Microbial communities in hummingbird feeders are distinct from floral nectar and influenced by bird visitation.

Human provisioning can shape resource availability for wildlife, but consequences for microbiota availability and exchange remain relatively unexplored. Here, we characterized microbial communities on bills and faecal material of hummingbirds and their food resources, including feeders and floral nectar. We experimentally manipulated bird visitation to feeders and examined effects on sucrose solution microbial communities. Birds, feeders and flowers hosted distinct bacterial and fungal communities. Proteobacteria comprised over 80% of nectar bacteria but feeder solutions contained a high relative abundance of Proteobacteria, Firmicutes and Actinobacteria. Hummingbirds hosted bacterial taxa commonly found in other birds and novel genera including Zymobacter [Proteobacteria] and Ascomycete fungi. For feeders, bird-visited and unvisited solutions both accumulated abundant microbial populations that changed solution pH, but microbial composition was largely determined by visitation treatment. Our results reveal that feeders host abundant microbial populations, including some bird-associated microbial taxa. Microbial taxa in feeders were primarily non-pathogenic bacteria and fungi but differed substantially from those in floral nectar. These results demonstrate that human provisioning influences microbial intake by free-ranging hummingbirds; however, it is unknown how these changes impact hummingbird gastrointestinal flora or health.