SRP343292 PRJNA774835 Relationships between Migration and Microbiome Composition and Diversity in Urban Canada Geese Microbiome analysis presents an opportunity to understand how urban environments affect avian physiology. For example, habitat use can affect microbiome diversity and composition, and hosts with more diverse gut microbiota are thought to be more resistant to pathogens and have increased fitness. However, microbiome analysis is an understudied aspect of avian ecology, particularly in the context of migration and urbanization in wild birds. For this study, we hypothesized, within urban birds, migrants would exhibit greater microbial diversity and inter-individual variation in microbiome composition than urban residents because they are exposed to more diverse habitats. We focused on Canada geese (Branta canadensis), one of many partially migratory species that exhibit reduced migration and more year-round residency in cities. We used 16S rRNA gene amplicon sequencing to quantify microbiome taxonomic composition in fecal samples from 32 GPS-tracked Canada geese, 22 of which were year-round residents of the Chicago area and 10 of which were migrants. Contrary to our prediction, urban resident geese had higher gut microbial diversity in all metrics and higher inter-individual variation than migrants. In terms of composition, migrants had a higher relative abundance of bacteria in the phylum Firmicutes, and the genera Terrisporobacter, Turicibacter, and Cellulosilyticum, which all have metabolic functions that may aid in goose digestion. Therefore, although resident geese may have higher gut microbial diversity, their microbiome may provide fewer potential health benefits and characterized by more stochasticity, potentially due to anthropogenic resources. Our results also suggest that migration may be a selective force for stable microbiomes. These patterns suggest that reduced migration for urban-adapted species may have important consequences for wildlife physiology and health.