temperature but was not correlated with elevation or precipitation for any other species. Malaria infection was pervasive and constant at all elevations on Oʻahu, supporting the hypothesis that temperatures at mid-elevation forests are permissive to year-round infection and reducing disease-free habitat. Climate change may drive native species extinct by extending the range of infectious diseases.